Introduction to Neurocritical Care

Neurocritical care is a super-specialized zone where intensive care is provided to patients with neurological and neurosurgical diagnosis. It provides both medical and surgical treatments to life-threatening conditions in such patients [1]. The first neurocritical care unit (NCCU) was established in 1932 at the Johns Hopkins University by a neurosurgeon named Walter Dandy and was solely dedicated to postoperative monitoring of neurosurgical patients under the guidance of anesthesiologists [2]. The earliest involvement of neurologists was in the 1950s in Europe during the poliomyelitis epidemic when neurosurgical patients required ventilator support due to bulbar and neuromuscular weakness [3, 4]. Neurosurgical conditions, including both nontraumatic (brain tumors, subarachnoid hemorrhage (SAH), intracranial aneurysms, spinal cord tumors, multiple spinal instrumentation) and traumatic (traumatic brain injury, spinal cord injury) mechanisms, might require intensive care support. In neurological conditions like myasthenia gravis, status epilepticus, and Guillian–Barré syndrome, acute ischemic stroke often requires intensive care intervention. A focused history and comprehensive neurological examination is the key to any treatment strategy for patients admitted to the NCCU. The important components of medical history include information from relatives, time since the symptoms first appeared, past psychiatric treatment, drug abuse, or any other significant medical details. The examination comprises higher mental function assessment followed by motor examination, sensory evaluation, cranial nerve examination, and testing of coordination, gait, and reflexes. The level of consciousness assessment is prudent in any neurological or neurosurgical patient. Apart from assessing arousal, which includes spontaneous eye opening, fixed gaze, and purposeful voluntary movements, various scores are used in the NCCU to monitor the level of consciousness, including the Glasgow Coma Scale (GCS), the GCS-Pupil (GCS-P), and the Full Outline of Unresponsiveness (FOUR) score. The main difference between the GCS score and GCS-P score is that the latter assesses brain stem function, i.e., the pupillary reflex. In the GCS-P score, the pupillary reactivity score is subtracted by the GCS score. The pupillary reactivity score is summarized as follows: both pupils are nonreactive to light: 2; single pupil is reactive to light: 1; and both pupils are reactive to light: 0 [5]. The minimum value in the GCS score is 3, whereas for the GCS-P score, it is 1. The FOUR score, apart from the level of consciousness assessment, also provides additional information on brain stem function, breathing pattern, visual tracking, and respiratory drive [6]. Delirium is a fluctuating state characterized by altered attention, spatiotemporal disorientation, disorganized thinking, and alteration of awareness. Delirious patients can be hypoactive, hyperactive, or, alternatively, both. Tools like the Confusion Assessment Method for the Intensive Care Unit (ICU) (CAM-ICU) [7] or the ICU Delirium Screening Checklist (ICU DSC) [8] can be used to assess the presence and degree of delirium. In these patients, neuroimaging plays multiple roles both during the acute phase and at the time of follow-up or the monitoring phase. In the acute phase, most of the time, computed tomography (non-contrast) of the head suffices, which helps in differentiating structural causes from nonstructural ones. Magnetic resonance imaging (MRI) may be indicated in some patients to identify smaller ischemic lesions. During monitoring or the follow-up phase, imaging modalities are helpful in identifying secondary brain injuries. More advanced neuroimaging modalities like MR spectroscopy, positron imaging tomography, etc. can help in predicting the outcome in patients with traumatic brain injury [9]. Neuromonitoring is a robust tool for neurointensivists who manage patients in the NCCU. The aims of neuromonitoring are to diagnose worsening neurological function, identify secondary brain injuries, improve the pathophysiological understanding of cerebral disease in critical illness, provide clear physiological data to guide and individualize therapy, and assist in prognostication [10]. Introduction of advanced monitoring modalities to the management of neurocritically ill patients has been shown to improve the overall outcome [11]. Various monitoring methods that can be used in the NCCU include intracranial pressure (ICP), cerebral oximetry, jugular venous oximetry (SjvO2), brain tissue oxygen tension (PbtO2), transcranial Doppler (TCD), cerebral microdialysis, electroencephalography (EEG), and somatosensory evoked potential (SSEP) [10]. Neurological biomarkers are quantitative indicators of brain dysfunction following neurological injuries. These include s-100β, neuron-specific enolase (NSE), amyloid-β and tau, glial fibrillary acidic protein, etc. An emerging body of evidence suggests that multi-marker panels may enhance sensitivity and specificity for acute neurological injury [12, 13].