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

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.