How to Measure Intracranial Pressure
Intracranial pressure should be measured using either an intraparenchymal ICP monitor or an external ventricular drain (EVD), with EVD preferred when hydrocephalus is present. 1
Recommended Invasive Monitoring Devices
The two gold-standard methods for ICP measurement are:
- Intraparenchymal monitors: Provide reliable, accurate continuous ICP data with lower infection risk and easier placement
- External ventricular catheters (EVD): Equally reliable and accurate, with the added therapeutic benefit of CSF drainage capability
When hydrocephalus is present, use an EVD when safe and practical, as it allows both monitoring and therapeutic CSF drainage. 1 This dual functionality makes EVD superior in this specific clinical context, despite slightly higher complication rates.
Technical Considerations for Invasive Monitoring
Both devices provide accurate measurements, but proper technique is critical:
- Use standardized insertion and maintenance protocols to ensure safety and reliability
- Continuously assess ICP waveform quality using structured protocols
- Interpret instantaneous ICP values in context of monitoring trends, cerebral perfusion pressure (CPP), and clinical evaluation
- Position the transducer at the level of the foramen of Monro for accurate readings
When to Monitor ICP
ICP monitoring is indicated as part of protocol-driven care in patients at risk of elevated intracranial pressure based on:
- Clinical features (e.g., coma, deteriorating neurological exam)
- Imaging findings (e.g., mass effect, midline shift, compressed cisterns)
- Specific diagnoses requiring tailored approaches (traumatic brain injury, subarachnoid hemorrhage, intracerebral hemorrhage, encephalitis)
Noninvasive Alternatives
While invasive monitoring remains the gold standard, noninvasive methods exist for situations where invasive monitoring is contraindicated (coagulopathy, bleeding diathesis, infection risk in immunocompromised patients) or unavailable 2, 3:
- Transcranial Doppler ultrasonography (TCD): Assesses cerebral blood flow velocity patterns that change with elevated ICP
- Optic nerve sheath diameter (ONSD): Measured via ultrasound; diameter >5-6mm suggests elevated ICP
- Transcranial color Doppler: Similar to TCD with added visualization
However, these noninvasive methods lack sufficient accuracy for routine clinical decision-making and cannot substitute for invasive monitoring when precise ICP values are needed to guide therapy. 3 They are best used for screening or when invasive monitoring is impossible.
Special Populations
In infants under 1 year with open fontanelles, epicutaneous transfontanelle ICP measurement using standard ICP probes placed on the skin over the fontanelle provides noninvasive monitoring comparable to invasive methods 4. This technique is particularly valuable in this age group for traumatic brain injury or intraventricular hemorrhage.
Critical Management Points
- ICP monitoring must be combined with clinical evaluation and imaging—not used in isolation 1
- Intracranial hypertension threshold is generally >20-25 mmHg, though this varies by clinical context
- Refractory ICP elevation strongly predicts mortality but should not be used alone for prognostication
- Calculate CPP continuously (CPP = MAP - ICP) and target individualized CPP goals based on autoregulation status when possible
The key pitfall is relying on clinical examination or imaging alone to estimate ICP—direct measurement is required for accurate assessment and treatment guidance. 5 ICP cannot be reliably estimated from clinical features or CT findings and must be directly measured when management decisions depend on knowing the actual pressure.