Nervous System Disorders in Critical Care¶
Chapter 318 | Part 8: Critical Care Medicine
KEY CLINICAL POINTS¶
- Management of intracranial pressure (ICP) is critical in preventing secondary brain injury, with goals of maintaining ICP <20 mmHg and cerebral perfusion pressure (CPP) ≥ 60 mmHg.
- Secondary brain insults (e.g., hypoxia, hypotension, fever) are common in critical illness and require aggressive prevention and treatment to avoid irreversible damage.
- Hyperperfusion syndromes (e.g., posterior reversible encephalopathy syndrome) and osmotic demyelination syndrome (central pontine myelinolysis) are distinct but potentially reversible conditions with specific etiologies and treatments.
- Critical illness polyneuropathy and ICU-acquired weakness are common complications of prolonged critical illness, requiring supportive management and early intervention.
- Neurotoxicity from immunotherapies (checkpoint inhibitors, CAR-T) and neuromuscular blocking agents (NMBAs) necessitates close monitoring and prompt treatment.
1. DEFINITION & OVERVIEW¶
Nervous system disorders in critical care encompass a wide range of conditions affecting the CNS and PNS, including traumatic brain injury, stroke, infections, metabolic encephalopathies, and complications of critical illness. These disorders often result from primary insults or secondary mechanisms such as hypoxia, ischemia, or systemic inflammation. The focus is on neurologic tissue preservation, prevention of secondary injury, and management of life-threatening neurologic complications.
1.1 Neurologic Critical Care Focus¶
Critical care neurology prioritizes maintaining cerebral perfusion, preventing secondary brain injury (e.g., ischemia, edema, herniation), and managing complications of systemic illness. Key interventions include ICP monitoring, neuroimaging, and targeted therapies for specific pathologies.
1.2 Common Neurologic Emergencies¶
Life-threatening neurologic conditions include sudden cardiac death (SCD), stroke, intracranial hemorrhage, status epilepticus, and sepsis-associated encephalopathy. Early recognition and intervention are critical to improve outcomes.
2. EPIDEMIOLOGY¶
Neurologic disorders in critical care are common in ICU settings, with incidence influenced by underlying conditions (e.g., sepsis, trauma, stroke). Risk factors include advanced age, comorbidities, and systemic inflammation. Mortality is high in severe cases, particularly with refractory ICP elevation or brainstem dysfunction.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Pathophysiology involves primary insults (e.g., trauma, stroke) and secondary mechanisms (e.g., ischemia, edema, hypoxia). Key processes include: - Brain edema (vasogenic vs. cytotoxic) - Ischemic cascade (excitotoxicity, free radicals, apoptosis) - Cerebral autoregulation and perfusion pressure - Neuroinflammation and immune-mediated injury
3.1 Brain Edema Mechanisms¶
Vasogenic edema (BBB disruption) and cytotoxic edema (cellular swelling) are central to secondary brain injury. Both contribute to increased ICP and cerebral herniation.
3.2 Ischemic Cascade¶
Ischemia triggers excitotoxicity (glutamate release), calcium influx, and free radical formation, leading to necrotic or apoptotic cell death. Cerebral autoregulation failure exacerbates perfusion deficits.
4. CLINICAL FEATURES¶
Clinical manifestations vary by etiology but include altered mental status, focal neurological deficits, seizures, and signs of increased ICP (e.g., papilledema, Cushing's triad). Complications include brain herniation, secondary ischemia, and long-term neurocognitive deficits.
4.1 Altered Mental Status¶
Confusion, delirium, or coma may result from metabolic encephalopathy, hypoxia, or direct CNS injury. Prognostic indicators include pupillary abnormalities and motor responses.
4.2 Signs of Increased ICP¶
Headache, vomiting, papilledema, and Cushing's triad (hypertension, bradycardia, irregular respirations) are critical signs requiring immediate intervention.
5. DIFFERENTIAL DIAGNOSIS¶
Differential diagnosis includes stroke, intracranial hemorrhage, metabolic encephalopathy, sepsis-associated encephalopathy, and drug-induced neurotoxicity. Structural vs. metabolic causes must be distinguished to guide management.
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnostic tools include neuroimaging (CT, MRI), EEG, lumbar puncture, and CSF analysis. Criteria for elevated ICP and specific syndromes (e.g., PRES, osmotic demyelination) are essential for accurate diagnosis.
Table 318-1: Neurologic Disorders in Critical Illness¶
| Localization Along Neuroaxis | Syndrome |
|---|---|
| Central Nervous System | Brain: Cerebral Hemispheres |
| Localization Along Neuroaxis | Syndrome |
|---|---|
| Central Nervous System | Spinal Cord |
| Peripheral Nervous System | Axonal Critical Illness Polyneuropathy, Neuromuscular Junction Disorders |
Table 318-2: Stepwise Approach to Treatment of Elevated ICP¶
| Step | Intervention |
|---|---|
| 1 | Elevate head of bed; midline head position |
| 2 | Drain CSF via ventriculostomy (if in place) |
| 3 | Osmotherapy: Mannitol 25–100 g q4h or hypertonic saline |
| 4 | Glucocorticoids for vasogenic edema (avoid in head trauma) |
| 5 | Sedation and neuromuscular paralysis if needed |
| 6 | Hyperventilation to Paco2 30–35 mmHg (short-term) |
| 7 | Pressor therapy to maintain CPP ‡60 mmHg |
| 8 | Decompressive craniectomy or hypothermia for refractory ICP |
6.1 Neuroimaging¶
CT is preferred for acute hemorrhage and structural abnormalities; MRI (DWI, FLAIR) detects ischemia and edema. Angiography identifies vascular causes (e.g., stroke, aneurysm).
6.2 EEG and CSF Analysis¶
EEG detects seizures (e.g., status epilepticus) and encephalopathy. CSF analysis helps differentiate infections (e.g., meningitis) from metabolic causes.
7. MANAGEMENT & TREATMENT¶
Management includes ICP control, seizure prevention, and treatment of underlying causes. Key interventions: osmotic agents, hyperventilation, decompressive craniectomy, and targeted therapies for specific syndromes (e.g., hypothermia for post-cardiac arrest).
7.1 ICP Management¶
Maintain ICP <20 mmHg and CPP ≥ 60 mmHg. Use osmotic agents (mannitol, hypertonic saline), hyperventilation (short-term), and ventriculostomy for CSF drainage.
7.2 Seizure Control¶
Anticonvulsants (e.g., levetiracetam, phenytoin) are used for seizures. EEG monitoring is critical for detecting nonconvulsive status epilepticus.
8. PROGNOSIS & COMPLICATIONS¶
Prognosis depends on the cause and severity of the disorder. Complications include long-term neurocognitive deficits, ICU-acquired weakness, and secondary infections. Early intervention improves outcomes, but severe cases (e.g., refractory ICP) have poor prognoses.
9. SPECIAL CONSIDERATIONS¶
Special populations (e.g., pregnant patients, children, elderly) require tailored approaches. For example, hypothermia is used in post-cardiac arrest care, while ICU-acquired weakness necessitates early physical therapy.
10. KEY POINTS & CLINICAL PEARLS¶
- Prioritize ICP management to prevent secondary brain injury.
- Use EEG and neuroimaging to differentiate metabolic vs. structural causes of altered consciousness.
- Osmotic agents and hyperventilation are first-line for elevated ICP.
- Monitor for ICU-acquired weakness and initiate early rehabilitation.
- Tailor treatment for immunotherapy-related neurotoxicity and drug-induced myopathies.