External Ventricular Drain (EVD)
An EVD is a catheter that is inserted by a neurosurgeon into the brain to release cerebrospinal spinal fluid (CSF) and lower intracranial pressure (ICP). It’s basically a tube that drains fluid from inside the brain into a bag next to the bed that can be measured. Drainage can be continuous at a set level, fixed volume per desired time (i.e., every hour), or as needed according to ICP elevations. At the prescribed height, CSF (and/or blood) will drain whenever the interventricular pressure exceeds that set by the height of the collection system. Flow ceases once the pressure equalizes between the CSF compartments in the brain and collection system.
The EVD must be positioned so that that the pressure transducer is in line with the patient’s ear. (Technically, it must point to the Foramen of Monro, which falls at the level of the external auditory meatus of the ear in the supine position and at the mid sagittal line (between the eyebrows) in the lateral position.) Most nurses “eyeball” it, but some will get a carpenter’s level or laser level to ensure that it’s place accurately. Whenever the patient sits up or lays down, the EVD must be adjusted also, which is a slight — but necessary — hassle.