Continuous Intracranial Multimodality Monitoring Comparing Local Cerebral Blood Flow, Cerebral Perfusion Pressure, and Microvascular Resistance

Summary

Maintaining cerebral perfusion pressure (CPP) above 70mm Hg is currently a mainstay of neurosurgical critical care. Shalmon, et al. recently showed poor correlation between CPP and regional cerebral blood flow (CBF) [1]. To study the relationship between CPP and CBF, at a microvascular level, we retrospectively analyzed multimodality digital data from 12 neurosurgical critical care patients in whom a combined intracranial pressure (ICP) — laser Doppler flowmetry (LDF) probe (Camino, San Diego) had been placed. Over the entire interval of continuous monitoring for all patients, 97% of local CBF data was at ischemic levels below a CPP of 70mm Hg. For CPP above 70mm Hg, local CBF data had considerable dispersion ranging from ischemic (71%), to normal (19%), and hyperemic (10%) levels. Elevated jugular bulb oxyhemoglobin saturation levels (SjO₂) complemented intervals of hyperemia. Autoregulation was impaired or absent in all monitored patients. We conclude that with disrupted autoregulation, CPP above 70mm Hg does not necessarily insure adequate levels of cerebral perfusion. Restoration and maintenance of adequate cerebral perfusion should be performed under the guidance of direct CBF monitoring.