CARDIOVASCULAR EFFECTS OF 1.0, 1.5, AND 2.0 MINIMUM ALVEOLAR CONCENTRATIONS OF ISOFLURANE IN EXPERIMENTALLY-INDUCED HYPOTHYROIDISM IN DOGS

This study was performed to determine the cardiovascular responses to isoflurane in euthyroid and hypothyroid dogs. Four healthy mixed-breed dogs were studied prior to thyroidectomy (PRE), 6 months after thyroi dectomy (HYP), and after 2 months of oral supplementation with 1-thyro xine (SUP). Heart rate (HR), cardiac output (Q), stroke volume (SV), s ystolic, diastolic, mean arterial blood pressure (SAP, DAP, MAP), and total peripheral resistance (TPR) were determined in awake dogs and in the same dogs when end-tidal isoflurane concentrations were 1.28%, 1. 92%, and 2.56%. Ventilation was controlled in anesthetized dogs and Pa ce, maintained between 38 to 42 mm Hg. Isoflurane caused significant ( P < .05) dose-dependent reduction in Q, SV, SAP, DAP, and MAP in the P RE, HYP, and SUP dogs. Cardiac output was lower in the HYP dogs than i n the PRE or SUP dogs during awake measurement. TPR was increased in t he awake HYP dogs compared with the PRE or SUP dogs. During anesthesia , HYP dogs tended to have lower Q, SV, SAP, and MAP than the PRE or SU P groups, but the only significant reduction was SAP during 1.5 MAC. T he cardiovascular responses to isoflurane in hypothyroid dogs are simi lar to euthyroid animals with a dose-dependent depression in Q, SV, an d arterial pressure. (C) Copyright 1996 by The American College of Vet erinary Surgeons