Influence of anesthesia on the response to carotid hypotension in dogs

Abstract

The systemic hemodynamic response to carotid sinus hypotension (CSH) was obtained by bilateral common carotid or brachiocephalic artery occlusion in trained, chronically instrumented dogs lightly premedicated with morphine and atropine. Responses were obtained before and after anesthesia of equivalent dose by pentobarbital (PB, 30 min post), chloralose (C, 30 min post), or halothane (H, 120 min post). After induction, the animals were intubated and mechanically ventilated by positive pressure with 30% O2 in N2. In the steady state, mean arterial pressure was unchanged with C and PB but decreased with H (-22 .+-. 5%). Cardiac output was decreased by all 3 anesthetics: PB, -34 .+-. 4%; C, -25 .+-. 8%; and H, -13 .+-. 8%. The pressor response to CSH was diminished by all 3 anesthetic agents PB, 48 .+-. 4% to 19 .+-. 5%; C, 58 .+-. 10% to 32 .+-. 2%; and H, 44 .+-. 4% to 21 .+-. 6%. The magnitude of the pressor response to CSH increased with time under PB and C. The response was even more depressed early after induction and tended to return toward control as a function of time after induction, which was associated with recovery from anesthesia. The magnitude of the change in both mean and pulsatile carotid sinus pressure with CSH was larger after anesthesia than before. Apparently all 3 anesthetic agents depress the responses of peripheral baroreceptor-mediated reflexes.