Tracheal aspirate pH is alkaline in pre-term human infants

The pH of sputum and exhaled breath condensate is abnormal in several pulmonary disorders. Though airway pH regulatory proteins may be abnormally expressed in human development, the tracheal aspirate pH of infants born prematurely has not been studied. Undiluted mid-tracheal aspirate samples were obtained on the first day of life from pre-term (23-30 weeks' gestation) and term (> or =37 weeks' gestation) infants for pH measurement; subsequently, pH was measured on days 7, 14 and 21 from the pre-term infants who remained intubated. Thirty-five pre-term infants and eight term infants had samples collected on the first day of life. The mean pH of the pre-term infant samples (8.31 +/- 0.35) was significantly higher than that of the term infants (7.83 +/- 0.39). The pH in pre-term infants' airways fell with prolonged endotracheal intubation; the maximal decrease was of -1.37 +/- 0.96 pH units to 6.89 +/- 0.77. Pre-term infants have a higher tracheal aspirate pH than full-term infants, and their airways tend to become more acidic with prolonged mechanical ventilation. The present data demonstrate for the first time that premature infants may have abnormal tracheal aspirate pH.