INCREASED INTRACRANIAL PRESSURE

A limited volume of extra tissue, blood, CSF, or edema can be added to the intracranial contents without raising the intracranial pressure (ICP). Clinical deterioration or death may follow increases in ICP that shift intracranial contents, distort vital brainstem centers, or compromise cerebral perfusion. Cerebral perfusion pressure (CPP), defined as the mean arterial pressure (MAP) minus the ICP, is the driving force for circulation across capillary beds of the brain; decreased CPP is a fundamental mechanism of secondary ischemic brain injury and constitutes an emergency that requires immediate attention. In general, ICP should be maintained at <20 mmHg and CPP should be maintained at ≥60 mmHg.

CLINICAL FEATURES

Elevated ICP may occur in a wide range of disorders including head trauma, intracerebral hemorrhage, subarachnoid hemorrhage (SAH) with hydrocephalus, and fulminant hepatic failure.

Symptoms of high ICP include drowsiness, headache (especially a constant ache that is worse upon awakening), nausea, emesis, diplopia, and blurred vision. Papilledema and sixth nerve palsies are common. If not controlled, cerebral hypoperfusion, pupillary dilation, coma, focal neurologic deficits, posturing, abnormal respirations, systemic hypertension, and bradycardia may result.

Masses that cause raised ICP also distort midbrain and diencephalic anatomy, leading to stupor and coma. Brain tissue is pushed away from the mass against fixed intracranial structures and into spaces not normally occupied. Posterior fossa masses, which may initially cause ataxia, stiff neck, and nausea, are especially dangerous because they can both compress vital brainstem structures and cause obstructive hydrocephalus.

Herniation syndromes (Fig. 21-1) include:

FIGURE 21-1
hmom20_ch21_f001.png

Types of cerebral herniation. A. Uncal; B. central; C. transfalcial; D. foraminal.

  • Uncal: Medial temporal lobe displaced through the tentorium, compressing the third cranial nerve and pushing the cerebral peduncle of the midbrain against the tentorium, leading to ipsilateral pupillary dilation, contralateral hemiparesis, and posterior cerebral artery compression.
  • Central: Downward displacement of the thalamus through the tentorium; miotic pupils and drowsiness are early signs.
  • Transfalcial: Cingulate gyrus displaced under the midline falx, leading to anterior cerebral artery compression.
  • Foraminal: Cerebellar tonsils displaced into the foramen magnum, causing medullary compression and respiratory arrest.

Treatment: Increased Intracranial Pressure

  • A number of different interventions may lower ICP, and ideally the selection of treatment will be based on the underlying mechanism responsible for the elevated ICP (Table 21-1).
  • With hydrocephalus, the principal cause of elevated ICP is impaired CSF drainage; in this setting, ventricular drainage of CSF may be sufficient.
  • If cytotoxic edema is responsible, as in head trauma or stroke, use of osmotic diuretics such as mannitol or hypertonic saline is an appropriate early step.
  • Elevated ICP may cause tissue ischemia; resulting vasodilation can lead to a cycle of worsening ischemia. Paradoxically, administration of vasopressor agents to increase MAP may actually lower ICP by increasing perfusion; therefore, hypertension should be treated carefully, if at all.
  • Free water should be restricted.
  • Fever should be treated aggressively.
  • Hyperventilation is best used for only short periods of time until a more definitive treatment can be instituted.
  • ICP monitoring may help guide medical and surgical decisions in selected pts with cerebral edema (Fig. 21-2).

After stabilization and initiation of the above therapies, a CT scan (or MRI, if feasible) is performed to delineate the cause of the elevated ICP. Emergency surgery is sometimes necessary to decompress the intracranial contents in cerebellar stroke with edema, surgically accessible tumor, and subdural or epidural hemorrhage.

TABLE 21-1: Stepwise Approach to Treatment of Elevated Intracranial Pressure (ICP)a

Insert ICP monitor—ventriculostomy versus parenchymal device

General goals: maintain ICP <20 mmHg and CPP ≥60 mmHg. For ICP >20–25 mmHg for >5 min:

  1. Elevate head of the bed; midline head position
  2. Drain CSF via ventriculostomy (if in place)
  3. Osmotherapy—mannitol 25–100 g q4h as needed (maintain serum osmolality <320 mosmol) or hypertonic saline (30 mL, 23.4% NaCl bolus)
  4. Glucocorticoids—dexamethasone 4 mg q6h for vasogenic edema from tumor, abscess (avoid glucocorticoids in head trauma, ischemic and hemorrhagic stroke)
  5. Sedation (e.g., morphine, propofol, or midazolam); add neuromuscular paralysis if necessary (pt will require endotracheal intubation and mechanical ventilation at this point, if not before)
  6. Hyperventilation—to PaCO2 30–35 mmHg (short-term use or skip this step)
  7. Pressor therapy—phenylephrine, dopamine, or norepinephrine to maintain adequate MAP to ensure CPP ≥60 mmHg (maintain euvolemia to minimize deleterious systemic effects of pressors). May adjust target CPP in individual pts based on autoregulation status.
  8. Consider second-tier therapies for refractory elevated ICP
    1. Decompressive craniectomy
    2. High-dose barbiturate therapy (“pentobarb coma”)
    3. Hypothermia to 33°C

aThroughout ICP treatment algorithm, consider repeat head computed tomography to identify mass lesions amenable to surgical evacuation. May alter order of steps based on directed treatment to specific cause of elevated ICP.
Abbreviations: CPP, cerebral perfusion pressure; CSF, cerebrospinal fluid; MAP, mean arterial pressure; PaCO2, arterial partial pressure of carbon dioxide.
FIGURE 21-2
hmom20_ch21_f002.png

Intracranial pressure (ICP) and brain tissue oxygen monitoring. A ventriculostomy allows for drainage of cerebrospinal fluid to treat elevated ICP. Fiberoptic ICP and brain tissue oxygen monitors are usually secured using a screwlike skull bolt. Cerebral blood flow and microdialysis probes (not shown) may be placed in a manner similar to the brain tissue oxygen probe.

Outline

INCREASED INTRACRANIAL PRESSURE is a sample topic from the Harrison's Manual of Medicine.

To view other topics, please or .

Harrison’s Manual of Medicine 20th edition provides 600+ internal medicine topics in a rapid-access format. Download Harrison’s App to iPhone, iPad, and Android smartphone and tablet. .