Subcutaneous perfusion before and during surgery in obese and nonobese patients

Hypoxia at the surgical site impairs wound healing and oxidative killing of microbes. Surgical site infections are more common in obese patients. We hypothesized that subcutaneous oxygen tension (Psq O2) would decrease substantially in both obese and non-obese patients following induction of anesthesia and after surgical incision. We performed a prospective observational study that enrolled obese and non-obese surgical patients and measured serial Psq O2 before and during surgery. Seven morbidly obese and seven non-obese patients were enrolled. At baseline breathing room air, Psq O2 values were not significantly different (p = 0.66) between obese (6.8 kPa) and non-obese (6.5 kPa) patients. The targeted arterial oxygen tension (40 kPa) was successfully achieved in both groups with an expected significant increase in Psq O2 (obese 16.1 kPa and non-obese 13.4 kPa; p = 0.001). After induction of anesthesia and endotracheal intubation, Psq O2 did not change significantly in either cohort in comparison to levels right before induction (obese 15.5, non-obese 13.5 kPa; p = 0.95), but decreased significantly during surgery (obese 10.1, non-obese 9.3 kPa; p = 0.01). In both morbidly obese and non-obese patients, Psq O2 does not decrease appreciably following induction of anesthesia, but decreases markedly (∼33%) after commencement of surgery. Given the theoretical risks associated with low Psq O2 , future research should investigate how Psq O2 can be maintained after surgical incision.