Determination of the optimal pressure support level evaluated by measuring transdiaphragmatic pressure.

The purpose of this study was to determine the optimum pressure support (PS) in six patients with respiratory failure. Esophageal pressure (Pe), gastric pressure (Pg), airway pressure, and transdiaphragmatic pressure (Pdi), obtained by subtracting Pe from Pg, were measured using a newly developed multiluminal nasogastric catheter. For each patient, different PS levels were selected every 20 minutes, and measurements were made at each PS level. We defined the optimum PS level as the level that showed the minimum Pe value. Respiratory rate (RR) decreased and tidal volume (VT) increased with an increase in PS level. RR and VT at the optimum PS were 19.7 +/- 5.5 breaths per minute and 11.7 +/- 4.5 ml/kg, respectively. Pdi decreased linearly with increasing PS level in all patients. Mean Pdi at the optimum Ps was 4.2 +/- 1.2 cm H2O. Based on the relationship between Pdi and PS level, we constructed an equation to estimate the optimum PS level as follows: Optimum PS level = [( Pdi during T-piece mode] - 4)/0.8. We conclude that Pdi measurement is helpful for titrating the required PS level.