Vascular responsiveness to brachial artery infusions of phenylephrine during isoflurane and desflurane anesthesia.

Abstract

Compared with equi-minimum alveolar anesthetic concentration (MAC) isoflurane, desflurane is associated with greater levels of sympathetic nerve activity in humans but similar reductions in blood pressure. To explore these divergent effects, we evaluated vascular alpha(1)-adrenoceptor responses in the human forearm during isoflurane and desflurane anesthesia to determine if alpha(1)-adrenoceptor responses were more substantially attenuated during desflurane administration. Bilateral forearm venous occlusion plethysmography was used to examine arterial blood flow and to determine changes in forearm vascular resistance during brachial artery infusions of saline and phenylephrine (0.2, 0.4, 0.8, and 1.6 microg/min) in 22 conscious subjects and during anesthesia with 0.65 and 1.3 MAC isoflurane or desflurane. Infusion of phenylephrine into the brachial artery increased the forearm vascular resistance in a dose-dependent manner. The arterial response to phenylephrine was significantly attenuated by 0.65 and 1.3 MAC desflurane and similarly attenuated during 1.3 MAC isoflurane (P < 0.05). Impaired arterial alpha(1)-adrenoceptor responsiveness occurred during desflurane. However, this effect was statistically similar (P > 0.05) to the impaired responses during isoflurane. Blood pressure decreases during volatile anesthesia may be, in part, caused by decreased alpha(1)-adrenoceptor responsiveness. alpha-receptors on blood vessels regulate constriction and dilation and therefore modulate blood pressure. This research indicates that vasoconstriction via the alpha(1)-receptor vascular response is impaired during isoflurane and desflurane anesthesia.