Equivalence of litmus paper and intragastric pH probes for intragastric pH monitoring in the intensive care unit

Abstract

Objective: To compare the accuracy of litmus paper-determined gastric pH to a nasogastric graphite antimony pH probe.

Design: A prospective clinical trial of gastric pH determination in patients enrolled in a study of histamine-2-receptor (H2) antagonists.

Setting: The medical intensive care unit (ICU) of a 450-bed county hospital.

Patients: Critically ill ICU patients requiring stress ulcer prophylaxis.

Interventions: Using a crossover design, the patients were randomized to initially receive an H2 antagonist by continuous infusion or intravenous bolus, and subsequently were crossed over to the other limb of the study.

Measurements and main results: Gastric pH was determined using pH-sensitive litmus paper at the initiation of each limb of the study and at 1, 2, 4, and 8 hrs after the initiation of H2 receptor antagonist therapy. In addition, gastric pH was continuously determined over the same time period utilizing a graphite antimony pH probe. Gastric pH measurements determined with litmus paper and intragastric pH probes demonstrated an excellent correlation (r2 = .93, p < .001). McNemar's test of correlated proportions could not demonstrate a significant difference between the two monitoring methods (chi-square = 0.5, p > .47), and the kappa statistic (0.95, p < .001) demonstrated excellent concordance. Bias measurement was 0.01 (95% confidence interval = -0.155 to 0.176).

Conclusions: Measurement of intragastric pH, using pH-sensitive litmus paper, is both sensitive and specific when utilizing a graphite antimony nasogastric pH probe as a reference standard. Litmus paper-determined gastric pH testing is both easy to perform and inexpensive. Therefore, based on the current data, we believe this technique (i.e., litmus paper determined gastric pH testing) to be the method of choice for determination of intragastric pH in patients at risk for stress gastric ulcers in the medical ICU.