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Neurologic Emergencies and Neurocritical Care
Clinical Vignette
A 62-year-old man with hypertension and diabetes mellitus type 2 was brought to the emergency department via Emergency Medical Services for evaluation of acute onset of obtundation. Over the course of approximately 1 minute, he changed from being fully alert and talking normally to minimally responsive. En route, his vital signs were blood pressure 156/82 mm Hg, pulse 92 beats/minute, oxygen saturation 95% on 2 L via nasal cannula. A finger stick glucose was 197 mg/dL.
He is stuporous on initial examination. His Glasgow Coma Score is 8 (verbal 2, eyes 1, motor 5). There is anisocoria (right pupil 6 mm and unreactive to direct and indirect light, left pupil 3 mm and briskly responsive to direct and indirect light). At primary gaze, the right eye is inferior and lateral relative to the position of the left eye ( Fig. 12.1 ). There is decreased tone in all extremities but more so on the left. To noxious stimulation, his right arm localizes, the left arm withdraws minimally, and his legs withdraw equally to a painful stimulus.
The differential diagnosis for abrupt onset stupor/coma is quite broad. Rapid assessment of reversible and treatable causes is paramount. Although multiple metabolic derangements can present with coma, rarely do they result in focal neurologic deficits as seen in this patient. Right cranial nerve III (oculomotor) dysfunction and asymmetric motor responses to pain in the upper extremities should prompt concern for a structural central nervous system etiology. The examination suggests midbrain dysfunction potentially consistent with vertebrobasilar ischemia or a transtentorial herniation syndrome. Rapid symptom onset fits best with either seizure or cerebrovascular etiology. Consideration of intracranial hemorrhage within any compartment (epidural, subdural, subarachnoid, intraparenchymal), and large vessel occlusion with ischemia or infarction are most likely. An immediate noncontrast head computed tomography (CT) is indicated and can assist with diagnosis.
The patient underwent a noncontrast head CT ( Fig. 12.2 ), which demonstrated an acute-on-subacute large right subdural hematoma. There is associated compression of the right hemisphere with subfalcine and uncal herniation. Neurosurgery completed an emergent craniotomy and subdural evacuation with limited radiographic improvement but excellent clinical improvement. Additional investigation revealed an acquired von Willebrand factor deficiency, which was likely to be the primary contributor to his spontaneous subdural hemorrhage.
Introduction
Nearly all subspecialties of neurology can have patients present with a life-threatening emergency. Over the past 15 years, many healthcare systems have created dedicated neurocritical care units and/or teams of neurocritical care providers who are specifically trained to care for this complex group of patients. With the ever-growing field of neurointensive care, the emphasis on early diagnosis and management to limit secondary injury is vital because there are still limitations in curative therapies.
Many of the other chapters in this work address specific disease processes in more detail. Diseases commonly managed in neurocritical care include severe traumatic brain injury (TBI), which is the leading cause of death between the ages of 1 and 45 ( Chapter 19 ), large vessel ischemic stroke, which constitutes approximately 3% of all ischemic stroke in the United States ( Chapter 15 ), status epilepticus occurring with an incidence of 41 cases per 100,000 ( Chapter 23 ), and subarachnoid hemorrhage ( Chapter 17 ). Together, they comprise a substantial portion of emergency and acute neurologic care.
Principles of Emergency Neurology and Neurocritical Care
The principles that guide management of any life-threatening emergency also hold true for care of acute neurologically injured patients. The dogged approach of A-B-Cs (airway-breathing-circulation) remains:
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Airway: ensure a patent airway via oropharyngeal suctioning, and assess the potential need for intubation. If needed, ensure adequate cervical spine stabilization
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Breathing: evaluate oxygenation and ventilation. Augment as needed to maintain normal oxygenation and ventilation
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Circulation: evaluate end organ perfusion via blood pressure monitoring and organ function. Administer intravenous crystalloid and blood products as needed to ensure adequate perfusion.
After addressing the A-B-Cs as noted previously, there is additional focus on D (disability) in the management of potential acute neurologic injury:
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Disability: although a rapid Glasgow Coma Scale ( Fig. 12.3 ) and brief cranial nerve examination are adequate for an initial rapid assessment, there needs to be a more thorough neurologic examination completed once the patient is stabilized. This may be a full neurologic examination or a thorough coma examination, depending on the patient's level of consciousness.
Clinical history may be limited in the very early stages of care, but prodromal symptoms (fever, behavioral change, headache, neurologic dysfunction), past medical history, and environmental factors (ingestion, trauma) are important and may substantially impact clinical decision making, diagnostic testing, and early treatment. High clinical suspicion for neurologic injury in those presenting with encephalopathy and/or coma is appropriate and may lead to early identification of cerebrovascular disease, structural brain lesion(s), or central nervous system (CNS) infection. The rapid neurologic assessment begins the goal of lesion localization.
Preservation of Normal Neurologic Function
Although the early restoration of normal neurologic function is ideal, commonly neurologic injuries are not fully reversible. Much of the focus in the management of neurologic emergencies and neurocritical care is the maintenance of normal neurologic physiology—ensuring adequate delivery of glucose and oxygen, removal of carbon dioxide, cessation of seizure activity, and maintenance of normal intracranial pressure (ICP)—to prevent secondary brain injury.
As noted previously, the neurologic assessment follows cardiopulmonary stabilization. This emphasizes the dynamic physiologic interplay between the cardiac, pulmonary, and nervous system. Injured brain/spinal cord has a reduced physiologic reserve compared with uninjured tissue. Normal cerebral autoregulation allows for maintenance of blood flow over a broad range of mean arterial pressure (MAP = 
systolic blood pressure + 
diastolic blood pressure), but injured brain can lose this autoregulatory feature. As a result, hypotension will cause oligemia or ischemia, whereas hypertension results in hyperperfusion. Although management of global hypoperfusion is addressed by standard resuscitation efforts, focal hypoperfusion as seen in ischemic stroke may be effectively reversed or reduced with prompt diagnosis and intervention as appropriate (intravenous tissue plasminogen activator [tPA] or mechanical thrombectomy). Normal brain perfusion is 25–50 mL blood/g brain tissue/min. If perfusion drops to 5 mL blood/g brain tissue/min, there is electrical quiescence (essentially brain function cessation given lack of oxygen, blood, and nutrients), and at less than 2 mL/g brain tissue/min, there is neuronal cell death.
Although maintenance of normotension is ideal, this may not be adequate to ensure normal brain perfusion. As there is normal intraarterial and venous pressure, so too is there a normal physiologic range for ICP. The cranial vault is a fixed volume encased by the calvarium with different compartments established by the dura. The ICP results from the volume of brain, blood, and cerebrospinal fluid within the cranial vault ( Fig. 12.4 ). In a normal physiologic state, the ICP is the same throughout the compartments (typically <20 mm H 2 O). However, in brain injury, there can be global elevation in the ICP, compartmental increase in ICP, or a combination of global and regional intracranial hypertension. Maintenance of normal ICP may require medical or surgical treatments, as discussed later, and is critical to survival and the preservation of neurologic function.
Specific Disease Processes
Coma/Stupor
Coma is the loss of awareness of external stimuli and voluntary reaction to these stimuli. There are varying degrees of coma, discussed in detail in Chapter 13 . The differential diagnosis for coma is broad and is not limited to central nervous system etiology.
The initial evaluation of comatose patients includes early treatment of reversible causes—typically considered toxic or metabolic—such as hypoglycemia, drug intoxication, uremia, and hyperammonemia. A thorough general physical examination may give clues to the underlying etiology. A neurologic examination will be limited, but abnormal findings indicative of focal or regional brain dysfunction can assist with determining central nervous system localization and potential causes. Most patients presenting in coma will undergo central nervous system imaging with noncontrast head computed tomography (CT). Many of the findings that would result in coma—intracerebral hemorrhage, hydrocephalus, brainstem compression—will be obvious, but subtle findings of anoxic brain injury or diffuse TBI may not be present on noncontrast head CT.
An important point of care in the comatose patient is to not prognosticate very early in the hospital course. While still determining the etiology of coma, in the presence of severe organ dysfunction or recent exposure to drugs or medications, it may be impossible to accurately predict an individual's clinical outcome. Providers tend to have a bias toward negative outcomes in the earliest points of critical neurologic illness, yet some comas are partially or fully reversible.
Intracranial Hypertension/Herniation
As touched on earlier in the chapter, intracranial hypertension and herniation is a feared complication of many neurologic diseases. There are multiple causes of increased ICP, including both central nervous system etiologies and systemic causes, such as fulminant cirrhosis. Patients with increased ICP can present with headache, papilledema, nausea, and vomiting that may progress to stupor/coma. If herniation occurs, focal weakness, pupillary changes, posturing, and cardiopulmonary arrest may occur ( Fig. 12.5 ).
The initial evaluation of patients presenting with signs/symptoms of increased ICP are rapid treatment followed by determining the cause. It may be appropriate to treat these patients with hyperosmolar therapy prior to obtaining CNS imaging, because herniation is a life-threatening illness that can result in irreversible neurologic injury. Early treatment consists of maneuvers to decrease ICP—elevation of the head of bed, maintaining the head in midline, and ensuring adequate pain control and sedation if intubated. Inducing hyperventilation in intubated patients with elevated ICP can provide a transient reduction in ICP by causing vasoconstriction of intracerebral vessels. However, the effect of hyperventilation lasts only a few minutes and carries the risk of ischemic brain injury. It should therefore only be used as a bridge to more definitive therapy such as hyperosmolar therapy or neurosurgical intervention.
There are two primary etiologies of cerebral edema: vasogenic and cytotoxic. Vasogenic edema results from an inflammatory process resulting in flow from the vasculature into the interstitial space. This is commonly seen with brain tumors and responds to treatment with high-dose steroids. Cytotoxic edema results from cellular death, such as following an ischemic stroke, and can respond to hyperosmolar therapy like mannitol and/or hypertonic saline.
The cranial vault is divided into different compartments by the dura—cerebral falx (left and right hemisphere) and the cerebellar tentorium (supratentorial and infratentorial fossa). When there is a pressure gradient different from one compartment to another, there is shift of brain tissue and resultant neuronal dysfunction. Subfalcine herniation results in a lateral hemisphere moving under the cerebral falx and compressing the anterior cerebral arteries, causing potential lower extremity paraparesis. Uncal herniation is movement of the medial temporal lobe (the uncus) across the cerebral tentorium and compressing the midbrain. Upward herniation results from posterior fossa lesion causing herniation of the cerebellum upward and causing compression of the midbrain. Additional herniation from the posterior fossa can cause the cerebellar tonsils to move into the foramen magnum and result in medulla and spinal cord compression. Lastly, if there is a breach in the cranial vault (from a hemicraniectomy), brain tissue can herniate out of the vault, termed fungating herniation.
Acute Ischemic Stroke
Nearly 800,000 strokes occur every year in the United States and result in more than 100,000 deaths and is a leading cause of disability. Advances in endovascular interventions have changed the acute stroke treatment paradigm. Despite these advances, there are still many ischemic strokes that are either unsuccessfully treated or cannot be treated.
Chapter 15 contains much more detail than what is presented here. Rapid evaluation for eligibility for intravenous tissue plasminogen activator (tPA) and/or endovascular therapy are still paramount in acute ischemic stroke evaluation. There are specific stroke processes that may require intensive care management. Large vessel occlusion that does or does not undergo endovascular therapy should have close neurologic monitoring given the potential for reperfusion injury or malignant cerebral edema.
Commonly, postintraarterial therapy uses blood pressure augmentation in attempts to maintain perfusion to at-risk tissue. For those with large-vessel occlusion, resultant cytotoxic edema can result in herniation, and the potentially life-saving hemicraniectomy may need to be offered ( Fig. 12.6 ). Another feared complication is hemorrhagic conversion of a stroke following intravenous (IV) tPA or endovascular therapy ( Fig. 12.7 ). This may require reversal of tPA and strict blood pressure augmentation. There is no true reversal agent for tPA, but given that it degrades fibrin administration of fibrin-rich products such as fresh frozen plasma, cryoprecipitate and fibrinogen concentrate can promote thrombus formation. Lastly, posterior circulation ischemic strokes require frequent neurologic examinations because obstructive hydrocephalus in the days following ictus may require acute neurosurgical intervention such as placement of an external ventricular drain (EVD) and/or suboccipital craniectomy.
Prognosis from large vessel ischemic stroke has drastically improved within the past several years, mainly as a result of the advances in endovascular therapy. Individuals with large vessel ischemic strokes are more likely to have a good neurologic functional outcome if there is a small area of core infarct and if the team is able to achieve reperfusion of the at-risk brain tissue as quickly as possible from the onset of stroke symptoms.
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