How to monitor raised Intracranial Pressure (ICP)?

How to Monitor Raised Intracranial Pressure

ICP monitoring should be performed using either an external ventricular drain (EVD) or intraparenchymal fiberoptic probe, with EVDs preferred when hydrocephalus is present or CSF drainage may be needed therapeutically. 1, 2

Indications for ICP Monitoring

Protocol-driven ICP monitoring is strongly recommended in patients at risk of elevated ICP based on clinical and/or imaging features. 1

High-Risk Clinical Scenarios Requiring Monitoring:

• Comatose patients with abnormal CT scan findings showing compressed basal cisterns, midline shift >5mm, or intracerebral hematoma >25mL 1
• Post-neurosurgical patients after intracranial hematoma evacuation with any of: GCS motor score ≤5, anisocoria/bilateral mydriasis, preoperative hemodynamic instability, or severe imaging findings 1
• Patients requiring sedation or paralysis where neurological examination is not feasible 1
• Conditions beyond TBI including subarachnoid hemorrhage, intracerebral hemorrhage, encephalitis, and acute hepatic failure 1, 3

When NOT to Monitor:

Do not place invasive ICP monitors in patients with normal CT scans and no clinical severity indicators or transcranial Doppler abnormalities - the risk of raised ICP is only 0-8% in this population, making the risk-benefit ratio unfavorable 1

Device Selection

External Ventricular Drain (EVD):

• Gold standard for ICP monitoring providing both accurate pressure measurement and therapeutic CSF drainage 2, 3
• Mandatory choice when hydrocephalus or significant intraventricular hemorrhage is present 2
• Higher complication rates: infection risk 10%, hemorrhage risk 2-4%, catheter placement failure 10% 1, 2

Intraparenchymal Fiberoptic Probe:

• Equally accurate for pressure measurement but cannot drain CSF 2
• Preferred when ventricular access is difficult or contraindicated, or when considering risk-benefit balance 1, 2
• Lower complication rates: infection risk 2.5%, hemorrhage risk 0-1% 1

Pre-Insertion Safety Protocol:

Evaluate coagulation status before insertion; consider platelet transfusion if patient has been on antiplatelet agents 2

Monitoring Protocol and Interpretation

Continuous Assessment Requirements:

• Monitor ICP and cerebral perfusion pressure (CPP) continuously with waveform quality assessment using structured protocols 1
• Calculate CPP as mean arterial pressure (MAP) minus ICP 1
• Interpret instantaneous ICP values in context of trends, CPP, and clinical evaluation - never in isolation 1

Critical Thresholds:

• ICP >20-25 mmHg defines intracranial hypertension requiring treatment 1, 4
• ICP 20-40 mmHg carries 3.95-fold increased risk of mortality and poor neurological outcome 1, 4
• ICP >40 mmHg increases mortality risk 6.9-fold and demands immediate aggressive intervention 1, 4
• Maintain CPP >50-60 mmHg (some protocols target >70 mmHg depending on autoregulation status) 1, 4, 3

Waveform Analysis:

Display high-resolution ICP waveforms to assess signal validity and identify pathological patterns (A-waves, B-waves, C-waves) that indicate specific intracranial dynamics 5

Multimodal Monitoring Integration

ICP monitoring is mandatory when using other intracranial monitors (brain tissue oxygenation, microdialysis) to provide interpretive framework 1

Complementary Monitoring:

• Add hemodynamic monitoring (cardiac output, intravascular volume assessment, echocardiography) in patients with hemodynamic instability 1
• Incorporate transcranial Doppler to assess cerebral blood flow and detect mass effect 4
• Serial neuroimaging remains essential even with invasive monitoring to detect new surgical lesions 1, 6

Clinical Context Considerations

Tailor monitoring indications and methods to specific diagnoses - TBI, SAH, ICH, and encephalitis have different monitoring needs and thresholds 1, 2

Important Caveats:

• Refractory ICP elevation strongly predicts mortality but should not be used alone for prognostication of functional outcomes 1, 2
• The BEST-TRIP trial showed no outcome difference between ICP-guided versus imaging/clinical-guided management, but this lacks external validity and should not eliminate monitoring in appropriate patients 1
• Clinical evaluation and imaging remain fundamental - monitoring augments but does not replace clinical assessment 1

Autoregulation-Guided Management:

Patients with preserved autoregulation may benefit from higher MAP/CPP targets, while those with pressure-passive responses require judicious blood pressure control 1