Yesterday, we learned about acute mountain sickness (AMS) and high altitude cerebral edema (HACE). Today we will tackle high altitude pulmonary edema (HAPE), the deadliest of the altitude illnesses.
HAPE generally occurs above 3000m, but incidence varies at different altitudes. At 4500m the incidence ranges from 0.2 to 6%. Factors that place people at increased risk for HAPE include male gender, colder temperatures, rapid ascent, and vigorous exercise. Pulmonary hypertension from any cause increases risk of HAPE, including ASD, VSD and patent foramen ovale.
HAPE is a noncardiogenic, hydrostatic edema. Triggered by hypobaric hypoxia, the pulmonary blood-gas barrier breaks down, which results in accumulation of plasma and red cells in the lung. Symptoms of HAPE begin mildly and generally occur 2-4 days after arrival to a new altitude. Patients will have non-productive cough, decreased exercise tolerance and dyspnea on exertion. Over the next 1-2 days the symptoms progress to dyspnea at rest, hypoxia and cough with pink, frothy or bloody sputum.
Similarly to AMS and HACE, the diagnosis of HAPE is clinical. Early diagnosis is key, decreased exercise tolerance and dry cough should raise suspicion for early HAPE. Immediate descent is the optimal treatment, but exertion must be minimized. If descent is not possible, supplemental oxygen should be given to patient and if available, a portable hyperbaric chamber should be used as an adjunct. Supplemental oxygen lowers pulmonary artery pressure and can can completely resolve pulmonary edema without descent, but may require 36 to 72 hours. In milder cases or areas where this is logistically feasible, patients can be treated with bed rest and supplemental oxygen. For severe cases or those with associated HACE, hospitalization, intubation and NIV may be required.
To prevent against HAPE, gradual ascent is crucial. There are a number of prophylactic medications that can be used, but nifedipine is preferred.
Hackett PH, Davis CB. “High Altitude Disorders.” Chapter 216. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide.
Schoene RB, Illnesses at high altitude. Chest 2008; 124:402.