Cerebral pharmacodynamics of anaesthetic and subanaesthetic doses of ketamine in the normoventilated pig

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Abstract
There are still divergent opinions regarding the pharmacodynamic effects of ketamine on the brain. In this study, the cerebral blood flow (CBF), cerebral metabolic rate for oxygen (CMRo2) and electroencephalogra‐phic (EEG) activity were sequentially assessed over 80 min in 17 normoventilated pigs following rapid i.v. infusions of anaesthetic (10.0 mg‐kg‐1; n = 7) or subanaesthetic (2.0 mg‐kg‐1; n = 7) doses of ketamine or of its major metabolite norketamine (10.0 mg‐kg‐1; n = 3). The animals were continuously anaesthetized with fentanyl, nitrous oxide and pancuronium. CBF was determined by the intra‐arterial mXe technique. Ketamine (10.0 mg‐kg‐1) induced an instant, gradually reverting decrease in CBF, amounting to ‐26% (PP2by 42% (PP2found 10–20 min after ketamine (10.0 mg‐kg‐1) administration, it is suggested that ketamine should be used with caution for anaesthesia in patients with suspected cerebral ischaemia in order not to increase the vulnerability of brain tissue to hypoxic injury. Ketamine (2.0 mg‐kg‐1) had no significant effects on CBF, CMRo2or EEG. It therefore seems that up to one fifth of the minimal anaesthetic i.v. dose can be used safely for analgesia, provided that normocapnaemia is preserved.