Measuring intramucosal pH in very low birth weight infants

Maintenance of adequate perfusion is essential for health of the intestinal mucosa. Methods available to assess intestinal perfusion provide informati on on mesenteric blood flow, which may differ from mucosal flow. Intramucos al pH (pH(i)) is influenced by tissue oxygenation and perfusion. Gastric pH (i) can be measured using the technique of tonometry. A prospective observa tional clinical study was performed to examine relationships between measur ed gastric pH(i) and mucosal CO2 (mCO(2)), and acid-base balance, gastroint estinal complications (necrotizing enterocolitis and perforation), and deat h in infants < 1500 g birth weight. A nasogastric tonometry catheter (size 5F) was inserted into the stomach of infants, and pH(i) was calculated from mCO(2) levels measured using saline tonometry. Measurements were performed at 3, 12, 24, and 48 h, then daily until arterial access was unavailable. Two hundred eleven sets of measurements were performed on 38 infants [birth weight (mean +/- SD), 863 +/- 241 g; gestation, 26.5 +/- 1.8 wk; and media n Clinical Risk Index for Babies score, 8.0 (interquartile range, 5.0-10.75 )]. Mean pH(i) was 7.27 (95% confidence interval, 7.26-7.28) and mean mCO(2 ) was 47.0 mm Hg (95% confidence interval, 45.7-48.3 mm Hg). pH(i) and mCO( 2) correlated significantly with arterial pH (pH(a)), arterial Pco(2) (Paco (2)), and arterial base excess. There were no significant relationships bet ween pH(a) and pH gap (pH(a)-pH(i)) or CO2 gap (mCO(2)-Paco(2)). Recurrent low pH(i) (< 7.2 on more than one occasion) and an mCO(2)/Paco(2) ratio of greater than or equal to 1.29 were significantly associated with an increas e in gastrointestinal complications. There were no statistically significan t associations with death. In conclusion, changes in pH gap and CO2 gap can occur without alteration in pH(a). Abnormalities in pH(i) might predict ga strointestinal complications in infants < 1500 g.