Effects of the high-flow modified to-and-fro anesthestic system on blood gas and respiratory rate in halothane anesthetized horses

Abstract

Ten healthy adult horses male or female, mean body weight of 424±44.1kg, were anesthetized with romifidine, tiletamine/zolazepam and halothane for 60 minutes using a modified to-and-fro rebreathing anesthetic system, added of 1 liter mechanical dead space. The gas flow rate was 10 liters oxygen/minute during all inhalation anesthetic time. Variables analysed were arterial blood pH, carbon dioxide partial pressure (PaCO2) and oxygen partial pressure (PaO2), and respiratory rate (RR). The horses were allowed to breath spontaneously, and were positioned in right lateral recumbency the arterial O2 values were significantly higher during halothane anesthesia when compared to the baseline values, and significantly lower after induction with tiletamine/zolazepam although arterial hypoxemia were not present. The arterial PaCO2 values were significantly higher from baseline values during halothane anesthesia occurring arterial hypercapnia and mild respiratory acidosis. The arterial pH changes paralleled the changes in PaCO2. Respiratory rate values were significantly lower during halothane anesthesia when compared to baseline values. All values remained within accepted range for lateral recumbent spontaneously breathing anesthetized horses.