The Science Journal of the American Association for Respiratory Care

2005 OPEN FORUM Abstracts

Exhaled breath condensate pH can be safely and continuously monitored in mechanically ventilated patients

B Walsh, RRT-NPS, J Hunt, MD, A Smith, D. Mackey MD, University of Virginia

Background: Over the past several years, there has been a growing literature regarding changes in airway lining fluid (ALF) pH in acute and chronic respiratory diseases that are characterized, at least in part, by inflammation. Investigators have demonstrated that the pH of exhaled breath condensate (EBC) is low (acidic) in multiple pulmonary inflammatory diseases including asthma, COPD, cystic fibrosis, pneumonia, and ARDS. A key advantage of EBC is the safety and ease of sample collection in spontaneously breathing patients. However, we wished to determine if that same advantage is present with mechanically ventilated patient.

Methods: We examined the use of measuring, gas-standardizing (removing CO2), and continuously monitoring exhaled breath condensate from the expiratory port of the Servo i ventilator (Maguet Inc.). We modified RTubeTM(Respiratory Research Inc.) device by removing the one-way valves from the system and attached a electric cooling system (CSC Subzero Electra Cool II) to an aluminum sleeve. A two chamber deareation and pH measuring device was designed, manufactured, and added to the bottom of the RTube. EBC is gravity feed into the first chamber where the solution is bubbled with oxygen to washout CO2. Overflow is then directed to the second chamber where oxygen is again bubbled into the solution to wash out any remaining CO2. The pH is measured in this last chamber by a micro combination pH electrode (Thermo Electron). The pH probe is connected to a 9 volt Flexilog 2000 (Oakfield Instruments) meter which is portable and can be down loaded to display trends and 6 second sampling data.

Results: We benched tested the above system at variable flows (2-120 l/minute) and ventilator settings. We recorded the graphics before and after applying the device to the ventilator. There were no changes in graphics or volume monitoring. With IRB approval we have monitored 7 different patients from 6-96 hours. We compared the pH of the accumulated EBC collected in the storage container with the geometric mean of all the pH data points collected during the continuous second-by-second measurement of EBC pH, and found a good correlation, internally validating that the continuous EBC pH measurement system is providing accurate, well gas-standardized readings for up to 96 hours.

Conclusion: Continuously monitoring EBC pH from the exhaust port of ventilators is achievable safely, and reliably provides data that may be useful in monitoring critically ill patients.

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