A neurological wake-up test in the neurointensive care unit: Pros and cons

Traumatic brain injury (TBI) induces a marked systemic biochemical stress response with the release of several stress-related hormones including cortisol and the catecholamines. A major aim of using continuous sedation in the neurointensive care unit (NIC) unit is to attenuate the TBI-induced stress response via reduction of the cerebral energy metabolic demands. In the era of modern multimodality monitoring and neuroimaging for patients with severe TBI, what is the role for neurological evaluation, a neurological wake-up test (NWT), of patients on continuous sedation and mechanical ventilation? In particular, does the information obtained by the NWT outweigh the risk of inducing a substantial stress response? The additional use of NWTs in NIC is controversial and is not mentioned in any recent TBI guidelines. Although daily interruption of continuous sedation is suggested for patients in general intensive care, reasons for not using the NWT in NIC may be a fear of an NWT-induced stress response and uncertainty to the additional value of NWTs in patients monitored with multimodality monitoring and frequent neuroradiological examinations. A recent survey showed that use of NWT varies markedly in Scandinavians’ NIC units where half of the evaluated centres never use the NWT, whereas others use the NWT up to six times daily. In a series of studies characterising the NWT-induced stress response, the NWT was found to induce a significant increase in ICP and CPP in severe TBI patients on controlled ventilation. Additionally, the NWT caused an increase in adrenocorticotrophic (ACTH) hormone, catecholamine and cortisol levels. In the absolute majority of patients, the ICP and CPP changes were modest and transient and the absolute increases in stress hormone levels were small. However, the stress response was marked in a small subset of patients. These studies suggest that the NWT is safe in the majority of patients but that the test should be individualised and avoided in patients reacting with markedly increased ICP and/or decreased CPP. Although important clinical information may be obtained from the NWT, future studies need to evaluate the risk-benefit ratio of the NWT in TBI management.