Effects of medetomidine administration on intracranial pressure and cardiovascular variables of isoflurane-anesthetized dogs

Intracranial pressure and cardiovascular variables after IV administration of medetomidine (0.03 mg/kg of body weight) were evaluated in 6 healthy, mixed-breed dogs anesthetized with 1.3% end-tidal isoflurane concentration and mechanically ventilated to normocapnia (Pa(CO₂)), 35 to 45 mm of Hg). Baseline values were determined for intracranial pressure, heart rate, arterial blood pressure, cardiac output, mean pulmonary artery pressure, pulmonary capillary wedge pressure, central venous pressure, end-tidal CO₂ tension and isoflurane concentration, arterial pH and CO₂ and O₂ tensions, and core body temperature. Cerebral perfusion pressure, cardiac index, systemic and pulmonary vascular resistances, plasma HCO₃^- concentration, and base excess were calculated. Intracranial pressure was measured, using a calibrated, fiberoptic transducer placed within the brain parenchyma and secured to the calvarium by means of a subarachnoid bolt. Cardiac output was determined by thermodilution. End-tidal CO₂ tension and isoflurane concentration were determined, using an infrared gas analyzer. Administration of medetomidine did not change intracranial pressure, but was associated with significant (P < 0.05) decreases in values for heart rate, cardiac index, end-tidal CO₂, and HCO₃^- and with significant increases in systolic, mean, and diastolic pressure; pulmonary artery pressure; systemic vascular resistance; central venous pressure; and pulmonary capillary wedge pressure.