Changing trends in monitoring brain ischemia: from intracranial pressure to cerebral oximetry.

PURPOSE OF REVIEW

Cerebral ischemia forms the pathophysiological basis of several acute neurological conditions. Successful management of these conditions depends on early and accurate identification of ischemia and prompt treatment. Several techniques of assessing ischemia have evolved over decades. But their importance in the management of neurological patients remains ambiguous.

RECENT FINDINGS

Current trends in monitoring cerebral ischemia follow two pathways: (1) Indirect methods of assessing global and regional cerebral perfusion [intracranial pressure/cerebral perfusion pressure (ICP/CPP), transcranial Doppler]; and (2) Assessment of adequacy of cerebral blood flow (CBF) at tissue level by monitoring global or regional oxygenation and metabolism (SjvO2, rSO2, PbtO2, microdialysis).Traditional approach to ICP/CPP monitoring has changed to more complex analysis of the ICP waveform to derive variables related to cerebral perfusion and vascular reactivity. Noninvasive techniques of cerebral perfusion pressure assessment are under investigation. Newer methods are being explored to derive indices of CBF autoregulation from various modalities of cerebral monitoring. Direct brain tissue oxygen tension monitoring and microdialysis facilitate regional monitoring of oxidative metabolism. However, there seems to be some complexity in interpreting the results from these monitors.

SUMMARY

A wide range of options are available for monitoring adequacy of regional and global CBF. But no single monitor per se fulfils the requirements of all clinical situations. Impact of these monitors on clinical outcomes is equivocal. Also, at present, many of these monitors are invasive and not cost-effective.