Effects of ketamine and magnesium on the minimum alveolar concentration of isoflurane in goats

P Queiroz-Castro
Christine Egger
M A. Redua
Barton W. Rohrbach Dr., University of Tennessee - Knoxville
Sherry Cox
Thomas Doherty

Abstract

Objective - To evaluate the effects of ketamine, magnesium sulfate, and their combination on the minimum alveolar concentration (MAC) of isoflurane (ISO-MAC) in goats. Animals - 8 adult goats. Procedures - Anesthesia was induced with isoflurane delivered via face mask. Goats were intubated and ventilated to maintain normocapnia. After an appropriate equilibration period, baseline MAC (MACB) was determined and the following 4 treatments were administered IV: saline (0.9% NaCl) solution (loading dose [LD], 30 mL/20 min; constant rate infusion [CRI], 60 mL/h), magnesium sulfate (LD, 50 mg/kg; CRI, 10 mg/kg/h), ketamine (LD, 1 mg/kg; CRI, 25 g/kg/min), and magnesium sulfate (LD, 50 mg/kg; CRI, 10 mg/kg/h) combined with ketamine (LD, 1 mg/kg; CRI, 25 g/kg/min); then MAC was redetermined. Results - Ketamine significantly decreased ISOMAC by 28.73.7%, and ketamine combined with magnesium sulfate significantly decreased ISOMAC by 21.14.1%. Saline solution or magnesium sulfate alone did not significantly change ISOMAC. Conclusions and Clinical Relevance - Ketamine and ketamine combined with magnesium sulfate, at doses used in the study, decreased the end-tidal isoflurane concentration needed to maintain anesthesia, verifying the clinical impression that ketamine decreases the end-tidal isoflurane concentration needed to maintain surgical anesthesia. Magnesium, at doses used in the study, did not decrease ISOMAC or augment ketamine's effects on ISOMAC.