The Linear Relationship Between Transcranial Doppler Pulsatility Indices and Intracranial Pressure Is Influenced by Trau
The pulsatility index (PI) and the intracranial pressure (ICP) may or may not be correlated; the evidence to date differs widely. A study of multiple measures of PI and the corresponding ICP in patients with severe traumatic brain injury (TBI) showed tha
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Abstract The pulsatility index (PI) and the intracranial pressure (ICP) may or may not be correlated; the evidence to date differs widely. A study of multiple measures of PI and the corresponding ICP in patients with severe traumatic brain injury (TBI) showed that some of the relationships were moderately strong when calculated as conventional Pearson correlation coefficients. However, that method makes no adjustment of any kind for statistical outliers in the data. With the TBI patients demonstrating a large fraction of skewed measurements, a set of robust correlations were calculated that demonstrated that the apparent relationships between PI and ICP were entirely attributable to the statistical outliers. We conclude that the fundamental relationship of PI to ICP is weakly positive at best. Keywords Traumatic brain injury • Vasospasm • Craniectomy • Pulsatility index • Intracranial pressure • Transcranial Doppler
Introduction Developing a noninvasive technique for measuring human intracranial pressure (ICP) has been a goal for many scientists and clinicians. One such technique that has garnered interest over three decades has been transcranial Doppler (TCD). TCD is a device that transmits and receives, from the red blood cells in the major cerebral arteries, ultrasound waves representing cerebral blood flow velocities. A wave form spectrum of the velocities during a cardiac cycle yields useful information such as peak systolic and peak diastolic
T.C. Glenn (), A.K. Sherma, D.L. McArthur, X. Hu, C.R. Hanuscin, M.S. Furreedan, D.A. Hovda, P.M. Vespa, and N.A. Martin Department of Neurosurgery, David Geffen School of Medicine at the University of California-Los Angeles, 10833, Le Conte Avenue, Los Angeles, CA 90095-7039, USA e-mail: [email protected]
velocities and calculations such as the Gosling pulsatility index (PI) can be derived [4, 11]. It is the relationship between the PI and ICP that has generated the greatest interest in noninvasive ICP determination. Several studies in a variety of patient types have determined that a moderate to strong positive correlation exists between PI and ICP [6, 7, 10, 12, 14]. One of the most recent studies conducted in a mixed population of intensive care (ICU) patients reported a significant coefficient of r = 0.94 between PI and ICP. However, other recent studies in normal pressure hydrocephalus and pediatric trauma patients have indicated that the PI and ICP correlations were weak, with an R2 = 0.22 and r = 0.4 respectively [5, 9]. Thus, there is no current consensus in the literature on the utility of PI to correlate with ICP in patients in the ICU setting. The purpose of this study was to investigate the relationship between the PIs of the major cerebral arteries and ICP in patients with severe traumatic brain injury (TBI). Additionally, potential confounding factors such as gender, vasospasm, and surgery were investigated.
Materials and Methods Patient Enrollment Eligible patients included severe (Glasgow Coma Scale [GCS] < 9) TBI patients aged 14 and over who we
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