Halothane and enflurane anesthesia and respiratory mechanics in prone dogs

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Abstract
Functional residual capacity (FRC), total lung capacity (TLC) and static deflation pressure-volume curves of the total respiratory system, lungs and chest wall were measured in 8 trained prone dogs with permanent tracheostomies 1st during the awake state and then during halothane (1.3-2.8 minimal alveolar concentrations (MAC)) or enflurane (1.4-1.9 MAC) anesthesia. The mean of the difference between TLC and TLC (awake) was -0.05 l for halothane and -0.07 l for enflurane anesthesia; the reduction in TLC was significant (P < 0.05) only for enflurane. Mean FRC did not change with either halothane or enflurane anesthesia. Halothane anesthesia had no significant effect on the elastic recoil pressures of the total respiratory system, lungs, and chest wall. Compliance of the total respiratory system increased significantly (P < 0.05) with halothane. Enflurane significantly (P < 0.05) increased the elastic recoil pressures of the total respiratory system and of the chest wall. Compliance of the lung decreased significantly with enflurane anesthesia (P < 0.05). Some of the dogs had paradoxic motion of the thoracic wall. The wall moved inward during inspiration, recoiled outward at end inspiration and had a normal motion during expiration. Tidal volumes were consistently larger and respiratory frequencies consistently less during 1.6 MAC of enflurane than during 1.6 MAC of halothane anesthesia. No consistent dose-response effect on any of the measured variables was observed with either anesthetic.