Effects on the intramuscular blood flow and cardiopulmonary function of anaesthetised ponies of changing from halothane to isoflurane maintenance and vice versa.

The research investigated how swapping between anaesthesia maintenance with two different gases, isoflurane and halothane, impacts the blood flow in the muscles and cardiopulmonary function of ponies. Results indicated that changing to halothane from isoflurane led to a decline in blood flow and cardiopulmonary function, but switching to isoflurane from halothane didn’t mark a statistically significant improvement.

Experiment procedure and parameters

• The experiment was conducted on six ponies, wherein anaesthesia was facilitated first with xylazine, ketamine and diazepam. This was then retained using halothane for an hour and substituted with isoflurane for another hour (halo/iso). The sequence of administering these volatile agents was alternated in another instance (iso/halo).
• Two major parameters were taken into account for the study – Mean Arterial Pressure (MAP) and Cardiac Output (CO). The values for these parameters did not show a significant difference when measured after an hour of anaesthesia, irrespective of the order in which the gases were administered.
• The change in anaesthetic gases led to an increase in MAP for both groups.

Observations on cardiac output

• In the halo/iso group, the CO remained stable even after shifting to isoflurane, recording at 8.64 [1.4] litres/minute.
• However, in the iso/halo group, a significant decrease in CO was noted upon introducing halothane, with the rate dropping to 6.16 [1.3] litres/minute after the second hour of anaesthesia.

Intramuscular blood flow

• Upon replacing isoflurane with halothane, a substantial decline in intramuscular blood flow was noticed in both upper and lower triceps brachii by 23 to 35 per cent.
• However, when isoflurane was used in place of halothane, there were no significant alterations in the blood flow.

Conclusion

• Based on the observations, it was concluded that switching to halothane from isoflurane resulted in a decline in both the intramuscular blood flow and the CO.
• However, the changeover from halothane to isoflurane did not lead to further degradation of cardiopulmonary function, but neither did it result in any statistically significant improvement.