Effect of sedation with detomidine and butorphanol on pulmonary gas exchange in the horse.

This research investigates how sedation using the drugs detomidine and butorphanol affects gas exchange in horse lungs. The study noted changes in ventilation, perfusion, and other characteristics, concluding that both drugs influence pulmonary and cardiovascular elements, potentially causing impairment of pulmonary gas exchange.

Research Method

• The researchers conducted their study on seven Standardbred trotter horses between the ages of 3-7 years and 380-520 kg in weight.
• They performed three iterative measurements on each horse: prior to sedation, after sedation using detomidine, and after additional administration of butorphanol.
• The team utilized the Multiple Inert Gas Elimination Technique (MIGET) to evaluate the distribution of ventilation-perfusion ratios (VA/Q) in the horses. This technique is widely recognized as a reliable method in studying pulmonary gas exchange.
• They also investigated the effects of the drugs on pulmonary function as well as hemodynamics – the physical aspects of blood circulation and related pressures.

Research Findings

• Following administration of detomidine, arterial oxygen tension (PaO2) in the horses decreased and arterial carbon dioxide tension (PaCO2) increased, compared to the readings from the unsedated state.
• There was a clear mismatch between ventilation (airflow) and perfusion (blood flow) in the horses’ lungs. However, they did not detect an increase in intrapulmonary shunt – a condition where blood bypasses oxygenation in the lungs.
• Detomidine sedation also resulted in a decrease in heart rate and cardiac output, as well as an increase in both systemic and pulmonary blood pressure and vascular resistance – a measure of the resistance that has to be overcome to push the blood through the circulatory system.
• Addition of butorphanol led to a notable decrease in ventilation and an increase in PaCO2. The difference in oxygen content between alveolar air and arterial blood (P(A-a)O2) remained impaired with butorphanol, even though the VA/Q distribution improved – indicating well-matched decreased ventilation and persistently low blood flow.
• Both detomidine and butorphanol sedation did not significantly increase intrapulmonary shunt.

Conclusion

• The study’s results suggest that detomidine and butorphanol sedation in horses impact both pulmonary and cardiovascular factors. These factors potentially contribute to the impaired pulmonary gas exchange – the process whereby oxygen is absorbed from the air into the bloodstream, and carbon dioxide is released from the bloodstream into the air.