Multimodal monitoring after traumatic brain injury: useless or useful?

Neurologic Assessment of the Neurocritical Care Patient

Sedation is a ubiquitous practice in ICUs and NCCUs. It has the benefit of reducing cerebral energy demands, but also precludes an accurate neurologic assessment. Because of this, sedation is intermittently stopped for the purposes of a neurologic assessment, which is termed a neurologic wake-up test (NWT). NWTs are considered to be the gold-standard in continued assessment of brain-injured patients under sedation. NWTs also produce an acute stress response that is accompanied by elevations in blood pressure, respiratory rate, heart rate, and ICP. Utilization of cerebral microdialysis and brain tissue oxygen monitoring in small cohorts of brain-injured patients suggests that this is not mirrored by alterations in cerebral metabolism, and seldom affects oxygenation. The hard contraindications for the NWT are preexisting intracranial hypertension, barbiturate treatment, status epilepticus, and hyperthermia. However, hemodynamic instability, sedative use for primary ICP control, and sedative use for severe agitation or respiratory distress are considered significant safety concerns. Despite ubiquitous recommendation, it is not clear if additional clinically relevant information is gleaned through its use, especially with the contemporaneous utilization of multimodality monitoring. Various monitoring modalities provide unique and pertinent information about neurologic function, however, their role in improving patient outcomes and guiding treatment plans has not been fully elucidated. There is a paucity of information pertaining to the optimal frequency of NWTs, and if it differs based on type of injury. Only one concrete recommendation was found in the literature, exemplifying the uncertainty surrounding its utility. The most common sedative used and recommended is propofol because of its rapid onset, short duration, and reduction of cerebral energy requirements. Dexmedetomidine may be employed to facilitate serial NWTs, and should always be used in the non-intubated patient or if propofol infusion syndrome (PRIS) develops. Midazolam is not recommended due to tissue accumulation and residual sedation confounding a reliable NWT. Thus, NWTs are well-tolerated in selected patients and remain recommended as the gold-standard for continued neuromonitoring. Predicated upon one expert panel, they should be performed at least one time per day. Propofol or dexmedetomidine are the main sedative choices, both enabling a rapid awakening and consistent NWT.

Detection of Impaired Cerebral Autoregulation Using Selected Correlation Analysis: A Validation Study

Multimodal brain monitoring has been utilized to optimize treatment of patients with critical neurological diseases. However, the amount of data requires an integrative tool set to unmask pathological events in a timely fashion. Recently we have introduced a mathematical model allowing the simulation of pathophysiological conditions such as reduced intracranial compliance and impaired autoregulation. Utilizing a mathematical tool set called selected correlation analysis (sca), correlation patterns, which indicate impaired autoregulation, can be detected in patient data sets (scp). In this study we compared the results of the sca with the pressure reactivity index (PRx), an established marker for impaired autoregulation. Mean PRx values were significantly higher in time segments identified as scp compared to segments showing no selected correlations (nsc). The sca based approach predicted cerebral autoregulation failure with a sensitivity of 78.8% and a specificity of 62.6%. Autoregulation failure, as detected by the results of both analysis methods, was significantly correlated with poor outcome. Sca of brain monitoring data detects impaired autoregulation with high sensitivity and sufficient specificity. Since the sca approach allows the simultaneous detection of both major pathological conditions, disturbed autoregulation and reduced compliance, it may become a useful analysis tool for brain multimodal monitoring data.

Subdural Empyema in the Setting of Multimodal Intracranial Monitoring

BACKGROUND

Multimodal intracranial monitoring is becoming an increasingly common tool in the management of patients with traumatic brain injury. Although numerous reports detailing the benefits of such advanced monitoring exist in the literature, there is minimal discussion of the possible complications that may arise in this patient population.

CASE DESCRIPTION

We report the case of a 32-year-old patient who had been assaulted and presented initially at an outside facility with a Glasgow Coma Scale score of 8. After transfer to our hospital, his Glasgow Coma Scale score was noted at 7T and multimodal monitoring with the Integra Licox brain tissue oxygen monitor and the Hemedex Bowman perfusion monitor was implemented, along with an external ventricular drain when a standard intracranial pressure monitor indicated increasing intracranial pressure. The patient's intracranial pressure normalized but he did require a course of antibiotics during this time for a fever and methicillin-resistant Staphylococcus aureus. The patient subsequently developed multifocal subdural empyemas requiring surgical evacuation. Postoperatively, the patient's intraoperative cultures remained without bacterial growth, likely related to the 2-week broad-spectrum antibiotic use.

CONCLUSIONS

To our knowledge, this is the first reported incidence of a subdural empyema developing in this setting. Although the safety profile of multimodal intracranial modeling is excellent, with increasing numbers of invasive bedside procedures, neurosurgeons must remain acutely vigilant for the development of infectious complications.