Abstract
IntroductionPositive end-expiratory pressure (PEEP) is commonly used in critical care medicine to improve gas exchange. Altitude sickness is associated with exaggerated reduction in arterial oxygenation. We assessed the effect of PEEP and pursed lips breathing (PLB) on arterial and tissue oxygenation under normobaric and hypobaric hypoxic conditions.MethodsSixteen healthy volunteers were exposed to acute normobaric hypoxia (Laboratory study, FiO2=0.12). The protocol consisted in 3-min phases with PEEPs of 0, 5 or 10 cmH2O, PLB or similar ventilation than with PEEP-10, interspaced with 3-min phases of free breathing. Arterial (pulse oximetry) and quadriceps (near-infrared spectroscopy) oxygenation, ventilation, cardiac function, esophageal and gastric pressures and subjects’ subjective perceptions were recorded continuously. In addition, the effect of PEEP on arterial oxygenation was tested at 4,350 m of altitude in 9 volunteers breathing for 20 min with PEEP-10 (Field study).ResultsDuring the laboratory study, PEEP-10 increased arterial and quadriceps oxygenation (arterial oxygen saturation +5.6±5.0% and quadriceps oxyhemoglobin +58±73 µmol.cm compared to free breathing; p<0.05). Conversely, PLB did not increase oxygenation. Oxygenation improvement with PEEP-10 was accompanied by an increase in expiratory esophageal and gastric pressures (esophageal pressure swing +5.4±3.2 cmH2O, p<0.05) but no change in minute ventilation, breathing pattern, end-tidal CO2 or cardiac function (all p>0.05) compared to PEEP-0. During the field study, PEEP-10 increased arterial oxygen saturation by +6.7±6.0% after the 3rd minute with PEEP-10 without further significant increase until the 20th minute with PEEP-10. Subjects did not report any significant discomfort with PEEP. ConclusionsThese data indicate that 10-cmH2O PEEP significantly improves arterial and muscle oxygenation under both normobaric and hypobaric hypoxic conditions in healthy subjects. PEEP-10 could be an attractive non-pharmacological tool to limit blood oxygen desaturation and possibly symptoms at altitude.
Highlights
Positive end-expiratory pressure (PEEP) is commonly used in critical care medicine to improve gas exchange
Neither T10 nor pursed lips breathing (PLB) induced significant improvement in SpO2 compared to FB and PEEP of 0 cmH2O (PEEP-0)
The present findings demonstrate that using a 10-cmH2O PEEP in healthy subjects under normobaric (FiO2 = 0.12) and hypobaric (4,350 m) hypoxia induced a significant increase in SpO2 (+5.6% and +6.7% on average after 3 min PEEP-10 compared to FB, respectively)
Summary
Positive end-expiratory pressure (PEEP) is commonly used in critical care medicine to improve gas exchange. We assessed the effect of PEEP and pursed lips breathing (PLB) on arterial and tissue oxygenation under normobaric and hypobaric hypoxic conditions. The effect of PEEP on arterial oxygenation was tested at 4,350 m of altitude in 9 volunteers breathing for 20 min with PEEP-10 (Field study). Conclusions: These data indicate that 10-cmH2O PEEP significantly improves arterial and muscle oxygenation under both normobaric and hypobaric hypoxic conditions in healthy subjects. At least part of the effect of PEEP and PLB on gas exchange is thought to result from an increase in alveolar pressure, leading to improved lung diffusion capacity and blood oxygenation [5,6]. In addition to increased ventilation, improved pulmonary diffusion is another mechanism associated with altitude acclimatization and enhanced blood oxygenation [11]. Any intervention that might improve pulmonary diffusion could potentially increase blood oxygenation and altitude tolerance
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