Objectives To evaluate the circulatory, respiratory and behavioral effects of isoflurane (ISO) anesthesia in llamas during mechanical ventilation and spontaneous breathing. Design Prospective randomised study. Animals Six adult, neutered male llamas (10±1years [mean ± SD], 179±32kg). Materials and methods Animals in which the minimum alveolar concentration (MAC) had been previously determined were anesthetized with ISO in oxygen. Inspired and end-tidal (ET) ISO were sampled continuously. Arterial blood pH, respiratory and circulatory variables, and clinical signs of anesthesia were recorded at three doses (1.0, 1.5 and 2.0 times the individual animal's MAC; mean MAC value 1.13%) of ISO during spontaneous and controlled ventilation. A series of Latin squares was used to determine order of dose. Controlled ventilation (CV) (target PaCO2 38±5mmHg [5.0±0.6kPa]) preceded spontaneous ventilation (SV) at each dose. Animals breathed spontaneously for approximately 10minutes prior to data collection. Body temperature was maintained at 37±0.6°C. Circulatory and respiratory data were analysed with a mixed model, least squares analysis of variance, for repeated measures taken at equally spaced intervals. p<0.05. Results Dose and mode of ventilation had significant influences on measured variables. For example, heart rate increased as dose increased; 67±14 beats minute−1 at 1.0 MAC-CV versus 77±6 beats minute−1 at 2 MAC-CV. Conversely, mean arterial pressure decreased with increasing dose; 82±13mmHg at MAC-CV versus 52±15mmHg at 2 MAC-CV. Arterial CO2 increased with increasing dose during SV; 45±5mmHg [6±0.6kPa] at MAC versus 53±4mmHg [7±0.5kPa] at 2 MAC. Reflex activity (e.g. palpebral reflex) and muscle tone (e.g. jaw tone) decreased while eyelid aperture increased with increasing anesthetic dose. Conclusions and Clinical Relevance The influence of ISO dose and mode of ventilation on circulatory and respiratory variables in llamas is qualitatively similar to that reported in other species. Changes in reflex activity and muscle tone may be used to guide appropriate anesthetic delivery in ISO-induced llamas.
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