oa Multimodality monitoring in neurocritical care

Monitoring the health of an injured brain is essential to forewarn neurological worsening and to gain insight into the pathophysiology of a complex disorder.

Clinical examination remains a cornerstone in monitoring patients with brain injury. The Glasgow coma score (GCS) is widely used but lacks information regarding brain stem functions like pupillary reaction and shows moderate inter-observer reliability. However, despite these shortcomings, GCS remains a robust indicator of the need for surgery and prognosis after cardiac arrest, hypoxic brain injury, and posterior circulation stroke. A new scoring system called Full Outline of Unresponsiveness has been proposed and shows excellent inter-observer reliability and includes points concerning brain stem functions.¹

The most commonly used monitoring modality is intracranial pressure (ICP) monitoring. ICP shows threshold physiology where the outcome of the patients changes after a threshold of 20 to 25 mmHg. Refractory ICP is a good predictor of mortality but not of the functional outcome after traumatic brain injury.

Brain injury causes varying degrees of disruption to cerebral blood flow and its autoregulation. Studying autoregulation provides a useful strategy for targeting cerebral perfusion pressure close to the autoregulatory range. Transcranial Doppler and ICMplus (Intensive Care Monitoring) are used to study autoregulation. ICMplus is a software-based tool that studies the correlation between slow changes in mean arterial pressure and ICP to evaluate the state of autoregulation throughout the duration of ICP monitoring.²

Brain tissue oxygen measures the partial pressure of oxygen in the extracellular fluid of the neural tissue. Reduction in brain tissue oxygen is a marker of cellular distress. A phase 2 trial on brain tissue oxygen monitoring demonstrated the safety and feasibility of the protocol-based management of brain tissue oxygenation and ICP, and a trend towards lower mortality and improved functional outcome in patients treated with combined oxygen and ICP protocol.³

Microdialysis is a point of care test that monitors substrate delivery and metabolism at the cellular level. The lactate-pyruvate (LP) ratio is an indicator of the redox state of cells and a high LP ratio is associated with an unfavourable outcome.⁴

The electroencephalogram (EEG) is used in critical care for monitoring sedation and diagnosis of seizure activity. EEG is a complex signal which requires advanced training and skills for interpretation. Novel EEG-based monitors are aimed at simplifying the signal for straightforward interpretation by bedside medical professionals. Cerebral function monitor (CFM) is a compressed single channel amplitude integrated EEG monitor mainly used for the detection of status epilepticus and burst suppression during thiopentone infusion. A novel technique that uses direct electrodes applied on the cortical surface called Electrocorticogram (ECoG) shows spreading depolarisations on the cortical surface that are caused by loss of ionic homeostasis and substrate delivery.⁵ These depolarisations are a sensitive indicator of impending neuronal death and may serve as a target for novel mechanistically oriented therapies.

Detection, prevention, and monitoring of secondary cerebral insults that alter the prognosis from the injury, remains at the centre stage in neurocritical care. In the future, integrated informatics derived from multimodality monitoring will play a pivotal role in clinical decision algorithms.