Effect of high PaCO2 and time on cerebrospinal fluid and intraocular pressure in halothane-anesthetized horses.

The research focuses on exploring the influence of varied arterial carbon dioxide tension (PaCO2) levels on cerebrospinal fluid pressure (CSFP) and intraocular pressure (IOP) in six halothane-anesthetized horses. The findings indicate that high PaCO2 significantly increases CSFP and systemic arterial pressure, while other vital statuses like heart rate, central venous pressure, and IOP remain essentially unaffected.

Research Method

• The research was conducted on six halothane-anesthetized male horses oriented in left lateral recumbency.
• Anesthesia was induced solely with halothane in oxygen, and steady-state anesthetic conditions were established 60 minutes into the experiment.
• Atracurium was used for neuromuscular blockade, with the horses being mechanically ventilated. Respiratory rate and peak inspiratory airway pressure were maintained within a defined range.
• CSFP and IOP were assessed at three levels of PaCO2—approximately 40, 60, and 80 mm of Hg.
• The research followed a switchback design, with the initial PaCO2 being repeated in the middle and at the end of the experiment, 30 minutes after establishing steady-state anesthesia. This pattern meant that measurements from the middle three periods would form a Latin square design replicated twice.
• Each experimental period was approximately 45 minutes long.

Research Findings

• Data from periods 2, 3, and 4 showed a significant increase in CSFP and mean systemic arterial pressure as PaCO2 rose. However, the changes in mean central venous pressure, heart rate, and IOP were not significant.
• Comparing measurements taken during periods 1, 3, and 5 helped evaluate time-related responses to anesthesia. These showed a significant rise in CSFP, a significant decrease in central venous pressure, and a small (non-significant) increase in systemic arterial pressure.

Research Significance

• The research provides insights into how different PaCO2 levels can potentially affect CSFP and IOP in halothane-anesthetized horses.
• The findings can contribute to the development of better anesthetic management strategies for equine surgery to maintain optimal CSFP and IOP during anesthesia. For example, monitoring and adjusting arterial CO2 tension while keeping changes to other physiological variables minimal could lead to less postoperative complications related to CSFP and IOP.