Zero-Calibrating External Ventricular Drains: Exploring Practice : Journal of Neuroscience Nursing

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Zero-Calibrating External Ventricular Drains: Exploring Practice

Pratt, Karen A.; Peacock, Sarah H.; Yost, Kaylie D.; Freeman, William David; Collins, Christina I.; McLaughlin, Diane C.

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Journal of Neuroscience Nursing 54(1):p 2-5, February 2022. | DOI: 10.1097/JNN.0000000000000622
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Practice variability exists in the procedure followed by nursing staff and providers for zeroing external ventricular drain (EVD) transducers. Some have been trained to open the nonvented cap (NVC) to atmospheric air to zero the EVD, whereas some have been trained to not remove the NVC.


At our institution, a transition to a new flushless transducer to meet manufacturer guidelines for use with intracranial pressure (ICP) monitoring occurred. This change stimulated evaluation of current institution procedural guidelines. The institution uses Lippincott procedures for both nurses and providers.1,2 The guidelines stated to follow manufacturer guidelines for zeroing. Available recommendations from national nursing guidelines and manufacturers were reviewed and compared (Table 1).1–5 All reviewed guidelines recommend removal of the NVC to air to zero the system to atmospheric pressure (NVC method).1–5 In theory, there is potential to introduce bacteria into the system when nursing zeroes the EVD using this clean, nonsterile technique and remove the NVC; however, there are no published cases or studies evaluating this.

TABLE 1 - Description of Published EVD Zeroing Methods
Lippincott1,2 Medtronic3 AANN4 Edwards5
Connect the flushless transducer to the bedside monitor with a pressure cable plugged into the designated pressure module. Align the zero point with the centerline of the patient's head, level with the middle of the ear, using a leveling device. The key to accurate ICP measurement is using the same landmark each time you check the zero-reference level. Lower the flow chamber to zero and turn the stopcock off to the dead-end cap. Lower the drip chamber until the “Pressure Level” arrow on the top of the drip chamber is set at the “0” level on the pressure scale. Rotate the knob on the main system stopcock so that it is turned off to fluid coming from the patient. Medtronic specifically points users to note all manufacturer recommendations for components used with their system. Turn the transducer stopcock off to the patient and remove dead-end cap (off to patient, open to air). Press the “zero” button on the bedside monitor. Adjust the level of the transducer vent port (the fluid-air interface) to correspond to the chamber where pressure is being measured. Remove the NVC and open the vent port to atmospheric pressure (air). Adjust the monitor to read 0 mm Hg. Check monitor calibration using the procedure recommended by the monitor manufacturer. Close the vent port to the atmosphere and replace the NVC. System is ready to begin monitoring pressure.
Abbreviations: AANN, American Association of Neuroscience Nurses; EVD, external ventricular drain; ICP, intracranial pressure; NVC, nonvented cap.

Current practice in our neuroscience intensive care unit deviates from these recommendations. The current bedside procedure for zeroing EVD at our institution (chamber method) is to perform hand hygiene, don clean, nonsterile gloves, and complete the following steps: (1) turn the stopcock, located on the Becker external drainage and monitoring system off to the patient; (2) set the drip chamber to 0 mm Hg; (3) ensure drain is level with foramen of Monro using a level; (4) press “Zero” on the ICP waveform on the Philips monitor and wait for the monitor to show “0”; (5) return drip chamber to the prescribed level; (6) turn the stopcock on the drain off to the drip chamber to obtain ICP reading from the monitor; (7) turn the stopcock off to the transducer and raise the chamber to obtain a manual reading of ICP by evaluating the meniscus in the tubing; (8) return the chamber to the ordered level; and (9) record values in electronic medical record hourly (Figs 1A–C).1,2

Position of stopcock and hydrophobic filter. A, Position of stopcock when zeroing per institutional guidelines. B, Position of stopcock when transducing intracranial pressure waveform. C, Position of stopcock when performing manual tidal or draining cerebrospinal fluid. D, Hydrophobic filters located at the top of drip chambers effectively keeping system open to air for zeroing without removal of the nonvented cap.


A project was initiated to align bedside practice and procedural guidelines. The team consisted of representatives from nursing and nursing education, advanced practice registered nurses in the neurosurgery and neurocritical care services, and the medical director of neurocritical care. The equipment used consisted of the Becker external drainage and monitoring system (Medtronic), Duet external drainage and monitoring system (Medtronic), TruWave flushless disposable pressure monitoring transducers (Edwards Lifesciences Corporation) designed for ICP monitoring, and Philips bedside monitoring system (Koninklijke Philips). In addition, single-subject observation was performed using manual tidal, zeroing of the EVD using both institutional procedure (nonremoval of the NVC) and Lippincott-recommended procedure (removal of the NVC).


PubMed search for “external ventricular drain nursing management” yielded 16 results, with 12 relevant to our discussion but did not specifically address zero-calibration procedure.4,6–16 Additional known literature was included in our evaluation; however, it also did not specifically address the process for zeroing an EVD.17–22 An Internet search including “guidelines for external ventricular drain nursing management” found practice guidelines from the American Association of Neuroscience Nurses and the American Association of Critical-Care Nurses. Review of current published guidelines identified that there are contradictions between published nursing guidelines and institutional practice. There were no studies found evaluating NVC removal and infection risk.


We found that each component of an EVD system is often made by different manufacturers and may be more applicable to the arterial line zeroing process with a closed system and a pressure bag rather than an EVD. A point of clarity was obtained by an individual review of manufacturer guidelines for each piece of equipment. The Medtronic Becker drain guidelines state that the transducer's manufacturer guidelines should be followed for use of the transducer; however, the transducer guidelines are created for use with a pressurized system that is completely closed to atmospheric air. The only time a transducer is ever connected to a drain for patient care is in the instance of monitoring ICP via an EVD and intraspinal lumbar cerebrospinal fluid pressures via a lumbar drain. The Becker drain has a hydrophobic filter and vent located at the top of the drip chamber (Fig 1D) that effectively keeps the drain open to atmospheric air and prevents introduction of pathogens. As the filter is hydrophobic, theoretically, the material does not get wet or become clogged should the system be laid in a horizontal position, although there is no known research that has evaluated this.

Catheter-associated ventriculitis is common, with rates of infection ranging from 0% to 22%.23,24 Risk for infection is associated with EVD management and frequency of EVD manipulation and cerebrospinal fluid sampling.25,26 EVD related infection can prolong length of stay and increase morbidity, mortality, and overall hospitalization costs. It is unknown whether NVC removal increases risk to the patient.

Our review has several limitations. There is risk of bias, because our center would prefer to use the chamber method rather than the NVC method. There is also lack of literature that specifically addresses the topic of NVC removal. Finally, as a single institution, we were limited to products/manufacturers available at our center, and it is possible that manufacturer recommendations differ because of differences in design, including the filter and vent mechanism.


On the basis of our review, there is insufficient evidence that either method of EVD zero-calibration is superior. In addition, there is insufficient evidence to suggest removing the NVC contributes to infection or causes harm. Further research is needed to make recommendations regarding the preferred method of zeroing and whether certain risk/benefits of one over the other exist.


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critical care; external ventricular drain; intracranial pressure

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