External Ventricular Drain

An EVD is a catheter inserted via a burr hole into the right or left lateral ventricle, in order to:

EVDs are usually inserted:

Indications

Diagnostic and therapeutic:

The components of the EVD from proximal to distal are:

Multi-stage access catheter
Inserted into the ventricle.
Patient connection line
Connects the drain to the monitoring and drainage apparatus.
3-way stopcock
Allows line to be:
- Transduced
  A non-flushing pressure transducer should be used, so the line cannot be inadvertently flushed into the brain.
- Drained
  Note that the EVD cannot simultaneously transduce ICP and drain CSF. When draining, the ICP waveform should transduce the drainage height.
- Sampled
  Attaching a 3mL syringe allows aspiration of CSF for sampling. Routine sampling ↑ the risk of ventriculitis.
Drip chamber
A small chamber with volume markers. This chamber:
- Can be adjusted relative to the pressure scale
  This allows the drainage height (pressure) to be selected.
  - When ICP exceeds the drainage height, CSF will vent from the EVD
  - Standard drainage height is 10-15cmH₂O
    Many scales provide options for both mmHg and cmH₂O.
- Collects CSF
  Allows hourly volumes vented to be measured.
- Can be periodically emptied into a drainage bag
Drainage bag
Collects CSF that is vented from the drip chamber.

1mmHg is ~1.3cmH₂O; 1cmH₂O is ~0.7mmHg.

Position and set up:

The pressure scale should be set at 0 relative to the:
- EAM in a supine patient
  This is level with the Foramen of Munro.
- Bridge of nose in a lateral patient
The EVD should be clamped prior to moving to prevent CSF over-draining
This includes raising or lowering the bed, transport, physiotherapy, etc.
The EVD should be re-leveled after each position change

Zeroing:

Do not remove the bung on the transducer - the zero should happen without the system opening to the atmosphere.

Check EVD is level with the tragus
Turn the 3-way tap off to patient
This is the tap at the level of the transducer, such that the transducer is ‘open to the drip chamber.’
Drop level of the drip chamber to 0
Zero pressure on monitor
Return trip chamber to desired height
Close 3-way tap to the transducer

The EVD will generally be set in one of two modes:

Continuous drainage is used for hydrocephalus (and in SAH, to prevent hydrocephalus); intermittent venting is used in TBI.

Continuous drainage
- EVD is left open at a set height
  CSF will passively drain when ICP > set height.
  - EVD ‘weaning’ may be performed by raising the set height - absence of CSF drainage indicates that ICP is not rising above this level
- High-volume CSF drainage is >30mL/hr
  Nursing notification should occur if EVD drainage is >20mL/hr.
- The EVD is generally not transduced in these circumstances, although it is good practice is to transduce every hour to confirm patency if there has been no CSF drainage
  A pressure transducer may not need to be attached if the EVD is being used in this way.
ICP monitoring/intermittent venting
- Continuously transduced
  Intermittently vented in case of ↑ ICP.

Other uses:

CSF sampling
CSF may be sampled from an EVD, generally to evaluate for the presence of ventriculitis.
Medication administration
Occasionally, medications (e.g. thrombolytics) are administered through an EVD.

Blocked EVD
- EVDs can become blocked with blood or other exudate
- Briefly lowering the EVD (‘dropping to the floor’) will detect blockage as CSF should flow under gravity when the EVD is lowered
  This should be done only for a few seconds to confirm CSF flow, over-draining should be avoided to prevent collapse of the ventricles and intracranial haemorrhage.
- A blocked EVD may be flushed to restore patency, and should be done by the neurosurgeon.

Bersten, A. D., & Handy, J. M. (2018). Oh’s Intensive Care Manual. Elsevier Gezondheidszorg.