False positives in determining the proper location of the esophageal pressure catheter during occlusion test

Abstract

Objective: To show that the esophageal pressure (P_es) - airway pressure (P_ao) loop, with airway occlusion at the end of expiration - known as the occlusion test and which is the gold standard to determine the proper placement of the esophageal pressure catheter, could yield false positive results when the catheter is accidentally inserted into the airway.

Methodology: Case report of 5 Adults with cranioencephalic trauma and no pulmonary involvement or any other trauma or associated pathology from a trauma intensive care (ICU) unit of a University Hospital. Placement of an esophageal balloon catheter for monitoring mechanical ventilation at weaning off the invasive mechanical ventilation system, is done.

Results: Once the esophageal catheter is placed, P_es-Time, P_ao-Time and P_es-P_ao loop charts are developed with airway expiratory occlusion. The datalogger software and the Galileo Gold ventilator (Hamilton Medical, Rhäzüns, Suiza) were used, together with an advanced application developed in Excel (Microsoft Office 2003) to organize and plot the variables monitored.

Conclusion: The occlusion test (P_es-P_ao Loop with airway occlusion at the end of the expiration) generates a 45º-slope plot, when the catheter is properly placed inside the Esophagus. This is considered the gold standard test. However, a similar plot can also be obtained if the esophageal catheter is accidentally introduced into the airway and the clinician inadvertedly overlooks the situation.