Evaluation of Intracranial Pressure Time Dose by the New Integra CereLink ICP Monitor

Intracranial pressure (ICP) monitoring is the most common neuromonitoring modality used in neurocritical care (NCCU). Its application both as a stand-alone monitoring or in association with other systems (brain oxygenation, brain microdialysis, electroencephalography, transcranial Doppler ultrasound, etc.) has several indications, which rely on local, national policies, and international guidelines. In 2014, ESICM with the Neurocritical Care Society released a multidisciplinary Consensus Statement to provide a guidance on Multimodality Monitoring in Neurocritical Care, including ICP: "ICP and CPP monitoring are recommended as a part of protocol-driven care in patients who are at risk of elevated intracranial pressure based on clinical and/or imaging features. (Strong recommendation, moderate quality of evidence)". The most recent Brain Trauma Foundation guidelines focused on the importance of ICP monitoring, especially in severe traumatic brain injury, but a living systematic review showed that the compliance rate to these guidelines was low (31%; range 18-83%). Most of the ICP monitoring guidance orbits around traumatic brain injury, while there are uncertainties around indication of ICP monitoring in non-traumatic brain injury (acute subarachnoid hemorrhage and intracerebral hemorrhage).

Similarly, ICP thresholds, threshold-based treatment strategies and their impact on outcome have not been established yet. The interpretation of data on ICP practice has a limited value without some reference to the intensity of therapy directed at control of ICP. The Therapy Intensity Level (TIL) may be a more sensitive measure of the severity of pathophysiology but the effect on outcome of existing differences in practice is unclear.

In most intensive care units, ICP values are summarized hourly in bedside charts by trained nurses, as end-hour ICP, and similar data have been used in large randomized clinical trials testing neuroprotective treatments for TBI patients.

However, several single center studies showed that this manual acquisition method is suboptimal and could miss episodes of high ICP compared to high-resolution, computerized acquisition systems. Computers allow also the computation offline of ICP derived parameters. Vik proposed that the degree of ICP above the treatment threshold can be estimated by the area under the curve (AUC) of ICP versus time in patients with TBI, i.e. the "ICP dose". A significant relationship between the ICP dose, the worst Marshall CT score, and patient outcome exists, suggesting that the AUC method may be useful in refining and improving the treatment of ICP in patients with TBI. Moreover, small cohort studies confirmed this relationship between the dose of ICP and patient outcome, suggesting that the dose of ICP may be useful in refining and improving the treatment of ICP in patients with TBI. In a single centre cohort TBI study, increased ICP dose was associated with mortality and poor functional outcome at 6 months. However, there was no association between episodic ICP data and outcome, proposing this index as candidate "biomarker" of the disease.

Even if the concept is attracting, all these computations have been collected a posteriori and no single ICP monitoring system was able to display the ICP dose continuously, making it useful at the bedside.