Neurology · Topic 8 of 22

Hydrocephalus, EVDs & Shunts

Neurology · CSF disorders

Hydrocephalus, EVDs & Shunts

Obstructive hydrocephalus is drained from above with an EVD, never by lumbar puncture; a shunt patient with headache and drowsiness has shunt failure until proven otherwise.

Key numbers

Normal ICP 5–15 mmHgICP 5–15 mmHg

Overdrainage: more than 20 mL per hour> 20 mL/h

Ventriculitis: about 10% of EVDs~10%

Shunt infection: first months, skin flora90% within 6 months

01 · AvoidNo lumbar puncture in obstructive hydrocephalus

Obstructive hydrocephalus must be drained upstream of the block, usually with an external ventricular drain; lumbar puncture removes CSF below it and can precipitate herniation. Communicating hydrocephalus can be drained from any site.

02 · DoLevel EVD at ear; clamp to move

Level the EVD to the external auditory meatus (tragus); clamp it before raising or lowering the head of the bed, then re-level before unclamping. With most systems, ICP reads accurately only with the drain clamped.

03 · FirstSuspect shunt failure: CT and neurosurgery now

A shunted patient with headache, nausea and vomiting, somnolence, fever or altered mental status has shunt failure until proven otherwise: get a noncontrast head CT (often with a shunt series) and urgent neurosurgical consultation.

What it is

Core idea

Communicating versus obstructive hydrocephalus must knowCommunicating hydrocephalus is failed CSF reabsorption (or rarely overproduction) with all ventricles enlarging; obstructive hydrocephalus is a block within the ventricular system, dilating the ventricles upstream of it.

Causes & risk factors

Why it happens

Ventriculitis: about 10% of EVDsVentriculitis complicates about 10% of EVDs, rising with catheter days, intraventricular blood and frequent sampling. Give one antibiotic dose at insertion only — no continuous prophylaxis — and remove the drain as soon as safe.

Proximal catheter obstruction: commonest shunt failureShunts fail by infection, mechanical failure (most common) or over- or underdrainage; the proximal ventricular catheter is the usual site of obstruction, followed by the valve and the distal catheter.

Diagnosis & monitoring

Work-up

Normal ICP 5–15 mmHgNormal ICP is 5–15 mmHg (about 8–20 cmH₂O); ICP above about 22 mmHg sustained for 10–15 minutes is usually treated. ICP is charted in mmHg but EVD height is set in cmH₂O.

NPH: gait, incontinence, dementia — tap testNormal pressure hydrocephalus causes a magnetic gait, urinary incontinence and dementia with enlarged ventricles and normal opening pressure; improvement after removing 30–50 mL of CSF predicts benefit from a ventriculoperitoneal shunt.

Do right now

In this order

First moves

Suspect shunt failure: CT and neurosurgery now

→

Acute hydrocephalus: place an EVD

→

Level EVD at ear; clamp to move

Why each step

Suspect shunt failure: CT and neurosurgery nowA shunted patient with headache, nausea and vomiting, somnolence, fever or altered mental status has shunt failure until proven otherwise: get a noncontrast head CT (often with a shunt series) and urgent neurosurgical consultation.

Acute hydrocephalus: place an EVDAcute symptomatic hydrocephalus — after SAH, intraventricular hemorrhage, meningitis, a brain tumor or shunt failure — is the strongest indication for an external ventricular drain, which both measures ICP and drains CSF.

Level EVD at ear; clamp to moveLevel the EVD to the external auditory meatus (tragus); clamp it before raising or lowering the head of the bed, then re-level before unclamping. With most systems, ICP reads accurately only with the drain clamped.

Management

Orders

EVD drains above its set heightAn open EVD drains CSF whenever ICP exceeds the drip-chamber height above the ear (often 5–15 cmH₂O): a lower setting drains more, a higher setting less.

EVD stopped draining: check stopcocks and kinksIf an EVD stops draining, check stopcocks, tubing kinks and disconnection, then lower the drain slightly; a dampened waveform suggests catheter obstruction — get a CT and call neurosurgery.

Ventriculitis: vancomycin plus cefepime or meropenemTreat EVD ventriculitis with empiric vancomycin plus cefepime or meropenem (MRSA and Pseudomonas cover), remove the infected catheter and replace it at a new site if still needed; CSF culture is the key test.

Wean with a 24-hour clamp trialWean by raising the drain, then a 24-hour clamp trial with ICP monitoring; success = ICP under 20 mmHg, stable exam, no ventricular enlargement on CT. Hold chemical VTE prophylaxis before removal.

Red flags & don'ts

Avoid harm

Overdrainage: more than 20 mL per hour complicationDraining more than about 15–20 mL/h suggests overdrainage, which risks ventricular collapse, subdural hematoma, aneurysm rebleeding and upward herniation; raise the drain height. Raising the head without re-leveling causes it.

Correct coagulopathy before EVD insertion avoidCoagulopathy is a relative contraindication to EVD placement: platelets below 100,000/mm³, INR above 1.4, or antiplatelet or anticoagulant use; scalp infection and midline shift are others.

Shunt infection: first months, skin flora complicationMost shunt infections occur within 2 months of placement and 90% within 6 months, usually from skin flora (Staphylococcus epidermidis, S. aureus); infected hardware needs neurosurgical removal.

Communicating or obstructive hydrocephalus?

Commonly confused

Problem	CSF reabsorption fails (rarely overproduction)
Typical causes	SAH, meningitis, leptomeningeal cancer, sinus thrombosis
CT	All ventricles enlarge symmetrically
Where CSF can be removed	Anywhere — lumbar drain or EVD

More detail

Reference

Show 7 reference facts

Communicating causes: SAH, bacterial or cryptococcal meningitis, leptomeningeal carcinomatosis, superior sagittal sinus thrombosis. Obstructive causes: IVH or inflammation blocking the aqueduct or fourth ventricle, posterior fossa or other mass, colloid cyst.

Acute obstructive hydrocephalus forces CSF into the periventricular white matter (transependymal edema); communicating hydrocephalus shows symmetric ventricular enlargement with a rounded third ventricle.

The choroid plexus makes CSF at about 20 mL/hour, which is why an obstructed system decompensates quickly.

Shunt overdrainage gives a headache worse upright and relieved lying down, slit-like ventricles, and subdural hematoma from torn bridging veins.

A shunt series is AP and lateral radiographs of the skull, chest and abdomen looking for fracture, disconnection or migration; its yield is variable, so it complements, not replaces, head CT.

In SAH, intermittent drainage (open only when ICP exceeds a threshold) has fewer occlusions, infections and later shunts than continuous drainage; in severe TBI, continuous drainage lowers ICP burden more effectively.

A lumbar drain is used for communicating hydrocephalus, CSF leaks after trauma or surgery, and to test shunt responsiveness in normal pressure hydrocephalus.

Pearl

Drain obstructive hydrocephalus upstream of the block — a lumbar puncture below it can pull the brain down.

Sources · Farkas J. Internet Book of Critical Care (EMCrit) — Elevated intracranial pressure (ICP), hydrocephalus section · Farkas J. Internet Book of Critical Care (EMCrit) — External Ventricular Drain (EVD) & Lumbar Drain · Ventriculoperitoneal Shunts in the Emergency Department: A Review. Cureus 2020 (Feb) · Merck Manual Professional — Normal Pressure Hydrocephalus · Brain Trauma Foundation — Guidelines for the Management of Severe TBI, 4th Edition, recommendation index (CSF drainage) · Obstructive Colloid Cyst of the Third Ventricle (case review; colloid cyst blocking the foramen of Monro causes acute obstructive hydrocephalus) · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).