Feeding through nasogastric tubes is an integral part of the care of critically ill patients. Improper placement of nasogastric tubes is not a rare occurrence and has been estimated to occur in 3% of all placements (Borgault and Halm 2009). Improper placement can lead to complications including esophageal perforation, pneumothorax, pulmonary aspiration and intracranial tube placement. Asphyxiation can result from aspiration of large volumes. Unfortunately, incorrect placement may remain undetected, resulting in enteral feed and medications being introduced directly into the lungs. Currently there are several methods for verifying proper placement of gastric tubes such as radiographic, auscultation, pH testing of aspirates and detection of CO2. Reviewing the recent literature may help to clarify which techniques are preferred for both proper positioning of the gastric tube on insertion and ensuring that it stays in place after insertion.
Review of the Literature
Bourgault and Halm (2009) performed a search of the literature using the key words enteral feeding/nutrition, nasogastric/feeding tubes, and placement/verification/confirmation to summarize the evidence of the efficacy of the different methods for verifying tube placement . The researchers examined 12 published studies that used auscultation, capnography, visual inspection, pH and bilirubin to verify feeding tube placement. Evidence was rated on a scale from 1-3 in terms of extent of support by evidence and amount of potential harm . They recommend that three methods currently used for verification of tube placement; aspirate inspection, the "bubble test" and auscultation be discontinued due to their unreliability and risk of harming the patient . CO2, pH and bilirubin testing may be useful for detecting when the tube has been placed in the lung, but they are unable to detect if the tube is in the esophageal junction or esophagus. In addition, they are not available for bedside use. They (Bergault and Halm) recommend radiography as the optimum method for placement verification. They do not address the issue of pediatric patients where it is advisable to minimize as much as possible the exposure to X-rays and do not discuss practices to ensure that the tube does not migrate after insertion.
The effect of implementation of a clinical practice guideline (CPG) for testing NG tube placement was examined by Peter and Gill (2008). Following an examination of the available literature a CPG was developed. The CPG included implementing a risk benefit assessment, replacement of litmus testing of gastric aspirates with pH testing and a discontinuation of the whoosh test. Following implementation of the CPG an audit was performed over a period of a month. They recommend the discontinuation of the whoosh test, the replace of the litmus test with the pH test and the use of a flowchart. In addition, they do not recommend the use of X-ray in every case where bedside testing methods fail (Peter and Gill 2008). Problems with the study includes possible inaccuracies due to incomplete or inconsistent data entry and further study is needed to determine which of the steps or combination of steps are most essential for clinical success.
Rauen et al. (2008) reviewed the literature about currently used practices for verification of tube position. Although the technique of air auscultation during air insufflation through the tube is still in clinical use, clinical research has in fact shown that this is an unreliable technique that can lead to inadvertent placement of the tube into the lungs.
Another technique, measurement of the pH of fluid aspirated immediately following tube placement, was found to be only partially efficacious. The theory behind this technique is that because gastric secretions are acidic and pulmonary secretions are alkaline, a simple pH test should be able to tell where the aspirate originated and hence where the tube is located. In fact, this technique is limited because the pH of gastric fluids can change under a number of conditions such as a result of ingestion of medications and is useful only if the pH is acidic meaning that the tube is located in the gastric system. The pH technique is therefore no longer recommended.
An additional method involving the use of aspirated fluid is visual inspection of the aspirated fluid. Pulmonary fluid is usually white or light yellow, while gastric fluid is dark yellow or green. However, as in the case of the pH technique, a number of factors can influence the color of the pulmonary fluid, so this technique is also not recommended.
Testing for the presence of Carbon Dioxide in the tube is a technique that is becoming more accepted. Because CO2 is found only in exhaled pulmonary gases the presence of this gas in the tube would indicate that the tube has entered the lungs. The authors (Rauen et al. 2008) cite several studies in which color-indicator carbon dioxide or end -- tidal carbon dioxide monitors were used to detect CO2. The technique was successful in all but one study, and it is recommended to develop a bedside technique for the use of this technology so that it can become more widely adopted.
Their final recommendation is to use radiography to verify positioning of both small and large bore tubes.
The use of capnography as compared to a colorimetric carbon dioxide detector was examined by Burns et al. (2006) in a prospective study involving 195 gastric tube insertions in 130 adult patients. The CO2 detector turns from purple to yellow to indicate the presence of CO2.
They found that inadvertent insertion into the lungs was associated with nasal insertions (P=0.3) and spontaneous breathing/non-intubated (P=0.1) and conclude (Burns et al. 2006) that the colorimetric device and capnography are equally accurate in detecting CO2 during gastric tube placement. The colorimetric device has the advantage of being lightweight and easy to operate, so it may be desirable to introduce it into wider use. A limitation of this study is that only adult sized gastric tubes were used.
Metheny (2006) used an evidence based approach to identify several risk for aspiration following tube insertion and how they may be modified. The factors named are malpositioned feeding tubes, gastric feeding despite markedly impaired gastric emptying, large gastric residual volume (GRV), and the supine position. Metheny (2006) recommends the use of radiographs to confirm initial placement. When gastric motility is impaired, gastric feedings may accumulate in the stomach and be a contributing factor to reflux and aspiration. She recommends that if sufficient expertise exists, small bowel feeding should be used in high risk patients (such as those that have large GRVs). Large GRVs are associated with aspiration in patients receiving small-bowel feedings. Unfortunately expert panels do not agree on how to proceed in the case of large GRVs, with some calling for withholding of feeding if the GRV is larger than 200 ml, while others state that the limit is 500 ml (Metheny 2006). Despite adverse effects such as nausea, vomiting, tardive dyskinesia and cardiac arrest the use of prokinetic agents should be considered to increase gastric emptying and thereby lower the danger of aspiration. The final risk factor discussed is bed elevation. A search of the literature revealed that there is a direct correlation between low bed elevation and aspiration. Expert panels therefore have recommended a head-of-bed elevation of 30° to 45° (unless contraindicated by the patient's medical condition).
This study was of special interest because it looked at a number of factors, examined them using an evidence based approach and presented the findings of expert panels.
A practice based approach to a review of the literature in these studies clarifies which methods are most efficacious for placement verification and the use of which techniques should be discontinued. Table 1 summarizes the studies referred to in this paper:
Summary of Studies Cited in the Review of the Literature?
Authors and Date
Bougault & Halm, 2009.
Peter & Gill, 2008.
Rauen et al., 2008.
Burns et al. 2006
7 studies that include 4729 feeding tubes or specimens
104 nurses (for audit)
195 gastric tube insertions
Adults and children hospitalized in 7 hospitals in Australia
Hospitalized adults and children
130 adult patients in MICU
Hospitalized adults and children
% accuracy, pH, bilirubin, enzymes pH, aspirate
Correct placement of NG tube
Detection of CO2
Outcomes of gastric tube insertions.
Radiographic confirmation should be used for verification of blindly placed tubes.
Aspirate was obtained for 97% of all tests and pH was ? 5.5 for 84%, after practice changes.
Correct placement should be confirmed by radiographic means.
Colorimetric device is as accurate as capnography in detecting CO2 during placement of gastric tubes
Elevate the head of the patient's bed to at least 30o
Research Recommendations / Nursing Implications
A number of recommendations can be drawn from these studies. Among them is support for the use of the radiographic technique for verifying tube placement. However the radiographic technique should also be supplemented with the detection of CO2 in the tube preferably through the colorimetric technique as it is simpler and less obtrusive. Testing…