External Ventricular Drains (EVD's)
The Problem:
These drains are catheters placed for several different reasons including acute obstructive hydrocephalus (eg. from a blood clot in the fourth ventricle), tumor obstructing the aqueduct or for communicating hydrocephalus such as after a SAH or meningitis. They are also placed temporarily after removing an infected VP shunt while the infection is treated with antibiotics prior to replacing another VP shunt.

These drains are subject to 3 famous problems:

  • infection
  • dislocation (usually during a turn or when pulled by a patient)
  • blockage
Therefore, samples for culture, cell count, protein, and glucose as well as CT scans can be useful if you are called to problem solve for EVD's. 		What We Do:
There are two ways to use these things. One way is to set the device at a certain level above the patient's ear and leave the valves open. Hence any pressure within the ventricle that exceeds this level (i.e. 10 cm above the head or 10 cm of H2O in pressure) will drain off. The level of the drain can then be adjusted to the desired spill over pressure. The other approach to EVD's is to drain off a fixed amount per unit of time, e.g., remove 10 cc per hour then reclamp. Remember the brain makes about 20 cc of CSF per hour. That is really the max amount you can safely drain. The total CSF volume is about 150 cc. Over draining can lead to the formation of acute subdurals.

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Evidence Footnotes:
1. reference
Authorship: Dr Valerie Taylor Last Revised: 29 May 2002