The effects of halothane and isoflurane on cardiovascular function in dorsally recumbent horses undergoing surgery.

This study investigates the impact of halothane and isoflurane on cardiovascular function in horses positioned dorsally (on their back) for surgery. The research concluded that isoflurane maintains superior heart function compared to halothane in these horses, although cardiac function was found to decrease progressively over time with both anesthetics.

Research Methodology

• The study was a prospective randomized clinical trial, which means the experiment was planned before it started and the horses were randomly assigned to one of the treatment groups.
• 25 adult horses with an average weight of 487kg were used in the experiment. The horses were chosen for elective surgery (surgery that is scheduled in advance).
• The horses were divided into four treatment groups – anaesthesia with isoflurane or halothane, each either spontaneous or controlled ventilation. Spontaneous breathing means the horses breathed on their own, whereas controlled ventilation implies a machine helped with the breathing.
• The cardiac function was monitored using transoesophageal and transcutaneous Doppler echocardiography, while arterial blood flow and resistance were measured through the femoral artery.

Results and Conclusion

• Four of the horses that were supposed to breathe spontaneously under isoflurane required controlled ventilation, meaning they were moved to a different group. This left three groups for analysis. Two horses were also removed from the halothane groups because dobutamine was used to keep their blood pressure stable.
• In both spontaneous and controlled ventilation groups, the cardiac index (which is a measure of heart function) was significantly higher, and the pre-ejection period (time before the heart pushes the blood out) was significantly lower with isoflurane compared to halothane. This suggests that isoflurane is more efficient at maintaining heart function than halothane, regardless of the ventilation mode.
• There was also a correlation between the cardiac index and PaCO2 such that the cardiac index increased by 0.45 L minute(-1)m(-2) for every kPa increase in PaCO2. This suggests that increasing carbon dioxide levels in the blood may improve heart function.
• Only under controlled ventilation was femoral arterial blood flow significantly higher with isoflurane compared to halothane.
• Regardless of the anesthetic used, the cardiac index decreased over time. This means that the heart function of the horses worsened progressively during the anaesthesia. Additionally, this decrease was observed regardless of the ventilation mode (spontaneous or controlled).
• In conclusion, even though isoflurane supported better cardiovascular function in horses during surgery, there was an observed progressive decline in cardiac function with both anaesthetics. Furthermore, this study suggests that there might be a higher need for controlled ventilation (IPPV) with the use of isoflurane.