Cardiovascular effects of equipotent isoflurane and alfentanil/isoflurane minimum alveolar concentration multiple in cats

Abstract

Objective - To determine whether administration of opioids to anesthetized cats induced less cardiovascular depression than that induced by an equivalent amount of anesthetic alone, and to measure endocrine responses to a noxious stimulus. Animals - 6 healthy female cats. Procedure - Anesthesia was induced with isoflurane and was maintained for 60 minutes at 1.3 isoflurane MAC. Blood gas tensions, pH, and plasma alfentanil and hormone concentrations, blood pressures, and cardiac output were measured. A noxious stimulus was applied for 5 minutes, while blood acquisition and measurements were repeated. Alfentanil was administered IV to achieve estimated plasma concentration of 500 ng/ml, and end-tidal isoflurane concentration was reduced by 35%. After another 60 minutes, blood was obtained and measurements were taken, then a second 5-minute noxious stimulus was applied while blood acquisition and measurements were retaken. Results-Alfentanil administration and reduction of isoflurane concentration significantly increased body temperature, heart rate, mean arterial pressure, mean pulmonary arterial pressure, stroke index, cardiac index, hemoglobin, oxygen delivery index, Pv(O2) and Pv(CO2) dopamine, epinephrine (EPI), norepinephrine (NOREPI), and cortisol values, and significantly decreased arterial and venous pH. Application of a noxious stimulus significantly increased heart rate, stroke index, cardiac index, Pa(O2), oxygen delivery index, arterial and venous pH, and NOREPI values, and decreased bicarbonate, Pa(CO2), Pv(CO2), and EPI values. Alfentanil administration blunted cardiac index, Pa(CO2), oxygen delivery index, arterial pH, Pa(O2) and EPI, and NOREPI responses to a noxious stimulus. Conclusions - Compared with isoflurane alone, alfentanil administration and reduction of isoflurane MAC improved cardiovascular variables, and blunted respiratory, hormonal, and most hemodynamic responses to a noxious stimulus in cats. Clinical Relevance - Use of the balanced opioid anesthesia regimen induced some beneficial effects in healthy cats; effects were similar to, although greater in nature, than effects induced by a noxious stimulus.