MILAN, ITALY—Although potentially fatal, high-altitude pulmonary edema (HAPE) is generally considered rare, occurring in 2% to 5% of skiers and mountain climbers undergoing rapid ascents while exercising. But new research shows that subclinical HAPE is more common than previously thought: Among 262 climbers ascending 3,359 m in one day, 40 (15%) had clinical or radiographic signs of interstitial pulmonary edema. And of the 197 climbers without such signs, 146 (74%) had increased closing volume, suggesting mild HAPE.[1]

“Although full-blown HAPE is rare, most climbers (three out of four) show evidence of pulmonary extravascular fluid accumulation, suggesting that lung fluid balance is on the edge in most people,” remarked first author George Cremona, MD, PhD. Thus, the risk of HAPE is “not limited to a few genetically susceptible individuals,” added Dr. Cremona, Director and Professor of Respiratory Medicine at San Raffaele University in Milan. “While other factors presumably also play a role in the development of the condition, it is likely that most people are susceptible if the altitude, rate of ascent, and physical effort are of sufficient magnitude,” he told PULMONARY REVIEWS.

HAPE requiring evacuation is rare, but evidence that rapid ascent and exercise can cause gas exchange abnormalities prompted Dr. Cremona and colleagues to investigate the effects on 262 alpinists of climbing Monte Rosa, a 4,559-m peak on the Italian-Swiss border. At an altitude of 1,200 m, before their ascent, the climbers underwent clinical examination, Lake Louise scoring for acute mountain sickness symptoms, electrocardiography, spirometry, oximetry, and tests of carbon monoxide transfer and closing volume; measurements were repeated the next day near the summit.

One climber was evacuated for HAPE. Among the 40 climbers with chest rales or radiography indicating less severe interstitial edema after ascent, none had HAPE-related symptoms. Yet closing volumes in 34 (92%) of the 37 such climbers available for measurement were markedly increased after ascent, as were closing volumes in 146 of the 197 climbers without clinical evidence of interstitial edema.

“The effect is related to patchy hypoxic vasoconstriction and increased cardiac output on climbing at altitude,” Dr. Cremona explained. “Certain parts of the pulmonary vascular bed experience very high flows, which leads to stress failure of pulmonary capillaries and thus extravascular fluid accumulation.”

CLOSING VOLUME MAY INDICATE HAPE

After ruling out bronchoconstriction or exercise as immediate causes, “we interpreted any increase in closing volume after ascent as evidence of increased lung fluid accumulation—that is, subclinical HAPE,” said Dr. Cremona, explaining, “Increased lung fluid accumulation [will] track along the outside of these small airways,” raising airway compression, and thus, the volume at which airways close. “There was a close relationship between closing volume increase and radiological and clinical signs of HAPE,” he also noted.

“The current recommendations are for climbers to be alert to undue breathlessness, dry cough or cough productive of frothy sputum, or fever,” symptoms of potentially fatal HAPE. But given subclinical HAPE’s prevalence, Dr. Cremona had this warning for all climbers, “Ascend gradually and ensure plenty of rest during the climb, as everyone is at risk.”

—Mimi Zucker, PhD

Reference
1. Cremona G, Asnaghi R, Baderna P, et al. Pulmonary extravascular fluid accumulation in recreational climbers: a prospective study. Lancet. 2002;359:303-309.

Return to table of contents