ABIM Neurocritical key terms

Hypoperfused but still viable brain tissue surrounding an infarct core, at risk of infarction yet potentially salvageable if blood flow is restored quickly. Its presence is the main rationale for emergent reperfusion therapy.

Blockage of a major intracranial artery, typically the internal carotid, proximal middle cerebral, or basilar artery, producing a large threatened territory. It often warrants endovascular thrombectomy in addition to thrombolysis.

Endovascular removal of clot from an intracranial artery using a stent retriever or aspiration catheter. Benefit is greatest when reperfusion is rapid and the infarct core is small in a patient with large vessel occlusion.

Severe progressive swelling of an infarcted hemisphere, usually after a large middle cerebral artery stroke, causing mass effect, herniation, and death. Decompressive surgery can be lifesaving in selected younger patients.

Focal contrast enhancement within an intracerebral hemorrhage on CT angiography, indicating active bleeding. It predicts hematoma expansion and poor outcome and can influence decisions about blood pressure control and reversal therapy.

Neurologic deterioration or new infarction occurring days after aneurysmal subarachnoid hemorrhage, driven by vasospasm, impaired autoregulation, and microthrombosis. Prevention centers on monitoring and maintaining euvolemia and adequate perfusion pressure.

Occlusion of dural sinuses or cortical veins producing headache, seizures, focal deficits, and hemorrhagic infarction. Anticoagulation is indicated even when hemorrhage is present, because the underlying problem is venous obstruction.

The principle that the skull is a rigid container holding brain, blood, and cerebrospinal fluid, so an increase in one component must be offset by a decrease in another or intracranial pressure rises.

The triad of hypertension, bradycardia, and irregular respiration caused by markedly raised intracranial pressure and brainstem ischemia. It is a late, ominous sign of impending herniation rather than an early warning.

Widespread shearing damage to white matter tracts from rotational acceleration-deceleration forces. It produces immediate coma out of proportion to initial CT findings and is best demonstrated on MRI.

Loss of sympathetic vascular tone after high cervical or upper thoracic spinal cord injury, causing hypotension with bradycardia rather than tachycardia. Treatment combines cautious volume resuscitation with vasopressors, usually norepinephrine.

Continuous seizure activity, or repeated seizures without recovery of consciousness, lasting long enough to risk neuronal injury, conventionally five minutes for convulsive seizures. It requires immediate benzodiazepines followed by a second-line antiseizure drug.

Prolonged electrographic seizure activity without prominent motor signs, presenting as altered consciousness, subtle twitching, or gaze deviation. Diagnosis requires EEG, and it is common in critically ill patients who fail to awaken.

An EEG pattern of high-voltage activity alternating with periods of near-flat suppression, used as a sedation target in refractory status epilepticus or for neuroprotection. It is titrated to a specified burst-suppression interval.

Repetitive, stereotyped sharp waves or spikes occurring at regular intervals over one hemisphere. They reflect focal cortical injury, most often from acute stroke, hemorrhage, or infection, and may be ictal in some patients.

Prolonged, usually video-linked recording used in the ICU to detect nonconvulsive seizures and to track sedation depth and reactivity. It is indicated in unexplained coma after convulsions, during neuromuscular blockade, and in refractory status epilepticus.

An acute immune-mediated polyradiculoneuropathy causing ascending weakness, areflexia, and possible respiratory or bulbar failure. ICU management centers on serial respiratory measurement and autonomic monitoring, alongside IVIG or plasma exchange.

Respiratory or bulbar weakness severe enough to threaten airway protection in myasthenia gravis, often triggered by infection or a medication change. Treatment uses plasma exchange or IVIG while avoiding drugs that impair neuromuscular transmission.

Acquired diffuse weakness, often with atrophy and reduced membrane excitability, developing after days of critical illness, sepsis, corticosteroids, or neuromuscular blockade. It prolongs ventilator dependence and is separated from neuropathy mainly by electrophysiologic testing.

A bedside measure of inspiratory muscle strength obtained when the patient inhales forcibly against an occluded airway. Trending it with vital capacity helps time intubation and extubation in neuromuscular respiratory weakness.

A state of unresponsiveness in which neither arousal nor awareness is present, with eyes closed and no response to command. It arises from dysfunction of the ascending reticular activating system or of both cerebral hemispheres.

A condition in which patients open their eyes and show sleep-wake cycles but have no reproducible awareness of self or environment. It differs from coma in that wakefulness is preserved without consciousness.

The irreversible cessation of all cerebral and brainstem function, including the drive to breathe, in a patient with a known cause and no confounders. It is a clinical diagnosis supported by a positive apnea test.

A procedure in which ventilator support is withdrawn while oxygen is supplied, to demonstrate absence of respiratory drive at a threshold carbon dioxide level. It completes the clinical determination of death by neurologic criteria.

Renal salt and water loss causing hyponatremia with hypovolemia after brain injury or subarachnoid hemorrhage. It is treated with volume and salt replacement, in contrast to the fluid restriction used for SIADH.

Deficient antidiuretic hormone release, often after pituitary or hypothalamic injury, producing large volumes of dilute urine, hypernatremia, and hyperosmolality. Treatment replaces free water and uses desmopressin cautiously.

Transient left ventricular dysfunction with reduced ejection fraction and troponin release after severe brain injury or subarachnoid hemorrhage, caused by catecholamine surge. It can produce pulmonary edema and hypotension that complicate blood pressure and vasopressor targets.

The pressure within the cranial cavity, normally below roughly 15 mmHg in adults. Sustained elevation threatens cerebral perfusion and causes herniation, so it is monitored with parenchymal probes or ventricular catheters.

The perfusion gradient across the brain, calculated as mean arterial pressure minus intracranial pressure. Targets aim to keep it high enough for adequate blood flow without relying on excessive vasopressor doses.

A directly measured local oxygen level in brain parenchyma reflecting the balance of oxygen delivery and consumption. Low values prompt adjustment of inspired oxygen, perfusion, or hemoglobin in severe traumatic brain injury.

A moving correlation between intracranial pressure and mean arterial pressure used to estimate cerebral autoregulation. It helps individualize blood pressure targets so perfusion pressure stays within the autoregulating range.

Ultrasound measurement of flow velocity in major intracranial arteries through the skull. It detects vasospasm, assesses autoregulation and microemboli, and can suggest raised intracranial pressure from waveform changes.

A rare, often fatal complication of high-dose or prolonged propofol infusion causing metabolic acidosis, rhabdomyolysis, hyperkalemia, renal failure, and cardiac dysfunction. Management requires stopping the drug and providing supportive care.

Diffuse brain dysfunction from organ failure, electrolyte disturbance, drugs, or infection, presenting with fluctuating attention and confusion. It is a diagnosis of exclusion that warrants thorough evaluation for structural and infectious causes.

Administration of mannitol or hypertonic saline to draw water out of brain tissue and lower intracranial pressure. It is used for acute deterioration and cerebral edema, with attention to osmolality, sodium, and renal function.

A catheter placed into the lateral ventricle to measure intracranial pressure and drain cerebrospinal fluid. It also permits therapeutic drainage for hydrocephalus and delivery of intraventricular drugs such as antibiotics or alteplase.

The planned discontinuation of interventions such as mechanical ventilation or vasopressors when they no longer serve the patient's goals. It is ethically and legally accepted and should follow clear family communication and symptom control.

A person authorized to make health care decisions for an incapacitated patient, guided by the patient's known wishes or, failing that, by best interests. Early identification and documentation in the ICU reduce later conflict.