🧠 What is an EVD

Overview of external ventricular drains and ICP monitoring

What is an External Ventricular Drain (EVD)?

An External Ventricular Drain (EVD) is a temporary device inserted into the ventricular system to allow controlled drainage of cerebrospinal fluid (CSF) and monitoring of intracranial pressure (ICP).

It is primarily used for temporary CSF diversion in patients with acute symptomatic hydrocephalus.

An estimated 24,380 ventriculostomies are performed annually in the United States, based on Nationwide Inpatient Sample data from 1997–2001 (Sekula RF, Cohen DB, Patek PM, et al. Epidemiology of ventriculostomy in the United States from 1997 to 2001. British Journal of Neurosurgery. 2008 Apr. PMID: 18348016).

Common Indications

1. Subarachnoid hemorrhage (SAH) [PMID: 42438063]
2. Intraventricular hemorrhage (IVH) [PMID: 42438063]
3. Traumatic brain injury with hydrocephalus [PMID: 42438063]
4. Posterior fossa lesions causing obstruction [PMID: 42438063]
5. CNS infections with hydrocephalus [PMID: 42438063]
6. Patients with chronic hydrocephalus in whom a pre-existing permanent CSF diversion system (e.g., a VP shunt) is infected or malfunctioning [PMID: 42438063]

Note

Source (all indications above): Lele AV, Sawant P, Blacker SN. External ventricular drain safety campaign and opportunities for global neuroanesthesiology quality and safety. Current Opinion in Anaesthesiology. 2026 Jul 13. PMID: 42438063

CT Abnormalities

The images below are illustrative examples sourced from Dr. Lele’s institution (Harborview Medical Center, University of Washington) — see each image’s source badge — and are not intended to represent every possible presentation.

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Clinical Pearls

• Leveling matters: Always level the EVD at the external auditory meatus for accurate ICP measurement.
• Transport risk: Common practice is to clamp the EVD for intra-hospital transport without continuously monitoring ICP. In a CSF-drain-dependent patient, this can let an ICP elevation go unrecognized. It is safer to keep monitoring ICP throughout transport and open the EVD to drain CSF as needed if ICP rises.

Note

Source (both pearls above): Lele AV, Hoefnagel AL, Schloemerkemper N, et al. Perioperative Management of Adult Patients With External Ventricular and Lumbar Drains: Guidelines From the Society for Neuroscience in Anesthesiology and Critical Care. Journal of Neurosurgical Anesthesiology. 2017 Jul. PMID: 28169966