To determine a practical pH cutoff level for safer confirmation of nasogastric tube placement

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Confirmation of correct nasogastric tube (NGT) placement is essential to ensure the safe delivery of nutrition without the risk of morbidity and mortality associated with misplacement in the lung resulting in aspiration, pneumonia, pneumothorax or death. Previous studies indicate a pH < 4 is indicative of gastric aspirate and hence a reliable indicator of correct NGT placement. At the Royal Children’s Hospital (RCH) in Melbourne, the current practice is to use this pH cut-off < 4 based on Metheny’s work, but this is not always clinically practical. The use of antacid medication and/or the presence of enteral feeds due to delayed gastric emptying may be contributing factors in a higher pH result, casting doubt on NGT position. A number of different clinical methods have been reported to determine NGT position including auscultation (listening for air passed down the tube), aspirate colour, administering oral fluids or flushing NGT with oral rehydration solution (ORS), but none are evidence-based methods. Radiography confirmation is the gold standard but has limited application secondary to availability, cost and radiation exposure. This study was undertaken to directly compare pH results of gastric aspirate samples with endotracheal aspirate samples, and particularly to examine potential overlap of pH results between the aspirate samples. This data can then be used to establish a reliable and clinically practical pH cut-off value for gastric aspirate without risking the safety of the patient by not identifying a misplaced NGT in the lung. Whilst undertaking this study, an adverse nasogastric-feeding incident occurred in the UK which led to the formation of a working party to challenge the assumptions and rituals of NGT placement. An NGT algorithm was developed using a risk assessment approach to improve the safety of NGT fed children and increase the awareness of the risks to health care providers. Subsequently, the National Patient Safety Agency (NPSA) published an alert that accepted a pH cut-off <5.5 as being an acceptable risk. This was decided by expert opinion and consensus rather than the result of new clinical research. This current study will provide further evidence for this consensus statement and ensure that our recommendations are based on evidence-based practice and lead to reduced patient risk. We compare the range of pH results between gastric and endotrachael aspirate samples, with particular interest in the area of overlap between the two samples. This data will help to determine a reliable and practical pH value to confirm NGT placement, without increasing the risk of not identifying a misplaced NGT.

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