NPPE - MOA

Case: 22 years old atheletic male went through a non-complicated appendectomy under general anesthesia. Patient became agitated on weaning sedation and started biting on the endotracheal tube (ETT). The patient was extubated, but on extubation developed severe pulmonary edema with desaturation. Patient recovered well with supplemental oxygen, non-invasive positive pressure ventilation (NIPPV), diuresis, and infusion of Dexmedetomidine, and was eventually extubated without complications. Why is post-extubation pulmonary edema called negative pressure pulmonary edema (NPPE)?

Answer: Post-extubation pulmonary edema is a common phenomenon in the PACU/ICU if a patient forcibly inhales against a closed glottis. This is also known as the Mueller or reverse Valsalva maneuver. This phenomenon occurs post-extubation due to laryngospasm, pharyngeal obstruction, or biting of the endotracheal tube during extubation. 

Conventional teaching holds that it occurs immediately, though this is not entirely true; a delayed NPPE has been reported up to 12 hours after extubation. People with obesity, short neck, obstructive sleep apnea, or acromegaly are at the highest risk, followed by young, healthy, athletic adults.

The correct term is negative pressure pulmonary edema, which refers to a non-cardiac form of pulmonary edema resulting from the development of negative interstitial pressure around the capillaries, drawing intravascular fluid into the interstitial space.

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References:

1. Mulkey Z, Yarbrough S, Guerra D, et al. Postextubation pulmonary edema: a case series and review. Respir Med 2008; 102:1659.

2. Holmes JR, Hensinger RN, Wojtys EW. Postoperative pulmonary edema in young, athletic adults. Am J Sports Med 1991; 19:365.

3. Tsai PH, Wang JH, Huang SC, Lin YK, Lam CF. Characterizing post-extubation negative pressure pulmonary edema in the operating room-a retrospective matched case-control study. Perioper Med (Lond). 2018 Dec 6;7:28. doi: 10.1186/s13741-018-0107-6. PMID: 30534363; PMCID: PMC6282297.