Actions of isoflurane and halothane in pregnant mares.

This research study examined the effects of two different types of anesthetic, halothane and isoflurane, in pregnant mares that were undergoing surgery. The findings showed similar cardiovascular measurements with the two anesthetics, a decreased respiratory rate with isoflurane, and comparable levels of arterial CO2 pressures with both. The study found a quicker recovery time from isoflurane and minor superficial injuries associated with recovery from both anesthetics.

Study Methods and Participants

• The study involved 18 healthy, pregnant mares that were all scheduled for laparotomy and uterine manipulation procedures.
• These mares were divided randomly into two equal groups, and each group was administered a different type of anesthetic.
• Before the administration of general anesthesia, IV administration of xylazine hydrochloride and thiamylal sodium was performed on the mares.
• One group received halothane (HALO), while the other group received isoflurane (ISO), both in oxygen.

Key Findings

• Cardiovascular measurements for the mares under both types of anesthesia were similar; the mean arterial blood pressure was 79mm of Hg under halothane and 82mm of Hg under isoflurane.
• The use of isoflurane led to a more significant decrease in respiratory rate, with a mean frequency of 4 breaths per minute compared to 9 breaths per minute with halothane.
• Both anesthetics led to an increased partial pressure of arterial CO2. However, there was a significant variation in the partial pressure of arterial O2 among the mares.
• Anesthesia led to a decrease in arterial O2 pressure over time, regardless of the anesthetic used.
• Mares that were given isoflurane recovered significantly faster from anesthesia than the group given halothane, a difference that was statistically significant (P < 0.05).
• Minor superficial injuries were associated with recovery from both types of anesthetics; these were observed in 5 mares under isoflurane and 1 mare under halothane.
• Neither anesthetic was associated with physical signs of postanesthetic myopathy (muscle disease) or vital-organ dysfunction.

Conclusion

This research contributes to the understanding of the effects of halothane and isoflurane on pregnant mares undergoing surgery. It was discovered that while both anesthetics display similar cardiovascular effects, isoflurane leads to quicker recovery times despite causing a more significant decrease in respiratory rate. There was no evidence that either anesthetic causes postanesthetic myopathy or vital-organ dysfunction. However, the use of these anesthetics was associated with minor superficial injuries during recovery. More research could further dissect these findings and their implications.