The effect of xylazine on intracranial pressure in anesthetized and standing horses

Objective To determine the effect of xylazine on intracranial pressure (ICP) in standing compared to isoflurane‐anesthetized horses. Design Prospective, crossover study design. Setting University Teaching Hospital. Animals Six adult horses donated to the University. Horses were determined to be healthy via physical examination, complete blood count, and neurological evaluation. Interventions Horses were anesthetized, maintained on isoflurane in oxygen in left lateral recumbency, and ventilated to normocapnia. Horses were instrumented for intraparenchymal measurement of ICP, invasive blood pressure, pulse oximetry, and end tidal gas analyzer. Xylazine 1 mg/kg was administered IV and ICP, systolic arterial pressure, mean arterial pressure (MAP), diastolic arterial pressure, and heart rate were recorded and cerebral perfusion pressure (CPP) was calculated for the following 15 minutes. Twenty‐four to 36 hours following anesthetic recovery, xylazine 1 mg/kg was administered IV and ICP, heart rate, and Doppler blood pressure (BPdop) on the tail were monitored for 15 minutes. Measurements and Main Results There was a decrease in ICP following administration of xylazine in anesthetized horses (P