Hemodynamic effects of ionized calcium in horses anesthetized with halothane or isoflurane

Objectives-To evaluate the effects of halothane and isoflurane on cardiovas cular function and serum total and ionized calcium concentrations in horses , and to determine whether administration of calcium gluconate would attenu ate these effects. Animals-6 clinically normal adult Thoroughbreds. Procedure-Catheters were inserted for measurement of arterial blood pressur es, pulmonary arterial blood pressures, right ventricular pressure (for det ermination of myocardial contractility), right atrial pressure, and cardiac output and for collection of arterial blood samples. Anesthesia was then i nduced with xylazine hydrochloride and ketamine hydrochloride and maintaine d with halothane or isofiurane. An IV infusion of calcium gluconate was beg un 75 minutes after anesthetic induction; dosage of calcium gluconate was 0 .1 mg/kg of body weight/min for the first 15 minutes, 0.2 mg/kg/min for the next 15 minutes, and 0.4 mg/kg/min for an additional 15 minutes. Data were collected before, during, and after administration of calcium gluconate. Results-Halothane and isofiurane decreased myocardial contractility, cardia c index, and mean arterial pressure, but halothane caused greater depressio n than isoflurane. Calcium gluconate attenuated the anesthetic-induced depr ession in cardiac index, stroke index, and maximal rate of increase in righ t ventricular pressure when horses were anesthetized with isoflurane. When horses were anesthetized with halothane, a higher dosage of calcium glucona te was required to attenuate the depression in stroke index and maximal rat e of increase in right ventricular pressure; cardiac index was not changed with calcium administration. Conclusions and Clinical Relevance-IV administration of calcium gluconate m ay support myocardial function in horses anesthetized with Isoflurane.