Pathophysiology of Acute Cardiogenic Pulmonary Edema (ACPE)

Pulmonary vascular congestion, interstitial edema, and alveolar fluid accumulation, which initially leads to hypoxemic respiratory failure but can progress to hypercapnic respiratory failure.

Benefits of NIPPV in ACPE

• Reduces work of breathing

• Recruits and stabilizes collapsed alveoli

• Increases intrathoracic and hydrostatic pressure, moving fluid from the lungs into the vasculature

• Increases tidal volume and minute ventilation, increasing PaO2 and decreasing PaCO2

Modes of NIPPV

Continuous  Positive Airway Pressure (CPAP)

• Delivers a constant pressure throughout the respiratory cycle

• Typically set between 5-15 cm H₂O

Bilevel Positive Airway Pressure (BiPAP)

• Delivers different levels of pressure during the inspiratory phase and the expiratory phase

• Inspiratory positive airway pressure (IPAP) is typically set to 8-10 cm H₂O

• Expiratory positive airway pressure (EPAP) is typically set to 3-5 cm H₂O

CPAP or BiPAP?

A meta analysis published in the Annals of Internal Medicine in 2010 found that both CPAP and BiPAP reduced the need for intubation when compared to standard therapy alone. However, a mortality benefit was only seen with CPAP. 

CPAP, when compared to standard therapy, reduced mortality (RR 0.64, CI 0.44-0.92) and the need for intubation (RR 0.44, CI 0.32-0.6).

BiPAP, when compared to standard therapy, reduced the need for intubation (RR 0.54, CI 0.33-0.86) but was not found to reduce mortality.

Conclusion

Evidence points to CPAP as the superior method of NIPPV in ACPE, as it reduces both the need for intubation and mortality. 

ACEP practice guidelines currently offer a Level B recommendation for the use of CPAP and Level C recommendation for BiPAP in dyspneic patients with acute heart failure syndromes.

References:

Silvers, Scott M., John M. Howell, Joshua M. Kosowsky, Ivan C. Rokos, and Andy S. Jagoda. "Clinical Policy: Critical Issues in the Evaluation and Management of Adult Patients Presenting to the Emergency Department with Acute Heart Failure Syndromes." Annals of Emergency Medicine 49.5 (2007): 627-69. Web.

Tintinalli, J. E., Stapczynski, J. S., Ma, O. J., Yealy, D. M., Meckler, G. D., & Cline, D. (2016).Tintinalli's emergency medicine: a comprehensive study guide. New York: McGraw-Hill Education.

Weng C, Zhao Y, Liu Q et al. Meta-analysis: noninvasive ventilation in acute cardiogenic pulmonary edema. Ann Intern Med 2010;152:590-600.