Effects of acepromazine on pulmonary gas exchange and circulation during sedation and dissociative anaesthesia in horses.

This research investigates the effects of an additional drug, acepromazine, on lung gas exchange and heart circulation in horses during sedation and dissociative anesthesia, compared to existing standard treatment. The findings suggest that acepromazine could improve blood oxygenation and heart circulation during both sedation and anesthesia.

Study Design and Methodology

• The study involved six healthy Standardbred trotters aged 3-12 years with weight ranging from 423 to 520 Kg. The research design was randomized and cross-over in nature, allowing each horse to be tested under both conditions (with and without acepromazine).
• The horses were anesthetized twice, once only with romifidine and butorphanol (RB) and the second time with RB plus acepromazine (ARB). This second trial occurred at least one week after the first to prevent any possible drug interaction or residual effects.
• All horses were laterally recumbent and allowed to breathe ‘room air’ that is normal atmospheric air spontaneously following sedation and during anesthesia. Various respiratory and haemodynamic variables were closely monitored and recorded.

Key Findings

• The study found that during sedation with RB alone, there was a significant decrease in arterial oxygen tension (PaO₂) – a measure of the amount of oxygen in the blood. This decrease was linked to increased mismatch in the ventilation-perfusion ratio which could potentially hamper breathing efficiency.
• In contrast, the arterial oxygen tension remained unchanged when sedation involved RB with acepromazine (ARBZ). Moreover, acepromazine reduced disturbances and falls in PaO₂ during anaesthesia which could indicate improved oxygenation.
• Regarding heart rate (HR) and cardiac output (Qt), the study reported that these were lower during sedation with RB alone compared to when acepromazine was also administered. Total systemic vascular resistance, mean systemic, and mean pulmonary arterial pressures were higher during anesthesia with RBZ compared to ARBZ, suggesting that acepromazine can have positive effects on cardiovascular responses.

Conclusions

• The researchers concluded that adding acepromazine to RB significantly improved haemodynamic variables and arterial oxygenation during sedation and anesthesia, bringing these variables closer to the baseline or norm. This potentially indicates better cardiovascular stability and improved lung function during both procedures.
• Although the anesthesia induced an increased pulmonary shunt and ventilation-perfusion mismatch, the addition of acepromazine reduced the severity of these side effects. Thus, the drug may provide certain advantages for sedation and anesthesia in healthy, normovolaemic horses.