Purpose: To compare intracranial pressure (ICP) amplitude, ICP slope, and the correlation of ICP amplitude and ICP mean (RAP index) as measures of compliance in a cohort of traumatic brain injury (TBI) patients.
Methods: Mean values of the three measures were calculated in the 2-h periods before and after surgery (craniectomies and evacuations), and in the 12-h periods preceding and following thiopental treatment, and during periods of thiopental coma. The changes in the metrics were evaluated using the Wilcoxon test. The correlations of 10-day mean values for the three metrics with age, admission Glasgow Motor Score (GMS), and Extended Glasgow Outcome Score (GOSe) were evaluated. Patients under and over 60 years old were also compared using the Student t test. The correlation of ICP amplitude with systemic pulse amplitude was analyzed.
Results: ICP amplitude was significantly correlated with GMS, and also with age for patients 35 years old and older. The correlations of ICP slope and the RAP index with GMS and with age were not significant. All three metrics indicated significant improvements in compliance following surgery and during thiopental coma. None of the metrics were significantly correlated with outcome, possibly due to confounding effects of treatment factors. The correlation of systemic pulse amplitude with ICP amplitude was low (R = 0.18), only explaining 3 % of the variance.
Conclusions: This study provides further validation for all three of these features of the ICP waveform as measures of compliance. ICP amplitude had the best performance in these tests.