[Clinical use of cerebral elastance and intracranial dynamics measurements]

The treatment of Intracranial Pressure (ICP) requires not only the determination of the pressure but also some kind of estimate of the relationship between intracranial volume and actual pressure. The measurement of the Pressure Volume Index (PVI) offers a quantitative assessment of such a relationship, provided that the measurement is safe and accurate. In 98 comatose patients admitted to the Intensive Care Unit for the treatment of head injury or subarachnoid hemorrhage the ICP was continuously recorded using ventricular or subdural catheters. In 68 patients the PVI was measured using the bolus technique every 12 hours; the intracranial dynamics was assessed according to Marmarou's equations. The preliminary part of the work reviewed the methodology: the interobserver variability was studied and the differences between the PVI data obtained through addition or withdrawal of fluid were determined. The data obtained by different observers did not differ substantially, due to the clear establishment of rules for the measurement. The PVI data obtained withdrawing fluid were lower than the data produced adding volume but the mean PVI calculated after 6 bolus changes of the intraventricular volume reached a good correlation coefficient (> 0.8) with all the measurements. After that the clinical use of the PVI was tested. The patients with a PVI lower than 15 ml showed an increased risk of developing intracranial hypertension in the first 72 hours after trauma of SAH. The group of patients with an intracranial compliance lower than 0.5 had a mortality rate of 27.3%, compared with the rate of 14.3% showed by the patients with a greater Compliance.