Supplemental Oxygen and Carbon Dioxide Each Increase Subcutaneous and Intestinal Intramural Oxygenation

Oxidative killing by neutrophils, a primary defense against surgical pathogens, is directly related to tissue oxygenation. We tested the hypothesis that supplemental inspired oxygen or mild hypercapnia (end-tidal PCO2 of 50 mm Hg) improves intestinal oxygenation. Pigs (25 ± 2.5 kg) were used in 2 studies in random order: 1) Oxygen Study: 30% versus 100% inspired oxygen concentration at an end-tidal PCO2 of 40 mm Hg, and 2) Carbon Dioxide Study: end-tidal PCO2 of 30 mm Hg versus 50 mm Hg with 30% oxygen. Within each study, treatment order was randomized. Treatments were maintained for 1.5 h; measurements were averaged over the final hour. A tonometer inserted in the subcutaneous tissue of the left upper foreleg measured subcutaneous oxygen tension. Tonometers inserted into the intestinal wall measured intestinal intramural oxygen tension from the small and large intestines. Oxygen 100% administration doubled subcutaneous oxygen partial pressure (PO2) (57 ± 10 to 107 ± 48 mm Hg, P = 0.006) and large intestine intramural PO2 (53 ± 14 to 118 ± 72 mm Hg, P = 0.014); intramural PO2 increased 40% in the small intestine (37 ± 10 to 52 ± 25 mm Hg, P = 0.004). An end-tidal PCO2 of 50 mm Hg increased large intestinal PO2 approximately 16% (49 ± 10 to 57 ± 12 mm Hg, P = 0.039), whereas intramural PO2 increased by 45% in the small intestine (31 ± 12 to 44 ± 16 mm Hg, P = 0.002). Supplemental oxygen and mild hypercapnia each increased subcutaneous and intramural tissue PO2, with supplemental oxygen being most effective.