Anesthetic Influence on Arteriolar Diameters and Tissue Oxygen Tension in Hemorrhaged Rats

Abstract

Arteriolar diameters and tissue O2 tensions were measured in the cremaster muscles of 68 hemorrhaged rats which were anesthetized with either i.m. ketamine, 125 mg/kg, plus 30 mg/kg supplements as needed, or enflurane, 2.2% inspired. Animals breathed room air or room air plus enflurane throughout the experiments. Arterioles in the cremaster muscle were identified according to successive orders of branching, and the internal diameters of 1st-, 3rd- and 4th-order vessels were measured at 30-s intervals. Cremaster muscle O2 tension was measured polarographically with Pt-Ir microelectrodes. Mean arterial pressure was controlled at 30-35 mmHg during 30 min of hemorrhage, and maximum shed blood volumes were similar (2.6 ml/100 g) in both groups. Principal responses to hemorrhage in rats receiving enflurance were constriction in 1st-, 3rd- and 4th-order arterioles and tissue hypoxia. In hemorrhaged rats receiving ketamine, the constrictor response to hemorrhage either was diminished (1st- and 3rd-order arterioles) or abolished (4th-order-arterioles) and tissue hypoxia did not occur. Ketamine, as compared with enflurane, diminishes or prevents arteriolar constriction and tissue hypoxia in the cremaster muscle of hemorrhaged rats.