Intracranial Pressure (ICP) Monitoring and External Ventricular Drains (EVD)

An external ventricular drain (EVD) is a catheter in a lateral ventricle. It drains cerebrospinal fluid (CSF) into a closed external collection system, and it reports intracranial pressure (ICP) through that same catheter. ICP monitoring records the pressure inside the skull. The team uses that number to keep cerebral perfusion pressure (CPP) in range.

Key Components

Flow Path

1. Ventricle: CSF enters at the catheter tip.
2. Catheter and tubing: CSF and the pressure signal both travel down to the drip chamber.
3. Drip chamber: The level sets the zero. The column shows the pressure.
4. Collection bag: Drained CSF gets measured, and sampled when ordered.

The skull is a fixed box. Blood, CSF and brain tissue share that space. Add volume to one and another has to give, or ICP climbs. The Monro-Kellie relationship and compensatory reserve set how much change the brain absorbs before ICP starts to climb.

What It Does

What It Depends On

• MAP: CPP = MAP − ICP. Lower the MAP and the pressure reaching the brain drops with it.
• Autoregulation: When static pressure autoregulation is intact, raising CPP can lower ICP (SIBICC).
• Drain patency and level: A wrong level or a blocked catheter changes the number. The patient has not changed.
• Temperature: SIBICC aims to avoid fever above 38 °C.
• Seizures: Seizures you cannot see can still raise ICP. SIBICC suggests considering EEG monitoring.

Drain Modes

• Continuous drainage: The drain stays open at the set level. BTF (Level III) says this may lower the ICP burden better than intermittent use.
• Intermittent drainage: The drain opens to let CSF out, then closes again. Use only the mode the order sets.

Drain Positions

• Closed to drainage, open to the transducer: This is the position for reading ICP. The number shows on the monitor.
• Open to drainage: CSF is leaving the skull. While it drains, the ICP number is not valid. What you see is measured from the drip-chamber level.
• Closed to the transducer: The trace goes flat. There is no ICP to show.

Indications

• Severe TBI with abnormal CT: ICP should be monitored in salvageable patients with GCS 3–8 after resuscitation and an abnormal CT (hematoma, contusion, swelling, herniation or compressed basal cisterns) (BTF 2007, 3rd edition, chapter VI).
• Severe TBI with normal CT: monitor if at least 2 of: age over 40 years, unilateral or bilateral motor posturing, or SBP below 90 mmHg (BTF 2007, 3rd edition, chapter VI).
• Initial GCS below 6: CSF drainage may be considered during the first 12 h (BTF, Level III).
• Hydrocephalus or other CSF diversion: The neurosurgical team owns that decision. The sources on this page set no criteria for it.

Contraindications

No numeric contraindication thresholds are set on this page. The neurosurgical team and local protocol decide. Clear these before placement, per protocol: coagulopathy or a low platelet count, anticoagulant or antiplatelet use, infection or skin breakdown at the insertion site, and a trajectory the imaging does not allow.

High-quality data on the best methods for EVD placement and management is lacking, says the Neurocritical Care Society consensus statement in the references. So these items rest on protocol and consensus, not on trial data.

Lumbar drains are outside the scope of this page. When only ICP is monitored, SIBICC does not recommend routine lumbar CSF drainage.

Limitations

• ICP alone does not show brain oxygenation. For patients with both an ICP and a brain oxygen monitor, SIBICC wrote a separate protocol.
• Change the zero point, the level or the clamp, and the ICP number changes with them.

Key Evidence

Leveling & Zeroing

1. Identify the reference: BTF names the midbrain as the zero point for an EVD. Many units use another bedside landmark. Confirm the one your protocol names.
2. Level: set the drip chamber to the reference point.
3. Zero: close the drain to air, zero, and open the drain to the ventricle.
4. Record: document the baseline ICP and CPP. Re-level after position changes. Re-zero only per protocol, or when the trace is in doubt.

Initial Settings

• Drain height: set by order (protocol-dependent).
• Alarms: set ICP and CPP limits per order.
• Drainage: continuous or intermittent, per order. Read ICP only with the drain closed to drainage (see Drain Positions).

Normal

• Pulsatile trace: The ICP waveform tracks the arterial pulse.

Abnormal Patterns

Slow Waves

You may see slow B-waves (about 0.3 to 4 cycles per minute) in normal and abnormal states. Their size drops under general anesthesia and deep sedation. Read them with the sedation level in mind, and with neurosurgery.

Positioning & Mobility

• Any change in head or body position means re-leveling. Re-zero only per protocol, or when the trace is in doubt.
• Head of bed: SIBICC's basic-care figure (Fig. 1) covers head-of-bed positioning for patients with an ICP monitor on ICU admission. Set the angle and head position per protocol.
• Secure tubing so it cannot pull on the catheter.

High-alert applies to IV heparin. Review anticoagulant and antiplatelet use before placement. Timing and reversal depend on protocol.

Bleeding & Platelets

• Thrombocytopenia and coagulopathy both raise the bleeding risk around the catheter.
• New blood in the drain: stop, call neurosurgery, and check the labs.

Doses vary by protocol; follow local protocols and medical direction.

Power or monitor failure: check the connections and the level. With the drain open and level, it still drains by gravity. Protocol-dependent. No primary source was fetched.

Readiness Criteria

• ICP controlled per the neurosurgery plan, with no active herniation.
• CSF output and color acceptable for the order set.

Weaning Steps

1. Clamp trial: per order, with ICP monitored during the trial.
2. Re-check: pupils, GCS and ICP at the set intervals.
3. Remove: only on the neurosurgical order.

Removal & Post-Removal Care

• Site care and dressing per protocol.
• Monitor for leak, bleeding and neurologic change.

Before You Move

1. Get the clamp and level orders for transport before the move, and confirm them at the bedside.
2. Secure the tubing and collection bag.
3. Brief the receiving team on the baseline ICP and CPP.

If You Are Not the Device Specialist

• EMS and transport crews keep to the existing clamp and level order. They do not manage the EVD beyond it.
• Do not open, zero or re-level the drain without an order.
• Watch the pupils, GCS and the ICP trace.
• Call for help for any change in the trace or the patient.

During Transport

• A small US survey (30 responding hospitals; 37.5% response rate) found that 66.7% of hospitals clamp routinely during transport. Adherence to intrahospital transport recommendations was low (16.7%). Whether to clamp is an order decision.
• Overdrainage: When the patient or the drain moves, an open drain at an unordered height can drain CSF too fast. That risks ventricular collapse and subdural hematoma. Before any move, close the drain to drainage or level it exactly as ordered. After the move, re-level and reopen only as ordered. Do not leave an open drain at an unordered height during movement.
• In the EVD Aware survey, 14.4% of anesthesiologists reported monitoring ICP routinely during transport.

Air Medical & Altitude

This page does not cover altitude changes in gas volume. For those, go to the flight physiology page.

Handoff

• Baseline ICP and CPP, the drain height and clamp status.
• Output and color over the last hours; any alarms.

Pediatric & Neonatal

• ICP: In children, an ICP threshold of 20 mmHg is generally used. A lower threshold may suit infants and young children (BTF pediatric, 3rd edition).
• CPP: Keep CPP at a minimum of 40 mmHg. The suggested target is 40–50 mmHg, with age-specific thresholds (BTF pediatric, Level III).
• Drain practice: Follow the pediatric neurocritical care protocol. Neonatal EVD management and pregnancy sit outside this page's scope.

Other

With severe TBI and a normal CT, BTF counts age over 40 years as one feature. Pair it with at least one other, and it justifies ICP monitoring.

Systematic Walk-Through

1. Indication and CT findings.
2. Drain mode and level.
3. Current ICP and CPP.
4. Output and color.
5. Pupils and GCS.
6. Escalation plan.

Pearls

• Without a level or a drain position, a number is incomplete.
• Output and color belong to the ICP read.
• Hyperventilation is temporary. It is not prophylactic.