Cardiovascular and respiratory effects of inspired oxygen fraction in halothane-anesthetized horses.

The research investigates the impact of different levels of inspired oxygen on the cardiovascular and respiratory effects in horses that have been anesthetized with halothane. It suggests that higher concentrations of oxygen in the gas inhaled by horses under anesthesia can lead to greater hypoventilation and imbalance in ventilation and blood flow in the lungs.

Objective of the Research

• The study primarily aims at understanding the cardiovascular and respiratory impact of varying fractions of inspired oxygen (0.30 and more than 0.85) in horses under halothane anesthesia. Knowledge about the effects of inspired oxygen fraction is limited. Therefore, this research attempts to fill that gap.

Methodology and Findings

• In this study, five horses were anesthetized with halothane and placed on their sides. Their cardiovascular and respiratory functions were monitored over a period of four hours under constant end-tidal halothane concentration.
• The factors monitored included mean systemic arterial blood pressure, cardiac output, central venous pressure, pulmonary arterial pressure, arterial pH, and arterial base excess. The readings were similar in horses irrespective of the level of oxygen in inspired air.
• However, the parameters such as end-tidal partial pressure of CO2, arterial partial pressure of CO2 and O2, and alveolar-to-arterial O2 tension difference were higher in the horses exposed to the higher oxygen concentration. This suggests that high-oxygen fraction can lead to greater hypoventilation (reduced ventilation) and ventilation/perfusion imbalance (mismatched air and blood flow in the lungs).

Post Anesthesia Findings

• Upon disconnecting the horses from the anesthesia circuit and allowing them to breathe room air, no difference was found in the arterial partial pressure of O2 among the two groups of horses. This means, the level of oxygen in the blood returned to similar levels in both groups once the horses started breathing normal air.
• Importantly, the horses recovered from the anesthesia without any complications, indicating that the effects observed during anesthesia did not have prolonged harmful effects.