What is an External Ventricular Drain (EVD) in hydrocephalus?

What is an External Ventricular Drain (EVD) in Hydrocephalus?

An External Ventricular Drain (EVD) is a temporary neurosurgical device that drains cerebrospinal fluid (CSF) from the brain's ventricles to an external collection system, used to treat acute symptomatic hydrocephalus by reducing intracranial pressure and improving neurological outcomes. 1

Primary Function and Mechanism

An EVD consists of a catheter surgically inserted through the skull into the lateral ventricle of the brain, connected to an external drainage system that allows controlled removal of CSF. 2 The device serves dual purposes:

• CSF drainage: Removes excess cerebrospinal fluid that accumulates when normal circulation or absorption is impaired 1
• Intracranial pressure monitoring: Provides real-time measurement of pressure inside the skull 3, 4

Clinical Indications for EVD Placement

Acute Symptomatic Hydrocephalus

In patients with acute symptomatic hydrocephalus, urgent CSF diversion through EVD should be performed to improve neurological outcome. 1 This represents a Class 1 recommendation with strong evidence. 1

Specific scenarios include:

• Aneurysmal subarachnoid hemorrhage (aSAH): EVD placement is indicated when hydrocephalus develops, which occurs in a significant proportion of these patients 1
• Intracerebral hemorrhage with hydrocephalus: EVD is a Class 1 indication when hydrocephalus causes decreased level of consciousness, as it reduces mortality 3
• Intraventricular hemorrhage: Particularly when accompanied by reduced consciousness (GCS ≤8) 3

When EVD is Reasonable in ICH/IVH

For intracerebral hemorrhage patients, EVD placement should be considered when: 3

• Glasgow Coma Scale score ≤8 with moderate to severe ICH/IVH
• Clinical evidence of transtentorial herniation
• Hydrocephalus with decreased level of consciousness (strongest indication)

Important caveat: Do NOT place EVD in patients with GCS score of 3, as these patients have extremely poor prognosis regardless of intervention. 3

EVD Management Protocols

Infection Prevention

Implementation and adherence to an EVD bundled protocol that addresses insertion, management, education, and monitoring are recommended to reduce complication and infection rates. 1 The infection risk ranges from <1% to 45% depending on management practices. 1

Key protocol elements include: 1

• Insertion technique: Aseptic technique, proper skin preparation, catheter selection (including antibiotic-impregnated options)
• Management: Type and frequency of dressing changes, CSF sampling frequency and technique, flushing protocols
• Monitoring: Healthcare professional training, tracking catheter days, monitoring infection rates

Drainage Strategy Considerations

The evidence shows conflicting approaches between continuous versus intermittent drainage: 5, 4

• For subarachnoid hemorrhage: Intermittent drainage carries elevated risk of complications (clogged catheter, hemorrhage, need for replacement), though some evidence supports early clamp trials 5
• For traumatic brain injury: Continuous drainage is conventionally accepted, though evidence is limited 4
• Weaning approach: Rapid weaning (>24 hours) does not reduce the need for permanent shunting and should not be routinely performed 2

Transition to Permanent CSF Diversion

Chronic Hydrocephalus Management

For patients with chronic symptomatic hydrocephalus following acute treatment, permanent CSF diversion (ventriculoperitoneal, ventriculoatrial, or lumboperitoneal shunts) is recommended to improve neurological outcome. 1, 2

Chronic shunt-dependent hydrocephalus occurs in 8.9% to 48% of patients with subarachnoid hemorrhage. 1 Predictors of shunt dependency include: 1

• Poor admission neurological grade
• Increased age
• Acute hydrocephalus requiring EVD
• High Fisher grades
• Presence of intraventricular hemorrhage
• Prolonged period of EVD use

Enhanced EVD Therapy

Intraventricular Fibrinolysis

For patients with GCS >3 and primary intraventricular hemorrhage or IVH extension from supratentorial ICH <30 mL requiring EVD, adding intraventricular thrombolytic (tissue plasminogen activator) to EVD is safe and reasonable compared with EVD alone to reduce mortality. 3 This combination hastens clot removal and results in further mortality reduction. 3

However, for spontaneous intracerebral hemorrhage without strong evidence from RCTs, the European Stroke Organisation cannot make strong recommendations about routine use of EVD with intrathecal thrombolysis. 1

Critical Pitfalls to Avoid

• Delayed placement: EVD should be placed early in patients with hydrocephalus and decreased consciousness, as delaying placement increases mortality 3
• Coagulation status: Evaluate and correct coagulation abnormalities before EVD insertion 3
• Inappropriate patient selection: Avoid EVD in GCS 3 patients with extremely poor prognosis 3
• Infection risk: Prolonged EVD use and multiple catheter placements significantly increase infection rates (8.1% for single EVD versus 33.3% for two consecutive EVDs) 6

Limitations of EVD

While EVD reduces mortality in appropriate patients, functional outcomes remain uncertain—the benefit for improving functional outcomes is not well established. 3 Additionally, routine ICP monitoring in all ICH patients without specific indications is not supported by evidence. 3