Effect of ketamine on cerebral cortical blood flow and metabolism in rabbits.

Abstract

The effects of intravenous ketamine (1 mg/kg) on cerebral cortical blood flow and O 2 uptake were evaluated in 13 anesthetized, ventilated rabbits. Blood flow was measured either directly (Group 1) or by the H 2 clearance method (Group 2). In those animals of Groups 1 and 2 with normal control arterial pH (pHa), ketamine produced a significant increase in cerebral cortical blood flow of 18 and 34%, respectively, but had no effect on cerebral cortical O 3 uptake. However, in rabbits with low control pHa, ketamine caused an increase in blood flow (30%) accompanied by a significant increase in O 3 uptake (22%). Ketamine produced nonsignificant changes in mean arterial blood pressure and arterial blood gases, except for a significant reduction in pressure in animals with low pHa. It is concluded that ketamine is a cerebral vasodilator without cerebral metabolic effect when mean arterial blood pressure and arterial Pcoj, Poj, and pH are held constant at physiologic levels. The vasodilator effect of ketamine is probably due to direct dilating action or activation of a cholinergic cerebral vasodilator system. (Stroke 1987;18:441-444)A FTER the introduction of ketamine as an anes-/ \ thetic agent in 1966, many studies were con-A. X . ducted on experimental animals and humans to characterize the effect of this agent on cerebral blood flow (CBF) and cerebral metabolic rate for oxygen (CMROj The wide difference in results reported in those publications, previously discussed by Schwedler et al,4 prompted the present study. We were interested in evaluating the possible cerebral metabolic effect of ketamine in a rabbit preparation to elucidate the role of a cholinergic cerebral vasodilator mechanism activated by ketamine recently proposed by Reicher et al 9 to explain their findings. Materials and MethodsThirteen male New Zealand rabbits weighing 2.7-3.5 kg were anesthetized with 6% halothane added to O 2 and room air. After tracheostomy, anesthesia was maintained via a tracheal tube with 0.5% halothane in Received May 29, 1985; accepted October 20, 1986. O 2 and room air until all surgical procedures were finished. Halothane was then discontinued, and the animals were maintained under 50% N 2 O-50% O 2 for at least 1 hour before the beginning of CBF and O 2 consumption measurements. Pancuronium bromide (Pavulon, Organon) at 0.2 mg/kg/hr was given to ensure muscle paralysis. Mechanical ventilation with a T-system was adjusted to maintain end-tidal CO 2 (ETCOj) at 3.5-4% monitored with a Beckman LB-2 analyzer. The femoral artery and vein were cannulated for blood pressure measurement, blood sampling, and drug administration. Two screw electrodes were placed in the left parietal region for continuous recording of the electroencephalogram (EEG). Rectal temperature was continuously monitored and maintained at 38.5-39.0° C by radiant heating or ice-water cooling of the animal. Arterial pressure, ETCO 2 , EEG, and hydrogen (HJ clearance were recorded on a Grass Model 7 polygraph. Arterial blood samples (0.5-0.8 ml) were collecte...

S(+)-ketamine/propofol maintain dynamic cerebrovascular autoregulation in humans

“…However, it is also possible that changes in CBF occur secondary to changes in MAP (i.e., impaired cerebrovascular autoregulation). 15,16 The present investigation shows that S(+)-ketamine in combination with low-dose propofol did not alter the dynamic cerebrovascular response to a decrease in MAP. As propofol in concentrations used in the present study does not influence cerebrovascular autoregulation, 9 the present data suggest that S(+)-ketamine does not influence dynamic and static autoregulation.…”

“…[12][13][14] This is consistent with studies in awake or N 2 O/O 2 -ventilated animals and humans where racemic ketamine increased CBF along with increases in MAP. 15,16 In contrast, in the presence of anesthetics depressing cerebral metabolism, ketamine did not change or decrease CBF. 1,17,18 This suggests that the effect of ketamine on CBF is related to the pre-existing cerebrovascular tone induced by the background anesthetic technique.…”

Effectiveness of ketamine in decreasing intracranial pressure in children with intracranial hypertension

“…The initial observations of ICP elevations have been related to the cerebral metabolic rate-enhancing effect of ketamine, accompanied by a corresponding increase in CBF, 12,20,23,27,35 as autoregulation is maintained during ketamine anesthesia. Other studies, however, have found no changes 26,31 or even CBF decreases 4,7 following ketamine administration.…”

Racemic ketamine does not abolish cerebrovascular autoregulation in the pig

“…ketamine, on CBF. Ketamine has been reported to increase CBF in awake or lightly anesthetized animals and humans (3,4), whereas no changes in CBF (20) or CBF velocity (21,22) were found on ketamine injection when, instead, cerebral depressant anesthetic drugs were used for background anesthesia.…”