Introduction: Intracranial pressure (ICP) monitoring as an absolute number is generally used in the management of various intracranial pathologies; however ICP waveform analysis carries valuable information regarding intracranial compliance in these states. More sophisticated analysis of the intracranial pressure waveform has yielded important relationships, but those methods have not gained widespread clinical utility (1,2. The pressure-volume compensatory reserve index (RAP) is a correlation coefficient between the ICP waveform amplitude and the mean ICP (ref) and has been found to predict outcome in traumatic brain injury (TBI)(1). The high-frequency centroid (HFC) is a power-weighted frequency spectrum of the ICP waveform that also correlates to outcome and mortality from TBI(6).
Methods: This study recorded ICP continuously in 19 TBI patients using either ventriculostomy or Camino and recorded CSF pressure in 2 control patients undergoing lumbar drainage for abdominal aortic aneurysm repair. .HFC and RAP were calculated for each patient. And these results were correlated to the outcome.
Results: Detailed ICP waveform analysis of 3 patients with acute TBI as representative of pool of 19 TBI patients and 2 control patients over 7 hours. Three TBI patients and 2 control patients had RAP value between 0.8-0.9 and 0.04-0.3 with P Value <0.03 and P value >0.15 respectively. Average mean ICP showed negative correlation between -0.6 to -0.3 with HFC in 2 TBI and 1 Control patients with P value <0.03. The remaining TBI and control patients had positive correlation.
Conclusions: In pathological states, grand RAP was significantly > 0 indicating that there is a strong linear trend between average mean ICP and average pulse ICP. In healthy controls, these correlations were not significant. We also found significant (or near significant) negative correlation between the average mean ICP and average HFC may be indicative of poor outcome (death or disability).
Patient Care: The project is ongoing however this will hopefully establish a reliable and clinically usable method of ICP waveform analyis which can lead to early detection of loss of intracranial compliance before there is significant rise in ICP. In this way we may be able to prevent or lessen intracranial hypertension related insult to brain and finally improve patient's prognosis.
Learning Objectives: This article will give us more insight into ICP waveform analysis in pathological states like TBI and their potential clinical use in deciphering exhaustion of intracranial compliance independent of absolute value of intracranial pressure.
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6) Robertson CS, Narayan RK, Contant CF, Grossman RG, Gokaslan ZL, Pahwa R, Caram P, Bray RS, Sherwood AM. Clinical experience with a continuous monitor of intracranial compliance. J Neurosurg 71: 673-680, 1989