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Traumatic brain injury (TBI) renders the brain more vulnerable to secondary insults. The increased vulnerability can probably be explained by a combination of disturbances in hemodynamics, metabolism and craniospinal dynamics. Reduced ability to compensate for added intracranial volume, i.e. reduced intracranial compliance (IC), is one possible mechanism. The aim of this thesis was to study the role of IC on the effect of secondary insults after TBI.

A rat TBI model was developed where IC could be altered without causing pathological increases in intracranial pressure (ICP). Reduction of IC was made by placing rubber film between the dura mater and bilateral bone flaps. A reduction of IC in terms of reduced Pressure Volume Index was confirmed. Microdialysis (MD) of extracellular fluid was used to monitor neurochemical changes. Reduced IC after TBI proved to increase the vulnerability of the brain to secondary intracranial volume insults according to neurochemical microdialysis markers. Reduced IC or intracranial volume insults alone did not cause any metabolic changes as compared to controls. Moderate posttraumatic hypotension (50mmHg for 30 min) induced 2 hrs after TBI, did not aggravate posttraumatic extracellular neurochemical changes significantly, irrespective of the level of IC. Although controversial, a mild to moderate hypotensive insult after initial posttraumatic stabilization may not be as detrimental as earlier believed.

The Spiegelberg Compliance Monitor and MD were simultaneously used in 10 TBI patients to get an impression of the clinical value of IC monitoring and the relationship between IC, temperature and MD Lactate/Pyruvate ratio. IC and MD could be monitored simultaneously in TBI patients. Higher L/P ratios were seen when IC was low. Patients with induced coma treatment had significantly higher average L/P ratios, possibly due to their poorer neurological condition. An indication was also found that in TBI patients with high temperatures, L/P ratio rose as IC decreased, but in patients with low temperature there was no effect of IC on L/P ratio. These data suggest the importance of avoiding hyperthermia in TBI patients, especially in patients with low or decreased IC (monitored or anticipated).