Does Noninvasive Ventilation Increase Mortality?
Does Noninvasive Ventilation Increase Mortality?
ABSTRACT & COMMENTARY
The use of noninvasive positive pressure ventilation (NPPV) has been shown to reduce the need for intubation and mortality in appropriate patients in respiratory failure. Those patients with acute, reversible exacerbations of chronic obstructive pulmonary disease (COPD) are probably the most appropriate for this form of therapy. When used in other conditions, such as the acute respiratory distress syndrome or congestive heart failure, results have been less positive. However, the use of NPPV is usually associated with a positive outcome. This study was designed to test whether NPPV could improve outcome in patients presenting to the emergency room (ER) in acute respiratory distress.
Patients were entered into the study if they were dyspneic, had a respiratory rate greater than 25, and had either evidence of hypercarbia while breathing room air, or hypoxia on supplemental oxygen. Patients with asthma, systemic shock, an immediate need for an artificial airway, or an explicit declaration not to be intubated were excluded. Randomization with sealed envelopes was used to assign each patient to medical management alone (bronchodilators, antibiotics, sedatives, vasopressors, and other disease-specific treatments) or medical management and NPPV. The primary end point was the need for intubation. Standard criteria for intubation included respiratory arrest or prolonged ventilation pauses with loss of consciousness, agitation requiring sedation, or cardiovascular instability (hypotension or bradycardia). Additional outcomes studied included the need for ICU admission, organ failures, and mortality.
Of the 16 patients randomized to the NPPV group, seven required intubation and four died, compared to the 11 patients in the control group in which four required intubation and none died. Average time to intubation was 26 hours in the NPPV group and 4.8 hours in the controls (P = 0.055). There was no difference in any demographic variable, APACHE II score, predicted mortality, diagnosis, or history of previous intubation between the groups at the time of randomization. The difference in mortality is not statistically significant (P = 0.123), although it is a disturbing trend. (Wood KA, et al. Chest 1998;113:1339-1346.)
COMMENT BY CHARLES G. DURBIN, Jr., MD, FCCM
Increasing use of NPPV is based on the assumptions that avoiding intubation will reduce upper and lower airway complications, decrease costs, and improve survival in some groups of patients. This is the first study to suggest that survival may actually be decreased by use of NPPV. It is not clear why this was true in this study. The small number of patients is a factor, although on first blush the trend is impressive. Were the groups different? Actually, the NPPV patients were slightly younger (56 vs 62 years, P = 0.21), possibly favoring a better outcome; however, presenting physiological abnormalities as measured by APACHE II scores suggested a slightly worse mortality (26% vs 19% mortality, P = 0.336).
It is possible that delay in intubating the patients needing intubation led to complications resulting in a worse outcome. Silent aspiration leading to pneumonia is one way this could occur. There is no evidence that this was true in this study. Higher oxygen consumption with the higher work of breathing in the NPPV group could have limited survival by diverting limited energy to this task. Again, there is no direct evidence that this was true in this study. Those patients ultimately dying had more organ failures, but cause and effect of these organ failures is not clear.
Because of the small number of patients in this study, it is important to recognize that a single death in the control group would have abolished the trend to a worse outcome. The control group had a predicted mortality of about 20% (1 or 2 deaths), thus, these patients actually fared better than predicted. The NPPV group on the other hand had an expected mortality of 26% and experienced a 25% death rate, exactly as predicted. It is likely that the trend to greater mortality is a statistical quirk rather than a real difference in outcome. In fact, the chi-squared test, which Wood and colleagues used for this comparison, should be applied with great caution to data in which there are less than five members in any category (in this case 0).
While a larger study is indicated to evaluate the role of NPPV in patients presenting to the ER, fear that this therapy will reduce survival should not be based on this study. Careful patient selection, monitoring for worsening conditions, and expert application of the technology are essential for patient safety and benefit.
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