Work Of Breathing At Moderate Ventilation Is Not Affected By Balloon-tipped Catheter Positioning Methods

Abstract

Measuring respiratory mechanics (work of breathing; Wb) requires one to measure pleural pressure, which is done by measuring esophageal pressure (PES) using a balloon-tipped catheter placed approximately at the lower third of the esophagus. The accuracy of PES to reflect pleural pressure requires the catheter be positioned at the correct depth. Our recent systematic review has identified several methods for determining the correct catheter depth: the occlusion method - depth is identified through various occlusion tests; the withdrawal method - catheter is withdrawn from the stomach until a negative pressure deflection during an inhalation is observed then is withdrawn an additional 10 cm; and inserting the catheter 45 cm distal from naris. It is unknown if different positioning methods significantly influences the resultant mechanics data. PURPOSE: Compare catheter depth and the Wb, via modified Campbell diagrams, between positioning methods. METHODS: Five healthy participants (2 female; 22 ± 2 years, 177.7 ± 7.4 cm, 73.2 ± 7.5 kg) visited the lab on 3 occasions. Participants provided written informed consent and had spirometry assessed. In visit 2, participants were instrumented with a balloon-tipped catheter and then depths determined for each of the aforementioned three methods. In visit 3, chest wall compliance is measured using the two-point method, then participants completed a trial of voluntary hyperpnea for 5 min at a moderate ventilation (50 L/min) at each depth. The testing order was randomized and balanced. One-way repeated measures ANOVAs were used to compare the depths and Wb across methods (significance = P < .05). RESULTS: We found no difference in depth (45.0 ± 0.0 vs. 45.8 ± 3.2 vs. 44.5 ± 3.7 cm; P = .62) or the Wb across position methods (3.8 ± 1.8 vs. 3.2 ± 1.2 vs. 3.1 ± 1.3 Joules; P = .38). CONCLUSION: Our current data suggest that the three most commonly used catheter positioning methods do not yield significantly different depths. Likewise, a difference in catheter depth of ~1.5 cm does not appear to be sufficient to alter the Wb obtained at moderate ventilation. Future work, with more varied catheter depths, is needed to identify the magnitude of depth difference that would yield a physiologically meaningful difference in respiratory mechanics data. Support: Hooper Undergraduate Research Award (NAU)