Non-invasive assessment of cerebral perfusion pressure in brain injured patients with moderate intracranial hypertension

Abstract

Background. A non-invasive estimation of cerebral perfusion pressure (CPP) using transcranial Doppler sonography was assessed in brain-injured patients by comparing conventional measurements of CPP (difference between mean arterial pressure and intracranial pressure) (CPPm) with the difference between APmean and the critical closing pressure of the cerebral circulation (CPPe). Methods. Twenty adults with bilateral and diffuse brain injuries were included in the study. CPPe was estimated using a formula combining the phasic values of flow velocities and arterial pressure. In group A (n=10) the comparison was repeatedly performed under stable conditions. In group B (n=10) the comparison was performed during a CO2 reactivity test. Covariance analysis was used to assess the relationships. Results. In group A, CPPe and CPPm were correlated (slope, 0.76; intercept, + 10.9; 95% CI, -3.5 to +25.4). During the increase in intracranial pressure (group B) (+1.9 (SD 1.5) mm Hg per mm Hg of PE′CO2,) the relationship persisted (slope, 0.55; intercept, +32.6; 95% CI, +16.3 to +48.9) but the discrepancy between the two variables increased as reflected by the increase in bias and variability. Conclusion. Non-invasive estimation of CPP can be used for brain monitoring of head-injured patients, but the accuracy of the method may depend on the level of intracranial hypertension. © The Board of Management and Trustees of the British Journal of Anaesthesia 2004.