Cerebral edema formation in dogs following hypotension induced with isoflurane and labetalol.

The effects of induced hypotension with isoflurane and labetalol on cerebral edema formation were compared following a cryogenic brain injury in dogs. Thirteen dogs received a maintenance anesthetic of 70% N2O, 0.5% isoflurane in O2 and a fentanyl infusion (3 micrograms.kg-1 x hr-1). All dogs were normoventilated (PaCO2 of 35-40 mmHg) and monitored for temperature, arterial blood pressure, central venous pressure (maintained between 7-10 mmHg), end-tidal CO2, end-tidal anesthetic level, and urine output. Following a right parietal craniectomy, a standard sized cryogenic brain lesion was made. The animals were randomly allocated in two groups. Group I (n = 6) received maintenance anesthesia, but within a 30 minute period, mean arterial pressure (MAP) was reduced to 60 mmHg with isoflurane varying in inspired concentration from 2 to 4%. Thereafter, the MAP was maintained at this level for 60 minutes. The inspired concentration of isoflurane was decreased, then discontinued to allow the MAP to return to baseline during the next 30 minutes. Group II (n = 7) received maintenance anesthesia, and MAP was reduced to 60 mmHg during a 30 minute period with intravenous labetalol (20 mg.kg-1). This MAP was maintained for one hour with a continuous labetalol infusion. The infusion was discontinued and the MAP returned to baseline during the next 30 minutes. The wounds were surgically closed. Anesthesia was discontinued, paralysis was reversed, and the animals were extubated and transported to a recovery room. Forty-eight hours postoperatively, all animals were reanesthetized, injected with Evans' blue dye and sacrificed. The brain was removed, fixed in formalin, and sent "blindly" coded for neuropathologic evaluation.(ABSTRACT TRUNCATED AT 250 WORDS)