Abstract
Six healthy adult horses two male and four female, mean body weight of 424 + 44.1kg, were anesthetized with xylazine, ketamine/diazepam and isoflurane for 60 minutes using a convertible to-and-fro and circle system. Variables analyzed were arterial blood pH, carbon dioxide partial pressure (PaCO 2 ) and oxygen partial pressure (PaO 2 ), respiratory rate(RR), and blood pressure. The horses were allowed to breath spontaneously, and were positioned in right lateral recumbency. The arterial O 2 values were significantly higher during isoflurane anesthesia when compared to the baseline values, and significantly lower after induction with ketamine/diazepam although arterial hypoxemia were not present. The arterial PCO 2 values were significantly higher from baseline values during isoflurane anesthesia occurring arterial hypercapnia and mild respiratory acidosis. The arterial pH changes paralleled the changes in PaCO 2 . Respiratory rate values were significantly lower during isoflurane anesthesia when compared to baseline values. All values remained within accepted range for lateral recumbent spontaneously breathing anesthetized horses. There were no significant differences between the circle and the to-and-fro system, demonstrating that either system is safe to maintain isoflurane anesthesia in adult horses.
Highlights
The anesthetic machine and breathing circuit for inhalation anesthesia delivers oxygen and anesthetic gases to the horse and remove carbon dioxide from the exhaled gases [1]
The disadvantages of the to-and-fro breathing system are an excessive heat generated by the absorbent, studies have shown no increase in the patients body temperature after 90 minutes of anesthesia, alkaline dust may be inhaled, relatively awkward to use, the soda lime nearest to the patient becomes expended first and increases mechanical dead space, and positioning the carbon dioxide absorption canister close to the patient head may be cumbersome [1,8]
Anesthetic apparatus design has permitted an easy connection of the patient to the to-and-fro system
Summary
The anesthetic machine and breathing circuit for inhalation anesthesia delivers oxygen and anesthetic gases to the horse and remove carbon dioxide from the exhaled gases [1]. Halothane and isoflurane are the most commonly used inhalant anesthetic agents in horses. These agents are usually delivered in a semiclosed circle system or a valveless to-and-fro system using an out-of-the circuit vaporizer [1,10]. In the horse, which is apparently predisposed to alveolar hypoventilation during inhalation anesthesia, it is suggested that adequate anesthetic apparatus design should be directed towards minimizing resistance and dead space and providing maximal and efficient carbon dioxide elimination. Compared to a circle system, the to-and-fro anesthetic circuit is relatively simple and of rugged construction, disassembled for cleaning, transportable, and it is possible a relatively rapid change in anesthetic concentration for a given fresh gas flow [1]
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