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How to monitor the brain during acute brain injury?
Clinically: The serial neurologic examination is still the best option.
Physiologically: ICP and cerebral blood flow (CBF).
ICP:
Both intraparenchymal monitors and ventricular catheters measure ICP and indirectly measure cerebral perfusion pressure (CPP).
ICP and CPP monitoring are recommended in patients who are at risk of elevated ICP based on clinical and/or imaging features.
Refractory ICP elevation is a strong predictor of mortality.
CBF:
Bedside techniques for monitoring CBF include both invasive methods such as thermal diffusion and laser Doppler flowmetry and noninvasive methods such as transcranial Doppler (TCD) ultrasonography and near infrared spectroscopy (NIRS).
Trends in blood flow velocity changes measured with TCD can help predict delayed ischemic neurologic deficits due to vasospasm after aneurysmal subarachnoid hemorrhage (SAH).
Electrophysiologically:
Electroencephalography (EEG) has been recommended in all patients with any acute brain insult and unexplained and persistent altered consciousness.
In addition, urgent EEG should be considered in patients with convulsive SE who do not return to functional baseline within 60 minutes after seizure medication and in those with refractory status epilepticus (RSE).
Furthermore, EEG also has been recommended during therapeutic hypothermia and within 24 hours of rewarming to exclude subclinical seizures in all comatose patients after cardiac arrest.
Metabolically: Oxygenation and substrate metabolism.
Brain hypoxia
This is associated with worse outcome. It is measured by either invasive methods such as bedside techniques, brain parenchymal oxygen tension (PbtO 2 ), and jugular bulb oxygen saturation (SjvO 2 ) or noninvasive bedside methods such as NIRS.
It is currently recommended to monitor brain oxygen in patients with or at risk of cerebral ischemia and/or hypoxia using either brain tissue (PbtO 2 ) and/or jugular venous bulb oximetry (SjvO 2 ).
Brain extracellular concentrations of energy metabolism markers
including lactate, pyruvate, and glucose, are accurately measured by microdialysis.
Monitoring cerebral microdialysis in patients with or who are at risk of cerebral ischemia, hypoxia, energy failure, and glucose deprivation should be considered only in combination with clinical indicators and other monitoring modalities for therapeutic interventions and prognostication.
