Sitting and Supine Esophageal Pressures in Overweight and Obese Subjects

Abstract

Esophageal pressure can be used to approximate pleural pressure and might be clinically useful, particularly in the obese e.g to guide mechanical ventilator settings in critical illness. However, mediastinal artifact (the difference between true pleural pressure and esophageal pressure) may limit acceptance of the measurement, and reproducibility of esophageal pressure measurements remains unknown. Therefore, we aimed to assess the effect of body posture on esophageal pressure in a cohort of obese but healthy subjects, some of whom had multiple measurements, to address the clinical robustness of esophageal manometry. Twenty-five overweight and obese subjects (BMI>25kg/m2) and 11 control lean subjects (BMI<25kg/m2) underwent esophageal manometry with pressures measured seated and supine. Twenty overweight and obese subjects had measurements repeated after ~1-2 weeks. Anthropometric data and sitting and supine spirometry were recorded. The average end-expiratory esophageal pressures sitting and supine were greater in the overweight and obese group than the lean group (sitting −0.1±2.1 vs. −3.3±1.2cmH2O, supine 9.3±3.3 vs. 6.9±2.8cmH2O, respectively). The mean differences between repeated measurements were small (−0.3 ± 1.7cmH2O sitting and −0.1 ± 1.5cmH2O supine). Esophageal pressures correlated with a number of anthropometric and spirometric variables. In conclusion, esophageal pressures are slightly greater in overweight and obese subjects than lean subjects; but changes with position are similar in both groups. These data indicate that mediastinal weight and postural effects on esophageal pressure are within a clinically acceptable range, and suggest that esophageal manometry can be used to inform clinical decision making across wide range of body types.

Transpulmonary pressure monitoring during mechanical ventilation: a bench-to-bedside review

“…Moreover, P TP at FRC in the supine position was negative in 7 out of 10 subjects, on average −3.3 ± 3.2 cm H 2 O, and it was still negative after correcting the value for the weight of the mediastinum. A study in obese patients found similar results: P eso increased from 0.1 ± 2.3 cm H 2 O to 9.4 ± 3.9 cm H 2 O when changing from the upright to the supine position respectively [49]. This study showed how the influence of mediastinum and tissue on P eso was similar in obese and normal subjects.…”

Two Steps Forward in Bedside Monitoring of Lung Mechanics: Transpulmonary Pressure and Lung Volume

“…Th ese results point toward a relatively constant increment in Pes attributable to 'mediastinal artifact' when supine, independent of the body mass index (BMI). Moreover, elevated IAP and reduced chest wall compliance appear to explain components of the higher end-expiratory Pes values encountered in both positions among overweight/obese subjects [12].…”

“…Recently, Owens et al [12] concluded that Pes measurement artifacts imposed by mediastinal weight and postural eff ects are within a clinically acceptable range. Th ese authors [12] compared the cha nges in end-expiratory Pes secondary to position changes in a cohort of overweight/obese spontaneously breathing patients with those occurring in lean subjects.…”

“…Recently, Owens et al [12] concluded that Pes measurement artifacts imposed by mediastinal weight and postural eff ects are within a clinically acceptable range. Th ese authors [12] compared the cha nges in end-expiratory Pes secondary to position changes in a cohort of overweight/obese spontaneously breathing patients with those occurring in lean subjects. Despite sitting and supine end-expiratory Pes values that were higher in the overweight/obese cohort than in the lean cohort, the observed changes in end-expiratory Pes as a result of repositioning from sitting to supine were unexpectedly similar in both groups [12].…”

“…Th ese authors [12] compared the cha nges in end-expiratory Pes secondary to position changes in a cohort of overweight/obese spontaneously breathing patients with those occurring in lean subjects. Despite sitting and supine end-expiratory Pes values that were higher in the overweight/obese cohort than in the lean cohort, the observed changes in end-expiratory Pes as a result of repositioning from sitting to supine were unexpectedly similar in both groups [12]. Th ese results point toward a relatively constant increment in Pes attributable to 'mediastinal artifact' when supine, independent of the body mass index (BMI).…”