The clinical and cardiorespiratory effects of
premedication with
acepromazine,
butorphanol or
diazepam in addition to
romifidine before induction of anaesthesia with
ketamine were studied in 6 horses on 4 random occasions. Administration of
romifidine alone or in combination with
butorphanol resulted in an increase in arterial blood pressure, accompanied by a significant decrease in heart rate with second-degree atrio-ventricular
heart block. Induction of anaesthesia with
ketamine returned the heart rate to baseline value, but the arterial blood pressure was significantly increased compared to baseline. Including
acepromazine in the
premedication prevented the
hypertension and
bradycardia induced by
romifidine. The respiratory rate was slightly decreased after
premedication in all groups, but returned to the baseline value after induction of anaesthesia. Mild
hypercapnia and significant hypoxaemia were observed during sedation and anaesthesia, reflecting an impairment of pulmonary function.
Premedication with
acepromazine before sedation with
romifidine resulted in a fast induction and good anaesthesia. Inclusion of
butorphanol in the
premedication resulted in individual variation in the quality of induction and anaesthesia. Addition of
diazepam to the sedation with
romifidine resulted in good muscle relaxation with a smooth induction and maintenance of anaesthesia and an increased time before the horses responded to noxious stimuli, compared with
romifidine and
ketamine anaesthesia. All horses reached a standing position at the first attempt, but horses premedicated with
diazepam in combination with
romifidine showed mild
ataxia after recovery.