The effect of experimentally induced hypothyroidism on the isoflurane minimum alveolar concentration in dogs.

Abstract

OBJECTIVE: To determine the effect of experimentally induced hypothyroidism on isoflurane (ISO) minimum alveolar concentration (MAC) in dogs. STUDY DESIGN: Prospective experimental study. ANIMALS: Eighteen adult female mongrel dogs, age 2-4 years and weighing 8.2-13.1 kg. METHODS: Hypothyroidism was induced in nine dogs by the intravenous administration of 1 mCi kg(-1) of (131) Iodine. The remaining nine dogs served as controls. Dogs were studied 9-12 months after the induction of hypothyroidism. Anesthesia was induced with ISO in oxygen via a mask. The trachea was intubated, and anesthesia was maintained using ISO in oxygen using a semi-closed rebreathing circle system. The dogs were mechanically ventilated to maintain an end-tidal carbon dioxide concentration between 35 and 45 mmHg. End-tidal ISO concentrations were measured with an infrared gas analyzer. The MAC was determined in duplicate using a tail clamp technique. The mean values for the groups were compared using a two sample t-test. RESULTS: The mean ± SD MAC of isoflurane in the hypothyroid and euthyroid dogs was 0.98 ± 0.31% and 1.11 ± 0.26%, respectively. The mean MAC of isoflurane in hypothyroid dogs was not significantly different from the mean MAC of isoflurane in the control dogs (p = 0.3553). CONCLUSION AND CLINICAL RELEVANCE: The MAC of ISO in dogs was not significantly affected by experimentally induced hypothyroidism. The dose of ISO in dogs with hypothyroidism does not need to be altered.