ASSESSMENT OF GASTRIC-ACIDITY IN INTENSIVE-CARE PATIENTS - INTERMITTENT PH REGISTRATION CANNOT REPLACE CONTINUOUS PH MONITORING

Objective. To test the accuracy of colour-scaled indicator papers to m easure pH values and to study the correlation between this method of m easuring gastric juice pH once daily and 24-h continuous intragastric pH monitoring in intensive care patients. Design. The accuracy of indi cator papers was tested in the laboratory using colourless solutions a nd aspirated gastric juice and was then verified with a laboratory pH meter. Continuous intragastric pH monitoring was performed in mechanic ally ventilated ICU patients. Percentages of time with a pH value < 3. 0 and median pH values by 24-h continuous intragastric pH monitoring w ere compared to pH values measured once daily with indicator paper. Se tting: A mixed ICU. Patients: A total of 150 measurements were taken b y continuous pH monitoring in 91 mechanically ventilated ICU patients. Measurements and results: The correlation between the pH measured wit h the indicator paper and subsequently verified with a laboratory pH m eter in colourless solutions was 0.96 [regression coefficient (RC) 0.9 8, 95% confidence interval (CI) 0.91-1.05]. Measured in gastric juice it was 0.95 (RC 0.95, 95% CI 0.88-1.01). The correlation between media n pH values, determined with 24-h continuous intragastric pH monitorin g, and values measured with indicator papers was 0.39 (RC 0.43, 95% CI 0.26-0.59). The mean difference in pH, as determined by the analysis of Bland and Altman [22], was 0.9 with a SD of 4.7. The correlation be tween the percentage of time with pH < 3.0, as obtained with continuou s registration, and median gastric pH values (also obtained with conti nuous registration) was - 0.94 (RC - 0.06, 95% CI - 0.06- - 0.05); the correlation between the time and gastric pH values (measured with ind icator paper) was - 0.40 (RC - 0.02, 95% CI - 0.03- - 0.02). Conclusio n: The colour-scaled indicator paper is an accurate method of measurin g pH values, but there is a poor correlation between gastric pH values measured once daily and a total measurement derived from 24-h continu ous intragastric pH monitoring. Changes in intragastric pH values cann ot be accurately studied when measuring acidity once daily. The influe nce of various treatment regimens on intragastric acidity in relation to the development of gastric colonization and nosocomial pneumonia sh ould be investigated either with continuous intragastric monitoring or with frequent measurements in aspirated gastric juice.