When MV was first developed for widespread clinical use during the poliomyelitis epidemic, attention focused on replacing the failing respiratory muscles by a perithoracic pump. This led to the development of the “iron lung,” the first form of noninvasive ventilation, which saved many lives.1,2 However, the device was cumbersome and impeded patient care. In addition, the iron lung proved of limited efficacy in the treatment of parenchymal lung disease. Thus delivery of mechanical assistance through an endotracheal tube that provided access to the lower airway was considered a significant advance, and positive pressure ventilation became the standard for MV.
Soon after the introduction of endotracheal MV, many complications of positive pressure ventilation were identified.3,4 These complications were found to be common and generated concern about the invasiveness of MV. ETI itself has been implicated in a large number of complications. Of these, some are directly related to the procedure, such as cardiac arrest following laryngospasm or difficult tube insertion and laryngeal or tracheal injury leading to long-term sequelae. Others are ascribable to the fact that the endotracheal tube bypasses the barrier of the upper airway: an important example is nosocomial pneumonia, which carries its own risk of mortality. Other complications are indirectly related to ETI, such as the need for sedation, which often prolongs weaning. These major safety considerations prompted efforts to develop noninvasive methods for delivering positive pressure ventilation. Thus, in patients with ARF, the main goal of NIPPV is to provide ventilatory assistance while lowering the risk of adverse events by reducing the need for invasive MV. Convincing evidence that NIPPV diminishes the risk of infectious complications has been obtained not only from pooled analyses of data from randomized controlled trials, but also from multivariate analyses of large cohort studies and from carefully performed case-controlled studies, all of which show large decreases in all categories of nosocomial infection.5–7 The reason is that NIPPV is associated with a reduction in the overall invasiveness of patient management: sedation is given at lower levels or not at all, and the use of central venous lines, urinary catheters, and other invasive devices is considerably reduced, as compared to patients receiving endotracheal MV.8
Another important factor in promoting the use of NIPPV is the growing number of patients who are either unwilling to accept ETI or considered poor candidates for endotracheal MV because of their poor underlying health status.9,10 In these patients, NIPPV can offer a chance of recovery with a low risk of complications. Further, by postponing ETI, NIPPV may provide a window of opportunity for the physician, family, and patient to make informed decisions about the goals of therapy.
The use of NIPPV in the acute setting has increased markedly since the first small case-series were published in the last decade of the twentieth century.11,12 A multicenter international study on MV was reported in 1998 by Esteban and colleagues.13 In this study, NIPPV was used in about 5% of ICU patients who required MV. However, because only patients who received MV for longer than 12 hours were included, the study may have missed many patients treated with NIPPV. In a similar observational study performed in 42 ICUs in France in 1997, 16% of patients with ARF received NIPPV as the first-line method of ventilatory support.14 Importantly, among those patients who were not intubated before ICU admission, 35% received first-line NIPPV. In 2002, the same group did an identical study in 72 ICUs in France, including most of those in the previous study.15 In the overall population of admitted patients, the percentage of patients who required some form of ventilatory support was the same in the two study periods. In 2002, the rates of NIPPV use among patients requiring ventilatory support had increased to 24% overall and 52% among patients who were not intubated before ICU admission. Although these results cannot be extrapolated to all countries, they indicate a strong trend toward increasing use of NIPPV in ICU patients with a variety of conditions, and they also reflect the current tendency to reduce the invasiveness of ICU management. Although many patients can be expected to benefit from this approach, great care should be taken to identify those patients who require immediate ETI, as delaying this procedure may reduce the chances of recovery in some patients.
Several types of ventilator can be used to deliver NIPPV to patients with ARF. Turbine ventilators specifically designed for NIPPV have been developed, but standard ICU ventilators can be used as well. Turbine ventilators designed for NIPPV deliver two levels of positive airway pressure synchronized on patient trigger or time trigger, and reproducing pressure support ventilation or pressure control plus PEEP.16 These ventilators are designed to compensate for air leakage, which is an important characteristic of NIPPV.17 Although the meaning of “leak compensation” varies from one ventilator to the next, leakage compensation usually results in less triggering dysfunction than with standard ventilators. The main adverse effect of leakage on inspiratory triggering is auto-cycling. Auto-cycling is thought to be more common when high levels of PEEP are used. The cycling mechanism at end-inspiration can also be affected by leakage. When leakage is marked, the ventilator may be unable to recognize the end of inspiration based on flow rate deceleration, unless the unit is equipped with a special adaptive mechanism. This mechanism exists in turbine ventilators and in some ICU ventilators offering an NIPPV option. Adequate patient monitoring may be essential to assess patient-ventilator interaction, to detect leaks, and to fine-tune pressure levels. Bench comparisons assessing in vitro ventilator performance suggest that both turbine ventilators specially designed for NIPPV and late-generation standard ICU ventilators are satisfactory for delivering NIPPV to ICU patients with severe dyspnea.16–19
The use of an ICU ventilator that works from wall gas supply requires warming and humidification of the gas prior to airway delivery. With endotracheal MV, the gas temperature drops in the endotracheal tube. This does not occur with NIPPV, and in addition warm gas at the mouth may be difficult for the patient to tolerate. Therefore, lower gas temperatures are used for NIPPV than for endotracheal MV. One option is to use a heat and moisture exchanger. Unfortunately, the internal volume of these devices imposes an additional workload on the patient by generating CO2 rebreathing. In patients with hypercapnic respiratory failure, this diminishes the effectiveness of NIPPV in reducing blood CO2 levels and correcting respiratory acidosis.20,21 A similar problem of CO2 rebreathing occurs when turbine ventilators (using ambient room air) equipped with a one-line circuit are used with low levels of PEEP.22,23 The expiratory flow generated to create the PEEP level is also used to flush the exhaled CO2 from the circuit. With low PEEP levels, high minute ventilation, and/or a high respiratory rate, this can have adverse clinical effects that may require addition of a nonrebreathing valve to the circuit.
The interface used to connect the patient to the ventilator is usually a full face mask covering both the nose and the mouth. Although nasal interfaces are available, their use in ICU patients frequently results in major leakage through the mouth that diminishes the effectiveness of NIPPV and promotes patient-ventilator asynchrony and discomfort.24,25 Full face masks are responsible for unwanted effects including skin breakdown over the nose, conjunctivitis related to leakage of air directed toward the eyes, rebreathing, claustrophobia, and overall discomfort.12,26 These problems prompted efforts to design improved interfaces. The first improvement consisted in varying the pressure sites on the face to achieve better tolerance during prolonged use, and subsequently much larger masks enclosing the entire face or head were developed.27,28 Use of a helmet has been suggested, primarily for patients with acute hypoxemic respiratory failure.29–31 Because helmets may induce more rebreathing than other masks, they may be less suitable for patients with hypercapnic respiratory failure. The helmet probably markedly improves patient comfort and tolerance, at the price, however, of decreased effectiveness in unloading the respiratory muscles. This latter point is of importance since several studies have established that good clinical tolerance is crucial to successful NIPPV. In their large observational survey, Carlucci and colleagues identified two independent predictors of failure: the severity score (as assessed by the Simplified Acute Physiology Score [SAPS] II) and clinical tolerance.14 Interestingly, recent physiologic studies with integral masks compared to standard full face masks seem to indicate comparable efficacy in terms of respiratory muscle unloading, suggesting that the theoretical risk of rebreathing associated with the large internal volume may be small or nonexistent in clinical practice.32,33
Acute Exacerbation of Chronic Respiratory Failure
Many of the studies in the field of NIPPV have been performed in patients with obstructive disease, mainly chronic obstructive pulmonary disease (COPD).12,34–38 All forms of acute or chronic ventilatory failure share several pathophysiologic pathways, but major differences exist as well. A few data suggest that NIPPV may be less effective in patients with chronic restrictive lung disease than in patients with COPD.39
Exacerbation of COPD is a common cause of admission to the hospital and ICU. In addition to worsening of dyspnea and bronchitic symptoms and to development of right ventricular failure and encephalopathy, rapid and shallow breathing with hypoxemia and hypercapnia characterizes these exacerbations. The pathophysiologic pathway involves an inability of the respiratory system to maintain adequate alveolar ventilation in the presence of major abnormalities in respiratory mechanics. This can be modified by NIPPV, which allows the patient to take deeper breaths with less effort, thus reversing the clinical abnormalities resulting from hypoxemia, hypercapnia, and acidosis.34,40 At baseline, the transdiaphragmatic pressure generated by these patients can be considerably higher than normal and represents a high percentage of their maximal diaphragmatic force, a situation that carries a major risk of respiratory muscle fatigue.34,41,42 The main role of NIPPV is to offer the patient a way to increase the tidal volume at a lower work level. The use of ventilatory modalities working in synchrony with the patient's efforts allows larger breaths to be taken with less effort. As a result of the increased alveolar ventilation, arterial partial carbon dioxide pressure (PaCO2) and pH values improve, and this in turn reduces the patient's ventilatory drive, thereby lowering the respiratory rate and improving the dyspnea.
The efficacy of NIPPV in patients admitted for acute exacerbation of COPD has been extensively studied. An international consensus conference recommended that NIPPV be considered a first-line treatment in these patients,43 and the British Thoracic Society Guidelines indicate that every hospital should be able to deliver NIPPV on a 24-hour-per-day basis for this indication.44 The first evidence that NIPPV markedly reduced the need for ETI came from case-control series reported in 1990.34 Subsequently, several prospective randomized trials confirmed that NIPPV reduced the need for ETI and the rate of complications, shortened the length of stay, and improved survival in patients with COPD.35,37,38,45–48 In a study by Kramer and associates, 74% of patients had COPD, and in this group NIPPV use was associated with a striking decrease in the ETI rate, from 67% to 9%.38 Two studies conducted in the United Kingdom established that NIPPV was also effective in non-ICU settings.35,48 Bott and coworkers35 reported major improvements in dyspnea and gas exchange with a significant decrease in mortality when patients who refused NIPPV were excluded from the analysis. In the largest ICU study reported to date, Brochard and colleagues randomized 85 patients with COPD to treatment with or without face mask pressure-support ventilation.37 The ETI rate was 74% in the controls given standard treatment and 26% in the NIPPV group. Benefits in the NIPPV group included a decreased rate of complications during the ICU stay, a shorter length of hospital stay, and more importantly, a significant reduction in mortality (from 29% to 9%). The overall decrease in mortality was ascribable to reductions in the need for ETI and in various ICU-related complications. In the United Kingdom, Plant and colleagues conducted a prospective multicenter randomized trial comparing standard therapy alone (control group) to NIPPV in 236 COPD patients admitted to general respiratory wards for ARF.48 Treatment failure (defined as fulfillment of criteria for ARF) was more common in the control group (27%) than in the NIPPV group (15%), and NIPPV was associated with a lower in-hospital mortality rate. Because of admission policies in the United Kingdom, patients who failed NIPPV were not routinely transferred to the ICU, and consequently the findings may not be relevant to all health care institutions. The authors emphasized that the benefits of NIPPV out of the ICU were marginal in the most severely affected patients (pH <7.30 on admission), in whom the mortality rate was high. Those patients would probably have done better with early ICU admission for early NIPPV delivery in the ICU environment.
These studies indicate that early NIPPV to prevent further deterioration must become an important component of first-line therapy for COPD exacerbation.49
A very low pH, marked mental status alterations at NIPPV initiation, presence of comorbidities, and a high severity score are associated with early NIPPV failure14 or late secondary failure after an initial improvement.50 Several of these factors seem to indicate that a longer time from onset of the exacerbation to NIPPV initiation may reduce the likelihood of success. Every effort should be made to deliver NIPPV early, and close monitoring is in order when NIPPV is started late. In addition, a randomized controlled trial found that NIPPV was less effective when started late in the course of COPD exacerbation.51 In this study, Conti and coworkers found a large reduction in the ETI rate, from 100% to 52%, contrasting with limited short-term benefits.51 The patients stayed in the emergency ward for a mean of 14 hours before being admitted to the ICU because they met criteria for ETI, and NIPPV was initiated only at ICU admission. Interestingly, NIPPV was associated with significant long-term benefits such as a decrease in the readmission rate.
Whether the results of randomized controlled trials apply to everyday ICU practice must be evaluated. This is particularly important with NIPPV, since there is a learning curve, as shown in two studies. In a single-center study by Carlucci and colleagues, the NIPPV success rate remained stable over the study period, but the patients treated with NIPPV during the last few years of the study period had more severe disease with higher PaCO2 levels and lower pH values.52 In an 8-year study performed in our institution, we found that NIPPV use increased gradually, in lockstep with a decline in conventional treatment with ETI.53 In parallel with this gradual increase in NIPPV use, the nosocomial infection and mortality rates diminished. These important results were obtained in the group of patients with acute exacerbation of COPD and hypercapnic pulmonary edema.
Several studies have suggested that NIPPV use may be associated with higher 1-year survival rates, as compared to standard ICU therapy or invasive MV.51,54–56 Although these studies have a number of methodologic flaws, the consistency of their results suggests a major benefit of NIPPV, the mechanisms of which remain to be elucidated.
Negative Pressure Ventilation
This technique is available in very few centers in the world. In acute exacerbations of COPD, it seems to provide better outcomes than conventional invasive MV and may be similar to face mask NIPPV.57–60
The study by Plant and associates cited above was performed in the respiratory wards, where the staff received 8 hours of training over the 3 months preceding the study.48 During the study, it was estimated that maintaining the level of expertise provided by the prestudy training required on average 1 hour of additional training per month in each center. Wood and colleagues performed a study in the emergency ward, but the patients had very low severity, and few had COPD.61 The results suggested that NIPPV use may have inappropriately delayed ETI. However, the small sample sizes, existence of several baseline differences across groups, and lack of accurate information on NIPPV settings make it difficult to draw conclusions from this study. The feasibility of treating patients with COPD out of the ICU has thus been demonstrated, but when evaluating whether this applies to a specific ward, the need to train the staff must be taken into account.
The use of a helium-oxygen mixture for NIPPV seems very promising in patients with COPD.62–64 Several randomized controlled trials are under way to determine whether this gas mixture increases the NIPPV success rate. Disappointingly, the first study found only modest benefits when helium was added to the gas mixture.
Cardiogenic Pulmonary Edema
Continuous positive airway pressure (CPAP) elevates intrathoracic pressure, decreases shunting, and improves arterial oxygenation and dyspnea in patients with cardiogenic pulmonary edema. Interestingly, CPAP can both substantially lessen the work of breathing and improve cardiovascular function by decreasing the left ventricular afterload in non–preload-dependent patients.65 Pressure support plus PEEP induces similar pathophysiologic benefits.
Most patients with cardiogenic pulmonary edema improve rapidly under medical therapy. A few, however, develop severe respiratory distress and/ or refractory hypoxemia and require ventilatory support until the medical treatment starts to work. This is particularly common in elderly patients, who may also have a mild degree of chronic bronchitis.66,67 Several NIPPV modalities have been used successfully, the goal being to avoid ETI.
Continuous Positive Airway Pressure or Pressure Support Plus Positive End-Expiratory Pressure
Randomized trials comparing either CPAP or pressure support plus PEEP to standard therapy found closely similar results with the two techniques in terms of improvement in arterial blood gases and breathing rate. Both CPAP and pressure support plus PEEP significantly reduced the rate of ETI.67–71 Several studies, however, indicate a need for caution. One compared pressure support plus PEEP to CPAP.72 Acute myocardial infarction was more common in the pressure support plus PEEP group than in the CPAP group. Although this difference may be ascribable to randomization bias rather than to a deleterious effect of pressure support plus PEEP, it invites caution in patients with coronary heart disease. No increases in the acute myocardial infarction rates were found in the NIPPV arm of a randomized controlled trial of pressure support and PEEP or in any of the observational studies, although the outcome of these patients may be worse than outcome in those with nonischemic causes of heart failure.71,73,74 Another study compared intravenous bolus therapy with high-dose nitrates to conventional medical therapy (a different medical therapy) plus pressure support plus PEEP.75 High-dose nitrate bolus therapy was far more effective clinically than NIPPV and resulted in better outcomes. These studies draw attention to the vulnerability of patients with cardiogenic pulmonary edema, particularly those with coronary heart disease.70,73 They indicate that both appropriate drug therapy and close monitoring are in order when using any form of NIPPV, especially in patients with coronary heart disease. In a randomized controlled trial, L'Her and associates showed that administration of CPAP to elderly patients with acute cardiogenic pulmonary edema in the emergency ward markedly improved physiologic parameters and 48-hour survival.67 Unfortunately, there was no effect on hospital survival.
It is also important to draw attention to the fact that most of the studies demonstrating benefits of CPAP or pressure support plus PEEP included patients who, on average, had marked hypercapnia and acidosis indicating acute ventilatory failure.67,70,71,73 A large multicenter study conducted by Nava and colleagues in patients with pulmonary edema found major benefits of NIPPV in the subgroup of hypercapnic patients, but no significant benefits in terms of ETI rate or outcome in the overall population, which included both hypercapnic and nonhypercapnic patients.76
In patients with hypercapnic pulmonary edema, ventilatory support with pressure support above PEEP is therefore a useful adjunct to medical treatment that reduces the ETI rate and improves outcomes. However, caution is needed when using NIPPV in patients with coronary heart disease.
Hypoxemic Respiratory Failure
Applying PEEP to the airway opening has been shown to increase functional residual capacity and to benefit respiratory mechanics and gas exchange.77 These findings led intensivists to use CPAP as a means of preventing clinical deterioration and reducing the need for ETI.70,78 Nevertheless, clinical data do not strongly support the use of CPAP in patients with acute lung injury (ALI),79 and far better clinical outcomes have been reported with the combined use of pressure support ventilation and PEEP.8,80,81 In patients with severe hypoxemia, ventilatory support should be able to relieve the dyspnea, improve oxygenation, and decrease the patient's effort to breathe. In a physiologic study, L'Her and coworkers confirmed the limited efficacy of CPAP alone in lessening the work of breathing.82 They showed that addition of pressure support was crucial to reduce patient effort and dyspnea, whereas effects on oxygenation were dependent on the PEEP level.
A recent investigation evaluated whether face mask CPAP produced physiologic benefits and reduced the need for ETI in patients with ALI.79 Despite an early favorable physiologic response to CPAP in terms of comfort and oxygenation, no differences were found in the need for ETI, in-hospital mortality, or length of ICU stay. In addition, the use of CPAP was associated with a higher rate of complications including stress ulcer bleeding and cardiac arrest at the time of ETI. Therefore, CPAP alone cannot be recommended as a means of avoiding ETI in patients with ALI. Its use should be limited to a short initial period when no other method is available.
Pressure Support and PEEP
Until the late 1990s, the most convincing successes with NIPPV were obtained in patients with acute respiratory acidosis in whom hypoxemia was not the main reason for respiratory failure. A randomized controlled trial by Wysocki and colleagues found no benefit of NIPPV in patients with no previous history of chronic lung disease, except in the subgroup of patients who developed acute hypercapnia.83 However, NIPPV has now been proved beneficial in carefully selected patients with a variety of patterns of hypoxemic respiratory failure.8,47,80,81,84–87 Recent studies suggest that in selected groups of patients NIPPV may reduce the need for ETI and improve outcomes.86,88–90 Patient selection generally involves excluding patients who have shock, neurologic disorders with a need for upper airway protection, respiratory arrest, or any other concomitant organ failure. In a randomized controlled study by Antonelli and coworkers, NIPPV using pressure support and PEEP was highly beneficial in hypoxemic patients free from COPD, hemodynamic instability, or neurologic impairment, who were randomized when they reached predefined criteria for ETI.81 Improvements in oxygenation were similar with the noninvasive and the invasive approach. Despite a 30% failure rate, patients treated with NIPPV had shorter durations of ventilation and ICU stay and experienced fewer complications. This study demonstrated that NIPPV could be effective in selected patients with hypoxemic respiratory failure but no hemodynamic or mental impairment. Other randomized controlled trials confirmed this beneficial effect.80 The benefits seem greatest in specific subgroups, as discussed below. However, as indicated further on, patients with severe community-acquired pneumonia and profound hypoxemia or patients with acute respiratory distress syndrome (ARDS) may not always benefit from NIPPV, and in inexperienced hands the use of this technique may expose some patients to the risks associated with inappropriately delayed ETI.15 Nevertheless, a recent study by Ferrer and colleagues indicates that NIPPV is effective in avoiding ETI and improving survival.87 The study population comprised 105 patients admitted to the ICUs of three hospitals for acute non-hypercapnic hypoxemic respiratory failure due to community-acquired pneumonia, ARDS, cardiogenic pulmonary edema, or other diseases. Compared with oxygen therapy, NIPPV decreased the need for ETI (25% vs. 52%), the incidence of septic shock, and the ICU mortality rate (18% vs. 39%) and increased the cumulative 90-day survival rate.
Because one of the main benefits of NIPPV may be a decreased rate of infectious complications,6,7,53 patients in whom MV carries a high risk for nosocomial infection may be particularly likely to benefit from NIPPV. Several trials have shown major benefits of NIPPV as a preventive measure during episodes of acute hypoxemic respiratory failure in solid organ-transplant patients or in patients with severe immunosuppression, particularly related to hematologic malignancies and neutropenia.8,86,88 Significant reductions in ETI use, infectious complications, length of stay, and mortality occurred with NIPPV. Because of the high risk associated with ETI in patients with severe immunosuppression, NIPPV seems of particular interest in this group.8,86,88,90 Similarly, patients experiencing Pneumocystis carinii pneumonia during the course of HIV infection seem to benefit from NIPPV, as shown in a case-control study by Confalonieri and associates.90
In the population with immunosuppression, careful patient selection and early initiation of NIPPV are key factors in decreasing the need for ETI and in maximizing benefits to the patients.
Several studies looked at the use of NIPPV after surgery.89,91,92 Auriant and associates conducted a randomized controlled trial in patients who experienced respiratory distress after lung resection.89 Because reintubation shortly after lung surgery carries a very grim prognosis, avoiding ETI in this situation is a major goal. NIPPV was associated with lower ETI rates and higher hospital survival. Furthermore, an uncontrolled study found evidence supporting a beneficial effect of NIPPV in patients with respiratory distress after bilateral lung transplantation.92 Thus, NIPPV seems useful in preventing reintubation after lung surgery.
A randomized controlled trial reported by Confalonieri and colleagues in patients with community-acquired pneumonia showed major benefits of NIPPV consisting of reductions in ETI rates, complication rates, and length of stay.47 These favorable effects, however, were almost entirely ascribable to the subgroup of patients with COPD. In a case-control study done by the same group in patients with Pneumocystis carinii pneumonia, NIPPV reduced ETI rates, length of stay, and mortality.90 Other studies found high rates of NIPPV failure in the subgroup of patients characterized by pneumonia with severe hypoxemia.84,93–95 By contrast, the benefits found in the study by Ferrer and associates were marked in the subgroup of patients with pneumonia.87 Therefore caution is necessary when using NIPPV in patients with severe community-acquired pneumonia. There is no consensus about recommendations for the use of NIPPV in this situation. The results of NIPPV in patients with severe community-acquired pneumonia may depend on the experience of the user and on the quality of patient monitoring.
Postextubation Respiratory Failure
The physiologic rationale for this approach in patients with COPD was recently demonstrated by Vitacca and coworkers.96 A case-control study by Hilbert and associates suggested that NIPPV might prevent reintubation in patients with COPD.97 A prospective randomized trial by Keenan and colleagues was performed in a population with postextubation respiratory distress that included only a few patients with COPD; no benefit of NIPPV was found.98 Another prospective randomized trial did not find any evidence that NIPPV decreased reintubation rates.99 By contrast, the preliminary results of another randomized trial provided indications of strong beneficial effects in COPD.100 Lastly, a recent multicenter trial by Esteban and associates suggested that NIPPV used for postextubation respiratory distress may delay reintubation and increase mortality.101
Thus there is considerable doubt about the effectiveness of NIPPV in obviating the need for reintubation in all patients with postextubation respiratory distress. Using NIPPV in patients with postextubation respiratory distress may increase morbidity rates, and perhaps also mortality rates, by inappropriately delaying reintubation. The benefits of NIPPV in the treatment of postextubation respiratory distress may be limited to those patients with COPD. When NIPPV is used, the need for ETI should be evaluated early, within the first 2 hours of NIPPV, in order to avoid adverse outcomes related to delayed ETI.
A number of patients with COPD require ETI because they fail NIPPV, have a contraindication to NIPPV (such as a need for surgery), or exhibit criteria for immediate ETI. However, when there is a need for prolonged ventilatory assistance, these patients can be switched to NIPPV after a few days of ETI.102,103 This approach was shown in two randomized controlled trials to reduce the ETI time.102,103 In a study by Nava and colleagues, complications were reduced and 60-day survival rates were higher with this approach.102 This benefit was not found in the other study, in which the total length of ventilation was increased in the NIPPV arm.103 A trial by Ferrer and coworkers suggested major benefits in COPD patients experiencing persistent weaning difficulties.104 This study included 43 mechanically ventilated patients who had failed a weaning trial for 3 consecutive days. Compared with the conventional-weaning group, the NIPPV group had shorter times on invasive MV and in the ICU and hospital, as well as higher ICU and 90-day survival rates. Multicenter trials are needed to confirm the safety and efficacy of this approach.
Patients Who Should Not Be Intubated
Several reports have described the effects of NIPPV in patients with acute respiratory failure who were poor candidates for ETI because of advanced age, debilitation, or a “do not resuscitate” order.9,10 The overall success rate in these reports approximated 60% to 70%. Gas exchange improved rapidly in successfully treated patients. Even when respiratory failure did not resolve, NIPPV provided symptomatic relief from dyspnea.
Patients with Severe Acute Asthma
A few studies indicate that NIPPV can be used in asthmatic patients. Two cohort studies found beneficial short-term effects of NIPPV in asthmatic patients whose condition was deteriorating despite medical therapy.105,106
Several studies used a new ventilatory mode known as proportional-assist ventilation, which is designed to improve the adjustment of ventilatory support to the patient's needs.107–110 In several comparative studies with pressure-support ventilation in one of the arms, the efficacy of the two techniques seemed similar, although very few patients required ETI. Studies in patients with greater disease severity are needed. A prospective randomized trial by Fernandez-Vivas and associates in 117 patients with mixed causes of ARF again showed no difference in clinical outcomes between NIPPV delivered with pressure support or with proportional-assist ventilation.110 Subjective comfort was better with proportional-assist ventilation, however, and intolerance was less common.
Several studies have suggested or demonstrated that fiberoptic bronchoscopy can be performed under NIPPV (CPAP for hypoxemic patients or pressure support plus PEEP),111–113 and that this approach resulted in better tolerance of the procedure and reduced complication rates and the need for ETI.113