Noninvasive Ventilation as an Aid to Weaning
ABSTRACT & COMMENTARY
Synopsis: Intubated patients with COPD and acute-on-chronic respiratory failure who were extubated after 48 hours of mechanical ventilation and supported as needed with noninvasive ventilation were weaned more rapidly, had shorter ICU stays, developed fewer nosocomial pneumonias, and were more likely to survive 60 days longer than patients weaned with pressure support via the endotracheal tube.
Source: Nava S, et al. Ann Intern Med 1998;128: 721-728.
In the last several years, noninvasive positive pressure ventilation (NPPV) has become established in the management of acute exacerbations of chronic obstructive pulmonary disease (COPD) as a means of avoiding endotracheal intubation and its associated complications. This randomized multicenter study from Italy sought to determine whether noninvasive ventilation improves the outcome of weaning from mechanical ventilation among COPD patients who had been intubated for management of acute-on-chronic ventilatory failure.
Intubated patients with acute hypercapnic respiratory failure underwent a weaning trial 48 hours after intubation. If this failed, patients were randomized either to extubation and application of NPPV via face mask or to continued invasive mechanical ventilation via endotracheal tube. Failure of the T-piece trial was defined as a respiratory rate greater than 35 breaths per minute, a PaO2 less than 50 mmHg (FIO2 = 0.40), a heart rate more than 145 beats per minute (or a fall in heart rate > 20%), severe arrhythmia, significant hyper- or hypotension, agitation, anxiety, or diaphoresis. NPPV was administered by face mask in the pressure support mode, at an inspiratory pressure sufficient to achieve acceptable blood gases and a respiratory rate less than 25 breaths per minute, initially for 22-24 hours per day with progressive reduction of both pressure and duration as tolerated. Invasive ventilation was delivered via pressure support ventilation, which was also reduced according to a fixed protocol. Successful weaning was defined as independence from all positive pressure support for 72 hours.
Patients in the two groups were well matched, with initial pH 7.18 ± 0.06 and PaCO2 94.2 ± 24.2 mmHg. At 60 days, 22 of the 25 NPPV patients (88%) were successfully weaned, as compared to 17 of 25 patients (68%) who were invasively ventilated during weaning. Mean duration of mechanical ventilation in the two groups was 10.2 ± 6.8 days vs. 16.6 ± 11.8 days in the NIPPV and invasive ventilation groups, respectively (P = 0.021). The probability of survival and weaning during ventilation was significantly higher among NPPV patients, and length of stay in the ICU was significantly shorter (15.1 ± 5.4 vs 24.0 ± 13.7 days, P = 0.0005). More NPPV patients survived 60 days following admission (92% vs 72%, P = 0.0009). None of the NPPV-weaned patients developed nosocomial pneumonia, whereas seven patients developed this complication who were invasively ventilated during weaning.
COMMENT BY DAVID J. PIERSON, MD
Nava and colleagues conclude that NPPV during weaning reduces weaning time, shortens the time in the ICU, decreases the incidence of nosocomial pneumonia, and improves the 60-day survival rate among COPD patients who initially require intubation and ventilatory support in the management of an acute exacerbation. Their study was well designed, carefully conducted, and provided impressive results.
Successful application of NPPV, either in initial management of acute-on-chronic ventilatory failure or as a bridge to weaning, as in this study, is not easy to achieve. Although several easy-to-use, relatively inexpensive pressure support ventilators are available, their successful use in dyspneic, fatigued, often agitated patients requires considerable expertise. Simply strapping on the nasal mask that comes with the device is an open invitation to failure. Rather, a properly instructed and experienced clinician with an array of potential patient-ventilator interfaces (nasal- and full-face masks of various sizes and designs) requires a substantial period of one-on-one time (typically 1-2 hours) with each patient in order to achieve satisfactory ventilation and patient tolerance. Even after being effectively set up and adjusted for a given patient, NPPV requires as much nursing and respiratory therapist time as invasive ventilation, if not more. Because it is a form of life support and applied in patients in a potentially life-threatening situation, NPPV for acute-on-chronic respiratory failure should be used in an appropriately monitored environment (such as an ICU).
If it can be achieved, though, NPPV offers several important advantages over invasive ventilation, either in initial management or as an intermediate stage in withdrawal of ventilatory support. It enables patients to cough and expectorate, permits communication through speech, allows the patient to eat, can be applied and discontinued as needed during the day, and does not breach the sterility barrier to the lower airway maintained by the larynx. In clinical practice, NPPV has found mixed success, in part because its use is often attempted in clinical settings in which it is unlikely to succeed (such as acute hypoxemic respiratory failure, or in patients who are combative or obtunded). However, the clinical setting in which this investigation was carried out-acute respiratory failure complicating severe COPD-represents the most appropriate circumstance yet identified. This study demonstrates that, in patients such as those studied by Nava et al, NPPV can serve as an effective bridge to ventilator weaning, allowing the clinican to taper inspiratory support gradually while restoring the patient to full spontaneous breathing, without the discomfort and complications of endotracheal intubation.
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