Effect of hypercapnia or xylazine on lateral ventricle and lumbosacral cerebrospinal fluid pressures in pentobarbital-anesthetized horses.

The study investigates the effects of increased carbon dioxide levels (hypercapnia) and the drug xylazine on the pressures in different parts of the horses’ brain and spinal fluid under anesthesia. The researchers determined that elevating carbon dioxide levels increased pressure significantly, but xylazine did not cause any notable changes.

Study Setup and Procedures

• The research was carried out on ten horses that were anesthetized with pentobarbital. Various bodily parameters like facial artery pressure, central venous pressure, heart rate and lateral ventricle cerebrospinal fluid (CSF) pressure were recorded.
• The arterial partial pressure of carbon dioxide (PaCO2) in the horses was manipulated to reach levels of 40, 60, and 80 mm Hg. This was done by adjusting the concentration of inspired carbon dioxide. Measurements were taken every five minutes for fifteen minutes at each PaCO2 level.
• At the end of each fifteen-minute period, an arterial blood gas analysis was performed.

Results and Observations

• The CSF pressure in the lateral ventricle (LV-CSFP) significantly increased (p < .05) at a PaCO2 of 80 mm Hg, but the cardiovascular variables remained unaffected by the changes in PaCO2.
• After reducing the PaCO2 back to 40 mm Hg, eight of the horses were administered an intravenous injection of xylazine. The recorded data over the next 60 minutes showed no significant changes as a result of the drug. Similarly, no changes were observed in two horses that did not receive xylazine, serving as the control group.
• In follow-up procedures, a lumbosacral subarachnoid catheter was placed to simultaneously measure LV-CSFP and lumbosacral CSF pressure (LS-CSFP) at PaCO2 levels of 40, 60, and 80 mm Hg. These observations found a Pearson Correlation Coefficient of 0.94 (p < .0001) between LV-CSFP and LS-CSFP, indicating a strong correlation.

Conclusions

• The study showed that variations in the CSF pressure can be detected both in the lateral ventricle and the lumbosacral space of the horses’ nervous system.
• Increasing the level of PaCO2 to 80 mm Hg significantly boosted the LV-CSFP, while the administration of xylazine did not change it in anesthetized horses with a normal level of carbon dioxide (normocapnic).
• Under the conditions of this experiment, the pressures of the CSF in the lateral ventricle and the lumbosacral space were tightly correlated.