Accuracy of pH strip testing and pH liquid testing versus standard pH meter of gastric contents in critically ill patients: a diagnostic accuracy study

Abstract

ObjectiveThe utilisation of pH level measurements from gastric contents may indicate the preferred tip position of a nasogastric tube or monitor the efficacy of stress ulcer prophylaxis in critically ill patients. We aimed to determine the accuracy of pH strip (pHS) tests and pH liquid (pHL) tests compared with the standard pH meter (pHM).DesignDiagnostic accuracy study.SettingGastric contents from medically critically ill patients.ParticipantsIn total, 113 gastric samples were collected from 27 critically ill patients.Outcome measureThe level of pH measured by pHM, pHS and pHL.ResultsThe pH values measured by pHM, pHS and pHL were 5.83 (IQR 5.12–6.61), 5.50 (IQR 5.00–6.00) and 5.75 (IQR 5.25–6.25), respectively. The pHS test showed greater accuracy, exhibiting a more positive correlation with the standard pHM measurement than the pHL test, with Y=0.95*X+0.56; rho=0.91, p<0.001, and Y=1.09*X - 0.72; rho=0.75, p<0.001, respectively. However, the pHS test demonstrated less agreement with the pHM than the pHL test, with biases of –0.27 versus 0.18, respectively. Noticeably, a slight variation in pHL from the standard pH values was found when we measured gastric contents with a pH lower than 5.ConclusionBoth the pHS and pHL methods were good options for measuring gastric pH in critically ill patients. However, it was advisable to find alternative approaches to the pHL testing method when anticipated gastric acidity levels fall below 5.Trial registration numberTCTR20220530004.