Inhaled carbon monoxide concentration during halothane or isoflurane anesthesia in horses.

This study focuses on measuring the concentration of carbon monoxide produced during equine anesthesia using two different anesthetics, halothane and isoflurane. In essence, it found that significantly higher carbon monoxide concentrations were recorded with the use of halothane compared to isoflurane, but the levels observed during the administration of either anesthetic for 90 minutes were not of clinical significance.

Research Methodology

• The research involved a clinical investigation of fifty client-owned horses.
• These horses were randomly assigned to be anesthetized either with halothane (26 horses) or isoflurane (24 horses), delivered via a circle rebreathing system using two large animal anesthetic machines.
• The machines used for anesthesia were assigned to a single anesthetic agent and were disassembled and soda lime changed prior to switching anesthetic agents.
• The anesthetic concentration and carbon monoxide concentration were measured in gas samples obtained from the inspiratory limb of the anesthetic circuit at 15-minute intervals for 90 minutes.
• The status of the soda lime (either new or used) and the mode of ventilation (either spontaneous or mechanical) were also recorded.
• The data obtained were analyzed using a five-factor ANCOVA with repeated measures.

Research Findings

• The inspired carbon monoxide concentration for both halothane and isoflurane increased from baseline, with the former showing a significantly greater increase.
• However, the baseline carbon monoxide was significantly greater in the isoflurane group than the halothane group.
• Oxygen flow rates were fairly consistent at both baseline and the 90-minute mark for both anesthetics, with no significant differences found between the two groups at any time point.
• Neither mechanical ventilation nor the status of the soda lime (new versus used) seemed to have any effect on the carbon monoxide concentration.

Conclusions

• While halothane was associated with significantly higher concentrations of carbon monoxide compared to isoflurane, the observed levels of carbon monoxide for either anesthetic over a period of 90 minutes were not considered clinically significant.
• The research shows implications for the choice of anesthetic in equine procedures, but further studies may be necessary to confirm these findings and explore other potential differences between the anesthetics.