2001 OPEN FORUM Abstracts
A POTENTIAL FOR MONITORINGESOPHAGEAL PRESSURE WITH OPEN-ENDED, FLUID-FILLED OR AIR-FILLED CATHETERS.
Alexander AdamsMPH, RRT, Robert Shapiro MD, Apostolos Armaganides MD. Regions Hospital/Universityof MN, St. Paul, MN.
Background: Esophageal pressure(Pes) provides the best estimate available for monitoring intrathoracic, extrapulmonarypressure. Such pressure monitoring allows the calculation of work of breathingand pressure time product, important parameters to the clinician treating patientswith lung injury. The Pes catheter is a perforated, balloon covered catheterused specifically for this monitoring purpose. We examined the pressure monitoringability of conveniently available, open ended nasogastric tubes (either airfilled or fluid filled) as possible substitutes for Pes catheters.
Methods: In an air tight limbextending from a standard ventilator circuit we placed an esophageal catheter(Bicore, Riverside, CA), small and large bore channels from a nasogastric tube(16 ga), small and large bore channels from a fluid filled nasogastric tubeand an airway pressure tap. Pressure tracings from the 6 channels were simultaneouslyrecorded and digitized under a range of ventilator setting and impedance conditions.Signals were compared by peak pressure achieved, pressure at 90% of target,and exponential curve fitting.
Results: The figure displaysan example that compares 3 tracings: balloon, fluid-filled and air-filled (identicalto Paw) catheters. By visual inspection and the measurements of intertracingcomparisons, the esophageal catheter signal was dampened by the balloon; thePes catheter reaches pressures more slowly and underattains peak pressures.The other catheters had better responsiveness to pressure change yet their signalsdisplayed artifacts; the signals did not correlate to exponential fits as wellas the Pes catheter.
Conclusion: Fluid or air filledcatheters measure pressures with greater fidelity than a standard esophagealcatheter yet their signals were more susceptible to artifacts. Static pressurescan be monitored by either open ended or balloon covered catheters while dynamicpressure tracings should be scrutinized for effects from dampening, phase lagor artifacts.