Noninvasive ventilation and positive-pressure strategies for routine emergency management of patients with respiratory failure have revolutionized ED practice. The ability to provide effective and life-saving respiratory support without the need for endotracheal intubation stands as one of the most incredible technological advances in modern emergency medicine, but the brief and bastardized deployment of these devices has left room for refinement.
First described in 1936 when an intrepid English physician strapped an Electrolux vacuum to a patient with pulmonary edema (have no worry—he advised that “the machine should be run for a few minutes first of all to get rid of dust”), noninvasive ventilation (NIV) quickly evolved into widely available and portable continuous and bi-level positive airway pressure (CPAP or BiPAP) units placed in EDs and bedrooms across the country. (Lancet. 1936;231:981; http://bit.ly/2KInydq.)
Uptake was brisk, and NIV found routine use in the spectrum of respiratory failure in less than a generation. Unfortunately, the systematic and scholastic method with which we typically introduce new interventions was eclipsed by the ability to simplify and streamline NIV, and early reflective respiratory support quickly gave way to what is now a bromidic and benighted practice, a rush to BiPAP and a troublesome evasion of nuance in critical ventilatory support.
CPAP use in patients presenting with cardiogenic pulmonary edema saves lives. (Lancet. 2006;367:1155.) The positive end-expiratory pressure induced by CPAP reduces right and left ventricular preload, afterload, and cardiac transmural pressure without negatively affecting myocardial contractility, driving an increase in ejection fraction without increasing cardiac myocyte workload. (J Accid Emerg Med. 2000;17:79; http://bit.ly/2KIY0Nq.) Contrary to the somewhat common misconception that NIV blows the water out of the lungs, the benefit of CPAP in patients with heart failure is largely from its actions on the Frank-Starling mechanisms, long forgotten and rarely considered in bedside practice.
The escalation to BiPAP involves oscillation between an inspiratory positive airway pressure (IPAP) triggered by the patient with a lower expiratory positive airway pressure (EPAP). The difference between IPAP and EPAP drives ventilation, and is responsible for relieving the work of breathing while decreasing elevated PCO2 in patients with hypercarbic respiratory failure. BiPAP is a critical intervention in patients with COPD, decreasing the need for endotracheal intubation in one of three patients and saving nearly as many from death or long-term morbidity. (Crit Care Med. 1997;25:1685.)
The problem—and my objection—comes when the forest of ED respiratory support is lost for the trees of familiarity and simplification. The fundamental benefits of NIV modes have been seemingly forgotten, and patients with respiratory failure secondary to pulmonary edema are placed on BiPAP without hesitation in departments across the country. Sometimes the EMS-applied CPAP unit is even ripped off in favor of the ostensibly superior bi-level ventilation brought to the bedside. This practice, however, represents a dumbing down of respiratory support at a minimum, and might lead to worse outcomes for some of our most critical patients.
One of the earliest trials comparing CPAP with BiPAP in patients with acute pulmonary edema was terminated early because of a higher rate of myocardial infarction in the BiPAP group. (Crit Care Med. 1997;25:620.) A subsequent investigation suggested a trend toward higher mortality and organ failure rates in patients receiving BiPAP (Chest. 1998;113:1339), and a trial nearly a decade later again hinted at higher rates of myocardial infarction in patients placed on BiPAP compared with CPAP. (Lancet. 2006;367:1155.)
The authors of a large and extremely well done systematic review and meta-analysis, however, reported no significant difference in patient-oriented outcomes between CPAP and BiPAP in patients with acute cardiogenic pulmonary edema. (Am J Emerg Med. 2013;31:1322.) Close examination of the data, including visual inspection of forest plots and (an admittedly liberal) interpretation of the reported data, shows an undeniable pattern of CPAP outperforming BiPAP in nearly every category. At some point, statistical snobbery and cries of non-significance have to give way to a sober admission that CPAP likely holds small but difficult-to-parse benefits over BiPAP in patients presenting with acute exacerbations of heart failure and pulmonary edema.
But even if these benefits are vanishingly small—or so minute that they are all but insignificant in the dynamic clinical environment of the emergency department—the routine use of BiPAP in patients with pulmonary edema lacks face validity and data of efficacy. These patients simply don't need assistance in ventilation and elimination of PCO2, and the addition of IPAP/EPAP oscillations adds complexity without benefit amid recurrent signals of harm. Claims of improved patient comfort and tolerance lack any true supporting data, and the oversimplification of NIV in the ED to BiPAP for all comers represents an abdication of rational respiratory support, a devaluation and distortion of a technological marvel and bulwark of emergency medicine.
We are fortunate to be equipped with readily available tools that help us save lives. These powerful interventions are flexible and forgiving, but settling for a one-size-fits-all deployment of NIV ignores the subtlety and nuance that underlies its strength. The use of CPAP in patients with respiratory failure due to pulmonary edema represents a rational return to considered and individualized use of noninvasive ventilation, a refined approach with the potential for better outcomes for our patients.
Dr. Pescatoreis the director of emergency medicine research for the Crozer-Keystone Health System in Chester, PA. He is also the host with Ali Raja, MD, of the podcast EMN Live, which focuses on hot topics in emergency medicine:http://bit.ly/EMNLive. Follow him on Twitter@Rick_Pescatore, and read his past columns athttp://bit.ly/EMN-Pescatore.