Auto-PEEP in the therapy of AMS in one person at 4,330 m

The human organism is exposed to considerable hypoxic stress at high altitudes. Our intention was to investigate if a special breathing pattern with expiration against the resistance of pursed lips leads to an elevation in oxygen saturation (SaO(2)). For the first time ever, oxygen saturation was measured continuously during the initial situation, during self-performed positive end-expiratory pressure breathing (auto-PEEP) itself, and during observation afterwards.

The investigation was performed on a 33-year-old male suffering from high-altitude illness (Lake Louise Score, 9) after a 4-day rapid ascent from 350 m to 4,330 m during an expedition to Mount McKinley (6,198 m). SaO(2) was measured continuously at 4-s intervals. After a rest of 1.5 h in a dorsal recumbent position with a slightly elevated (about 15 degrees ) upper body, the patient used a wristwatch to breathe according to a special time pattern (inspiration 2 s, expiration 8 s against the resistance of pursed lips). After 30 min, breathing was then allowed without any restrictions, and the inspiration/expiration ratio was approximately 1:1.

There was a relatively sharp rise in SaO(2) from an average of 62% to 85% within only 5 min after auto-PEEP began. This was followed by a comparable rise to values of 95% at the end of the auto-PEEP period. During normal breathing, SaO(2) decreased slowly within half an hour to values of about 70% and remained at this level. The person reported relief in symptoms and no exhaustion. Vertigo-an indication of hypocapnia caused by hyperventilation-was not observed.

The 30% rise in SaO(2) and the improved saturation level after auto-PEEP are remarkable. Elevated intra-thoracal pressure may lead to a reopening of collapsed alveoli in addition to an improved gradient of alveolar-capillary pressure. In addition, a pressure-induced displacement of interstitial fluid resulting in a reduced diffusion distance may lead to improved alveolar-capillary diffusion. This would explain the slower rise in SaO(2) after 10 min of auto-PEEP and the elevated level of SaO(2) compared to the initial level before auto-PEEP.

As a result of the substantial and lasting improvement in SaO(2) in combination with relief in AMS symptoms and its easy use, auto-PEEP (30 min every 2 h) can be a useful therapy option in the event of high-altitude-induced hypoxia and AMS.