Noninvasive Ventilation in Pulmonary Edema
CPAP and NIPPV improve symptoms but do not alter death rates compared with standard oxygen therapy.
The widely held belief that noninvasive ventilation is beneficial in patients with acute pulmonary edema is based on studies that were either not randomized or too small to show unequivocal outcome effects, particularly with respect to mortality. In a multicenter study from the U.K., investigators randomized 1156 emergency department patients with acute pulmonary edema to one of three treatments: standard oxygen therapy, continuous positive airway pressure (CPAP), or noninvasive intermittent positive pressure ventilation (NIPPV, also called bilevel positive airway pressure; JW Emerg Med Mar 3 2004).
In all groups, oxygen was delivered to maintain peripheral oxyhemoglobin saturation above 92%. CPAP was started at 5 cm water and was increased to a maximum of 15 cm water. NIPPV was started at an inspiratory pressure of 8 cm water and an expiratory pressure of 4 cm water and was increased to maximum pressures of 20 cm and 10 cm, respectively. The assigned treatment was administered for a minimum of 2 hours. Blood gas analyses were performed at 1 hour and 2 hours. Patients rated their degree of dyspnea on a visual analog scale at enrollment and at 1 hour. Overall, 19% of patients did not complete treatment for reasons such as discomfort, worsening arterial blood gas values, and respiratory distress. Discomfort was significantly more common with noninvasive ventilation.
In a comparison between standard oxygen therapy and the two modes of noninvasive ventilation (CPAP or NIPPV), the primary outcome of death within 7 days did not differ significantly. In a comparison between CPAP and NIPPV, the composite primary endpoint of death or tracheal intubation within 7 days did not differ significantly. Fewer than 5 patients in any group were intubated, but 56 of 367 patients in the standard oxygen-therapy group were changed to CPAP or NIPPV to maintain target oxygen saturation. Mortality rates at 30 days did not differ between groups in either comparison. However, compared with standard oxygen therapy, noninvasive ventilation yielded greater reductions in some secondary outcome measures, including dyspnea, heart rate, acidosis, and hypercapnia.
Comment(1): The finding that noninvasive ventilation did not decrease mortality compared with standard oxygen therapy is not surprising because oxygen therapy was titrated to maintain adequate levels in all groups. Nonetheless, trying noninvasive ventilation in ED patients with acute heart failure is reasonable. If tolerated, treatment will improve symptoms and patient comfort, even if the state of the heart, not the therapy, is what ultimately dictates mortality.
J. Stephen Bohan, MD, MS, FACP, FACEP
Published in Journal Watch Emergency Medicine July 9, 2008
Comment(2): The results of this open randomized trial of noninvasive ventilation failed to show a reduction in the risk for death or intubation. The finding that fewer noninvasive-ventilation recipients than oxygen-therapy recipients experienced respiratory distress or metabolic abnormalities did not translate into any clinically meaningful change in outcome. The authors conclude with a "glass-is-half-full" assessment of their findings; nonetheless, this trial provides little support for noninvasive ventilation as an initial approach to patients with acute heart failure.
Harlan M. Krumholz, MD, SM
Published in Journal Watch Cardiology July 9, 2008
Citation(s): Gray A et al. Noninvasive ventilation in acute cardiogenic pulmonary edema. N Engl J Med 2008 Jul 10; 359:142.