Objective: To clarify the effects of hypercapnia (increased PaCO2) on gastric mucosal oxygenation during anaesthesia in dogs.
Design: Prospective, controlled animal study.
Setting: Experimental research laboratory of an university hospital.
Subjects: Six chronically instrumented dogs.
Interventions: Dogs were anaesthetized (sevoflurane 1.5 MAC), mechanically ventilated (etCO2 = 35 mmHg) and randomly assigned to the following protocols: in a first series, ventilation was adjusted to increase etCO(2) to 45, 55, 65 and 70 mmHg. In a second series, animals were ventilated to achieve 70 mmHg of etCO2, which was maintained for 120 min to test if effects are transient or prolonged and to achieve a similar time course in both protocols.
Measurements and main results: Gastric mucosal oxygenation (microHbO2) was assessed continuously by tissue reflectance spectrophotometry. Mean arterial blood pressure (MAP) and cardiac output (CO) were continuously measured. Blood was sampled for blood gas analysis and lactate concentration. Hypercapnia increased gastric mucosal oxygenation concentration dependently from 48 +/- 6% (35 mmHg etCO2) to 51 +/- 4, 54 +/- 5, 56 +/- 5 and 59 +/- 3% (etCO2 45, 55, 65 and 70 mmHg, respectively). This reflected changes in CO (68 +/- 16, 74 +/- 16, 82 +/- 12, 91 +/- 11 and 97 +/- 16 ml kg(-1) min(-1), respectively) and systemic oxygen delivery (10 +/- 2, 11 +/- 3, 13 +/- 2, 14 +/- 2 and 14 +/- 2 ml kg(-1) min(-1), respectively). These effects persisted for 2 h (microHbO2 53 +/- 6 vs. 64 +/- 4%, CO 73 +/- 16 vs. 92 +/- 15 ml kg(-1) min(-1), DO2 12 +/- 4 vs. 14 +/- 3 ml kg(-1) min(-1), etCO2 35 and 70 mmHg, respectively).
Conclusions: Hypercapnia increased systemic and regional oxygenation. If this experimental finding may be transferred to the clinical setting, permissive hypercapnia might be used to augment the oxygenation of the splanchnic region, e.g. gastrointestinal mucosa.