Determination of a Practical pH Cutoff Level for Reliable Confirmation of Nasogastric Tube Placement

Background: Enteral feeding is a common method of nutrition support when oral intake is inadequate. Confirmation of correct nasogastric (NG) tube placement is essential. Risks of morbidity/mortality associated with misplacement in the lung are well documented. Studies indicate that pH <= 4 confirms gastric aspirate, but in pediatrics, a pH of gastric aspirate is often > 4. The goal of this study was to determine a reliable and practical pH value to confirm NG tube placement, without increasing the risk of not identifying a misplaced NG tube. Methods: Pediatric inpatients older than 4 weeks receiving enteral nutrition (nasogastric or gastrostomy) were recruited over 9 months. Aspirate samples were pH tested at NG tube placement and before feedings. If pH > 4, NG tube position was confirmed by chest radiograph or further investigations. In addition, intensive care unit (ICU) patients who required endotracheal suctioning were recruited, and endotracheal aspirate samples were pH tested. Results: A total of 4,330 gastric aspirate samples (96% nasogastric) were collected from 645 patients with a median (interquartile range [IQR]) age of 1.0 years (0.3-5.2 years). The mean (standard deviation [SD]) pH of these gastric samples was 3.6 (1.4) (range, 0-9). pH was > 4 in 1,339 (30.9%) gastric aspirate samples, and of these, 244 were radiographed, which identified 10 misplaced tubes (1 with pH 5.5). A total of 65 endotracheal aspirate samples were collected from 19 ICU patients with a median (IQR) age of 0.6 years (0.4-5.2 years). The mean (SD) pH of these samples was 8.4 (0.8) (range, 6-9.5). Conclusion: Given that the lowest pH value of endotracheal aspirate sample was 6, and a misplaced NG tube was identified with pH 5.5, it is proposed that a gastric aspirate pH <= 5 is a safer, reliable, and practical cutoff in this population. (JPEN J Parenter Enteral Nutr. 2011;35:540-544)