Continuous measurement of intracranial pressure in awake rats after experimental closed head injury.

The present study validates a method for continuous measurement of intracranial pressure (ICP) in freely moving rats after experimental induction of impact-acceleration injury. Rats subjected to either mild or moderate trauma were individually placed in a Bas-Ratturn system, equipped with a sensor that synchronously turns the cage in response to the locomotor activity of the animal. In this way correct probe positioning is permanently assured and damage due to coiling is avoided. The evolution of ICP and mean arterial blood pressure (MABP) in injured rats was compared with that of a non-traumatized sham group. Since the animals regained consciousness after surgery, interference of anaesthesia on these sensitive parameters should be minimised. The results showed that immediately after induction of neurotrauma, ICP was significantly higher in traumatized rats (sham: 7.7 +/- 0.5 mmHg; mild trauma: 10.4 +/- 0.7 mmHg; moderate trauma: 14.9 +/- 2.4 mmHg; P<0.05). Regression analysis showed a stable ICP up to 3 h post-insult for all three conditions. From 4 h onwards till the end of the experiment at 10 h post-insult, a significant increase in ICP was seen for sham-operated and mildly traumatized rats (16.1 +/- 3.4 and 30.5 +/- 6.9 mmHg, respectively; P<0.05), but not for moderately traumatized rats (47.3 +/- 11.9 mmHg). The method allows observation of ICP for a critical period up to 3 h. As such the method can be regarded as clinically relevant to study early pathological aspects of intracranial hypertension and to define a therapeutic window for pharmacological intervention after traumatic brain injury (TBI).