Effects of xylazine and ketamine hydrochloride on the electroencephalogram and the electrocardiogram in the horse.

This research investigates the effects of two drugs, xylazine and ketamine hydrochloride, on the brain and heart function in horses, as measured by electroencephalograms (EEGs) and electrocardiograms (ECGs). The study found that both drugs caused noticeable changes in the EEG and ECG measurements, including changes in brainwave patterns and heartbeat regularity.

Study Design and Methods

• The study was conducted on six mature horses to whom the researchers administered xylazine and ketamine hydrochloride intravenously.
• Continuous EEGs were taken from each horse to measure brain activity. ECGs and respiratory rates were also measured to monitor heart function and breathing.

Findings

Neurological effects

• In their normal state, the mature horses displayed fast brain activity alongside slower and spindle-type brain activity.
• After being sedated with xylazine, the horses displayed a distinct pattern of brain activity, with slower frequencies becoming dominant and mixed frequencies present too. Some fast activity was still noticeable in most of the horses.
• Administration of ketamine three minutes after xylazine altered the brain activity further, increasing the high-voltage slow activity while mixed frequencies remained.

Cardiac & Respiratory effects

• About 23 seconds after the injection of xylazine, all horses experienced a second-degree heart block, a condition where the electrical signals between the chambers of the heart are partially blocked.
• In four out of the six horses, the heart block disappeared roughly 90 seconds after ketamine was injected. The remaining two horses maintained the heart block throughout the 15-18 minute recording period.
• Respiratory rates decreased after xylazine administration and became irregular following the ketamine injection, exhibiting a cyclic rate of 19 to 30 breaths per minute.
• Xylazine caused a 13% to 41% reduction in heart rate. Following the administration of Ketamine, heart rates either increased or remained unchanged.

From these findings, the researchers concluded that both xylazine and ketamine hydrochloride have prominent effects on EEG and ECG measurements in horses, indicating significant impacts on brain and heart function.