Chapter 61: Post-Injury Inflammation and Organ Dysfunction

Our increasing ability to keep severely injured patients alive eventually created a new clinical syndrome known as post-injury multiple organ failure (MOF). As advances in prehospital and acute hospital care conquered “the golden hour”; the trimodal distribution of trauma deaths described in the 1970s and 1980s slowly flattened its first mode and MOF emerged as the leading cause of late trauma death.^1,2,3

Much of the advances in the treatment of trauma and shock have been stimulated by military experience (see Chapter 13)⁴ and refined by research in civilian trauma centers. In World War I, soldiers’ death on the battlefield was initially attributed to toxins released by dead or dying tissue (Table 61-1).⁵ Cannon et al, via observations on the battlefield in 1917, expanded this concept to question the role of hypovolemia; however, it was not until the 1930s that Blalock et al established that reduced circulating blood volume was the dominant cause of shock and mortality.⁶ Casualties in World War II were initially resuscitated with freeze-dried plasma and later with stored whole blood. This continued in Korea where blood and plasma were administered until blood pressure returned to normal. In addition to rapid transport for definitive care in field medical units, prompt blood and plasma resuscitation improved battlefield survival but resulted in late deaths due to oliguric renal failure. In the 1960s, Shires et al proposed that extracellular fluid deficits (third space losses) compounded traumatic shock and demonstrated in animals that survival improved with the addition of balanced salt solutions.⁷ Consequently, crystalloid resuscitation was added to blood and plasma resuscitation in the Vietnam War and resuscitation end points focused on maintaining adequate urine output. Helicopter evacuation enabled rapid transport of casualties and the overall mortality rate decreased. Although late deaths from renal failure declined, a new entity termed “shock lung” emerged as the primary cause of late deaths.⁵ This new disorder became recognized in civilian trauma centers, and was named the adult respiratory distress syndrome (ARDS).⁸ In the 1970s, subsequent improvements in advanced organ support such as mechanical ventilation (MV), vasoactive drugs, total parenteral nutrition, and hemodialysis armed physicians with better treatment to sustain the critically ill. Death from isolated pulmonary failure became rare, and a new syndrome of “multiple, progressive, or sequential systems failure” was recognized.⁹

Eiseman et al coined the term “multiple organ failure” at the Denver General Hospital (now known as Denver Health Medical Center) in 1977, and provided the first clinical description of 42 patients with progressive organ dysfunction.¹⁰ During the late 1970s MOF was thought to be the “fatal expression of uncontrolled infection.”¹¹ In addition, at this time, studies indicated that organ failure was a bimodal phenomenon with distinct patterns: rapid single-phase MOF due to massive tissue injury and shock or delayed two-phase MOF due to moderate trauma and shock followed by delayed sepsis.^12,13 While infection remained a frequent cause of organ failure, by the mid-1980s it was convincingly shown that organ failure occurred in the absence of infection and the concept of “generalized auto-destructive inflammation” emerged.^14,15

By the 1990s, noninfectious inflammatory models of MOF became the focus.¹⁶ In this conceptual framework, patients are resuscitated into a state of early systemic hyperinflammation, referred to as the systemic inflammation response syndrome (SIRS). A mild response is presumed to be beneficial and resolves in most patients as they recover. In the “one-event” model, a massive traumatic insult overwhelms the capacity of the patient to respond to resuscitation and precipitates organ failure. In the more common, alternative “two-event” model, patients who are initially resuscitated to a moderate response (primed) are vulnerable to a second (activating) event that can also precipitate hyperinflammation leading to early organ failure. The timing of the second hit may vary from occurring shortly after the first hit, where the two are indistinguishable, to a delayed event conspicuous 12–36 hours later. Patients who escape early MOF become susceptible to infection during the so-called compensatory anti-inflammatory response syndrome (CARS). If infected during this window, patients are at risk of developing late MOF. Other second hits include abdominal compartment syndrome (ACS), sepsis, fat embolus, MV, blood transfusions, long bone fixation, and other secondary surgical procedures.¹⁷ ACS, in particular, emerged in epidemic proportions in the early 1990s as a result of tremendous advances in trauma care in the 1980s (including ATLS, trauma systems, damage control, and surgical critical care) which decreased the number patients bleeding to death early after hospital admission. This proved to be an iatrogenic complication that has largely been eliminated by massive transfusion protocols with avoidance of excessive crystalloids, earlier hemorrhage control and abandonment of supranormal oxygen delivery resuscitation directed by pulmonary artery catheter.

In the late 2000s, the MOF pathogenesis model (Fig. 61-1) proposed that injury triggered simultaneous, opposite responses: the proinflammation (SIRS) and the anti-inflammation (CARS).¹⁸ The term “compensatory” inflammation is now considered a misnomer as CARS appears to occur in response to the injury (not to SIRS). In this paradigm, the development of MOF is related to the intensity and the balance between these opposing inflammatory responses to trauma. Severe SIRS, due to unbalanced early proinflammation via activation of the innate immune system, causes early MOF and can eventually result in a fulminant proinflammatory death. On the other hand, early anti-inflammation, via inhibition of the adaptive immune system and apoptosis, is directed at limiting proinflammation, creating a preconditioned state where the host is protected against second hits, and hastening the healing process. When countering unbalanced proinflammation, persistent anti-inflammation can result in a severe systemic anti-inflammatory response syndrome (SARS, a proposed, more appropriate terminology for CARS), setting the stage for immunoparalysis, impaired wound healing, recurrent nosocomial infections, and late MOF.^18,19

More recently, the Inflammation and Host Response to Injury Large-Scale Collaborative Research Program (Glue Grant), sponsored by the National Institutes of Health (NIH), confirmed that alterations in the genomic expression of the classical inflammatory and anti-inflammatory responses occurred simultaneously.²⁰

These new constructs evolved from translational research, a two-way exchange between clinical observations and bench-level experimental studies that remains the foundation of contemporary MOF research. Research during the past decade has progressed toward further explaining these inflammatory mechanisms at the cellular and subcellular levels. New strategies to reduce secondary insults and to modulate the inflammatory responses in the early and late post-injury periods are currently undergoing intense research investigation.

In the 2000s, there were two major ICU initiatives that reduced ICU deaths. The first was the Glue Grant Standard Operating Procedures, which ensured consistent implementation of evidence-based care for standard ICU interventions.²¹ The second was the Surviving Sepsis Campaign, which emphasized sepsis screening and rapid implementation of a sepsis bundle, including antibiotics within 1 hour and volume resuscitation.²² As a result, patients are now surviving longer in ICUs with low-level organ dysfunction and are being discharged to long-term acute care facilities. There they suffer an indolent death from a newly described MOF phenotype, the persistent inflammation-immunosuppression catabolism syndrome (PICS), described later in the chapter.²⁰ In sum, the phenotypic expression and the epidemiology of post-injury MOF has changed considerably over the past 20 years. Yet, as we will describe in the next sections, MOF remains morbid, lethal, and resource intensive.²¹

There is no specific measurement that identifies MOF. Thus, defining MOF given the absence of a definitive gold standard is a challenge.²³ The syndrome seems to fit well with Justice Stewart’s famous quote: “I may not be able to define it, but I know it when I see it.” As a consequence, researchers have used different definitions for the syndrome resulting in widely different epidemiological descriptions.

Since there is no gold standard, validation of current definitions must be done examining the association of different scores with objective adverse outcomes, reflecting clinical status (VFD: ventilator-free days, IFD: intensive-care-free days, and death) and resource utilization (length of ICU stay [ICU-LOS] and MV days). VFD and IFD have been recently proposed as alternative outcomes for critically ill patients that account for patients who died early and consequently had shorter MV and ICU times.²⁴ The validation process can be greatly enhanced if conducted on a homogenous population observed for an extended period of time, as in our long-term Denver MOF dataset. Covering a long period of time (1992–2008), this database contained prospectively collected clinical data on patients at risk for post-injury MOF, for the first 28 post-injury days. To our knowledge, this is the longest, sustained prospective database on post-injury MOF using standardized data collection methods. Acutely injured patients admitted to the surgical intensive care unit (SICU) at the Denver Health Medical Center (DHMC, a state-designated level I trauma center verified by the American College of Surgeons Committee on Trauma) were studied prospectively.

An analytic dataset of 1440 patients from 1992 to 2004 enrolled in the Denver MOF dataset, was used for a validation of two widely used MOF definitions: the Denver score²⁵ and the Multiple Organ Dysfunction Score (MODS).²⁶ For other scores, the reader is referred to the excellent review by Baue.²⁷ The Denver score, first proposed by our group in 1991, originally included eight organ systems (cardiovascular, pulmonary, renal, hepatic, gastrointestinal, hematologic, central nervous system [CNS], and metabolic). The score was later revised and gastrointestinal, hematologic, CNS, and metabolic failures were excluded since their addition did not improve the characterization of MOF. In brief, the Denver score grades on a scale from 0 to 3 the dysfunction of four systems (pulmonary, renal, hepatic, and cardiovascular), evaluated daily throughout the patient’s ICU stay with the total score ranging from 0 to 12 (Table 61-2). The Marshall MODS was developed in 1994 and validated based on probability of subsequent mortality in a sample of 692 patients from a Canadian ICU.^26,28 It grades the dysfunction of six organ systems (pulmonary, renal, hepatic, cardiovascular, hematologic, and neurologic) from 0 to 4 (Table 61-3). For both scores, organ dysfunction must be graded daily, and the sum of simultaneously obtained individual organ scores corresponds to the daily MOF score. The Denver MOF score ranges from 0 to 12, and MOF is declared when the daily score is greater than 3. The authors of the MODS did not propose a cutoff to declare MOF, but traditionally a daily score greater than 5 has been used.

Patients fitting the following criteria were entered in the Denver MOF dataset:

1. Moderate to severe injury (injury severity score [ISS] >15)—patients with this level of injury or worse are all likely to be admitted to the ICU, minimizing selection bias.

2. Survival longer than 48 hours from injury—studies at the time of this validation demonstrated that physiologic derangements prior to 48 hours were confounded by the primary injury or incomplete resuscitation.²⁹

3. Admission to DHMC within 48 hours of injury—due to delay in admission, early risk factors shown to be associated with MOF were not observed or recorded.

4. Age greater than 15 years—it has been demonstrated that MOF presents differently among children, and that the currently used organ dysfunction measures may not be appropriate to the pediatric population; thus, children were not included in this analysis.³⁰

5. No isolated traumatic brain injury (TBI)—nonneurologic organ dysfunctions in TBI patients seem to have a different pathophysiology and presentation compared to those with torso injuries.³¹

In addition, we excluded patients with burn and/or hanging injuries, as they were most often treated primarily at other centers and their risk factors for MOF are different from torso injuries. Daily physiologic and laboratory data were collected through day 28. There were 1389 patients, typically young, healthy males, with moderate to severe injuries, mostly due to blunt force in motor vehicle accidents. Mortality and number of VFD days were low, but health care resource utilization was high, with over one-third of these patients requiring longer than 14 admission days in the surgical ICU (LOS) and/or more than 7 days of MV. The incidence of MOF was 22% with a case-fatality rate of 30% according to the Denver MOF score, as opposed to an incidence of 50% with a case-fatality rate of 15% according to the MODS (using the traditional >5 cutoff). When comparing the patients identified by each score, we noted three major groups: (1) a severe injury group of patients classified by both scores as MOF with high rates of risk factors (high ISS, shock, and advanced age), mortality and health care utilization, (2) a moderate injury group classified as MOF by the MODS but not by the Denver MOF score with medium risk factor rates, medium health care utilization and low mortality, and (3) a mild injury group which included patients classified as no MOF by both scores for whom risk factor rates, utilization, and mortality were all low. These findings suggest that the MODS tends to be more sensitive, while the Denver MOF score tends to be more specific.

We used the area under the receiver-operating characteristics (AUROC) curve to compare the association of the two scores (Denver MOF score and MODS) with the objective adverse outcomes. (death, VFD <21 days, ICU-LOS >14 days, and MV >7 days). Figure 61-2 shows the two scores’ AUROCs for mortality. Overall, both scores were associated with areas greater than or equal to 75 for all outcomes, and greater than or equal to 80 for mortality (ideal value = 100). The AUROC for the Denver score was slightly greater than that for the Marshall score regarding prediction of death, VFD, and MV. The differences, however, were not significant, suggesting similar, good performances for both scores.

Since its initial description, MOF’s incidence has changed dramatically, although some controversy remains. Indeed, large US and Australian studies have shown a steady decline in the incidence of MOF over the past decade, likely due to new therapeutic approaches.^32,33,34,35 Conversely, a large German study reported an increase in the MOF incidence.³⁶ Yet, the different reports unanimously recognized that the mortality and morbidity associated with MOF remain high.^{32,33,34,36,37,38,39,40,41}

The controversies on MOF incidence are related to a number of factors, including disparate definitions, as highlighted above, as well as differences in populations and resuscitation practices. We recently conducted a large, comprehensive examination of the recent trends in post-injury MOF using the aforementioned Glue Grant dataset.³³ This contemporary, longitudinal, prospective study includes several US trauma centers who shared standard operating procedures (SOPs) minimizing intervention heterogeneity.⁴² SOPs included: early resuscitation, mechanical ventilation (including guidelines for ventilator discontinuation), ventilator-associated pneumonia, insulin infusion, nutrition and venous thromboembolism prevention.⁴² Our hypotheses were (1) the incidence of post-injury MOF has decreased and (2) rates of MOF-related morbidity and death have not changed significantly. Adult patients with severe blunt torso injuries and hemorrhagic shock were enrolled from 2003 to 2010 and followed through day 28 or discharge.

We studied 1643 patients enrolled from 2003 to 2010 by four centers that enrolled more than 20 eligible patients per biennial. Of these, 252 (15%) did not survive. MOF developed in 223 (13.6%) patients of whom 81 (36%) died. Table 61-4 details the distribution of admission risk factors, fluids, transfusions, complications, outcomes as well as MOF incidence and MOF-related outcomes across the biennial periods. Anatomic injury severity remained relatively stable while measures of shock upon admission had a slight improvement over time. Blood transfusions remained stable while 12 hours crystalloids’ volume decreased. MOF crude incidence decreased over time (p = 0.0033), while MOF-related mortality, VFD and IFD remained stable at high levels. The Kaplan-Meyer analysis confirmed these findings (Fig. 61-3). Applying the MODS definition produced similar results, that is, a significant decline in MOF incidence and no change in MOF mortality over time.

A Cox proportional hazards (Cox PH) model demonstrated that the MOF significant downward trend from 2003 to 2010 was independent from included admission risk factors (p < 0.0001). The adjusted MOF risk decreased by 16% (hazard ratio = 0.86) by each period of 2 years for an estimated 50% decrease over the entire study period. Conversely, adjusted MOF-related death did not change over time (p = 0.6907). Inclusion of crystalloids and blood component transfusions did not significantly alter these results.

The risk factors for developing MOF included demographic characteristics (advanced age, male sex, obesity), injury severity (higher ISS), and physiologic derangement (admission acidosis, number of transfused units of red blood cells [RBC]/12 hours). MOF-related death was positively associated with female sex, ISS and number of RBC units transfused in the first 12 hours post-injury.

Lung failure incidence decreased significantly over time, but remained the most common organ failure over the study time period affecting over half of these patients (see Table 61-4). Cardiovascular dysfunction, as measured by inotrope requirement, also became significantly less frequent, while renal and liver failures persisted at similar levels. Adjustment for admission risk factors confirmed these results.

The mortality associated with individual organ failures (with or without involvement of other organs) was highest for cardiovascular dysfunction (39%), followed by failure of the kidneys (38%), liver (19%), and lungs (12%). Only 1% of the patients had isolated dysfunction of the kidneys, liver, or heart. Mortality for isolated cardiovascular dysfunction was 58%, while for renal failure was 15%; none of the patients with isolated liver dysfunction died. In contrast, 32% of the patients in this series had isolated lung dysfunction, and this rate remained relatively stable over the study period (from 2003 to 2010). This suggests that there was a decrease in the progression from lung dysfunction to MOF over time.⁴³ On the other hand, it also suggests that we have advanced little in preventing lung dysfunction. Mortality of isolated lung failure remained stable over time (3–6%). MOF without lung dysfunction is rare: only 8% of the MOF patients did not have lung involvement.

MOF onset retained the traditional multimodal distribution (Fig. 61-4A), with the highest peak within the first 3 days post-injury and a smaller peak afterward. Approximately half of MOF cases occurred within 3 days (Fig. 61-4B). The onset of individual organ failure varied little over the biennials. Lung, cardiac, and renal failures were early events occurring on days 2 or 3, while liver failure is usually detected later, around day 6.

The time interval between MOF onset and death is usually short, with death ensuing in 2 days in 58% of the cases and within a week in 80% of the cases. Early MOF (within 3 days post-injury) carried a higher mortality than later MOF (Fig. 61-4B). In the biennial 2009–2010, 50% of the early MOF patients died, compared to 40% of those with MOF onset between 4 and 7 days and none of those with late MOF.

The Burden of MOF: MOF patients in this multicenter series endured longer ICU stays (median 18 days; IQR 9–29) compared to all non-MOF patients (median 8 days; IQR 4–16). Similarly, MOF victims required much longer ventilation (median 14 days; IQR 7–24) compared to non-MOF patients (median 5 days; IQR 2–12). Stratification by MOF and survival status showed that MOF survivors were the group who demanded more ICU and ventilation resources. MOF survivors were responsible for 20% of the total ICU and mechanical ventilation days invested in the critical care of this population even though they represented only 9% of the total population.

Based on national estimates of critical care costs,⁴⁴ the total cost of the critical care delivered to MOF patients in this dataset amounted to $19,990,420 (ICU with mechanical ventilation = $16,479,606 + ICU without mechanical ventilation = $3,510,814). This corresponded to 22% of the total ICU cost for this population (ICU with mechanical ventilation = $69,238,641 + ICU without mechanical ventilation $20,580,321 = Total ICU cost $89,818,962). The estimated median cost per MOF patient was $77,202, compared to $38,442, which was the presumed cost of caring for non-MOF patients.

Initial Responses to Trauma

Initial responses to trauma involve several systems: hemostatic, inflammatory, endocrine and neurological. The two-hit model of post-injury MOF, described in a previous section and illustrated in Fig. 61-1, was derived from a two-way translational model in which information was exchanged between epidemiological studies, predictive models, and basic investigations using in vivo and in vitro models. As mentioned above, severe trauma patients are resuscitated into an early state of systemic inflammation or SIRS. The American College of Chest Physicians and the Society of Critical Care Medicine defined SIRS as two or more of the following criteria: (1) temperature less than 36.8°C or greater than 38.8°C, (2) heart rate more than 90/min, (3) respiratory rate more than 20 breaths/min or pco₂ less than 32 mm Hg, and (4) WBC less than 4000/mL or greater than 12,000 mL or greater than 10% immature forms.

The current framework for the immunoinflammatory response to trauma is illustrated in Fig. 61-5. SIRS is the manifestation of the immunoinflammatory activation that occurs in response to ischemia–reperfusion (I/R) injury and factors released from disrupted tissue. The injured cell releases endogenous damage-associated molecular patterns (DAMPs, alarmins), which are analogous to the microbial pathogen-associated molecular patterns (PAMPs), released in sepsis.^45,46,47 This analogy is not surprising as the human mitochondria derived from bacterial endosymbionts during the evolutionary process. Both PAMPS and DAMPS/alarmins activate innate immunity.

Liu et al⁴⁸ showed that up to 70% of unique proteins measured in the plasma of blunt trauma victims were intracellular molecules that could function as DAMPS/alarmins and trigger pattern recognition receptors. Our laboratory was the first to describe the proteome description of human mesenteric lymph collected from critically ill or injured patients using a label-free semiquantitative mass spectrometry based approach.⁴⁹ A total of 477 proteins were identified, including markers of hemolysis, extracellular matrix components, and general tissue damage in addition to the classical serum proteins. Hemolysis, a common event post-trauma, releases hemoglobin to the extracellular environment, where it becomes a redox-reactive DAMP molecule.⁵⁰ Extracellular hemoglobin can also bind to PAMPs and triggers toll-like receptor-mediated signal transduction. High levels of extracellular hemoglobin can generate reactive oxygen species, which affects the innate immunity.

Among the proteins we identified in the mesenteric lymph, there were several markers of tissue damage including the cytoskeletal proteins actin, tubulin, cofilin-1, spectrin, gelsolin, and profilin-1.⁴⁹ We also detected 16 mitochondrial proteins suggesting the presence of lysed mitochondria, presumably from cell death. There have been reports showing that circulating mitochondrial DNA and formyl peptides can mediate organ injury through PMN activation.⁴⁵

We recently performed a mass spectrometric analysis of the plasma metabolome of severely injured patients, including a subgroup that underwent resuscitative thoracotomy in the Emergency Department of the Denver Health Medical Center, compared to healthy controls.⁵¹ Metabolomics describes the metabolites present in a biologic matrix and is reflective of the host’s pathologic state or response to stimuli. We observed a trauma-dependent metabolic state of hypercatabolism that provides carbon and nitrogen sources to compensate for trauma-induced energy consumption and negative nitrogen balance. This state is characterized by sugars consumption, lipolysis and fatty acid use, accumulation of ketone bodies, proteolysis and nucleoside breakdown. Unexpectedly, metabolites of bacterial origin (including tricarballylate and citramalate) were detected in the plasma of these trauma patients (see the section “Role of the Gut” later in the chapter).

Plasma from trauma patients showed accumulation of mannitol, heme, and oxidative stress markers.⁵¹ It should be noted that mannitol’s increase could reflect also therapy (as it is present in blood transfusions), although our data suggested limited transfusion effect, as we detected no difference in metabolite levels between resuscitative thoracotomy patients (who received limited transfusions) and other trauma patients, whose blood samples preceded intravenous fluid or blood products.

This metabolomic analysis confirmed the presence of an altered lipidomic profile, a hallmark of trauma-induced metabolic adaptation.⁵¹ Fatty acid mobilization (accumulation of acylcarnitines) and lipid breakdown (buildup of ketone bodies and breakdown products of fatty acids—eg, choline, glycerol, ethanolamine, glycerol phosphate, and glycerophosphocholine moieties) were observed. In addition, elevations in post-injury proinflammatory arachidonate metabolites (prostaglandin E2 and leukotriene B4) supported the proposed immunomodulatory effect of diets balancing the ratio of omega-3 and omega-6 fatty acids in reducing post-injury MOF.⁵² Moreover, the hyperactivation of lipid metabolism in response to trauma results in the accumulation of anionic compounds such as ketone bodies, further promoting acidosis.

We also detected significant increases in proteolysis as shown by the accumulation of several amino acids (alanine, aspartate, cysteine, glutamate, histidine, lysine, and phenylalanine) and cyclic dipeptide cyclo(glu-glu), which have been reported to have biologic activity including an immunomodulatory role in the stimulation of T lymphocytes.⁵¹ Glutamate and cysteine accumulation could fuel new reduced glutathione (GSH) synthesis (Fig. 61-2), thereby serving as physiologic protection from the increase in trauma-dependent oxidative stress. In addition, there was significant nucleoside breakdown for metabolic purposes as demonstrated by trauma patients’ increased levels of purine (xanthine, hypoxanthine, and inosine) and pyrimidine catabolites (uracil, 5,6-dihydrocuracil, and 3-aminobutyrate).⁵¹

Notably, we did not observe post-injury accumulation of glutamine.⁵¹ A potential explanation is that trauma enhanced consumption of this specific amino acid for direct cellular energy production or for fueling transamination reactions. However, although glutamine supplementation in critically ill patients has been a long-sought therapeutic approach, no evidence has been produced to date demonstrating the benefit of glutamine supplementation.⁵³ While the levels of most amino acids were increased in response to trauma, tryptophan and its associated metabolites decreased in trauma samples. Finally, increased nicotinamide, a breakdown product of the purine metabolite NAD, may signal exhaustion of NAD+/NADH reservoirs potentially compromising many energy and redox-related processes dependent on these cofactors.

In trauma, hemorrhagic shock following injury produces whole-body hypoperfusion, followed by subsequent reperfusion during resuscitation, which stimulates the release of cytokines, proinflammatory lipids, chemokines, and proteins that prime polymorphonuclear neutrophils (PMNs) within 3–6 hours after injury.¹⁷ The systemic anti-inflammatory response syndrome (SARS) mediated defects in adaptive immunity include decreased antigen presentation, macrophage paralysis, depressed T-cell proliferative responses, increased lymphocyte and dendritic cell apoptosis, and shift from T_H1 to T_H2 lymphocyte phenotype.^18,19

As discussed in the first section, recent evidence has challenged the concept of sequential pro- and anti-inflammatory responses and proposed that these processes occur simultaneously.²⁰ In this Glue Grant study, investigators isolated blood leukocytes from a subgroup of 167 adult severe blunt trauma patients (out of 1637 adult, blunt trauma patients enrolled by seven US trauma centers), who consented to blood sampling (within 12 hours and at 1, 4, 7, 14, 21, and 28 days post-injury). The genetic expression of the leukocytes of these patients was compared to three different groups: (1) 37 healthy controls matched on age, sex, and ethnicity, (2) 133 adults with severe burn injuries, and (3) 4 healthy adults who received low-dose bacterial endotoxin. Their data suggested that severe blunt trauma produced significant changes in the expression of over 80% of the leukocyte transcriptome over the first 28 days compared to healthy subjects. The closer to the injury point, the larger the changes detected. The term “genomic storm” was coined to reflect the extent of the leukocyte transcriptome reprioritization in response to severe injury. The overexpressed genes were related to both the innate and adaptive immunity, while genes related to T-cell function and antigen presentation had decreased expression. The genomic response to blunt injury was remarkably similar to the response observed in groups 2 (burns) and 3 (endotoxemia). In addition, abnormal gene expression was long lasting, that is, still present 28 days after injury, but no evidence of a second-hit was observed. Post-injury complications were associated with greater and prolonged overexpression compared to patterns expressed by patients who had uncomplicated recoveries, although there was no major differences in which genes were invoked. Also, somewhat surprising was the minimal effect of the severity of anatomic injury (as measured by the ISS), acidosis and blood transfusions within the first 12 hours on gene expression. Based on this model, the authors proposed that rather than sequential, the SIRS-SARS response is synchronous and that it is the failure to return to homeostasis that defines the patients who will have a complicated recover.

It should be noted, however, that despite providing compelling evidence, the abovementioned investigation had a relatively small sample, limited to blunt torso trauma, and focused on circulating leukocytes.²⁰ It is conceivable that there are different expression patterns in localized inflammation in different tissues, as well as in lymphoid organs and the reticuloendothelial system.

As described in the Epidemiology section, there has been a notable decrease in the incidence of late MOF. Furthermore, late MOF rarely results in death, but leads to prolonged ICU stays and need for mechanical ventilation.³³ This observation has led to the description of a new phenotype, namely, the persistent inflammation, immunosuppression, and catabolism syndrome (PICS).¹⁹ These patients have manageable organ dysfunction, suffer recurrent inflammatory insults/nosocomial infections, have a persistent acute phase response with neutrophilia and lymphopenia, experience progressive loss of lean body mass (despite good nutritional supplementation), poor wound healing, and develop decubitus ulcers. They are discharged to acute long-term care facilities, where they die an indolent death or experience sepsis recidivism requiring ICU readmission. The elderly with baseline comorbidities and sarcopenia as especially prone. This refractory clinical phenotype translates to long-term impairment of cognitive and functional status from which recovery is uncertain.^19,54 Clinically, PICS was initially defined by the following criteria: ICU stay greater than or equal to 14 days, persistent inflammation (C-reactive protein concentration >150 μg/dL and retinol binding protein concentrations <10 μg/dL), immunosuppression (crudely defined by a total lymphocyte count <800/mm³), and a catabolic state (serum albumin <3.0 mg/dL, creatinine height index <80%, and weight loss >10% or BMI <18 kg/m² during the current hospitalization). Studies are underway to better define the phenotype, its true significance and novel interventions to prevent it or its progression. Multiple mechanisms are likely involved and multimodality interventions will be required. As the population ages, this MOF phenotype is likely to be next challenging horizon in surgical critical care.

As we are learning from the study of trauma-induced coagulopathy (see Chapter 13), the acute traumatic insult may result in a variety of post-injury clinical phenotypes depending on several factors such as severity and duration of shock, the specific organs and tissues injured, mechanism, extent and location of tissue disruption, time from injury to resuscitation, resuscitation protocols, etc.^55,56,57 Therefore, it is entirely possible that all these theories apply to explain the development of diverse MOF phenotypes.

Role of the Gut

The gut is the last organ to have its circulation restored after ischemia, and is thought to play a pivotal role in the pathogenesis of post-injury MOF.^18,47 Initially, the dominant hypothesis linking the gut to MOF was related to bacterial translocation: intestinal mucosa increased permeability allowed gut bacteria and/or endotoxin to be translocated to the circulation leading to sepsis and MOF. However, inconsistent results regarding the role of bacteria and endotoxin in the genesis of MOF led to experiments demonstrating that the mesenteric lymph acted as a bridge between the gut and the systemic circulation, allowing gut-derived inflammatory mediators to reach the systemic circulation.^58,59,60 Via the thoracic duct, these mediators reach the pulmonary circulation and affect the lungs before other organs. This is consistent with human studies demonstrating that post-injury respiratory dysfunction almost always precedes heart, liver, and kidney failure.⁶¹

Our recent description of the post-injury plasma metabolome highlighted the presence of citramalate (methylmalonate) and tricarballylate, likely of bacterial origin.⁵¹ These findings suggest that bacterial metabolites, and not bacteria themselves as previously thought, may translocate during reperfusion of ischemic splanchnic beds to manifest systemic pathology. Alternatively, bacterial metabolites such as citramalate may elaborate systemically during trauma-induced hemolysis.⁶² The precise source of these nonmammalian metabolites and their role in post-injury pathophysiology deserve further investigation, which could include MS-metabolomic analysis for bacterial metabolites in postshock mesenteric lymph and blood product cell lysates.

Role of the PMN and Macrophages

PMN kinetics is different between MOF patients and non-MOF patients. Both groups develop neutrophilia at 3 hours post-injury; however, in patients who develop MOF there is a rapid neutropenia between 6 and 12 hours post-injury suggesting end-organ sequestration.⁶³ PMNs marginated to end organs cause direct local cytotoxic cellular effects via degranulation, and the release of nitric oxide and reactive oxygen species. They also have remote systemic proinflammatory cytokine effects, releasing proinflammatory mediators including IL-6, IL-8, and TNF-α. In non-MOF patients, neutrophil priming and neutrophilia are not followed by neutropenia, and neutrophil counts normalize over the ensuing 36 hours without end-organ damage.⁶⁴

Following trauma there is an immediate increase in adhesion molecules, including L-selectin and CD18, which allow PMNs to slow and roll along the endothelium and marginate out of circulation.⁶⁵ Antibodies directed against the CD11b/CD18 components of the adhesion receptor complex between leukocytes and endothelium significantly attenuate lung injury and prevent the neutropenia associated with tissue sequestration during experimental sepsis; further supporting that adherence of neutrophils to endothelium is a critical step in local tissue injury.⁶⁵

Circulating monocytes and tissue macrophages also become primed after severe injury and most authorities agree that microvascular endothelium has an integral role in post-injury priming of the innate inflammatory response.⁶⁴ Finally, other studies have demonstrated that the organ damage is dependent on complement activation through the classical pathway mediated by natural IgM antibody produced by B1 lymphocytes.⁶⁶

Role of Platelets

Our group demonstrated the predictive role of thrombocytopenia, especially when persistent, as a predictor of post-injury multiple organ failure.^67,68 In the mid-1990s, Gawaz et al measured the platelet surface expression of fibrinogen receptor on GPIIb-IIIa, of von Willebrand factor receptor GPIb, and of granule glycoproteins (thrombospondin, GMP-140, GP53) using flow cytometry and platelet-specific monoclonal antibodies. These authors observed irreversible degranulation of granule glycoproteins in MOF patients, which correlated positively with the severity of organ dysfunction.⁶⁹ Platelet-neutrophil interaction has been shown to be important in different models of acute lung injury including acid-aspiration, sepsis and transfusion injury.⁷⁰ In fact, blocking this interaction completely reversed acute lung injury in animal models.⁷¹ The Matthay group showed in a mouse model that transfusion-related acute lung injury (TRALI) depended on participation by both platelets and neutrophils, and that depletion of platelets or antiplatelet therapy with aspirin prevented TRALI. Similarly, in a rat model of trauma/hemorrhagic shock, we observed that animals pretreated with a platelet P2Y12 receptor antagonist were protected from post-injury acute lung injury.⁷² Furthermore, isoflurane, an halogenated ether known to interfere with platelet-granulocyte aggregation, attenuated acute lung injury (ALI) through an anti-platelet mechanism, partially through inhibition of the platelet ADP pathway.⁷³ We translated these observations to the clinical sphere, and documented that pre-injury antiplatelet therapy was associated with a decreased risk of lung dysfunction and multiple organ failure in high-risk blunt trauma patients who received blood transfusions.⁷⁴ Recently, Boyle et al confirmed that therapy with aspirin (a potent, long-lasting suppressor of platelet aggregation, via inhibition of cyclo-oxygenase enzymes that prevent thromboxane A2 production), given either before or during hospital stay, was associated with a reduction in ICU mortality among patients with established adult-respiratory distress syndrome (ARDS).⁷⁵ The results of the multicenter trial LIPS-A (Lung Injury Prevention with Aspirin, clinicaltrials.gov identifier NCT01504867) should provide interesting evidence on the therapeutic use of this antiplatelet agent.

Cytokines

The hemodynamic, metabolic, and immune responses are mainly regulated by endogenous mediators referred to as cytokines, produced by diverse cell types at the site of injury and by systemic immune cells.⁶⁵ Cytokines bind to specific cellular receptors resulting in activation of intracellular signaling pathways that regulate gene transcription and influence immune cell activity, differentiation, proliferation, and survival. They also regulate the production and activity of other cytokines, which may either augment or attenuate the inflammatory response. There is also significant overlap in bioactivity among different cytokines.³³ Cytokines can be classified into proinflammatory (TNF-α, MIP, GM-CSF, IFN-γ, IL-1, IL-2, IL-6, IL-8, IL-17, etc.) and anti-inflammatory cytokines (IL-4, IL-10, IL-13), which downregulate synthesis of the proinflammatory cytokines.⁶⁵

Jastrow et al⁷⁶ assessed the temporal cytokine expression (every 4 hours during 24 hours post-injury) during shock resuscitation in severely injured torso trauma patients. Median concentrations of IL-1 receptor antagonist (IL-1Ra), IL-8, eotaxin, granulocyte colony-stimulating factor (GCSF), granulocyte-macrophage colony-stimulating factor (CSF), inducible protein 10 (IP-10), monocyte chemotactic protein-1, and macrophage inflammatory protein-1 (MIP-1) were significantly greater in MOF patients compared with those in the non-MOF subgroup at each time interval. Adams et al⁷⁷ demonstrated that IL-8 can activate PMNs via two different receptors, and differential early expression of these receptors may provide an explanation for why some patients are at higher to develop MOF.

The cytokine pattern after trauma also differs for patients developing early (<3 days) versus late (>3 days) MOF. Analysis of cytokine serum biomarkers revealed that whereas early onset MOF was associated with an initial peak of IL-6 and IL-8 followed by a comparatively rapid return to baseline values, late MOF was characterized by a significant secondary increase of the proinflammatory cytokines IL-6 and IL-8.⁷⁸ Moreover, plasma levels of soluble tumor necrosis factor-alpha receptors (sTNF-R p55, sTNF-R p75) progressively increased during the 10-day observation period, and higher values were associated with lethal outcome.

Although inflammatory mediators’ levels vary greatly according to injury-related factors as well as the patient’s individual characteristics, most studies agree that the changes start very early post-injury.⁷⁹ This underscores the importance of measuring inflammatory mediators very early and at short intervals after injury.⁶⁶ Indeed, a 2009 German study including 58 multiple injured patients (ISS >16) found that IL-6, IL-8, and IL-10 differentiate patients with MOF (n = 43) and those without MOF (n = 15) within 90 minutes of injury.⁷⁹

PAMPS and DAMPS

The 1994 “danger theory” of the inflammatory response following trauma or infection proposed that the role of the immunological system was more than differentiating self from nonself but to protect the body from danger.^{46,80,81,82,83,84} In the “danger model,” immunological responses are triggered by specific types of cell death. If a healthy, undamaged cell dies an apoptotic death, it is scavenged without triggering an immune response. Conversely, a noncontrolled and abnormal cell damage via trauma or infection, causing lysis or apoptosis, releases intracellular contents and signals “danger,” triggering both innate and adaptive responses.^81,83,85 As Matzinger eloquently put it “the Danger model holds that the immune system is governed from within, responding to endogenous signals that originate from stressed or injured cells.”⁸⁵

Pathogen-associated molecular patterns (PAMPs) are exogenous microbial molecules that alert the organism to pathogens and are recognized by cells of the innate and acquired immunity system, primarily through Toll-like receptors (TLRs), and activate several signaling pathways (eg, NF-κB).⁸⁰ The new awareness of the close relationship between trauma- and pathogen-evoked responses led to proposal of the term “alarmin” to differentiate the endogenous molecules derived from cell damage from the pathogen-derived molecules.⁸⁰ Together, alarmins and PAMPs comprise the DAMPs. Major DAMPs are HMGB1 (high mobility group box protein-1), heat-shock proteins, uric acid, and DNA. The HMGB1 is a nuclear protein which binds to nucleosomes and promotes DNA bending. HMGB1 has been associated with SIRS and end-organ damage in animals, and shown to be elevated in trauma patients more than 30-fold above healthy controls as early as 1 hour post-injury.^80,86,87

A recent study by Zhang et al showed that injury releases mitochondrial DAMPs (MTDs) into the circulation with functionally important immune consequences.⁴⁵ The authors suggest that since mitochondria are evolutionary endosymbionts derived from bacteria, the released MTDs have conserved similarities to bacterial PAMPs. Thus, these MTDs signal through innate immune pathways identical to those activated in sepsis to create a sepsis-like state. This mechanism may be the key link between trauma, inflammation, and SIRS.

Toll-Like Receptors

TLRs are transmembranal proteins present in most body cell types, which form the major pattern recognition receptors that transduce signals in response to DAMPs.⁸⁸ They were shown to participate in the recognition of endogenous alarmins released from damaged tissues after ischemia/reperfusion injuries. Innate immune system responses are then initiated, including NF-kappa-B activation, cell activation, and proinflammatory cytokine production. Inhibition of TLR2 or TLR4 seems to be protective from ischemia/reperfusion injury in certain organs (hepatic, renal, cerebral, and heart) but not in the gut. It is conceivable that because the gut mucosa is continuously exposed to local bacterial endotoxins, local TLRs are uniquely regulated to prevent persistent inflammatory activity. In spite of the distinct roles played by TLR2 and TLR4 in individual organs, our understanding of how the multiple TLR members interact among each other in ischemia/reperfusion injuries is still limited, which may hinder the interpretation of interventions aimed at a specific TLR.

Heat Shock Proteins

HSPs are a family of DAMP molecular chaperones (eg, Hsp70 and Hsp90) necessary for the folding of newly synthesized proteins in the cell and also for the protection of proteins during exposure to stressful situations such as heat shock, which causes proteins folded previously to unfold.⁸⁹ Extracellular heat shock proteins (HSPs) can interact with several receptors (including TLRs), and have been implicated in inducing secretion of proinflammatory cytokines. However, highly purified HSPs do not show any cytokine effects suggesting recombinant HSP products may be contaminated with PAMPs that may be responsible for the reported in vitro cytokine effects of HSPs. Thus, the reported HSP’s role in antigen presentation and cross-presentation and in vitro cytokine functions may be attributable to molecules bound to or chaperoned by HSPs.

Complement

The complement system is considered a major component of the innate immunity response with several functions including: recognize and eliminate microorganisms, clear immune complexes and apoptotic cells, and mediate inflammation.⁸² However, research has shown complement to also enhance the adaptive response.⁹⁰ The complement system connects the innate and adaptive immune responses and also links the immune system with the coagulation system.⁹¹

Complement system activation occurs immediately after trauma leading to production of biologically active peptides.^47,82 Proinflammatory complement activation products include C3a, C3b, and C5a (chemotaxis of leukocytes; degranulation of phagocytic cells, mast cells, and basophils; smooth muscle contraction and increased vascular permeability), and leads directly to the generation of the terminal C5b–C9 complex (the complement membrane-attack complex) that leads to lysis of the target cells at the end stage of the complement activation cascade. Furthermore, complement activation results in the production of oxygen free radicals, arachidonic acid metabolites, and cytokines. However, excessive intravascular C5a may lead to neutrophil function “paralysis,” rendering them incapable to respond to C5a or other chemo-attractants, a paradox that has been equated to a “Pyrrhic victory of the innate immunity.”⁹² Several studies suggest that complement activation, especially serum C3 and C3a levels as well as C5a, reflects severity and treatment of injury and organ failure.^93,94,95,96

Complement regulatory proteins (CD55, CD46, CD55, CD59), the C5a receptor (CD88) inhibitors of complement, such as C4b-binding protein (C4BP) and factor I, modulate the complement cascade and protect against complement-mediated tissue destruction. Several studies in polytrauma patients indicate that these regulatory factors are significantly altered post-injury suggesting “a trauma-induced complementopathy.”^96,97,98

Oxidative Stress

Oxidative stress occurs when the level of toxic reactive oxygen intermediates (ROIs) overcomes endogenous antioxidant defenses as a result from either oxidant production excess or antioxidant defense depletion.⁹⁹ ROIs are normally generated by mitochondrial oxidation, metabolism of arachidonic acid, activation of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase in phagocytes, and activation of xanthine oxidase (XO) and play important roles in cellular homeostasis, mitosis, differentiation, and signaling.⁴⁷ Excess ROIs, however, cause direct oxidative injury to cellular proteins and nucleic acids, and disrupt cell membranes by inducing lipid peroxidation.^88,99

Ischemia/reperfusion (I/R) injury leads to significant disturbances in the production of ROIs.^47,88 During ischemia, hypoxemia leads to a shift from aerobic to anaerobic metabolism, with consumption of and decreased production of adenosine triphosphate (ATP). As ATP decreases, changes in cell membrane permeability result in intracellular Na⁺ increase causing cellular swelling and cell membrane damage. ATP reduction also increases cytosolic Ca²⁺ levels leading to phospholipase and protease activation resulting in cell damage. Increased ATP hydrolysis is followed by rising levels of AMP and purine metabolites. As reperfusion increases O₂ availability, oxidation of purines produces urate and superoxide radicals, which can produce the toxic hydroxyl radicals. In addition, superoxide radicals may be generated by a plasma membrane–associated NADPH oxidase system, which can be activated by macrophages, neutrophils, and other immunologic cells.¹⁰⁰ ROI secreted from PMNs after I/R injury induces cytokines, chemokines (IL-8), HSP, and adhesion molecules (P-selectin, ICAM-1) leading to cell and tissue damage.⁴⁷

Under normal conditions, NO production greatly exceeds O₂^– production in the endothelial cell (EC).¹⁰¹ However, with reperfusion, the balance between NO and O₂^– shifts in favor of O₂^–. The relatively low level of NO by constitutive endothelial nitric oxide synthase (NOS-I) reacts with the now abundant O₂^– to generate peroxynitrites, leaving little NO available to reduce arteriolar tone, prevent platelet aggregation, and minimize PMN adhesion to EC.¹⁰² In addition, NO seems to upregulate the production of proinflammatory cytokines.¹⁰¹ Thus, altering the redox state of the cell may contribute to the ongoing inflammatory cytokine production and progression to MOF. ROIs also play a role as second messengers in the intracellular signaling pathways of inflammatory cells, in particular, activation of NF-κB and activator protein 1 (AP-1), which can be activated by both oxidants and antioxidants depending on the cell type and on intracellular conditions.⁹⁹

Endogenous antioxidant defenses, including enzymatic (superoxide dismutase, catalase, glutathione peroxidase) and nonenzymatic (vitamins E and C, provitamin A, glutathione, bilirubin, urate) groups that combat oxidative stress, were the focus of interventions to modulate the inflammatory response to critical illness. However, the results of the large randomized clinical trials REDOX^100,103,104 and METAPLUS,¹⁰⁵ both demonstrating harm in systemic administration of antioxidants, have discouraged research in this direction.⁵³ For both glutamine and antioxidants, the greatest potential for harm was observed in patients with MOF that included renal dysfunction.¹⁰⁴ It is possible, that antioxidants can only be effective at specific sites and/or specific cells as opposed to a systemic alteration in the redox balance.¹⁰¹

Later Risk Factors

Abdominal Compartment Syndrome

A hallmark of the post-injury inflammatory state is generalized capillary leak and associated tissue edema. There has been change resurgent interest in this phenomenon as intra-abdominal hypertension has accompanied the recent widespread application of damage control procedures (see Chapter 38).¹⁰⁶ Increased intra-abdominal pressure (IAP) is associated with a host of physiologic derangements that include high ventilator pressures, decreased cardiac output, and impaired renal function, a constellation of signs that are named abdominal compartment syndrome (ACS). Usually associated with abdominal injuries (primary ACS), these effects can also be observed following extra-abdominal injury or following large-volume resuscitation for nontraumatic or nonsurgical conditions (secondary ACS).¹⁰⁷

The incidence of ACS varies greatly according to the resuscitation strategy but is primarily dependent on the severity of injury and the degree of shock. Mesenteric I/R increases microvascular permeability, causing bowel wall edema that can directly cause decreased bowel motility, decreased barrier function, and further capillary leak. Splanchnic hypoperfusion during shock is compounded by even mild increases in IAP (which can reduce the abdominal perfusion pressure) and low plasma oncotic pressure from crystalloid resuscitation (which worsens edema). As with any compartment syndrome, the increased pressure within the compartment rises above postcapillary pressure causing a functional venous and lymphatic obstruction. Under these conditions, the intestinal epithelium microvilli secrete fluid into the gut lumen. Transudation of free fluid into the peritoneal space also contributes to further IAP increases. The combination of bowel wall edema, intraluminal fluid secretion, and fluid accumulation in the peritoneal cavity further increases IAP and gut ischemia, which affects the inflammatory response as described above. While ACS physiologic effects usually reverse on decompression, the immunomodulatory effects may persist and trigger MOF.¹⁰⁸

ACS incidence has lowered to as 0–2% in high-performing trauma centers, a substantial decrease in this highly lethal condition compared to 15% reported by earlier studies.¹⁰⁶ Although life-threatening post-injury ACS is preventable, most patients with major shock and trauma develop some transient increase in intra-abdominal pressure. If this pre-ACS state is combined with renal impairment or severe lung injury, MOF is unknown.¹⁰⁶ As an isolated entity, sub-ACS IAH is probably negligible, but in combination with other distant organ dysfunctions, this syndrome could be detrimental.

Blood Transfusions

The goals of transfusion in the injured patient are to maintain adequate oxygen-carrying capacity. However, there is substantial, solid evidence that blood transfusions are a risk factor for the development of MOF independent of shock or injury severity.^{37,67,109,110,111} Indeed, blood transfusions fit many of the criteria for causation, that is, strength of the association, temporal relationship (risk factor precedes outcome), dose–response relationship, consistency, and reproducibility. Knowledge of this association has resulted in more judicious use of blood products during resuscitation (see Chapter 12).³⁷ Despite this reduction in the use of red blood cells, early blood transfusion remains one of the most powerful independent risk factor for post-injury MOF.³³ Reductions in blood transfusion in the resuscitation period correlate with improved outcome and less MOF.³⁷ Blood products are immunoactive, contain proinflammatory cytokines and lipids, and have an early immunosuppressive effect predisposing the patient to SARS, infection, and late MOF.¹¹¹

The age of transfused blood is also important, with progressive daily increases in proinflammatory cytokines in stored blood products. Transfusing packed red blood cells (PRBCs) stored more than 3 weeks in the first 6 hours post-injury is associated with a higher rate of MOF, while PRBC units with shorter storage times are associated with decreased MOF prevalence and less morbidity and mortality. Leukodepletion does not remove the potential for blood to act as a second hit, as PRBCs contain proinflammatory mediators. Initially, this was believed to be related to the generation of the PAF, IL-6, and IL-8 during storage. Later studies found that biologically active lipids (lysophosphatidylcholines) accumulate in stored blood and are capable of PMN priming. “Passenger leukocytes” present in stored blood have been implicated as pivotal components by the finding that prestorage leukoreduction decreases the PMN priming and transfusion-mediated lung injury in animal models. Proposed mechanisms include induction of T-cell anergy in the recipient, decreased natural killer cell function, altered ratio of T-helper to T-suppressor cells, and soluble proinflammatory cytokines produced by leukocytes during storage. Together, these effects can suppress the recipient immune system and promote a worse proinflammatory state leading to increased infection and complications.

Proteomic analysis of PRBC and leukoreduced-PRBC, after depletion of the 14 most abundant proteins, detected PRBC-related proteins including: structural proteins, protein 14-3-3, band 3, the α- and β-hemoglobin chains, and enzymes involved in essential metabolic function such as glycolysis and redox cycling to protect against oxidative damage.¹¹² Furthermore, storage of unmodified PRBC supernatant resulted in increased concentrations of both leukocyte specific proteins (moesin, MPO, MMP-8, MMP-9) and platelet specific proteins (integrin alpha 2b, platelet glycoprotein V) which are removed by prestorage leukoreduction. Several structural proteins also increased including actin, α-actinin-1, vinculin, and talin-1. The latter three are important scaffolding proteins responsible for stable presentation of adhesion molecules. In addition, several glycolytic enzymes also increased including α-enolase, involved in plasmin activation and extracellular matrix degradation.^113,114 Conversely, mannose-binding lectin 2, the complement protein C4b, protein C, and prothrombin significantly diminished in PRBC supernatant, which could inhibit innate immunity. Leukoreduced PRBC showed accumulation of an active phospholipase, which could explain the production of arachidonic acid, and the 5-LO metabolites 5-, 12-, and 15-HETE via cleavage of lipids from RBC membranes, which have the capacity to cause transfusion-related acute lung injury in vivo.¹¹⁵

Other blood-derived products (platelets, plasma, and coagulation factors) are also immunoactive and could act as second hits (see Chapter 13). Transfusion of fresh frozen plasma (FFP) has been shown to be associated with MOF among severely injured, massively transfused patients, although no details about when plasma was given or about plasma:PRBC ratios were available in that study.¹⁰⁹ Proteomic analysis of fresh frozen plasma by our group suggested that plasma of female donors had higher levels of factor V and antiproteases as well as complement factors H and C4b compared to male donor plasma.¹¹⁶ These preliminary data were derived from a small sample but suggest that, during resuscitation, female donor plasma may more efficiently augment factor V levels, increase circulating antiprotease concentrations, thus potentially decreasing indiscriminate alternative pathway activation of complement.

Proteomic analyses of platelet supernatants of healthy donors suggested a storage and sex-dependent impairment of blood coagulation mediators, proinflammatory complement components and cytokines, energy, and redox metabolic enzymes. Specifically, the analysis of the platelet supernatants suggested storage-dependent platelet activation, which was more pronounced among female donors.^117,118

Infections

Osler recognized in 1904 that “except on few occasions, the patient appears to die from the body’s response to infection rather than from the infection.”¹¹⁹ The association of infection and MOF has been widely explored. In the late 1970s, intra-abdominal abscess (IAA) was the inciting event in half of the cases.¹²⁰ As a result of the appropriate use of presumptive antibiotics for abdominal trauma and prompt diagnosis of hollow viscus injury, the incidence of post-injury IAA decreased and its progression toward MOF followed. The epidemiology of post-injury infections changed and nosocomial pneumonia became the principal infection associated with MOF (see Chapter 3).

While the anti-inflammatory response may be protective because it limits unnecessary inflammation potentially auto-destructive, it is associated with relative immunosuppression predisposing the host to infections.¹²¹ Data from both clinical and animal studies suggest diminished production of proinflammatory type 1 and increased production of inhibitory type 2 cytokines by T cells. Monocytes/macrophages and suppressor T lymphocytes have been implicated as key modulators that downregulate immune functions.

Another area of research interest has been the potential role of persistent hypercatabolism in the development of infections.⁶⁵ Although energy expenditure can increase dramatically following injury, the associated hypercatabolism is a critical metabolic alteration. If not supported by exogenous nutrients, the consequent obligatory protein turnover quickly erodes somatic protein stores and then the critical visceral mass. The resulting acute protein malnutrition causes well-documented adverse immunologic consequences and is a recognized cofactor for the development of post-injury infection (see Chapter 3).

Secondary Operation

The second operation can be considered a controlled traumatic event where surgical trauma takes the place of the initial injury. Additional stresses of secondary operations include higher intraoperative fluid administration, hypothermia, hypotension, tissue hypoxia, and intraoperative blood loss.⁶⁵

The timing of the second operation has been studied over the last decade mostly as related to operative fracture fixation. In 1989, Bone et al published a prospective randomized study showing that, compared to early stabilization of femoral fractures, delayed stabilization resulted in higher incidence of adult respiratory-distress syndrome, fat embolism, and pneumonia, as well as longer ICU stay.¹²² While early definitive fracture fixation decreases post-injury morbidity and improves recovery, it is not without consequences when performed within the priming window. A 2003 randomized controlled trial by Pape et al demonstrated that early external fixation followed by delayed conversion to intramedullary instrumentation was associated with a decreased inflammatory response to the operative fixation.¹²³ The same group compared the inflammatory response of injured patients with femoral shaft fracture who were divided into two groups according to their initial treatment: (1) damage control orthopedics (DC) group if the femoral fracture was initially stabilized with an external fixator and (2) intramedullary nailing (IMN) group if they underwent primary IMN.¹²⁴ Despite more severe injuries in the DC group, patients had a less severe and shorter postoperative SIRS and did not suffer significantly more pronounced organ failure than the IMN group. DC patients undergoing conversion while their SIRS score was raised suffered the most pronounced subsequent inflammatory response and organ failure. According to these data, DC treatment was associated with a lesser SIRS than early total care for femur fractures.

Our group recently examined outcomes associated with early total care with IMN (ETC group) versus damage control external fixation (DC group) for 462 multiple injured patients with femoral shaft fractures.¹²⁵ Although minimal differences were noted between DC and ETC groups regarding systemic complications, DC was a safer initial approach, significantly decreasing the initial operative exposure and blood loss. We also explored the application of the DC concept to spine fractures and observed similar beneficial effects regarding pulmonary complications, infections, mechanical ventilation time, and length of ICU stay.¹²⁶ Collectively, these findings suggest that a secondary operation can act as an additional inflammatory insult and amplify the post-injury inflammatory response and precipitate MOF.

Preventing the onset of MOF through therapies directed at modulating the balance of SIRS and SARS will offer more practical benefit to injured patients than efforts to treat MOF once established, when the treatment is largely supportive.³³

Protective Resuscitation Techniques

Certain resuscitative strategies protect against distant organ injury after periods of gut I/R.⁵⁸ Resuscitation with isotonic crystalloids proposed in the late 1960s contributed to a decrease in mortality and acute renal failure, but was implicated in the emergence of ARDS as a major source of morbidity and mortality in the ICU. There is still controversy about the use of isotonic crystalloids compared with colloids. The multicenter, randomized, double-blind SAFE trial showed no difference in mortality, single organ failure, and MOF between the groups receiving saline and the group receiving albumin.¹²⁷ A preplanned subgroup analysis of trauma patients, however, seemed to favor the use of crystalloids, although the difference was not significant at the 95% confidence level (relative risk, 1.36, 95% confidence interval, 0.99–1.86, P = 0.06). In fact, when patients with brain injury were excluded, no difference was detected (death rate in both groups = 6.2%, relative risk, 1.0, 95% confidence interval, 0.56–1.79, P = 1.00). A 2012 large Australian and New Zealand randomized clinical trial found similar survival in the overall sample and in the subgroup of trauma patients.¹²⁸ A 2013 Cochrane systematic review compared colloids with crystalloids and showed no difference in mortality of trauma patients.¹²⁹ The lack of a survival advantage combined with the higher costs of colloids favors the use of crystalloids in trauma resuscitation (see Chapter 12).

A systematic review (considered up to date as of 2007) comparing hypertonic with isotonic crystalloid solutions for the resuscitation of patients with trauma or burns or those undergoing surgery did not provide enough data to determine there was a difference in outcomes.¹³⁰ The authors, however, pointed out that confidence intervals were wide and recommended further trials were needed. Hypertonic resuscitation (hypertonic saline and 6% Dextran 70) was compared with lactated Ringer’s solution (LRS) in adult, blunt trauma patients by Bulger et al in a recent randomized clinical trial.¹³¹ The study, stopped after the second interim analysis for potential safety concern (increased mortality in the subgroup of nontransfused patients receiving hypertonic saline) and futility, demonstrated no significant difference in ARDS-free survival (hazard ratio, 1.01; 95% confidence interval, 0.6–1.6). Although there was improved ARDS-free survival in the subset requiring massive transfusion (hazard ratio, 2.2; 95% confidence interval, 1.1–4.4), a subsequent analysis of patients in severe shock (systolic blood pressure <70 mm Hg) suggested that treatment with hypertonic saline was associated with worsened hypocoagulation and hyperfibrinolysis.¹³² Hypertonicity has an effect on multiple immune response functions, which may translate into improved outcomes in select populations, using alternative modes of administration.¹³³ It is conceivable that the beneficial effect of hypertonic saline may be realized if administered locally (as opposed to systemically). In order to test this hypothesis, we are currently conducting a prospective phase I trial administering nebulized hypertonic saline to moderately injured patients (NCT01667666). Similarly, low-dose albumin was shown to protect against shock-induced lung, EC, and red blood cell injury, as was the intraintestinal administration of a pancreatic protease inhibitor.⁵⁸

Judicious use of blood products reduces the incidence of MOF. A 12-year analysis of our MOF dataset suggests that reduction of blood use was implicated in the decreased incidence of MOF in our trauma center.³⁷ Current transfusion guidelines support the safety of restrictive transfusion practices in trauma patients.^134,135 Other techniques to reduce the deleterious effects of PRBCs are washed PRBCs and prestorage leukoreduction.¹¹¹ The beneficial effects of washed PRBC units are acknowledged but the preparation time, lack of apparatus to wash units in many blood banks, and the short outdate of washed units (24 hours) make this practice unrealistic in most trauma settings. Prestorage leukoreduction may reduce biologically active lipids in stored PRBC and trials have shown modest improvements in outcomes, except for cardiac surgery patients, among whom a dramatic, 50% reduction in mortality was reported.^136,137

Finally, blood substitutes have offered promising results in trauma populations. Only two hemoglobin substitutes have been studied extensively in injured patients: the diaspirin cross-linked hemoglobin from the Baxter Corporation (Hemassist); and the polymerized, pyridoxylated human hemoglobin (PolyHeme) from Northfield Laboratories.^111,138,139 Other products have been studied in nonacutely injured, surgical patients, including: Hemopure (HBOC 201), Hemolink, and Hemospan.^138,139

Our experience in the trauma setting with PolyHeme suggests it provides an immunologic advantage relative to blood in the injured patient by diminishing PMN priming and decreasing IL-6 and IL-8.¹⁴⁰ In a recent clinical trial, patients resuscitated with PolyHeme, without stored blood for up to 6 U in 12 hours post-injury, had outcomes comparable with those for the standard of care. Although there were more adverse events in the PolyHeme group, the benefit-to-risk ratio of PolyHeme was favorable when blood was needed but not available.¹⁴¹ In a recent meta-analysis of blood substitutes, the authors concluded that these products were associated with an increased risk of mortality and myocardial infarction.¹⁴² However, because the authors included studies on such diverse populations, the results of the meta-analysis were questionable.¹⁴³ In fact, in studies with trauma patients, the associations were not significant. Although as of 2015 the Food and Drug Administration (FDA) has not approved any blood substitutes, South Africa’s Medicine Control Council approved Hemopure in April 2001 for use in acutely anemic patients (http://www.hst.org.za/news/south-africa-becomes-first-country-approve-blood-substitute, accessed September 17, 2015).¹³⁸

Protective Lung Ventilation

In addition to direct injury and secondary inflammatory-mediated injury discussed below, the lung is also subject to ventilator-induced lung injury (see Chapter 57). While the mechanical ventilator is an indispensable therapy for lung failure, the administration of positive pressure ventilation can result in lung injury that is functionally and histologically identical to that seen in ARDS. Conversion from negative pressure ventilation to positive pressure ventilation is associated with unequal distribution of tidal volumes to the heterogeneously involved lung parenchyma. Areas of low compliance (as seen in pulmonary contusion, edema, or infection) force tidal volumes to areas of high compliance resulting in increased alveolar pressures, overdistension, and injury to uninvolved lung tissue. Mechanical injuries to the lung (barotrauma, atelectrauma, volutrauma) initiate a local inflammatory reaction and biotrauma with release of inflammatory mediators from damaged cells, recruitment of PMNs to the site of injury, and local inflammatory reaction mediated by circulating leukocytes. Mechanical stresses on the living cell are translated into intracellular inflammatory signal transduction and the combination of mechanical damage from positive pressure ventilation and the inflammation increases pulmonary dysfunction.¹⁴⁴

The effects of ventilator-induced lung injury extend beyond the lung. Impaired oxygen delivery amplifies post-traumatic I/R injury. Inflammatory cytokines generated in the lung spill over into the systemic circulation and have the capacity to increase the inflammatory state (priming) and promote remote organ dysfunction via direct cell signaling (activation).

Clinical evidence of the contributing effects of MV on the incidence of MOF was demonstrated in the ARDS Network lung-protective ventilation (LPV) trials.¹⁴⁵ A 2007 Cochrane Library systematic review showed that day 28 mortality was significantly reduced by LPV (relative risk, 0.74; 95% confidence interval, 0.61–0.88).¹⁴⁶ A 2013 update of this Cochrane review does not show any different results.¹⁴⁷ Current evidence supports PLV as the standard therapy for patients at risk for ARDS.

Adrenal Insufficiency and Cortisol Replacement Therapy

Serum cortisol levels in polytrauma patients have been shown to be 30 μg/dL or greater for at least a week.¹⁴⁸ Adrenal insufficiency (AI: random serum cortisol <25 μg/dL or stimulation test increase <10 μg/dL), seems to be a frequent occurrence in trauma patients, that if left untreated is associated with increased mortality.^149,150 The major limitation of these retrospective reviews, however, is related to patient selection bias, as only patients in whom AI is suspected have cortisol measurements and/or stimulation tests. An RCT in trauma patients is urgently needed to better define whether AI is a risk factor for, or a symptom of, post-injury MOF, and the role of administration of cortisol post-injury.

A recent task force from the Society of Critical Care Medicine and the European Society of Intensive Care Medicine appraised the current evidence and delivered general recommendations regarding AI and cortisol replacement therapy in critically ill patients.¹⁵¹ Although the recommendations did not specifically address trauma patients, it is reasonable to assume that AI behaves similarly in trauma as in other SIRS-inducing conditions. The task force recommended that AI should be suspected in hypotensive patients who have responded poorly to fluids and vasopressor agents, who present a delta serum cortisol of less than 9 μg/dL after adrenocorticotrophic hormone (250 μg) administration or a random total cortisol of less than 10 μg/dL. Although the task force supported the use of stimulation tests in AI diagnosis, the sole use of a random cortisol level has been shown to be sufficient and rarely discordant with the results of the stimulation tests.¹⁴⁸ Specifically, among patients most likely to benefit from treatment with glucocorticoid (vasopressor-dependent septic shock and patients with early severe ARDS, ie, Pao₂/Fio₂ of <200 and within 14 days of onset), the task force recommended that the decision to treat with corticosteroids be based on more on the presence of the clinical criteria and not solely on the results of adrenal function. Glucocorticoids should be tapered down slowly, and reinstitution should be considered if there are signs of sepsis, hypotension, or worsening oxygenation.

The dose of corticosteroid should be sufficient to downregulate the proinflammatory response without causing immunodeficiency and impaired wound healing. Therapy with high-dose corticosteroids (>1000 mg/d of hydrocortisone or equivalent) has not improved outcomes and was associated with higher complication rates. The use of extended course, stress-dose corticosteroids (200–350 mg/dL of hydrocortisone or equivalent) in critically ill patients has been associated with improved outcomes (reduction in mortality, length of stay, and MV requirements). A note of caution on the use of etomidate as an anesthetic induction agent in critically ill patients: this agent has been associated with inhibited cortisol production for up to 48 hours, and to be an independent risk factor for death.¹⁵²

Insulin and Glycemic Control

While glycemic control (≤180 mg/dL) is undoubtedly important, tighter glucose control (81–108 mg/dL) in critical care patients has had conflicting results.^153,154,155 The recently published NICE-SUGAR study¹⁵⁶ demonstrated an increased death risk associated with intensive glucose control compared with more conventional glycemic goals. Interestingly, in this study, trauma patients were one of two subgroups to exhibit the opposite trend, albeit not statistically significant. A review of our Denver MOF showed that, after exclusion of diabetes patients, most patients (77%) of patients maintained mean glucose less than or equal to 180 mg/dL but only 10% between 81 and 108 mg/dL (tight glucose levels). Interestingly, older patients benefitted more from tight glucose control levels than their younger counterparts.¹⁵⁷

In addition to its role in glucose control and induction of anabolic processes, one must account for the immunomodulatory effects of insulin, which can attenuate SIRS and modulate the proliferation, apoptosis, differentiation, and immune functions of monocytes/macrophages, neutrophils, and T cells associated with severe trauma, burn injury, or sepsis.¹⁵⁸

Immunonutrition

Two aspects are relevant in immunonutrition: the delivery route (enteral vs parenteral) and the diet composition.¹⁸ Although controversy exists concerning the safety of feeding the hypoperfused small bowel, evidence supports that early enteral nutrition (EEN) is not only feasible but also associated with decreased incidence of nosocomial infections (see Chapter 60). EEN effects go far beyond mere nourishment; rather EEN induces a complex immunologic response.¹⁵⁸ EEN supports the function of the mucosal-associated lymphoid tissue (MALT) that produces 70% of the body’s secretory IgA.¹⁵⁹ Naive T and B cells target and enter the gut-associated lymphoid tissue (GALT) where they are sensitized and stimulated by antigens sampled from the gut lumen and thereby become more responsive to potential pathogens in the external environment. These stimulated T and B cells then migrate via mesenteric lymph nodes and the thoracic duct and into the vascular tree for distribution to GALT and extraintestinal sites of MALT. Lack of enteral stimulation (ie, use of TPN) causes a rapid and progressive decrease in T and B cells within GALT and simultaneous decreases in intestinal and respiratory IgA levels. Previously resistant TPN-fed lab animals, when challenged with pathogens via respiratory tree inoculation, succumb to overwhelming infections. These immunologic defects and susceptibility to infection are reversed within 3–5 days after initiating EN.¹⁵⁹ Indeed, feeding the gut in critically ill patients has been shown to reverse shock-induced mucosal hypoperfusion and impaired intestinal transit as well as attenuate gut permeability defects and lessen the severity of CARS.¹⁸

Regarding content, to be effective, immunonutritional therapies must ameliorate cellular defense, oxidative stress, and mitochondrial function without increasing SIRS. As mentioned in previous sections, rigorous studies on immunomodulating diets, so far, have been disappointing.^53,100,104

TLR-Directed Interventions

Because TLR activation leads to an intense and immediate inflammatory reaction in response to I/R injury, targeting TLRs may be a promising intervention strategy to reduce MOF. Yet, because TLR activation occurs through a variety of mechanisms, generating full antagonists is technically difficult. The development of eritoran, a potent and full antagonist of LPS at TLR4, is a significant advance and offers hope that other TLR-selective antagonists may become available in future years.¹⁶⁰

Immunomodulation

In the immunodepression stage of the inflammatory response to injury, it may be useful to enhance immune function to prevent infections that can act as second insults. An analysis of leukocyte gene expression associated with post-trauma gram-negative bacteremia in the Glue Grant dataset showed that both innate and adaptive immunity appeared to be suppressed by 96 hours post-injury.¹⁶¹ These findings suggested that immunostimulants, such as interferon-gamma, in patients with decreased immune gene expression, may be a promising therapeutic approach. GM-CSF was tested in small trauma populations and shown to counteract trauma-induced monocyte function depression while IFN-γ had the capacity to enhance HLA-DR on B and T lymphocytes.^162,163

Mesenchymal stem or stromal cells (MSC) have been shown to exert protective effects through the release of promitotic, antiapoptotic, anti-inflammatory, and immunomodulatory soluble factors.¹⁶⁴ Initially, MSC cells were believed to regenerate dysfunctional, damage organs, however, later it became clear that their beneficial effects were mediated by secretion of factors. MSCs tend to migrate toward sites where there is inflammation or injury, thus dysfunctional organs are potential targets. Since most approaches targeting a single pathway or mechanism have not been promising, MSCs are attractive because they tackle several pathways modulating multiple immune cells and the oxidative process, in addition to their antibacterial properties. A few phase I trials have been completed showing an acceptable safety profile.^165,166 At the time of this writing, no phase II trial results are available.

In the 2015 Shock Society Thirty-Eighth Annual Conference on Shock, Sordi and colleagues from Europe presented promising results using artesunate (a medication commonly used to treat falciparum malaria) in a rat model of hemorrhage-induced organ dysfunction.¹⁶⁷ Artesunate treatment was associated with lower levels of creatinine and lung myeloperoxidase activity as well as increased activation of Akt and eNOS, reduced activation of GSK-3 beta and NF-kappa B activation, and attenuated increase in serum TNF-alpha associated with the hemorrhagic shock. These findings suggest that artesunate attenuated organ dysfunction (lungs and kidneys) likely via activation of the Akt-eNOS survival pathway, and/or by reducing inflammation via inhibition of GSK-3 beta and NF-kappa B. Based on these experiments, the group received funding from the Wellcome Trust for a Phase IIa, single-center, placebo-controlled, randomized, phase II clinical trial of Artesunate for Trauma Organ Protection (TOP-ART) (ISRCTN15731357, available at www.isrctn.com and www.c4ts.qmul.ac.uk/organ-failure-protection/top-art, accessed December 18, 2015).