Hemodynamic effects of ionized calcium in horses anesthetized with halothane or isoflurane.

This research investigates how two types of anesthesia, halothane and isoflurane, affect the cardiovascular function of horses, focusing on their effect on calcium levels in the blood. The study finds that administering a solution of calcium gluconate can mitigate some of the negative impacts these anesthetics have on heart function.

Research Methodology

• The study was conducted on six clinically normal adult Thoroughbred horses. The horses were fitted with catheters to measure various aspects of cardiovascular function like arterial blood pressures, pulmonary arterial blood pressures, right ventricular pressure, and cardiac output. Blood samples were also collected using these catheters.
• Anesthesia was induced using xylazine hydrochloride and ketamine hydrochloride, then maintained with either halothane or isoflurane.
• After 75 minutes of anesthetic induction, an intravenous (i.v.) infusion of calcium gluconate was started. The dosage of the calcium infusion was progressively increased over the next 45 minutes.
• The researchers collected data at several points, including before, during, and after the administration of the calcium gluconate.

Findings

• Both halothane and isoflurane reduced myocardial contractility (the ability of the heart muscle to contract), the cardiac index (a measure of cardiac function), and the mean arterial pressure. However, halothane had a stronger negative effect than isoflurane did.
• Calcium gluconate was shown to counteract the decrease in cardiac index, stroke index (a measure of how much blood the left ventricle ejects per beat), and maximal rate of increase in right ventricular pressure when the horses were anesthetized with isoflurane.
• In the case of halothane-anesthetized horses, higher dosages of calcium gluconate were needed to see similar results. Even then, it did not change the cardiac index.

Conclusion

• The results suggest that the intravenous administration of calcium gluconate can support heart function in horses that have been anesthetized with isoflurane. However, its effectiveness is reduced against the effects of halothane anesthesia.