Use of the injection test to indicate the oesophageal balloon position in patients without spontaneous breathing: a clinical feasibility study

Abstract

Objective To investigate the clinical feasibility of the injection test for balloon placement during oesophageal pressure measurement in patients without spontaneous breathing. Methods The injection test was performed in 12 mechanically ventilated patients under deep sedation and paralysis. During withdrawal of the balloon from the stomach and air injection into the gastric lumen of the catheter, the presence of the injection test wave in the balloon pressure tracing indicated that the whole balloon was positioned above the lower oesophageal sphincter (LES). The positive pressure occlusion test was performed at different balloon positions. Results In each patient, the injection test wave appeared at a distinct balloon depth, with a mean ± standard deviation of 41.9 ± 3.3 cm and range from 37 cm to 47 cm. The optimal ratio of changes in the balloon and airway pressure (0.8-1.2) during the positive pressure occlusion test was obtained when the balloon was located 5 cm and 10 cm above the LES in nine (75%) and three (25%) patients, respectively. Conclusions The injection test is feasible for identification of the whole balloon position above the LES during passive ventilation. The middle third of the oesophagus might be the optimal balloon position.

Keywords: Esophageal pressure; balloon; mechanical ventilation; passive; position.

Figure 1.

Modification of the catheter.

Figure 2.

Schematic of relationship between whole balloon and lower oesophageal sphincter (LES).

Figure 3.

Changes in airway pressure (P_AW), balloon pressure (P_B), and cardiac artifact in P_B tracing at different balloon positions. Mean and standard deviation are also shown.

Figure 4.

Ratio of change between balloon pressure and airway pressure (ΔP_B/ΔP_AW) during positive pressure occlusion test (a) and the absolute deviation of the ΔP_B/ΔP_AW ratio from unity (b) at different balloon positions in each patient. Solid marks represent the ΔP_B/ΔP_AW ratio that was closest to unity in each patient when the whole balloon was positioned above the lower oesophageal sphincter (LES); the median (horizontal line) and interquartile range (box) are also shown. Each grey line represents a single patient.