Monitoring gastric pH levels

Stress gastritis in critically ill patients can be prevented by neutralizing gastric acid. Antacids are commonly used to accomplish this, but whatever the agent used, proper pH monitoring by aspiration of gastric fluid is necessary. This technique is labor intensive, but alternative methods have not proved practical. A simple pH probe in a nasogastric tube was tested to evaluate its accuracy in determining gastric pH in critically ill patients. Thirty-one patients in the surgical intensive care unit were studied for an average of 5.2 days with a range of one to 21 days. A nasogastric tube with a graphite and antimony pH sensor implanted in the tip (GrapHProbe ST, Zinetics Medical) was placed in each patient. The probe can be attached to a pH meter to read the gastric pH. Double aspiration samples from the nasogastric tube were taken for pH determination by pH paper, which guided antacid treatment to keep the pH equal to or greater than 5.0. Patients were monitored at two hour intervals and a total of 1,940 paired measurements were available for comparison. Comparison of values was based on a correlation of 1.5 pH units or whether or not the difference between the readings would have altered antacid therapy. Seventy-one per cent of the paired measurements were within 1.5 pH units. In only 4.3 per cent of the measurements would antacid treatment have been withheld based on the pH probe when compared with the aspiration pH. In 21 per cent of the measurements, treatment was indicated by the pH probe but not by the aspiration pH. The pH probe is a reliable, rapid method for monitoring gastric pH. It is less labor intensive than gastric aspiration and provides similar information in the patient at risk for stress gastritis.