Q How do you measure intracranial pressure when an external ventricular drain is ordered at a negative number?

A Joan Walsh, DNP, APRN, CNS, CCNS-BC, CNRN, SCRN, replies:

External ventricular drains (EVDs) are used in the critical care setting for cerebrospinal fluid (CSF) diversion and intracranial pressure (ICP) monitoring. Patients with neurologic impairments such as aneurysmal subarachnoid hemorrhage, traumatic brain injury, intraventricular hemorrhage, and hydrocephalus often require EVDs as part of their care.1–3  The drainage catheter is generally placed in the right lateral ventricle to avoid the speech and language centers of the brain.3  Drainage of CSF lowers the volume within the skull and subsequently lowers ICP.

The EVD catheter is connected to a drainage system composed of pressurized tubing, a system stopcock located at 0 cm of H2O, a drip chamber (burette), and a collection bag.3,4  If ICP monitoring is...

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