The primary defense against surgical pathogens is oxidative killing by neutrophils. Oxygen is a substrate for this process, and the reaction critically depends on tissue oxygen tension throughout the observed physiological range. It is therefore unsurprising that subcutaneous tissue oxygen tension (PsqO2) is inversely correlated with the risk of surgical wound infection. Primary determinants of tissue oxygen availability include arterial oxygen tension, hemoglobin concentration, and local perfusion.