Christopher R. Newey, DO
DESCRIPTION 
The Monroe–Kelli doctrine states that the cranium is a fixed volume composed of CSF, blood, and brain tissue and that an increase in any of these must be offset by an appropriate decrease in another content. If there is not an appropriate offset, the intracranial pressure (ICP) will increase. Intracranial compliance (i.e., change in volume divided by change in ICP) decreases with increased ICP. This can affect cerebral blood flow by affecting cerebral perfusion pressure (CPP) [i.e., mean arterial pressure (MAP) minus ICP], which ultimately can cause neurological deficits. Normal ICP ranges from 5 to 15 mm Hg. Normal CPP is >50 mm Hg.
EPIDEMIOLOGY
Incidence
The epidemiology varies depending on the underlying etiology.
RISK FACTORS
The risk factors comprise stroke, head injury, intracranial tumor (primary or secondary), CNS infection, and eclampsia.
GENERAL PREVENTION
Avoiding precipitating event, serially monitoring known intracranial lesions.
PATHOPHYSIOLOGY
As mentioned, the Monroe–Kelli doctrine describes the maintenance of normal ICP where if one intracranial constituent increases, another must decrease. Cerebral autoregulation is the natural attempt to maintain cerebral blood flow adequate for metabolic demands of the brain. As ICP increases, the autoregulation curve is disrupted causing a linear increase in cerebral blood pressure with increasing MAP. Once compliance limit has been reached (i.e., an ICP of approximately 20 mm Hg), parenchyma becomes displaced resulting in various herniation syndromes.
ETIOLOGY
- CSF flow obstruction (e.g., tectal mass)
- Mass lesions, e.g., hematoma and neoplasm
- Hemorrhage, e.g., epidural, subdural, intraparenchymal, and subarachnoid
- Venous obstruction, e.g., cerebral venous thrombosis
- Ischemic strokes, especially cerebellar infarcts, NIHSS >20, CT head with >50% MCA involvement, or DWI volume >145 cm3 within 14 hours of event
- Traumatic brain injury
- Infections, e.g., meningitis and encephalitis
- Seizures, e.g., generalized and status epilepticus
- Hepatic encephalopathy
- Malignant hypertension
- Idiopathic, e.g., pseudotumor cerebri
- Eclampsia
- Hydrocephalus
- Pneumoencephalus
COMMONLY ASSOCIATED CONDITIONS
Commonly associated conditions depend on the underlying etiology: Pregnancy, liver/kidney failure, malignancy, cardiovascular disease, and hypercoagulable state.
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HISTORY
Patients may give a history of headache (especially positional with recumbency), nausea/vomiting (especially projectile), blurry vision, difficulty walking, diplopia, weakness, altered mental status, prior cancer, and hematological disorder.
PHYSICAL EXAM
- Assess ABCs
- Determine level of consciousness
- Evaluate for Cushing's triad: Hypertension, bradycardia, and respiratory irregularity. Classic triad is seen infrequently (~33%), but if two signs present examine for increased ICP
- Respiratory patterns can help localize (e.g., Cheyne–Stokes: Bilateral cortex, hyperventilation: Midbrain, apneustic: Pons, cluster: Pons, ataxic: Medulla)
- Fundoscopy examination to evaluate for papilledema and/or engorged retinal veins
- Pupillary response to light: Small reactive (diencephalic), fixed/dilated (3rd nerve), midposition and fixed (midbrain), pinpoint and reactive (pons), and large and fixed with hippus (tectal plate)
- Evaluate cranial nerves for palsy. Cranial nerve VI susceptible to injury with increased ICP but can be false-localizing sign
- Motor examination for posturing (i.e., decorticate and decerebrate) and false-localizing sign (e.g., Kernohan's notch: Weakness ipsilateral to lesion due to herniation and compression of contralateral cerebral peduncle)
- Determine the Glasgow coma examination (GCS) score by determining eye opening (patients 1–4), verbal response (patients 1–5), and motor response (patients 1–6). Maximum score is 15, minimum score is 3
DIAGNOSTIC TESTS AND INTERPRETATION
Lab
Initial Lab Tests
Complete blood counts, coagulation profile including PT/INR and PTT, and type and screen should be ordered in preparation for possible surgical or medical (e.g., FFP) intervention. Metabolic profile. Check serum osmolarity.
Follow-Up & Special Considerations
Daily labs, including blood counts, metabolic profiles, and coagulation panels.
Imaging
Initial Approach
- CT head should be obtained to evaluate for intracranial blood, hydrocephalus, cerebral edema, midline shift, cistern compression, and mass.
- It is estimated that ~10% of patients with increased ICP will have normal head CT.
Follow-Up & Special Considerations
Serial CT heads are indicated to monitor for increasing or decreasing mass effect.
Diagnostic Procedures/Other
- MRI of the brain has little role in the emergent setting of increased ICP. However, it can better define intraparenchymal lesions, such as a tumor.
- Angiography is useful to evaluate for sources of mass effect, such as aneurysm in cases of subarachnoid hemorrhage, large vessel occlusion in cases of ischemic strokes, AV malformations.
- Lumbar punctures are contraindicated in increased ICP. If performed, can lead to brain herniation and eventual death. Once increased ICP has been ruled out, lumbar puncture can safely be performed.
- Indications for ICP monitor include GCS <8 and either an abnormal head CT or ≥2 of the following risk factors (age >40 years, systolic blood pressure <90 mm Hg, and/or decerebrate/decorticate posturing). If hydrocephalus is present in subarachnoid hemorrhage patients, an intraventricular device is needed for external drainage.
- Measurement of intracranial pressure can be accomplished via several anatomic spaces:
- Intraventricular (gold standard) disadvantages: Highest risk of hemorrhage and/or infection, must maintain transducer at the level of the ear. Benefits: Monitoring ICP and also allow for CSF drainage.
- Intraparenchymal: Lower rates of hemorrhage and infection, but cannot recalibrate after placement and readings may vary by 3 mm Hg. No CSF drainage.
- Subdural
- Subarachnoid
- Epidural (typically used in patients with liver failure)
- Other than infection and hemorrhage, other complications of ICP monitoring include malfunction/obstruction and/or malposition.
- Normal ICP is typically defined as <15 mm Hg. ICP waveforms have 3 components. P1 is the arterial wave (or percussion), P2 is the rebound wave (or tidal wave), and P3 is the venous outflow (or dicortic wave). An elevated P2 waveform indicates poor compliance.
Pathological Findings
- Varies depending on the underlying etiology.
- Pathological specimens may show evidence of gliosis, infection/inflammation, hemorrhage, and/or neoplasm.
- On ICP monitoring, the emergence of elevated ICP (20–100 mm Hg) for several minutes to hours is called a plateau wave (Lundberg A wave). Lundberg B waves are an elevation of ICP (10–20 mm Hg) that lasts a few seconds to minutes and are thought to be related to respiratory fluctuations in PaCO2. Lundberg C waves are rapid sinusoidal fluctuations corresponding to arterial pressure.
DIFFERENTIAL DIAGNOSIS
- The differential diagnosis for increased ICP is broad.
- DDx: Seizures, metabolic coma, encephalopathy, dilated pupil from medication or physiological anisocoria, meningeal irritation, migraine
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MEDICATION
First Line
- Osmotic agents:
- Mannitol 20%: Typically loaded at 1–1.5 g/kg followed by maintenance of 0.5 g/kg every 4–6 hours if needed. The goal is titrate to serum osmolarity of 300–320 mOsm. The half life is 0.16 hour but is efficacious up to 1.5–6 hours. Use in caution in renal patients or patients who are volume depleted and/or hypernatremic. Note possible overshoot of ICP when mannitol is discontinued.
- Hypertonic saline (23%): Typically given as a 30 cc bolus >10 minutes via central access followed by 3% hypertonic saline infusion at 1 mL/kg/hour with goal Na of 150–155. Be careful to not infuse 23% too rapidly as pulmonary edema can occur.
ADDITIONAL TREATMENT
General Measures
- A change in the volume of parenchyma, blood, or CSF can affect ICP. Intravascular component occupies ~10% of the space is easiest to change
- Optimize cerebral perfusion pressure (CPP = MAP – ICP) to 60–110 mm Hg since hypotension worsens clinical outcome
- Head of bed 30–45 degrees
- Treat agitation and pain
- Treat fever with acetaminophen and/or cooling devices (either surface or intravascular). An increase in 1°C increases cerebral metabolism and can increase ICP 5–7%
- Avoid hyper- or hypoglycemia
- Avoid hypotonic solutions (e.g., 0.45 NS or lactated ringers, or dextrose containing solutions) but maintain euvolemia
- Minimize shivering
- Prompt nutritional support
- Prophylactically treat for seizures since seizures can increase metabolic demand and affect outcome
- Keep neck straight and avoid jugular vein compression
Additional Therapies
- Hyperventilation to PaCO2 of 25–30 mm Hg can reduce CBF by 3%. If actively herniating and on mechanical ventilation, disconnect patient from ventilation and manually bag. Effective but brief benefit, longer-term deleterious.
- Barbiturates: Pentobarbital at 5–20 mg/kg bolus followed by 1–4 mg/kg/hour titration can reduce metabolic demand and thus decrease ICP. Use with caution in patients with cardiac/respiratory compromise, ileus, infection, or hypotension. Monitor patients with EEG when in coma. Goal pentobarbital level is 3–5 mg%.
- Induced hypothermia to 32–34°C can reduce cerebral oxygen metabolism and reduce inflammation.
- Paralytics can reduce metabolic demand but carry risk of intensive care unit (ICU) myopathy/neuropathy.
- Lidocaine (1.5 mg/kg IVP) prior to endotracheal intubation to blunt the rise in ICP.
- Steroids (dexamethasone 6–10 mg IV) have been shown effective in vasogenic cerebral edema.
COMPLEMENTARY AND ALTERNATIVE THERAPIES
Pain/agitation control as needed with narcotics, sedatives, seizure prophylaxis, control nausea, and vomiting.
SURGERY/OTHER PROCEDURES
Early neurosurgical consultation is necessary in cases of increased ICP. Mortality with medical management alone 50–80%. Surgical decompression (i.e., frontotemporoparietal bone hemicraniectomy) may be an option for malignant cerebral edema in select patients with large infarcts. Patients are selected on the basis of age, timing of surgery, and neuroimaging findings. Flap should be 12 cm in diameter and also includes duraplasty. Additionally, debulking surgery may be an option for tumors. Consider placement of pressure monitoring devices and CSF drainage.
IN-PATIENT CONSIDERATIONS
Admission Criteria
ICU admission with signs of increased ICP. Discharge will be based on stabilization and continuous management of the underlying cause.
IV Fluids
IV fluids to prevent hypovolemia.
Nursing
- Serial neurological examinations are necessary
- Cardiac and respiratory monitoring
- Strict ins and outs must be maintained
Discharge Criteria
Discharge depends on causation.
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FOLLOW-UP RECOMMENDATIONS
Patients should have follow up after discharge with appropriate departments.
Patient Monitoring
Serial neurological examinations are necessary. Additionally, arterial lines, Swan–Ganz catheters, ICP monitoring devices, and/or central venous catheters may be necessary.
DIET
Nutritional support via NG or PEG tube.
PATIENT EDUCATION
ICU is necessary for monitoring patients with signs of increased ICP.
PROGNOSIS
- Depends on the etiology, course, and severity.
- Poorer prognostic indicators: Increased ICP despite aggressive medical therapy, hypothalamic dysfunction (diabetes insipidus), unstable blood pressure. Neuroimaging loss of basal cisterns or collapse of ventricular system, progressive cerebral edema.
COMPLICATIONS
- Monitor for complications of prolonged bedrest and malnutrition: Serial duplex scans for DVTs. Prophylaxis for DVTs if not contraindicated. Serial chest x-rays for pneumonia, especially if intubated. Nutritional markers.
- PT and OT when able.
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