If you work in a neuro-critical care unit (or consult on the neurologically devastated), chances are you will see an External Ventricular Drain (EVD) at one point or another. If you don’t know the parts of an EVD, you may neither understand nor take full benefit of this useful device.
Indications and Purpose:
An EVD has two basic components: the collection system and the actual catheter itself. The catheter is placed either in the OR or at the bedside as a sterile procedure, and the tip rests in the ventricle (typically placed in the right frontal region, accessing the frontal horn of the lateral ventricle). While placement may vary, the right frontal approach tends to provide most superficial anatomic access to the ventricular system and poses the least risk to sensitive brain tissue. Once the catheter and monitor/ collection setup are joined, the EVD simultaneously measures intracranial pressure and allows for CSF or blood drainage from the ventricular system. Indications can vary depending on the medical or surgical nature of the patient’s condition, but generally EVDs are indicated in a few broad cases:
- ICP monitoring/ drainage for
- moderate to severe intracranial hypertension syndromes
- severe TBI
- acute, symptomatic hydrocephalus
- ICP and hemorrhage control after IVH or SAH
- Postop ICP monitoring from multiple types of neurosurgical interventions
- VP shunt malfunctions requiring explanation or repair
It may look like an unapproachable contraption, but it actually is a relatively simple device (see figure 1). Essentially, it contains 5 components:
- EVD catheter
- Connecting tubing
- Stop-cocks (5 all together)
- Transducer and monitor setup
- Leveling manifold (in cm H2O)
- Adjustable EVD/ burette
- CSF collecting reservoir
- EVD catheters have the tip resting in the lateral ventricle (figure 2).
- EVD should always be LEVELED at external auditory meatus when supine and/or the midsagittal line when the patient is positioned laterally (i.e. the zero mark on the measurement apparatus in figures 2 and 3 should be at the EAM).
- EVD will then have a specific pressure SETTING (i.e. the adjustable burette can be moved up or down to a set pressure level in cm H2O). This is dictated by the neurosurg team and the patient’s condition.
- The decision to have the patient’s CSF actively draining is usually made in consultation with neurosurgery. Independent draining is NOT advised.
- Drain OFF: allows CSF to interact with flushless transducer to produce ICP waveforms and measurement of ICP and CPP (figure 3)
- Drain ON: allows CSF to drain if ICP exceeds the level dictated by the adjustable burette (figure 4). CSF/ blood can then be measured over time, sampled, or simply shunted to the collection bag.
- The EVD is a plastic highway to the patient’s brain: infection control/ surveillance is paramount. Drainage, duration of EVD placement, and dressing changes should be standardized and done in concert with neurosurgical support. Complications can include nosocomial ventriculitis or meningitis (4). Risk factors predisposing patients to these worse outcomes can include:
- Extended duration of EVD placement
- Extended ICU and hospital stay
- Non-antibiotic coated catheter
- Increased frequency of CSF flushing or drainage
- The head of the bed MUST stay in a position where the head remains leveled with respect to the EVD. Failure to do so can result in under or over drainage of CSF!
- DO NOT connect to high pressure systems, flushes, or infuse any medication/ fluid without expressed permission from neurosurgical support.
- Usually the EVD is seldom left to drain for extended periods of time once a patient is stable and has acceptable ICPs. Leaving the EVD “open” should only be done with neurosurgical services being aware.
- Sudden changes in mental status, confusion, or sudden onset of headache in EVD patients should be treated as an emergency, with neurosurgical services being made aware immediately
- EVDs are commonplace in neuro-critical care units and require standardized setup and protocols to help monitor ICP and drain CSF.
- EVDs are made of basic components that allow for diagnostic monitoring of ICP and therapeutic drainage of CSF.
- There are basic safety concerns that you should be aware of, especially if the neurologic exam changes or if EVD infection is suspected.
- Medtronic EVD Manufacturer page. https://www.medtronic.com/us-en/healthcare-professionals/therapies-procedures/neurological/drainage-monitoring-external.html.
- Perioperative Guide for EVDs and LDs. Society of Neuroscience, Anesthesia, and Critical Care. https://cdn-links.lww.com/permalink/jna/a/jna_2016_12_28_lele_jna-d-16-00274_sdc2.pdf
- Cadena R, Shoykhet M, Ratcliff JJ. Emergency Neurological Life Support: Intracranial Hypertension and Herniation. Neurocrit Care. 2017;27(Suppl 1):82-88. PMID: 28913634.
- Sorinola, Abayomi, et al. “Risk factors of external ventricular drain infection: proposing a model for future studies.” Frontiers in Neurology 10 (2019): 226. PMID: 30930840.
Title image taken from Wikimedia Commons.