In 2000, Greif and colleagues39described an approximate 50% reduction in the incidence of postoperative infection in patients administered 80% O2 during and for 2 h after an operation vs those receiving 30% O2. Tissue and wound Po2, however, depend not just on the inspired concentration of O2 but also on perfusion; this, in turn, is affected by the arterial Pco2. In humans, “the skin blood flow measured on the chest decreased by an average of 8% during hyperventilation; blood flow on the hand (thenar eminence) decreased by 60%; and blood flow on the foot decreased by 51%.”40 In contrast, hypercapnia increased tissue Po2. This raises the question, would maintenance of normocapnia, or even slight hypercapnia, reduce wound infections or improve perfusion to ischemic chronic leg ulcers in diabetics? Hyperbaric O2 is a useful form of treatment for chronic infections and leg ulcers,44 but availability and cost limit its use45 and are likely to do so even more as the numbers of such patients increase. For the reasons given above, preventing a fall in Pco2 when breathing O2, whether normobaric or hyperbaric, may increase perfusion and thereby, one hopes, aid in tissue healing.