Predictive Values for Time from Transducer Stopcock Closure to Accurate Intracranial Pressure Reading

Background: When using an external ventricular drain (EVD) to monitor intracranial pressure (ICP), nurses need to know how long to wait after each manipulation of the transducer before the displayed ICP value represents an accurate signal. This study explores ICP signal equilibration time (EqT) under clinical conditions. Methods: This was a prospective ex vivo study using a simulated skull, standard EVD tubing, and a strain gauge transducer. All 270 trials simulating 90 combinations of different pressures and common clinical conditions were completed in August 2021. Each trial was recorded on video. Videos were scored using video editing software to obtain the exact start and stop time for each trial. Results: The mean EqT was 44.90 (18.77) seconds. One hundred fifty (55.56%) observations did not reach their expected value within 60 s. The longest mean EqTs were noted when blood was present in the EVD tubing (57.67 [8.91] seconds), when air bubbles were in the tubing (57.41 [8.73] seconds), and when EVD tubing was not flat (level) (50.77 [15.43] seconds). An omnibus test comparing mean EqT for conditions with no variables manipulated (30.08 [16.07] seconds) against mean EqT for all others (47.18 [18.13] seconds) found that mean EqTs were significantly different (P < 0.001). Conclusions: Even when no additional variables were introduced, the mean EqTs were ~ 30 s. Common clinical variables increase the length of time before a transducer connected to an EVD will provide an accurate reading. Nurses should wait at least 30 s after turning the EVD stopcock before assuming ICP value reflects accurate ICP.