The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts

AIRWAY PH, ESOPHAGEAL IMPEDANCE/PH, AND TRACHEAL PEPSIN DURING MECHANICAL VENTILATION

Ashli O'Rourke1,Michael D. Davis1, Brian K. Walsh1, John Slovensky1, John F. Hunt1, Thomas Pajewski1



Background: Several studies have shown the value of exhaled breath condensate (EBC) pH as a biomarker for airway acidification and lung inflammation. Walsh et al (Respir Care 2006, 51:1125-1131) first reported the ability to continuously monitor EBC pH in mechanically ventilated patients using the Airway Lining Fluid Analyzer (ALFA, Respiratory Research, Inc, Austin, TX). ALFA identifies acidification of the airway caused by acid aspiration or by acid formed in the airway intrinsically. We wished to develop methodology to distinguish these two forms of airway acidification. We performed ALFA monitoring concurrent with Sleuth esophageal pH/impedance monitoring (Sandhill Scientific, Inc, Highlands Ranch, CO), and measurements of gastric pepsin in tracheal aspirates (TA) using a specific activity assay. We have now performed these concurrent measurements in (43) patients undergoing surgery (primarily spinal procedures) using total intravenous anesthesia (without paralysis) and endotracheal mechanical ventilation with the Servo I (Maquet) in both the operating room and ICU settings. Of the 43 patients enrolled, we excluded 16 from analysis; 9 due to early termination of surgery, 2 due to an inability to place the Sleuth probe, 1 due to theft of a laptop making data inaccessible, and 1 due to an inability to obtain tracheal aspirate. Results indicate that ALFA monitoring seems most sensitive for acid aspiration; pepsin in TA appears most specific for aspiration in general, but pepsin measures are unable to determine timing of aspiration well. Sleuth impedance monitoring was of limited value in anesthetized patients and esophageal pH was not as sensitive as ALFA. Sleuth identified reflux events in 3 patients (11%) of the population studied. Patients with reflux events captured on Sleuth had significantly higher pepsin levels in their tracheal aspirates (median of 41529 ng/dl vs 6488 ng/dl in non-reflux population); these events had correlating acute drops in EBC pH recorded on ALFA. These combined monitoring modalities provide the most comprehensive method described to date for monitoring reflux/aspiration in mechanically ventilated patients; this monitoring may prove elucidating when investigating ventilator associated pneumonia and ventilator-induced lung injury.