Introduction: Intracranial pressure(ICP) monitoring is a common practice in the management of various neurological disorders. Sophisticated analyses of the ICP waveform have yielded important information regarding intracranial compliance in these states, but have not gained widespread clinical utility(1). The pressure-volume compensatory reserve index(RAP) is a correlation coefficient between the ICP waveform amplitude(pulse ICP) and the mean ICP and has been found to predict outcome in traumatic brain injury(TBI)(2).
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. RAP was calculated for 11 patients stratified based on their Glasgow outcome Scale(GOS) into good outcome(GOS of 5,n=5) and worst outcome group(GOS of 1-2,n=6).
Results: A lag phase of 1-2 heart beats was noticed between Pulse ICP and mean ICP in all subjects and elimination of lag phase between these two variables resulted in changes in the statistical significance of mean RAP values. Detailed ICP waveform analysis of 4 TBI subjects with 2 belonging to each outcome group as a representative pool was performed. The mean RAP values were 0.5-0.7 and 0.3-0.9 in good and worst outcome groups respectively,with significant p-values(p<0.05) in all subjects. However,in subjects who went on to die from uncontrolled increased ICP,RAP ranged from 0.63 to 0.89 during the active phase of uncontrollable ICP. In 2 healthy individuals,the RAP values were between 0.04-0.3;however this correlation was not significant.
Conclusions: In our detailed analysis of 4/19 TBI subjects,mean RAP was significantly >0,indicating that there is a strong linear correlation between average mean ICP and average pulse ICP. In healthy controls,these correlations were not significant. There seems to be a trend toward higher mean RAP in patients with a poor outcome compared to those with a good recovery. Analysis of additional subjects is ongoing.
Patient Care: This project aims to continue ICP waveform analysis of all the TBI patients enrolled in our study for various indices including RAP. We hope our project will lead to better understanding of ICP waveforms and its potential clinical application in obtaining robust and real time information on intracranial compliance in pathological states.
Learning Objectives: This study gives us valuable insights into ICP waveform analysis in pathological states like TBI and their potential clinical use in deciphering current state of intracranial compliance independent of absolute value of ICP.
References: 1) Westhout FD, Pare LS, Delfino RJ, Cramer SC. Slope of the intracranial pressure waveform after traumatic brain injury. Surg Neurol 2008; 70(1):70-74.
2) Balestreri M, Czonyska M, Steiner LA. Intracranial hypertension: what additional information can be derived from ICP waveform after head injury? Acta Neurochir (Wien) 2004; 146:131-141.