Fig. 1. Subcutaneous oxygen partial pressure in the upper arm during colon resection surgery in patients receiving supplemental oxygen (inspired oxygen concentration of 80%) and an end-tidal carbon dioxide partial pressure of 35 mmHg (normocapnia) and patients receiving supplemental oxygen and a carbon dioxide partial pressure of 50 mmHg (mild hypercapnia). The  open circles represent the value in each patient. The  squares show the group means (95% confidence intervals); the group means differed significantly (  P = 0.006).