Noninvasive Ventilation in the ED: Choose your Patients Wisely
August 1, 1998
Noninvasive Ventilation in the ED: Choose your Patients Wisely
ABSTRACT & COMMENTARY
Source: Wood KA, et al. The use of noninvasive positive pressure ventilation in the emergency department: Results of a randomized clinical trial. Chest 1998;113:1339-1346.
This study was intended to assess the role of noninvasive positive pressure ventilation (NPPV) by nasal mask in non-asthmatic patients with acute respiratory failure (ARF). Patients were enrolled if they presented to the ED with moderate-to-severe dyspnea, tachypnea, and had arterial blood gasses consistent with ARF. Patients were excluded if they required immediate endotracheal intubation, had an asthma exacerbation, could not tolerate the nasal mask, had facial or thoracic trauma, or if dysrhythmias were noted. Subjects were randomized to receive either NPPV or conventional therapy. NPPV was delivered using a bilevel positive airway pressure (BiPAP) device initially set at 8 cm H2O inspiratory pressure and 2-4 cm H2O expiratory pressure. The primary outcome was need for endotracheal intubation.
Only 27 of 87 patients presenting with ARF were enrolled in the study; the majority of those not enrolled required urgent intubation. Seven of the 16 subjects (59%) in the NPPV group ultimately required intubation, compared to five of 11 subjects (46%) in the control group. Among those requiring intubation, the time from presentation to intubation was 26 hours in the NPPV group vs. 5 hours in controls. The NPPV group trended toward a greater hospital mortality rate, but there were no differences between the groups in complication rates, length of ICU stay, or duration of mechanical ventilation. Wood and associates conclude that NPPV initiated in the ED offers no advantages over conventional therapy and may be associated with poorer outcome and delay of necessary therapy.
COMMENT BY DAVID KARRAS, MD, FACEP
Even after a decade of research on NPPV and a large body of literature devoted to the subject, only a handful of controlled trials have been published. A recent meta-analysis found strong evidence for recommending NPPV for acute exacerbations of COPD and congestive heart failure.1 There is insufficient evidence to support using NPPV as therapy for ARF related to other etiologies, including status asthmaticus, noncardiogenic pulmonary edema, pneumonia, and acute respiratory distress syndrome.2
The fact that less than a third of patients presenting to the ED with acute respiratory failure were candidates for the present study points to one problem in studying and using NPPV: the therapy is not indicated for most dyspneic patients. By examining a relatively inhomogeneous population of patients with ARF, and by enrolling patients in the ED rather than in the ICU, Wood et al made their study protocol more of a real-world scenario than those studies enrolling only patients with specific diseases and only after initial stabilization. The small sample size is a significant limitation of this study. Nonetheless, the disturbing results should give us reason to pause before initiating NPPV in the ED and remind us that careful patient selection is critical to the success of NPPV.3