Acute hypercapnia increases hepatic surface PO2: an experimental study in the rat

Objective: To assess whether acute hypercapnia affects hepatic tissue oxyge n tension as measured at the surface of the rat liver. Design: Prospective, controlled study. Setting: University medical school laboratory. Subjects: Male Sprague-Dawley rats weighing 250-450 grams. Interventions: An 8-point surface oxygen electrode was used to measure tiss ue oxygen tension (P1O2) in the rat liver during normocapnia (PaCO2 33-49 m mHg), while breathing 5% CO2 (PaCO2 54-70 mmHg), and while breathing 10% CO 2 (PaCO2 74-101 mmHg). Measurements were made at baseline in all 3 groups, following which 5% or 10% carbon dioxide was added to the inhaled gas mixtu re in the two hypercapnic groups. Measurements were then taken again at 10, 15, 30, 40, and 50 minutes. Measurements and Main Results: There were no significant differences betwee n the groups at baseline with mean P1O2 being 29.4 +/- 2.1 mmHg in the cont rol group, 30.2 +/- 5.7 mmHg in the 5% group, and 29.7 +/- 5.5 mmHg in the 10% group. At 10 minutes there was an increase in mean P1O2 to 38.7 +/- 4.4 mmHg in the 5% group (p < .005), and to 48 +/- 3.0 mmHg in the 10% group ( p < .001). The mean P1O2 values for both hypercapnic groups remained signif icantly elevated when compared to the control group for the remaining 50 mi nutes of the experiment. Conclusion: We conclude that acute hypercapnia leads to increased hepatic t issue oxygen tension as measured at the surface of the liver.