The EVD is leveled to a common reference point that corresponds to the skull base, usually the tragus or external auditory meatus. The EVD is set to drain into a closed, graduated burette at a height corresponding to a particular pressure level, as prescribed by a healthcare professional, usually a neurosurgeon or neurointensivist. Leveling the EVD to a set pressure level is the basis for cerebrospinal fluid (CSF) drainage; hydrostatic pressure dictates CSF drainage.