Techniques for evaluation of right ventricular relaxation rate in horses and effects of inhalant anesthetics with and without intravenous administration of calcium gluconate

Objectives-To determine the most repeatable method for evaluating right ven tricular relaxation rate in horses and to determine and compare effects of isoflurane or halothane with and without the added influence of intravenous ly administered calcium gluconate on right ventricular relaxation rates in horses, Animals-6 Thoroughbred horses from 2 to 4 years old. Procedure-6 models (2 for monoexponential decay with zero asymptote, 3 for monoexponential decay with variable asymptote, and 1 for biexponential deca y) for determining right ventricular relaxation rate were assessed in consc ious and anesthetized horses. The 2 methods yielding the most repealable re sults then were used to determine right ventricular relaxation rates in hor ses anesthetized with isoflurane or halothane before, during, and after IV administration of calcium gluconate. Right ventricular pressure was measure d, using a catheter-tip high-fidelity pressure transducer, and results were digitized at 500 Hz from minimum rate of change in ventricular pressure. Results-2 models that used monoexponential decay with zero asymptote repeat edly produced an estimate for relaxation rate and were used to analyze effe cts of anesthesia and calcium gluconate administration on relaxation rate. Isoflurane and halothane each prolonged right ventricular relaxation rate, with greater prolongation evident in halothane-anesthetized horses. Calcium gluconate attenuated the anesthesia-induced prolongation in right ventricu lar relaxation rate, with greater response obtained in isoflurane-anestheti zed horses. Conclusions and Clinical Relevance-Right ventricular relaxation rate in hor ses is assessed best by use of a monoexponential decay model with zero asym ptote and nonlinear regression. Intravenous administration of calcium gluco nate to isoflurane-anesthetized horses best preserves myocardial relaxant f unction.