Transcranial Doppler sonography pulsatility index (PI) reflects intracranial pressure (ICP)

Abstract

Background: In patients with intracranial pathology, especially when comatose, it is desirable to have knowledge of the intracranial pressure (ICP). To investigate the relationship between ICP and transcranial Doppler (TCD) derived pulsatility index (PI) in neurosurgical patients, a prospective study was performed on patients admitted to our neurointensive care unit.

Methods: Daily TCD mean flow velocity (mFV) measurements were made. TCD measurements were routinely performed bilaterally on the middle cerebral artery (MCA). PI (peak systolic-end diastolic velocities/mean flow velocity) was calculated.

Results: Eighty-one patients with various intracranial disorders who had an intraventricular catheter for registration of the ICP were investigated: 46 (57%) patients had subarachnoid hemorrhage, 21 (26%) patients had closed head injury, and 14 (18%) patients had other neurosurgical disorders. A total of 658 TCD measurements were made. ICP registrations were made parallel with all TCD measurements. A significant correlation (p < 0.0001) was found between the ICP and the PI with a correlation coefficient of 0.938: ICP = 10.93 x PI - 1.28. In the ICP interval between 5 to 40 mm Hg the correlation between ICP and PI enabled an estimation of ICP from the PI values with an SD of 2.5. The correlation between the cerebral perfusion pressure (CPP) and PI was significant (p < 0.0001) with a correlation coefficient of -0.493. When separating the measurements in severely elevated (>120 cm/s) and subnormal (<50 cm/s) TCD mFV values, the correlation coefficient between ICP and PI was 0.828 (p < 0.002) and 0.942 (p < 0.638), respectively.

Conclusions: Independent of the type of intracranial pathology, a strong correlation between PI and ICP was demonstrated. Therefore, PI may be of guiding value in the invasive ICP placement decision in the neurointensive care patient.