Impact of Baydur Ratio Correction on the Reliability of Esophageal Pressure Measurement

Tidal changes in esophageal pressure (ΔPes) are used as a surrogate for pleural pressure changes (ΔPpl) to assess chest wall mechanics. The Baydur ratio evaluates pressure transmission and guides catheter positioning. The effects of correcting ΔPes using the Baydur ratio on the accuracy of ΔPpl estimation and its dependence on ventilation mode, spontaneous inspiratory effort, and body position, remain unclear. In ten pigs, ΔPpl was measured using intrapleural balloon catheters, while Pes was recorded at three esophageal locations in supine and prone positions. Animals underwent controlled and assisted ventilation. Baydur ratios were derived during assisted ventilation and from external chest compressions during controlled ventilation. ΔPes before and after correction was compared with ΔPpl using mixed-effects models and Bland-Altman analysis. Additionally, we quantified the proportion of values with (ΔPes-ΔPpl) ≤ 1 cmH₂O. During assisted ventilation, ΔPes showed good agreement with posterior ΔPpl. Baydur correction improved scaling and association (slope 0.76 vs 0.50; r 0.81 vs 0.79, p<0.01) and increased values within ±1 cmH₂O from 29% to 45% when the Baydur ratio fell outside the accepted range. During controlled ventilation, ΔPes showed weaker association and wider limits of agreement, without improvement after correction. Similar patterns were observed in prone position. ΔPes more accurately reflected posterior ΔPpl during assisted ventilation. Baydur correction improves scaling and association, particularly when the Baydur ratio falls outside the accepted range, but does not improve and may worsen agreement during controlled ventilation.