Midazolam and ketamine induction before halothane anaesthesia in ponies: cardiorespiratory, endocrine and metabolic changes.

This study explores the effects of premedication with midazolam and ketamine on vital signs and metabolic markers before anesthesia in ponies. The goal was to see how these drugs affected the animals and guided a humane induction to anesthesia.

Methodology

• The experiment involved six Welsh gelding ponies which were administered 0.03 mg/kg of acepromazine intravenously as a premedication.
• They were then induced to anesthesia with 0.2 mg/kg midazolam and 2 mg/kg ketamine. The anesthesia was maintained for 2 hours using 1.2% halothane concentration in oxygen.
• Several parameters including heart rate, electrocardiograph (ECG), arterial blood pressure, respiratory rate, blood gases, temperature, haematocrit, and a variety of hormones and metabolites were measured. These measurements were taken pre and post premedication, immediately after induction and at regular intervals during and after anaesthesia.

Findings

• The induction process was quick, calm, and resulted in good muscle relaxation. There were no changes observed in heart and respiratory rates.
• Nevertheless, a decrease in body temperature, presence of excess oxygen (hyperoxia), and development of respiratory acidosis were noted during the anaesthesia. Additionally, slight hypotension (low blood pressure) was observed, reducing to a minimum value of 76 +/- 10 mm Hg at 40 minutes into anaesthesia.
• Owing to the anaesthesia, no significant variations were observed in the levels of dynorphin, beta-endorphin, ACTH, catecholamines and glucose.
• In contrast, notable changes were observed in plasma cortisol, AVP and lactate concentrations, all of which increased during anaesthesia.
• Recovery was quick and smooth, with ponies standing up within approximately 46 +/- 6 minutes.
• When compared with thiopentone or detomidine/ketamine, the combination of midazolam/ketamine caused slightly more respiratory depression but less hypotension.
• In addition, midazolam was found to have reduced the hormonal stress response often seen during halothane anaesthesia, indicating a good potential for use in horses.

The study concludes by suggesting that midazolam/ketamine, in combination with acepromazine, represents an effective and humane induction method for anaesthesia in ponies, factoring in its relatively minimal adverse impact on cardiorespiratory performance and hormonal stress responses. It also encourages further studies in horses.