Trauma patients rarely, if ever, enjoy the luxury of an overnight fast; therefore, pulmonary aspiration of gastric contents presents a very real risk for them. In addition, the stress of trauma or the administration of opiate analgesics will profoundly inhibit gastric emptying. Induction of general anesthesia in these cases is usually accomplished with a “rapid sequence” technique and the use of Sellick’s maneuver (“cricoid pressure”).17,18 This induction sequence is performed with airway rescue devices at hand and the “difficult airway algorithm,” developed by the American Society of Anesthesiologists, is invoked if it fails.19 Institution of regional anesthesia in a trauma patient does not remove the risk of pulmonary aspiration; the patient may aspirate at any time if he loses consciousness and his protective airway reflexes become obtunded.
Rapid Sequence Induction and the Suspected Cervical Spine Injury
Virtually every experienced trauma anesthesiologist has his own “tried and true” method of securing the airway in these patients, many of whom present for intubation in the emergency room.20 Common characteristics of emergent orotracheal intubation include Sellick’s maneuver, maintenance of the neck of the patient in the neutral position and removal of the anterior portion of the cervical collar in order to facilitate laryngoscopy. Airway rescue devices are usually at hand, as should be the resources needed to perform a tracheotomy.
Many trauma anesthesiologists will confirm the appropriate position of an endotracheal tube, which they themselves have not inserted, using one or more of the following techniques: auscultation of breath sounds, capnography, repeat direct laryngoscopy, or fiberoptic bronchoscopy. The desire to immediately reintubate a patient with a functioning esophageal obturator already in place must be tempered by the knowledge that its insertion may have produced substantial upper airway trauma. If possible, any exchange of airway devices may best be reserved for the formal operating room environment.
Pediatric and geriatric patients possess substantial deviations from what is considered “normal adult” cardiovascular, pulmonary, hepatic, and renal physiology. They may respond to volume depletion with precipitate hypotension, apnea may be poorly tolerated, and drug clearance may be unpredictable (it is generally reduced) in the presence of immature or senescent hepatorenal function. They share an inability to maintain normal body temperature under conditions of stress and an impressive coagulopathy may develop in the presence of hypothermia.
The Morbidly Obese Patient
Even under optimal circumstances, the anesthetic care of the morbidly obese patient presents many challenges. At the top of the list are airway considerations: obese patients may be difficult to ventilate, difficult to intubate, and may possess a markedly reduced functional residual capacity, resulting in rapid arterial desaturation in the presence of ineffective ventilation of the lungs. Their body habitus may make effective arterial or venous access very difficult to achieve. They may present with numerous medical comorbidities, including hypertension, coronary artery disease, congestive heart failure, obstructive or restrictive lung disease, diabetes mellitus, deep vein thrombosis, and hepatic steatosis; these may be in varying states of compensation at the time of injury. Considerations such as these accompany the patient into the postoperative period, complicating the recovery phase.
Unique physiologic changes complicate the care of the pregnant trauma patient. Circulating progesterone relaxes the lower esophageal sphincter, allowing free reflux of gastric contents into the hypopharynx; even in the absence of traumatic injury, a rapid sequence induction with Sellick’s maneuver is essential in order to prevent massive aspiration. Circulating plasma volume is increased, producing an edematous upper airway and extremities; intubation may be difficult and reliable vascular access may be a challenge to secure. Tracheotomy may be rendered hazardous by an enlarged, hypervascular thyroid gland. Also, the gravid uterus exerts upward pressure on the bases of the lungs, reducing functional residual capacity; this results in rapid arterial desaturation if ventilation is ineffective. In addition, when the patient is supine, the gravid uterus rests upon her aorta and inferior vena cava, reducing venous return to the heart. Therefore, profound hypotension and fetal asphyxia may occur if she is not positioned on her side, or at least with the left hip elevated, for transport, induction, and surgery itself.
Of course, not all pregnant trauma victims are healthy prior to injury: gestational diabetes mellitus, pregnancy-induced hypertension, seizure disorders, gestational asthma, deep vein thrombosis, various coagulation abnormalities, and morbid obesity may be present, with all of their medical, surgical, and anesthetic implications. Also, one must remember that there are two patients who require attention: the mother and the fetus. Emergent evacuation of the uterus should always be anticipated and may be necessary in the event of maternal arrest. The fetus cannot survive in the absence of effective uteroplacental perfusion and the mother cannot be effectively resuscitated as long as the gravid uterus reduces venous return to the heart.
Open or closed brain trauma may occur as an isolated finding or as one of several injuries in a victim of multiple trauma. In most of these patients, the blood-brain barrier is disrupted and cerebral edema is present. Many of these patients will be obtunded, lack protective airway reflexes, and possess ineffective spontaneous ventilation. The resulting hypoxemia and hypercarbia will increase intracranial pressure and will have detrimental effects on the viability of injured neural tissue. They are also clearly at risk for pulmonary aspiration of gastric contents. Consequently, emergent endotracheal intubation is usually indicated in order to protect the airway and to control oxygenation and ventilation. Since the salvage of cells within the ischemic penumbra of injured neural tissue is of paramount importance, maintenance of a normal perfusion pressure and oxygen carrying capacity in the blood is essential. The institution of hyperventilation is indicated for the control of intracranial hypertension, if present, as is the administration of osmotic diuretics and hypertonic saline. These considerations should be kept in mind from the time of initial intubation in the emergency room, through the period of diagnostic imaging, into the operating room and in the postoperative recovery phase.
Many of the considerations for traumatic brain injury also are present in the patient with acute spinal cord injury. Succinylcholine may be used to facilitate emergent intubation in these patients at the time of their initial presentation; however, its administration is contraindicated later in their hospital course due to the risk of abrupt, fatal hyperkalemia.
The administration of succinylcholine to the patient with an open globe injury is now considered by many to be safe.21 Used to facilitate endotracheal intubation, it does not result in the extrusion of vitreous humor and it is the muscle relaxant of choice if the patient requires a rapid sequence induction. Patient movement or “bucking” during the course of the anesthetic, however, will place the patient at risk for this complication and it must be avoided.
Patients with this disease may develop fatal hyperthermia, skeletal muscle rigidity, rhabdomyolysis, and dysrhythmias when exposed to inhaled anesthetic agents or succinylcholine. The disease is caused by inherited or spontaneous mutations of the RYR1 or CAC1NAS genes, which regulate calcium ion transport in the sarcoplasmic reticulum. Definitive diagnosis is made by subjecting biopsied muscle to the halothane- or caffeine-contracture test. Most anesthesiologists will consider any member of a kindred afflicted with malignant hyperthermia to be at risk for developing the reaction, even in the absence of a personal history, and will avoid the administration of triggering agents to these individuals.22 Malignant hyperthermia presents with a spectrum of reactions, ranging from mild to severe, and it is treated by immediately discontinuing any inhaled anesthetics or succinylcholine and by administering dantrolene sodium. The Joint Commission for the Accreditation of Hospital Organizations requires that a supply of dantrolene sodium be present in every surgical suite. Supportive measures include cooling the patient, hydration, and the treatment of acid–base disturbances. Other genetic disorders that are associated with malignant hyperthermia include hypokalemic periodic paralysis, central core disease, multiminicore disease, and Duchenne’s muscular dystrophy. Treatment protocols and resources for patients may be quickly accessed on the website of The Malignant Hyperthermia Association of the United States.23
Many trauma victims present with a documented history of substance abuse. Common intoxicants include ethanol, cocaine, marijuana, phencyclidine, ketamine, opiates, and any one of a number of amphetamine compounds. Of compelling concern to the anesthesiologist are the pulmonary and cardiovascular effects of central nervous system stimulants, in particular, when they are inhaled. The inhalation of “crack cocaine” or “crystal meth” can produce pulmonary thermal injury, abrupt hypertension, myocardial ischemia, and malignant ventricular dysrhythmias.24 Also, chronic abuse of “crystal meth” has been linked to the development of a severe dilated cardiomyopathy, thought to be the result of continual catcholamine elevation.25 In addition, severe intoxication with cocaine, amphetamines, and certain major tranquilizers may produce muscle rigidity and an elevation of core body temperature; these signs and symptoms may be confused with malignant hyperthermia.26 In most of these clinical situations, the administration of dantrolene sodium is generally ineffective.
The course of an anesthetic for a “screening laparoscopy” in a healthy, stable trauma patient is generally uneventful. However, the associated pneumoperitoneum may be poorly tolerated in patients with limited myocardial or pulmonary reserve: abrupt hypotension, hypoxemia, or both may develop, and may not resolve until deflation of the abdomen.27 The institution of invasive monitoring or the use of transesophageal echocardiography may be helpful if pneumoperitoneum cannot be avoided.
Most healthy, stable trauma patients will compensate for the reductions in cardiac output and functional residual capacity that occur during movement from the supine to the prone position.28 However, patients with limited myocardial or pulmonary reserve may develop abrupt, profound hypotension, or hypoxemia, or both, after prone positioning; this is particularly evident in the morbidly obese patient. In addition, the obese patient may become very difficult to ventilate because of increases in intra-abdominal and intrathoracic pressure. The simplest remedy is to avoid the prone position in an unstable patient and to use the lateral position, if at all possible. If the prone position is essential for surgical access, one may consider the use of an operating table that does not inhibit the free excursion of thorax and abdomen; an example of this is the orthopedic spine table.
Ophthalmic complications may occur following the use of the prone position for surgery. Postoperative blindness is the most devastating of these; it may be caused by central retinal artery occlusion, ischemic optic neuropathy and rarely, ischemia of the visual cortex. Its incidence has increased as the number of lengthy spine procedures has increased.29,30 Associated factors include intraoperative anemia or hypotension, operative procedures of long duration, diabetic or hypertensive retinal vascular disease, excessive in fluid administration, and pressure on the globe. A national registry exists, the purpose of which is to monitor the incidence of this complication.31
The use of single-lung ventilation delivered by a double lumen tube will facilitate surgery on the thoracic aorta. These large endotracheal tubes are relatively inflexible and intubation with this airway device requires an experienced anesthesiologist. Experience is particularly important should the patient also possess an associated injury to the cervical spine or be at risk for aspiration of gastric contents. Fiberoptic bronchoscopy is essential for the confirmation of appropriate endotracheal tube placement following initial intubation. It is also helpful in repositioning a tube that has slipped out of position during the course of surgery. Patients with traumatic injuries to the thoracic aorta may also have associated pulmonary contusions; if substantial injury to the nonoperative lung is present, it may be impossible to effectively oxygenate or ventilate the patient once the operative lung is deflated. This may be detected prior to positioning and the initiation of surgery by simply collapsing the operative lung and observing the oximeter for signs of arterial desaturation.
Mass Casualties and Disasters
The administration of anesthesia in the face of mass casualties presents any number of logistic and medical challenges. Supplies may be limited, standard equipment or facilities poorly functional, and conventional anesthetic techniques impossible to institute. Recent eyewitness reports from medical volunteers in Haiti illustrate these problems.32 If general inhalation anesthesia cannot be administered, continuous infusions of etomidate or ketamine produce relatively reliable hemodynamic stability and are the cornerstones of total intravenous anesthesia delivered under extreme conditions.33 Etomidate lacks analgesic potency and does not produce muscle relaxation; analgesics and adjuvant muscle relaxation must be administered if it is used. Adrenocortical suppression may also occur if large doses are given over a long period of time. Ketamine infusions produce reliable anesthesia, amnesia, analgesia, and modest muscle relaxation. However, in anesthetic doses the drug produces an increase in intracranial and intraocular pressure and should be used with caution, if at all, in the presence of head trauma or an open globe injury. Also, large doses of ketamine may produce a prolonged emergence from general anesthesia, accompanied by impressive psychomimetic side effects. With both of these drugs, the airway should be secured with a cuffed endotracheal tube should the patient be at risk for aspiration of gastric contents.
If resources are limited, regional anesthesia may present as the only safe option for anesthetic care.34 Neuraxial anesthesia and simple peripheral nerve blocks may be employed to produce surgical anesthesia; however, careful patient selection for these techniques in this setting is of paramount importance.35,36 Contraindications to the use of regional anesthesia in the extreme trauma setting include hemodynamic instability, infection at the site of needle insertion, sepsis, abnormal coagulation, and known allergy to the proposed local anesthetic agent.