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Questions and Answers
What is a cause of raised ICP due to obstruction?
What is a symptom of raised ICP?
What is a treatment for raised ICP?
What is a indication for ICP monitoring?
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What is a method of ICP monitoring?
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What is a pathological effect of raised ICP?
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What is the normal range of intracranial pressure (ICP)?
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What is the percentage of brain tissue that affects ICP?
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What is the formula to calculate cerebral perfusion pressure (CPP)?
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What is the most potent stimulus that affects cerebral blood flow (CBF)?
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What is the range of mean arterial pressure over which cerebral autoregulation maintains CBF?
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What is the threshold of ICP above which it is considered raised?
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Study Notes
Intracranial Pressure
- Normal ICP is 10-15 mmHg (136-204 mm H2O).
- Normal Cerebral Blood Flow (CBF) is 55-60 ml/min/100gm brain tissue.
Cerebral Blood Flow
- In gray matter, CBF is 75 ml/min/100 gm brain tissue.
- In white matter, CBF is 45 ml/min/100 gm brain tissue.
- Cerebral Perfusion Pressure (CPP) = mean arterial pressure - ICP.
- CPP = (diastolic pressure + 1/3 of pulse pressure) - ICP.
Factors Affecting CBF
- Systemic BP
- CO2 concentration and H ions in arterial blood (most potent stimulus)
- O2 concentration
Cerebral Autoregulation
- Ability to maintain CBF at a constant level over a wide range of mean arterial pressure (50-160 mmHg).
- When mean arterial pressure is low, cerebral arterioles dilate to allow adequate flow, and vice versa.
- Cerebral autoregulatory system fails when mean arterial BP falls below 50 mmHg or above 160 mmHg.
Raised ICP
- Persistent elevation of ICP more than 20mmHg.
- Common causes:
- Localized masses (hematoma, tumor, abscess, etc.)
- Obstruction to CSF path (obstructive hydrocephaly)
- Obstruction to major venous sinuses (cerebral venous thrombosis, depressed skull fracture over major venous sinus)
- Diffused brain edema or swelling (diffused head injury, encephalitis, lead encephalopathy)
- Idiopathic (pseudotumor cerebri)
Pathological Effects of Raised ICP
- Decrease CPP resulting in cerebral ischemia
- Distortion and herniation of the brain
Symptoms and Signs of Raised ICP
- Headache (most common)
- Vomiting
- Diplopia
- Ataxia
- Papilledema
- 6th nerve palsy (false localizing sign)
- Signs of brain herniation
- Hypertension, bradycardia, and respiratory irregularities (Cushing's response)
Treatment of Raised ICP
- Treatment of underlying cause (tumor resection, hematoma evacuation)
- Head elevation with neck straight
- Ventricular drainage (external or internal)
- Mannitol
- Hypertonic saline
- Loop diuretics (frusemide)
- Steroid (dexamethasone) for chronic raised ICP
- Barbiturate coma using short-acting barbiturate (thiopental)
ICP Monitoring
- Indications:
- GCS < 8
- CT findings (operative or non-operative)
- Post-operative hematoma evacuation
- High-risk patients (above 40 years, hypotension, patients who require ventilation)
- Methods:
- Non-invasive (clinical deterioration, transcranial Doppler, manual feeling of craniotomy flap or skull defect)
- Invasive (catheter connected to electrodes inserted intraventricular, subdural space, or intraparenchymal)
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Description
This quiz covers the basics of intracranial pressure, cerebral blood flow, and cerebral perfusion pressure. Learn about the normal values and formulas used to calculate these important neurological parameters.
