ABSTRACT
OBJECTIVE: To characterize the cardiopulmonary effects of dexmedetomidine, with or without vatinoxan, in isoflurane-anesthetized cats. STUDY DESIGN: Randomized, crossover experimental study. ANIMALS: A group of six adult healthy male neutered cats. METHODS: Cats were instrumented during anesthesia with isoflurane in oxygen. Isoflurane end-tidal concentration was set to 1.25 minimum alveolar concentration (MAC). Dexmedetomidine was administered using a target-controlled infusion system to achieve and maintain 10 target plasma concentrations ranging from 0 to 40 ng mL-1. Furthermore, vatinoxan or an equivalent volume of saline was administered using a target-controlled infusion system to achieve and maintain a target plasma concentration of 4 µg mL-1. Isoflurane concentration was adjusted after each change in dexmedetomidine concentration to maintain a concentration equivalent to 1.25 MAC. Heart rate (HR), arterial blood pressure, central venous pressure (CVP), pulmonary artery pressure (PAP), pulmonary artery occlusion pressure (PAOP), body temperature, cardiac output, arterial and mixed-venous blood gas and pH and drug concentrations were measured. Additional variables were calculated from the measurements. RESULTS: Dexmedetomidine alone resulted in decreased HR, cardiac index, stroke index and oxygen delivery, and increased systolic, mean (MAP) and diastolic arterial pressure, CVP, PAP, PAOP, systemic vascular resistance index, rate-pressure product, left ventricular stroke work index and oxygen extraction ratio. Vatinoxan resulted in severe hypotension at target plasma dexmedetomidine concentrations <10 ng mL-1. Vatinoxan attenuated the cardiovascular effects of dexmedetomidine at the 10 and 20 ng mL-1 targets, but MAP could be maintained above 60 mmHg only when isoflurane concentration was <1.25 MAC. Less improvement in cardiovascular function was seen with vatinoxan at the 40 ng mL-1 target plasma dexmedetomidine concentration. CONCLUSIONS AND CLINICAL RELEVANCE: Vatinoxan, at the plasma concentration maintained in this study, attenuated the cardiovascular effects of dexmedetomidine in isoflurane-anesthetized cats. However, its administration resulted in hypotension, which may limit its clinical usefulness.
