Effects of 'Head Up' Prone Position on Transcranial Color Doppler-Based Estimators of Intracranial Pressure in Moderate to Severe Acute Respiratory Distress Syndrome Without Brain Injury: A Cross-Over, Longitudinal, Physiological Study.

Background: Prone positioning is recommended in acute respiratory distress syndrome (ARDS) to ensure adequate gas exchange. However, it may lead to an increase in intracranial pressure (ICP), mostly due to a reduction of venous return from the brain. ICP can be noninvasively estimated with transcranial color-coded Doppler (TCCD) using methods based on the relationships between the pulsatility index (PI) and ICP or methods based on the estimate of cerebral perfusion pressure (eCPP) and estimate of ICP (eICP). This study was aimed at assessing the effects of a 30° reverse Trendelenburg ('head up') prone position on two noninvasive estimators of ICP (eICP and PI).

Methods: This is a cross-over, longitudinal, physiological study conducted on a cohort of adult patients fulfilling Berlin definition criteria for moderate to severe ARDS without brain injury but with clinical indication to prone positioning. We registered TCCD parameters of cerebral hemodynamic and systemic hemodynamic parameters, blood gas exchange data, and respiratory mechanics parameters in a horizonal supine position, in a 30° semirecumbent supine position, in the standard prone position, and, finally, in the 30° 'head up' prone position, obtained by tilting the entire bed to a reverse Trendelenburg position. One-way repeated measures analysis of variance was used to analyze data.

Results: In 20 patients included, switching from a supine position to the standard prone position resulted in a significant increase in mean ± SD PI (from 0.99 ± 0.22 to 1.29 ± 0.25, p < 0.01) and eICP (from 12.5 ± 3.8 to 17.5 ± 4.1, p < 0.01), whereas moving from this latter position to the 'head up' prone position resulted in a decrease in the mean ± SD PI (from 1.29 ± 0.25 to 1.0 ± 0.23, p < 0.01). Hemodynamic and respiratory mechanics parameters did not differ.

Conclusions: The 30° 'head up' prone position may limit the increase in PI in moderate to severe ARDS without brain injury. As a noninvasive estimator of ICP, PI may allow detection of changes in ICP when moving from the 'head up' semirecumbent supine position to the standard prone position and from this latter position to the 'head up' prone position.