Effect of ephedrine and phenylephrine on cardiopulmonary parameters in horses undergoing elective surgery.

This study examined the effects of ephedrine and phenylephrine on heart and lung function in horses under anesthesia for surgery, coming to the conclusion that ephedrine is favorable over phenylephrine to manage hypotension induced by anesthesia due to an improved delivery of oxygen to tissues.

Methodology

• The study was done as a proactive randomized clinical study involving fourteen horses under isoflurane anesthesia for a specific surgical procedure (digital palmar neurectomy).
• When the mean arterial pressure (MAP) of the animals fell below 60mmHg – signaling hypotension – either ephedrine (0.02 mg kg(-1) minute(-1); n = 7) or phenylephrine (0.002 mg kg(-1) minute(-1); n = 7) was administered until the target MAP was achieved, marking a 50% increase over the initial MAP before infusion.
• Cardiopulmonary monitoring, including measurement of blood pressure, collection of blood for pH and gas analysis, and monitoring of cardiac output, was conducted using an arterial and a Swan-Ganz catheter.
• The monitored parameters were recorded at set intervals (5, 30, 60, and 90 minutes) after achieving the target MAP.

Results

• In both groups, the MAP and systemic vascular resistance (SVR) rose significantly at all measured intervals post-infusion which indicates an increase in blood pressure and resistance in systemic circulation.
• The group administered with ephedrine showed an increased cardiac index (CI) and systemic oxygen delivery index when compared to the group administered with phenylephrine, which suggests ephedrine improved the oxygen delivery per minute in these horses.
• The group administered with phenylephrine exhibited higher SVR, but there was no decrease in oxygen extraction compared to the ephedrine group.
• There were no significant differences in the ventilation parameters between both groups after the infusion.

Conclusions

• The researchers concluded that ephedrine and phenylephrine increased MAP, but they did so differently – ephedrine increased both CI and SVR, while phenylephrine only increased SVR, resulting in decreased cardiac output.
• Ephedrine resulted in better tissue oxygenation than phenylephrine, which might be the reason why it’s preferred to treat anesthesia-induced hypotension in horses.
• The ability of ephedrine to increase blood flow and pressure makes it preferable to phenylephrine in treating isoflurane-induced hypotension in horses during surgical procedures.