Noninvasive Ventilation in Hypoxemic Respiratory Failure

Abstract & Commentary

Synopsis: The use of noninvasive positive pressure ventilation (NPPV) is effective to reduce intubation and mortality in patients with acute hypoxemic respiratory failure.

Source: Ferrer J, et al. Am J Respir Crit Care Med. 2003;168:1438-1444.

Noninvasive positive-pressure ventilation (NPPV) was assessed in 105 patients with severe acute hypoxemic respiratory failure. Patients had a PaO2 £ 60 mm Hg or SpO2 £ 90% while breathing oxygen at a maximal concentration of 50% without hypercapnia. They were randomized to receive NPPV or high-concentration oxygen therapy without positive pressure. The primary outcome variable was intubation rate. Both groups had similar characteristics.

Compared with oxygen therapy, NPPV decreased the need for intubation (25% vs 52%; P = .01), decreased the incidence of septic shock (12% vs 31%; P = .028), decreased intensive care unit mortality (18% vs 39%; P = .028), and increased the cumulative 90-day survival (P = .025). Both arterial hypoxemia and tachypnea improved more as a function of time in the NPPV group (P = .029 for each). Multivariate analyses showed that NPPV was independently associated with decreased risks of intubation (odds ratio, 0.20; P = .003) and 90-day mortality (odds ratio, 0.39; P = .017). The use of NPPV prevented intubation, reduced the incidence of septic shock, and improved survival in these patients compared with high-concentration oxygen therapy.

Comment by Dean Hess, PhD, RRT

There is as much high-level evidence for the use of NPPV as for any therapy used in critical care. More than 20 randomized controlled trials have investigated this therapy in the past 10 years. The strongest evidence for use of NPPV is for patients with COPD exacerbation, this having been subjected to several recently published meta-analyses.1-3 In such patients, NPPV decreases need for intubation and mortality. There is also accumulating evidence that NPPV decreases the risk of nosocomial pneumonia.

The evidence supporting the use of NPPV in patients with acute hypoxemic respiratory failure is generally considered weaker than that for COPD exacerbation. That said, previous randomized studies have reported benefit for patients with respiratory failure following solid organ transplant,4 immunocompromised patients,5 patients developing respiratory failure following lung resection surgery,6 and those with multiple etiologies of hypoxemia.7

The present study provides additional evidence for the use of NPPV in patients with acute hypoxemic respiratory failure. The causes of respiratory failure in this study were varied and included pneumonia, cardiogenic pulmonary edema, thoracic trauma, acute respiratory distress syndrome (ARDS), acute severe asthma, postoperative respiratory failure, and interstitial pneumonitis. The results of this study indicate that the use of NPPV in patients with acute hypoxemic respiratory failure decreased the need for intubation, the incidence of septic shock, and the levels of tachypnea and arterial hypoxemia, and also improved ICU and 90-day survival compared with patients receiving high-concentration oxygen therapy.

It is important to note that patients were ventilated using the BiPAP Vision ventilator (Respironics Inc) Murrysville, Pa), and that an oronasal mask was used as the first choice. Unlike other ventilators designed specifically to provide NPPV, the Vision ventilator is able to deliver high oxygen concentrations. Moreover, an oronasal mask decreases leak and thus allows application of higher expiratory pressure levels. Although the conclusion is speculative, prior anecdotal experience of poor patient response to NPPV in this patient population may have been due to the use of equipment that was unable to provide sufficient oxygen and expiratory pressure levels.

Evidence is accumulating that NPPV should be considered in patients presenting with acute hypoxemic respiratory failure. NPPV should be considered in patients in whom the cause of hypoxemic respiratory failure is likely to be resolved quickly (that is, over several days). NPPV may be less successful in patients with severe hypoxemia related to ARDS, in whom the course of mechanical ventilation can be expected to be more prolonged. Such patients may be better served by invasive ventilatory support and application of the ARDSnet management strategy. However, this has not been subjected to high-level study.

NPPV decreases the intubation rate, but does not eliminate the need for intubation. In this study, as in previous studies, the intubation rate in patients receiving NPPV was 25%—significantly less than that for those randomized to conventional therapy, but still substantial. Sometimes clinicians believe that NPPV is not effective because some patients require intubation despite the best efforts to apply it. As demonstrated in this study, 1 in 4 patients who receive NPPV eventually need to be intubated in spite of the clinicians’ best efforts to avoid intubation. Nonetheless, the intubation rate is lower with NPPV than with conventional therapy. Moreover, the use of NPPV not only reduces the intubation rate, but it also affords a survival benefit for patients.

Clinician efforts to use NPPV to avoid intubation improve patient-important outcomes. Accumulating evidence suggests that this applies not only to patients with COPD exacerbations, but also to those with acute hypoxemic respiratory failure. n

References

1. Peter JV, et al. Crit Care Med. 2002;30:555-562.
2. Keenan SP, et al. Ann Intern Med. 2003;138:861-870.
3. Lightowler JV, et al. BMJ. 2003;326:185-189.
4. Antonelli M, et al. JAMA. 2000;283:235-241.
5. Hilbert G, et al. N Engl J Med. 2001;344:481-487.
6. Auriant I, et al. Am J Respir Crit Care Med. 2001;164: 1231-1235.
7. Antonelli M, et al. N Engl J Med. 1998;339:429-435.

Dean Hess, PhD, RRT, Respiratory Care, Massachusetts General Hospital Department of Anesthesiology, Harvard Medical School, is Associate editor for Critical Care Alert.