Intracranial pressure monitoring is affected by transducer blood contamination

Abstract-Text (inkl. Referenzen und Bildunterschriften)

Funding: Helene Fuld Health Trust National Institute for Evidence-Based Practice in Nursing and Healthcare Research Grant. Natus Medical Inc. donated equipment.

Background. Acquired brain injury patients may have placement of an external ventricular drain (EVD) to manage elevated intracranial pressure (ICP). Successful ICP management requires accurate monitoring and reporting of ICP via a pressure transducer. This study examines the impact on ICP accuracy when a transducer is contaminated by solutions of varying viscosity.

Methods. This preclinical laboratory comparative design study used an acrylic pressure chamber filled with 6,000mL of saline to simulate a human skull model. Two Edwards TruWave strain gauge transducers (arbitrarily selected as control (CONT) and Experiment (EXP)) were attached to 2 EVD drainage systems and connected to the chamber via EVDs (Natus). After priming both transducers with saline, they were leveled to the center of the chamber and zero calibrated. To simulate changes in ICP, the chamber was moved to 6 different elevations (Figure 1). At each position, 4 metrics were recorded: time until each transducer 1st reached the expected pressure; time until the pressure stabilized for 30 seconds; pressure 1 minute after the position change; and final resting pressure. Eight study conditions include: (1) priming of both transducers with saline; (2-6) priming only the EXP transducer with a 10, 25, 50, 75, 100% glycerol:saline solution; (7) the EXP transducer was re-zeroed when primed with 100% glycerol; (8) primed the EXP transducer with human blood. Data was continually acquired via Natus CNS (formerly Moberg) at 256 Hz.

Results. Wilcoxon signed rank test models reveal statistically significant differences for CONT vs EXP in median: (1) time to first reach expected pressure (9.5 [5.5-14.5.0] vs 18.0 [11.0-27.0] sec; P<.0001); (2) time to stability (9.5 [5.5-17.0] vs 23.0 [14.0-32.0] sec; P<.0001); (3) pressure at 1-minute (11.0 [8.5-28.5] vs 9.0 [8.0-27.0] mmHg; P<.0001); and (4) final resting pressure (11.0 [9.0-29.0] vs 9.0 [8.0-27.0] mmHg; P<.0001).

Conclusion. High viscosity contaminates (e.g., blood) in the transducer impact the time between transient changes and stable measurement in ICP monitoring. Contaminate in the transducer results in a longer time for ICP values to stabilize and the resulting pressure is significantly lower than the expected pressure. Future study iterations should explore the long-term effects of transducer contamination on the validity of pressure values and the time necessary for a measurement to stabilize following a transient (e.g., opening EVD).