• Xiu-Mei Sun, Guang-Qiang Chen, Hua-Wei Huang, Xuan He, Yan-Lin Yang, Zhong-Hua Shi, Ming Xu, and Jian-Xin Zhou.
• Department of Critical Care Medicine, Beijing Tiantan Hospital, Capital Medical University, Address: No 6, Tiantan Xili, Dongcheng district, Beijing, 100050, China.
• BMC Anesthesiol. 2018 Feb 14; 18 (1): 21.

BackgroundAccurate measurement of esophageal pressure (Pes) depends on proper filling of the balloon. Esophageal wall elastance (Ees) may also influence the measurement. We examined the estimation of balloon-surrounding elastance in a bench model and investigated a simplified calibrating procedure of Pes in a balloon with relatively small volume.MethodsThe Cooper balloon catheter (geometric volume of 2.8 ml) was used in the present study. The balloon was progressively inflated in different gas-tight glass chambers with different inner volumes. Chamber elastance was measured by the fitting of chamber pressure and balloon volume. Balloon pressure-volume (P-V) curves were obtained, and the slope of the intermediate linear section was defined as the estimated chamber elastance. Balloon volume tests were also performed in 40 patients under controlled ventilation. The slope of the intermediate linear section on the end-expiratory esophageal P-V curve was calculated as the Ees. The balloon volume with the largest Pes tidal swing was defined as the best volume. Pressure generated by the esophageal wall during balloon inflation (Pew) was estimated as the product of Ees and best volume. Because the clinical intermediate linear section enclosed filling volume of 0.6 to 1.4 ml in each of the patient, we simplified the estimation of Ees by only using parameters at these two filling volumes.ResultsIn the bench experiment, bias (lower and upper limits of agreement) was 0.5 (0.2 to 0.8) cmH2O/ml between the estimated and measured chamber elastance. The intermediate linear section on the clinical and bench P-V curves resembled each other. Median (interquartile range) Ees was 3.3 (2.5-4.1) cmH2O/ml. Clinical best volume was 1.0 (0.8-1.2) ml and ranged from 0.6 to 1.4 ml. Estimated Pew at the best volume was 2.8 (2.5-3.5) cmH2O with a maximum value of 5.2 cmH2O. Compared with the conventional method, bias (lower and upper limits of agreement) of Ees estimated by the simple method was - 0.1 (- 0.7 to 0.6) cmH2O/ml.ConclusionsThe slope of the intermediate linear section on the balloon P-V curve correlated with the balloon-surrounding elastance. The estimation of Ees and calibration of Pes were feasible for a small-volume-balloon.Trial RegistrationIdentifier NCT02976844 . Retrospectively registered on 29 November 2016.

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