Sevoflurane versus halothane anesthesia after acute cryogenic brain injury in rabbits: Relationship between arterial and intracranial pressure

The relationship between intracranial pressure and arterial blood pressure during sevoflurane or halothane anesthesia was evaluated in New Zealand white rabbits after cryogenic brain injury. Fourteen rabbits were randomized to be anesthetized with 1.5 MAC of sevoflurane or halothane in oxygen. All animals were paralyzed with pancuronium, and mechanically ventilated. A cryogenic lesion was created over the left hemisphere. Thirty minutes later, the intracranial pressure had risen to a mean value of 15 mm Hg. The inhaled concentration of anesthetic drugs was then increased to achieve a blood pressure of 35 mm Hg. Baseline measurements were made of monitored variables including mean arterial pressure, intracranial pressure, esophageal temperature, end-tidal CO₂, and arterial blood gases. Neosynephrine was then infused to raise the blood pressure from 35 to 100 mm Hg during 20 min. The P(a)CO₂ was maintained between 38 and 42 mm Hg. At baseline, there were no significant differences in mean arterial pressure, intracranial pressure, and blood gas values between the two groups. The intracranial pressure in the sevoflurane anesthesia group increased from 11 ± 1 to 44 ± 4 mm Hg as mean arterial pressure increased from 35 to 100 mm Hg. Intracranial pressure in the halothane anesthesia group increased from 9 ± 1 to 32 ± 3 mm Hg during the same range of blood pressure. Linear regressions of intracranial pressure on mean arterial pressure were performed for each of the two anesthetic groups. The slope of the regression line for the sevoflurane animals (0.491) was significantly greater than that for the halothane animals (0.323, p < 0.05). This study suggests that after cerebral injury, neosynephrine-induced increases in blood pressure in animals receiving sevoflurane are associated with higher levels of intracranial hypertension than in comparable halothane anesthetized animals.