Measurement of pleural pressure with oesophageal catheter-tip micromanometer in anaesthetized humans.

In spontaneously breathing anaesthetized subjects, we studied a new technique for the measurement of changes in pleural pressure. Seven ASA physical status I patients undergoing general anaesthesia (enflurane 1-2 MAC, nitrous oxide 50%, and oxygen) for minor orthopaedic surgery were studied in the supine position. Changes in oesophageal pressure (delta Pes) were measured by means of a catheter-tip pressure transducer. This micromanometer was positioned according to an occlusion test where delta Pes were compared with the changes in airway opening pressure (delta Pao). Optimizing the signal/noise ratio, we observed a linear relationship between delta Pes and delta Pao. In each patient, the delta Pes/delta Pao relationship was highly reproducible. Using the linear regression analysis to characterize the delta Pes/delta Pao relationship, we have developed a different approach for the positioning of oesophageal catheter. After statistical analysis of the observed delta Pes/delta Pao relationship, a "calibration" factor can be used in order to correct the observed slope of the delta Pes/delta Pao relationship to its theoretical value. We conclude that an oesophageal catheter-tip micromanometer can be used in anaesthetized supine patients to measure changes in pleural pressure.