Zeroing a Transducer on an External Ventricular Drain.

BACKGROUND

External ventricular drains (EVDs) are commonly used in severely brain-injured patients to diagnose intracranial hypertension. The accuracy of the intracranial pressure reading is dependent on zeroing the external transducer to air. Recent concern about zeroing techniques has been identified in the neuroscience community. The open method requires removing the nonvented cap, and the closed method requires zeroing through the filter at the top of the burette. This critical appraisal seeks to explore whether zeroing a transducer on an EVD through the filter of the burette provides the same baseline zero as opening the transducer to air.

METHODS

Independent searches in CINAHL, PubMed, and Web of Science were conducted using "external ventricular drain* OR EVD AND transducer"; secondary search terms included "zero AND transducer" AND "ventric."

RESULTS

Database search produced 1 single observation study and 2 clinical practice guidelines from neuroscience professional organizations. The single observation study provided no evidence of equivalence between the 2 zeroing methods; the 2 clinical practice guidelines reference the open method. The transducer manufacturer's instructions for use direct the clinician to open the transducer to air by removing the nonvented cap.

CONCLUSION

The question "Does zeroing the transducer on an EVD through the filter of the burette provide the same baseline zero as opening the transducer to air?" cannot be answered with the results of this appraisal. However, evidence found in the literature does suggest an open method to ensure the most accurate physiological value for treatment decisions.