Subcutaneous Oxygen Pressure in Spontaneously Breathing Lean and Obese Volunteers: a Pilot Study
Oxidative killing is the primary defense against surgical pathogens; risk of infection is inversely related to tissue oxygenation. Subcutaneous tissue oxygenation in obese patients is significantly less than in lean patients during general anesthesia. However, it remains unknown whether reduced intraoperative tissue oxygenation in obese patients results from obesity per se or from a combination of anesthesia and surgery. In a pilot study, we tested the hypothesis that tissue oxygenation is reduced in spontaneously breathing, unanesthetized obese volunteers.
Seven lean volunteers with a body mass index (BMI) of 22 ± 2 kg/m2 were compared to seven volunteers with a BMI of 46 ± 4 kg/m2. Volunteers were subjected to the following oxygen challenges: (1) room air; (2) 2 l/min oxygen via nasal prongs, (3) 6 l/min oxygen through a rebreathing face mask; (4) oxygen as needed to achieve an arterial oxygen pressure (arterial pO2) of 200 mmHg; and (5) oxygen as needed to achieve an arterial pO2 of 300 mmHg. The oxygen challenges were randomized. Arterial pO2 was measured with a continuous intraarterial blood gas analyzer (Paratrend 7); deltoid subcutaneous tissue oxygenation was measured with a polarographic microoxygen sensor (Licox).
Subcutaneous tissue oxygenation was similar in lean and obese volunteers: (1) room air, 52 ± 10 vs 58 ± 8 mmHg; (2) 2 l/min, 77 ± 25 vs 79 ± 24 mmHg; (3) 6 l/min, 125 ± 43 vs 121 ± 25 mmHg; (4) arterial pO2 = 200 mmHg, 115 ± 42 vs 144 ± 23 mmHg; (5) arterial pO2 = 300 mmHg, 145 ± 41 vs 154 ± 32 mmHg.
In this pilot study, we could not identify significant differences in deltoid subcutaneous tissue oxygen pressure between lean and morbidly obese volunteers.
KeywordsSubcutaneous oxygen pressure Spontaneous breathing Obesity Tissue oxygenation Volunteers
This work was supported by the Research Fund of the Department of Anesthesiology, Washington University School of Medicine and the Department of Anesthesiology, University of Bern. None of the authors has a personal financial interest in this research.
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