[Intracranial pressure during ketamine administration with spontaneous respiration. An animal experimental model]

A sequence of i.v. ketamine injections, 0.5, 2.0, and 5.0 mg/kg body weight, was given to thirty piglets. At the beginning of the investigation, 10 of these animals had a normal intracranial pressure and stable circulation. The intracranial pressure of the remaining 20 piglets was raised to 30 mm Hg, and an additional haemorrhagic shock was induced in 10 of these animals. Those animals with a normal intracranial pressure showed no alteration there of at any of the three doses given, and the arterial pCO2 remained practically unchanged. In contrast, all animals with a raised intracranial pressure, both with and without superimposed haemorrhagic shock, had a significant rise in intracranial pressure and pCO2. These two parameters were found to correlate well with each other. We conclude that in the model used, where the animals were breathing spontaneously, the intracranial pressure rise seen following ketamine application is secondary to the increase in pCO2.