Respiratory mucus pH in tracheostomized intensive care unit patients: Effects of colonization and pneumonia.

Daily, we studied the effects of colonization and pneumonia on the pH of respiratory mucus in 23 critically ill patients. Sixteen patients had tracheobronchial colonization, and 11 of these subsequently developed pneumonia. Two other patients developed pneumonia without prior colonization. For the 13 patients with pneumonia, there was a significantly greater decrease in pH below the value recorded on the day of intubation vs. that for the ten patients who did not have pneumonia. In the 11 patients who developed initial colonization and then pneumonia, the pH did not change after colonization, but became acidic with the development of pneumonia. The pH returned to basal levels after recovery from pneumonia. We tested the pH value to differentiate between colonization and infection in these intubated critically ill patients. A decrease in pH greater than or equal to 0.2 below the pH value on the day of intubation could predict the presence of pneumonia with a positive predictive value of 90%. This decrease in pH occurred before or on the same day as the development of radiologically detectable pneumonia in most cases. Daily monitoring of the pH of tracheal mucus may be of value in critically ill intubated patients.