Key message
• There is not enough evidence to suggest that carbon dioxide (CO₂) testing should be added to current checking procedures.
• More studies are needed to determine if CO₂ testing is beneficial for children undergoing insertion of an enterogastric tube.
Why is it important to know if the tube is accidentally placed in the airway?
The insertion of a thin, flexible plastic tube through the nose or mouth (enterogastric tube) is a common medical procedure in children to provide both nutrients and medicine when the child is not able to take these by mouth. A wide range of children require this procedure, either in the short or long term. There are several reasons why a feeding tube is required, including the inability to swallow or medical conditions that affect the ability to tolerate an adequate level of nutritional intake.
Most tubes are inserted and used without incident. However, if a tube is misplaced into the lungs and used to provide nutrition or medicine, this can lead to significant harm and even death. Confirmation of tube placement in the stomach is required following insertion and before using the tube. Traditionally, the first-line method to confirm the correct placement of the tube is to obtain a small amount of stomach content and test the levels of acidity of the sample. Stomach contents are very acidic, so a sample with a high acid level should confirm that the tube is correctly placed. Difficulty in obtaining such samples due to the small diameter of tubes used and the smaller amounts of stomach content in children may result in the acid test being inconclusive. If this happens, the child will need an X-ray to check correct placement. This method provides accurate confirmation of tube placement but involves a delay and exposes the child to radiation.
The monitoring of carbon dioxide (CO₂) in exhaled breath is an established tool used in the practice of medicine when patients need help breathing better. It has been suggested that this monitoring device could be used to detect if a feeding tube has been incorrectly placed in the lungs by testing for the presence of CO₂.
What did we want to find out?
We wanted to know whether using CO₂ measuring tools for checking and re-checking the placement of enterogastric tubes compared to the reference standard of radiography (X-ray) or direct visualisation (where a small camera is inserted into the body to guide placement of the enterogastric tube) would be beneficial for children in terms of reducing risk.
What did we do?
We looked for studies that examined the use of CO₂ detection (capnography or colorimetry) compared to the reference standard during blind (where the person inserting the tube cannot see where the tube is going in the body) placement of gastric tubes in children. CO₂ can be measured either continuously via an electronic monitor (called capnography) or intermittently using a device which changes colour in the presence of CO₂gas (colorimetric capnometry). We looked at both of these methods in our review.
What did we find?
We reviewed the available evidence on the use of CO₂ detection through capnography or colorimetric capnography for checking and re-checking the placement of enterogastric tubes in children. We included three studies in the review, two using capnography and one using colorimetry as the testing method, all against the reference standard of chest X-ray. There were 139 tube insertions across the three studies. CO₂ testing correctly identified 130 tubes as not being in the lung, six tubes incorrectly as being in the lung, and three tubes correctly as being in the lung. There were no cases of feeding tubes being identified as not in the lung when they actually were, the scenario that presents the greatest risk to the patient. We were not able to combine the results of the three studies using formal statistical tests.
To whom do the results of this review apply?
The children in the studies were hospitalised and aged newborn to 16 years; however, the average age was less than 15 months. All children were considered eligible unless they were too ill to participate, had a medical condition that would drastically affect the stomach acid secreting ability, had previous stomach surgery, or patients with facial fractures.
What are the limitations of the evidence?
There is a lack of high-quality research in the area, specifically in children. Using CO₂ detection methods to check and re-check the placement of enterogastric tubes in children could be an effective way of reducing the risk of these procedures, but there is not yet enough evidence. Further studies are needed to determine the safety of replacing the current practice, considering the different methods of CO₂ detection, including the full age range of children undergoing these procedures, and looking at different tube sizes.
How up-to-date is this evidence?
The search is current to September 2023.
There is currently not enough evidence to suggest that CO₂ detection for inadvertent respiratory tract placement of EGTs in children should be added to current checking procedures. Future studies should aim for larger samples across a range of ages and evaluate different types of CO₂ monitoring (capnography and capnometry), using a range of EGT sizes in participants who are both spontaneously breathing or who require mechanical ventilation with or without impairments of conscious level.
The insertion of an enterogastric tube (oral or nasal) (EGT) is the passage of a tube through the nose or mouth into the stomach. In a paediatric setting, EGTs are used within clinical practice for a variety of reasons including enteral feeding, decompression, post-gastrointestinal surgery, patient assessment, and drug and fluid administration. Confirmation of EGT placement is required immediately following insertion and thereafter prior to each use, including after the administration of enteral feed or medication. Although the majority of these tubes are inserted and used without incident, there is an established risk that the tube can be misplaced into the lungs or move out of the stomach. This misplacement can result in significant harm or mortality. As such, diagnostic tests are required to assess the placement of EGTs and to rule out the target condition of potential airway placement.
Various methods are used to determine EGT position, including bedside assessment and observing for signs of respiratory distress. Air insufflated (blown) through the EGT in combination with epigastric auscultation (listening to the stomach with a stethoscope) for whooshing sounds has also been used. Although these tests are widely recognised, they are not officially recommended for use as standalone measures of EGT placement.
Current American and UK guidelines recommend a combination of aspirate testing and radiological confirmation of EGT placement in infant, child, and adult populations. In adults, objective measures of pH of the aspirate may be used, with a pH reading between 1 and 5.5 considered a reliable method for excluding placement in the pulmonary tree. However, testing for acidity of aspirate obtained from the EGT does not accurately differentiate between bronchial and gastric secretions in paediatric practice. Additionally, there may be difficulty in obtaining aspirate from the EGT especially within a paediatric population due to the size of the EGT and the smaller volumes of gastric secretions produced.
Radiography or direct visualisation are the only reliable methods of confirming EGT placement (valid at time of X-ray and point of insertion, respectively) in this population and are thus considered the reference standard. However, within the paediatric population, there is a known difficulty with obtaining radiographs that visualise the entire course of the EGT and a recognised risk in radiation exposure in the paediatric setting.
The measurement of carbon dioxide (CO₂) in exhaled air is a recognised and mandatory standard of care for confirming and monitoring endotracheal tube or airway placement under general anaesthesia. The measurement of CO₂ can be achieved in one of two ways: capnography or colorimetric capnometry. Capnography is the measurement of inspired and expired CO₂ using the absorption of infrared light by CO₂ molecules to estimate CO₂ concentrations. These measurements are then displayed against time to give a continual graphical trace. Colorimetric capnometry involves the detection of CO₂ using an adapted form of pH filter paper impregnated with a dye that changes colour from purple to yellow in the presence of CO₂; however, this method does not provide a continual reading. The monitoring of CO₂ emanating from an EGT inadvertently passed into the airways would utilise this phenomenon in a reverse manner, confirming tracheobronchial placement rather than the intended stomach.
To determine the diagnostic accuracy of capnometry and capnography for detecting respiratory EGT placement in children compared to the reference standard.
We searched the Cochrane Register of Diagnostic Test Accuracy Studies, Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, CINAHL, and Medion database on 4 September 2023. There were no limits on language or publication status.
We included studies that compared the diagnostic accuracy of CO₂ detection (assessed by either capnometry or capnography) for EGT placement in the respiratory tract with the reference standard, and those that evaluated the diagnostic accuracy of CO₂ detection for differentiating between respiratory and gastrointestinal tube placement, in children. We included both prospective and retrospective cross-sectional studies. We included diagnostic case-control studies where patients acted as their own controls whereby the same EGT and end placement was tested both via index and reference test concurrently.
Two review authors independently extracted data and assessed methodological quality using QUADAS-2. There were no disagreements. Where data were available, we reported test accuracy as sensitivity and specificity. Calculation of both sensitivity and specificity with a 95% confidence interval (CI) was only possible for one study. We calculated specificity with a 95% CI for all included studies. Due to the low number of included studies, we were not able to perform meta-analysis or conduct our planned investigations of heterogeneity.
We identified three studies for inclusion in the review, all of which provided data on test accuracy of capnography or capnometry against the radiological test standard. Across the three studies, there were a total of 121 participants and 139 EGT insertions with low event data for false-positive (n = 6 insertions) and true-positive (n = 3 insertions) scenarios. No event data were available for false-negative scenarios.
Overall, the body of evidence has a low risk of bias, although further clarity regarding patient enrolment (whether consecutive or random) and details about the conduct of the index and reference tests would have enhanced the overall quality of the evidence base included in the review.