Effects of low dose ketamine on haemodynamic and electroencephalographic variables during surgery in isoflurane anaesthetised horses

The dissociative anaesthetic ketamine is reported to provide potent analgesia after administration of subanaesthetic doses in human beings. To evaluate the analgesic effects of ketamine as an adjunct to inhalation anaesthesia in horses, haemodynamic and electroencephalographic changes were recorded for 10 min after injection of ketamine (0.5 mg/kg iv; n=7) or equal volumes of 0.9% NaCl solution (n=5) in surgically stimulated horses anaesthetised at approximately 1.3% end-tidal concentration of isoflurane. Neither the haemodynamic variables (mean arterial blood pressure and heart rate) nor the quantitated EEG variables (theta/delta ratio, alpha/delta ratio, beta/delta ratio, median power frequency) and 80% spectral edge frequency were affected significantly by the ketamine dose used. Comparing data obtained from both groups of horses, our results suggest that iv administration of 0.5 mg/kg bwt of ketamine was ineffective in suppressing haemodynamic and electroencephalographic responses to surgical stimulation.