169 A Blinded, Prospective Comparison of the Accuracy of Zeroing Methods for External Ventriculostomy Drain (EVD) Transducers

INTRODUCTION: In neurosurgical ICUs, external ventriculostomy drain (EVD) transducers are zeroed using one of two methods: an “open” method (removing the non-vented cap from the transducer) or a “closed” method (lowering the buretrol to zero). While the closed method has the advantage of maintaining a closed, sterile system, it goes against manufacturer guidelines and may compromise accuracy. METHODS: This was a blinded, prospective bench study. An EVD collection system (Integra) was connected to a saline bag. The height of the saline bag was changed to generate pressures from 5-30 mmHg which were confirmed by a manometer connected in series (ground truth). One examiner zeroed the transducer (Edwards Lifesciences TruWave arterial line transducer) using one of the methods dictated by a random number generator. Another examiner, blinded to both the zeroing method and manometer level, then recorded the pressure from the monitor. Paired T-tests then compared the accuracies of each zeroing method. RESULTS: 408 data points were collected across two separate transducers and collection systems. Mean differences from ground truth for open and closed methods were 0.55 and 0.29 mmHg, respectively (p=0.0001). Successful trials, defined as accurate within 1 mmHg of ground truth, were 85.8% and 99%, respectively. CONCLUSIONS: While transducers are designed for arterial lines and recommend opening the cap for zeroing, here we demonstrate that EVD systems can be zeroed more accurately without opening the system to air. Both methods appear to be highly accurate, but the closed method may have the added benefit of minimizing the risk of contamination during zeroing.