Intracranial Pressure Monitoring Techniques

🔹 Introduction

Intracranial Pressure (ICP) is the pressure within the cranial vault, exerted by brain tissue, cerebrospinal fluid (CSF), and cerebral blood. Monitoring ICP is crucial in neuroanesthesia and neurocritical care to prevent secondary brain injury due to brain herniation, ischemia, or hypoperfusion.

📌 Normal ICP Values

• Adults: 5–15 mmHg
• Children: 3–7 mmHg
• Infants: 1.5–6 mmHg
• ICP > 20 mmHg (sustained) is pathological and requires intervention

🔑 Cerebral Perfusion Pressure (CPP)

CPP = MAP – ICP
Target CPP:

• Adults: 60–70 mmHg
• TBI (per BTF guidelines): Maintain CPP > 60 mmHg
• CPP < 50 mmHg = cerebral ischemia risk

🔹 Indications for ICP Monitoring

• Severe Traumatic Brain Injury (TBI) with GCS ≤ 8 and abnormal CT
• GCS ≤ 8 with normal CT but with ≥2 of:
• Age > 40
• Systolic BP < 90 mmHg
• Abnormal posturing
• Acute hydrocephalus
• Cerebral edema (post-surgery, stroke)
• Aneurysmal subarachnoid hemorrhage (SAH) with hydrocephalus
• Intracerebral hemorrhage with mass effect

🔹 Types of ICP Monitoring Techniques

ICP can be monitored using:

• Invasive methods (gold standard)
• Minimally invasive / non-invasive methods (supplementary or adjunct)

🔴 Invasive ICP Monitoring Techniques (Gold Standard)

🧾 Summary Table: Invasive ICP Monitoring Techniques

1. 🧪 Intraventricular Catheter (EVD – External Ventricular Drain)

✅ Description:

• Catheter inserted into lateral ventricle via a burr hole (commonly right frontal horn)
• Connected to a pressure transducer and drainage system

✅ Advantages:

• Gold standard for ICP monitoring
• Allows CSF drainage → therapeutic benefit
• Can sample CSF for analysis
• High accuracy and reliability

❌ Disadvantages:

• Invasive → risk of infection (ventriculitis), hemorrhage
• Requires skill, may be difficult in midline shift or small ventricles

✅ Ideal for:

• Hydrocephalus
• Severe TBI with raised ICP
• Post-op neurosurgical monitoring

2. 🌡️ Intraparenchymal Fiberoptic Transducer

✅ Description:

• Probe (e.g., Codman, Camino) inserted into brain parenchyma, usually frontal white matter
• Fiberoptic or strain-gauge sensor measures pressure

✅ Advantages:

• Easier and faster to place than EVD
• Low infection risk
• Suitable when ventricles are small or displaced

❌ Disadvantages:

• No CSF drainage
• Drift in calibration over time
• Slightly less accurate than EVD

✅ Ideal for:

• Diffuse cerebral edema
• TBI with small ventricles

3. 🔩 Subdural / Subarachnoid Bolts or Screws

✅ Description:

• Bolt inserted into subdural or subarachnoid space through burr hole
• Transducer attached to measure ICP

✅ Advantages:

• Less invasive
• Moderate accuracy

❌ Disadvantages:

• No CSF drainage
• Risk of clot formation → inaccurate readings
• Not commonly used now

4. 🧫 Epidural Transducer (Least Invasive)

✅ Description:

• Placed between skull and dura mater
• ICP estimated using pneumatic or fiberoptic sensors

✅ Advantages:

• Lowest risk of infection or hemorrhage

❌ Disadvantages:

• Poor accuracy, not in contact with CSF
• Largely obsolete in modern practice

🟡 Non-Invasive / Indirect ICP Monitoring

These methods estimate ICP but are not reliable enough for standalone use in critical care.

1. Transcranial Doppler (TCD)

• Measures blood flow velocity in cerebral arteries
• Uses pulsatility index (PI) as a surrogate for ICP
• Increased PI (>1.3) suggests elevated ICP

2. Optic Nerve Sheath Diameter (ONSD)

• Ultrasound of optic nerve sheath
• ONSD > 5 mm in adults suggests raised ICP
• Bedside, rapid, and reproducible

3. Tympanic Membrane Displacement

• Based on CSF pressure transmission to the cochlea
• Not widely used clinically

4. MRI/CT-based Estimation

• Midline shift, ventricular compression, sulcal effacement suggest raised ICP
• Static, not continuous monitoring

🔬 ICP Waveform Analysis

ICP waveform has 3 peaks:

Poor compliance: P2 > P1 → warning of raised ICP

🧮 Lundberg Waves (Abnormal ICP Waves)

🔍 Suggested References

1. Miller’s Anesthesia, 9th Edition – Neuroanesthesia and TBI chapters
2. Cottrell and Young’s Neuroanesthesia – ICP monitoring chapter
3. StatPearls – Intracranial Pressure Monitoring
4. British Journal of Anaesthesia (BJA) – Articles on cerebral monitoring
5. Brain Trauma Foundation Guidelines – TBI management

📝 Viva Corner (Sample Q&A)

1. Q: What is the gold standard technique for ICP monitoring?
   A: External Ventricular Drain (EVD)
2. Q: How do you calculate CPP?
   A: CPP = MAP – ICP
3. Q: What waveform change suggests poor brain compliance?
   A: P2 > P1 in ICP waveform
4. Q: Name a non-invasive bedside tool to assess ICP.
   A: Optic Nerve Sheath Diameter (ONSD) ultrasound
5. Q: What does a Lundberg A wave indicate?
   A: Plateau wave → severe intracranial hypertension and risk of herniation