The response of the canine cerebral circulation to hyperventilation during anesthesia with desflurane

Abstract

Arterial CO2 tension (PaCO2) is an important factor controlling cerebral blood flow (CBF) and cerebral vascular resistance (CVR) in animals and humans. The normal responsiveness of the cerebral vasculature to PaCO2 is approximately 2 ml.min-1.100 g-1.mmHg-1. This study examined the effect of desflurane, a new volatile anesthetic, on the responsiveness of the cerebral vasculature to changes in PaCO2. Mean arterial pressure (MAP), CBF, CVR, intracranial pressure (ICP), and cerebral metabolic rate for O2 (CMRO2) were measured in five dogs anesthetized with desflurane (0.5-1.5 MAC) at normocapnia (PaCO2 = 40 mmHg) and at two levels of hypocapnia (PaCO2 = approximately 30 and approximately 20 mmHg). Under desflurane anesthesia, similar changes in CBF and CVR occurred with hyperventilation at all MAC levels of desflurane. At 0.5 MAC, CBF decreased significantly, from 81 +/- 6 to 40 +/- 3 ml.min-1.100 g-1 (P less than 0.05, mean +/- SE) when PaCO2 was decreased from 40 to 24 mmHg; i.e., the CBF decreased approximately 2.6 ml.min-1.100 g-1.mmHg-1. At 1.0 MAC desflurane, CBF decreased significantly, from 79 +/- 10 to 43 +/- 5 ml.min-1.100 g-1 with hyperventilation (2.0 ml.min-1.100 g-1.mmHg-1); at 1.5 MAC desflurane, CBF decreased from 65 +/- 6 to 38 +/- 2 ml.min-1.100 g-1 with hyperventilation (1.6 ml.min-1.100 g-1.mmHg-1). Despite the significant decreases in CBF with hyperventilation, there was no significant change in ICP. Dose-dependent decreases in MAP were observed with increasing concentrations of desflurane but were not significantly affected by ventilation.(ABSTRACT TRUNCATED AT 250 WORDS)