Target condition being diagnosed
The insertion of an enterogastric tube (oral or nasal) (EGT) is the passage of a tube, appropriate for its intended purpose, through the nose or mouth into the stomach (Stewart 2011). 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 (Klasner 2002). With an estimated one million tubes being purchased per annum in England and Wales alone (Hanna 2010) and an average time interval to change tubes ranging from 8 to 168 hours (Shiao 1996), passage of an EGT is an extremely common clinical intervention. Although the majority of these tubes are inserted and used without incident, non-optimal placement is common with rates for children aged up to 13 years ranging from 20.9% to 43.5% (Ellet 2005), increasing to 56% for preterm infants (Weibley 1987) and 59% for neonates (Quandt 2009).There is a significant recognised risk that the tube can be misplaced into the lungs or move out of the stomach. Published reports of incidents have included oesophageal, peritoneal or intestinal placement, and even nasogastric (NG) tubes placed within the brain (Burns 2001). Additionally, severe pulmonary complications, indeed paediatric mortality, have been reported as a direct result of EGT placement within the respiratory tract (Creel 2007). The incidence of unsuspected EGT respiratory placement errors in the paediatric population is relatively low based on reported cases, however the complications are severe and potentially lethal (Metheny 2014). Ellet 1998 reports that the age of the child, level of consciousness, presence of abdominal distension, vomiting and the use of an orogastric (rather than a nasogastric) tube all serve to increase tube misplacement error rates of any type in the paediatric population.
Between September 2005 and March 2010, 21 deaths and 79 cases of harm relating to feeding through misplaced NG feeding tubes were reported in adults, children and infants in the United Kingdom (National Patient Safety Agency 2011b). All of these reported incidents were due to respiratory complications of misplaced EGTs (Hanna 2010). Eleven deaths and one case of serious harm were documented in England and Wales in 2005 (National Patient Safety Agency 2011a) and two further deaths resulted from the incorrect confirmation of EGT placement (National Patient Safety Agency 2012). In the UK, the Department of Health 2011 raised the significance of these occurrences in the Never Events Policy Framework which indicates non-adherence to evidence base policy and procedure within NHS organisations. Therefore, diagnostic tests are required to assess the placement of EGTs and to rule out the target condition of potential airway placement.
Confirmation of EGT placement is required immediately following insertion and thereafter prior to each use, including after the administration of enteral feed or medication. EGT placement should also be checked at least once a day during continuous feeding and also following episodes of vomiting, retching or coughing spasms (National Patient Safety Agency 2011b). The American Association of Critical Care Nurses 2009 also suggests the checking of EGT after oropharyngeal suction or when there is a suggestion of tube misplacement. Any new or unexplained respiratory symptoms or a drop in oxygen saturation readings is a further indication for seeking repeated confirmation of EGT placement (Durai 2009).
There are various methods 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 (Fletcher 2011). Although these tests are widely known about, they are not officially recommended for use as standalone measures of EGT placement. Current guidelines from the American Association of Critical Care Nurses 2009, the American Society for Enteral and Parenteral Nutrition (Bankhead 2009) and the National Patient Safety Agency 2011a recommend a combination of aspirate testing and radiological confirmation of EGT placement in infant, child and adult populations. However, there is a recognised difficulty with obtaining radiographs which visualise the entire course of the EGT and a recognised risk in radiation exposure in the paediatric setting (Bankhead 2009). In a small number of patients for whom the EGT has been placed under direct vision of a surgeon or anaesthetist (for example, perioperatively, during endoscopy or on endotracheal intubation), it may be possible to forego chest x-ray confirmation (National Patient Safety Agency 2011a). Observation of gastric secretions which differ in colour and consistency to those obtained from tracheal, bronchial or intestinal secretions (Metheny 2001), and the presence of bubbling at the proximal end of the tube (Metheny 1990), are additional methods of determining EGT placement. However, these methods have been found to be unreliable. Testing for acidity of aspirate obtained from the EGT does not accurately differentiate between bronchial and gastric secretions in paediatric practice. Nevertheless, objective measures of pH may be used, with a pH reading between 1 to 5.5 considered a reliable method for excluding placement in the pulmonary tree (National Patient Safety Agency 2011b). The ability to undertake pH measurement relies on obtaining aspirate from the EGT and in adult patients success rate can range from 33% to 96% (Hanna 2010; Kearns 2001; Metheny 1989; Metheny 1999; Neumann 1995; Welch 1994). Difficulty in obtaining aspirate may be increased in paediatric populations due to the use of fine bore tubes and smaller gastric fluid volumes (Khair 2005). In the event of failing to obtain gastric aspirate, infants and children are repositioned onto their side to allow the tip of the EGT to advance into the stomach (National Patient Safety Agency 2011a), although this does not guarantee availability of aspirate for testing. If aspirate is obtained the transient raised gastric pH levels of newborns and a reduced ability to produce gastric hydrogen chloride in infants (Bain 2005) mean that pH testing of aspirate may remain inconclusive. Concurrently, radiography or direct visualisation are the only reliable methods of confirming EGT placement in this population and are thus considered the reference standard (Bankhead 2009; Elpern 2007; National Patient Safety Agency 2011a).
The measurement of carbon dioxide (CO₂) in exhaled air is a widely used clinical observation and is a recognised standard of care during tracheal intubation or laryngeal mask airway (Ahrens 2003; The Intensive Care Society 2009). This can be achieved in one of two ways; capnography and 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. Detection of a CO₂ waveform is the test threshold for index test positivity for capnography. Colorimetric capnometry involves the detection of CO₂ using an adapted form of pH filter paper, impregnated with a dye which changes colour from purple to yellow in the presence of CO₂. The colour change is the index test threshold for test positivity for colorimetric capnometry. This method, however, does not provide a continual reading and can only be used as a semi-measurement of the amount of CO₂ in the expired gas (Frakes 2002).
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 (Thomas 1998), provided that there is circulation to deliver CO₂ to the lungs and an absence of complete bronchospasm preventing gas exchange (The Intensive Care Society 2009). CO₂ monitoring for this clinical application has been suggested; indeed it has been a concept acknowledged in the literature for over 20 years (Mercurio 1985).
Alternative bedside methods for detecting EGT placement have been suggested in the literature (e.g. measurement of gastric enzymes by Metheny 1997 or an electromagnetic technique as evaluated by Kearns 2001). However, CO₂ monitoring is the only currently available technique identified as a potential viable alternative to the reference standard in detecting inadvertent airway placement of an EGT appearing in clinical guidelines (The Intensive Care Society 2009). Therefore, we have chosen to focus on the detection of CO₂ only to keep the review manageable and maximise clinical relevance of the comparison.
The measurement of CO₂ in exhaled air is a recognised and mandatory standard of care for confirming and monitoring endotracheal tube or airway placement under general anaesthesia. Additionally, it is also a mandated form of monitoring for patients undergoing moderate and deep sedation (Weaver 2011). The monitoring of CO₂ from an EGT has been suggested as a replacement for the current reference standard. CO₂ detection may, therefore, be used to rule out inadvertent respiratory tract placement of an EGT; the misplacement error associated with the highest morbidity and mortality risks. As such, the incidence of false negative results, whereby CO₂ detection falsely rules out airway placement of the EGT, has greater clinical significance in terms of patient safety than the incidence of false positive readings. However, a false positive result, whereby CO₂ detection falsely diagnoses an EGT as being in the lung, may still impact on patient care by delaying feeding whilst another EGT is placed and verified.
Several studies have examined the accuracy of colorimetric capnometry in predicting gastric placement of EGT in adults. Very high levels of specificity and sensitivity were reported against a reference standard radiograph control (Araujo-Preza 2002; Thomas 1998) or air insufflation and epigastric auscultation (Elpern 2007; Meyer 2009). Similar results have been reported with capnography when using a radiograph control (Kindopp 2001); and when both capnography and colorimetric capnometry were compared against both radiograph and epigastric auscultation controls (Burns 2006). However, Ellet 2005 notes that in the paediatric population research is limited with evidence obtained from small sample studies thus suggesting further research using CO₂ monitoring is required to determine correct placement of EGTs and reduce the reliance on radiography as a means of safe verification (Ellet 2007). Additional issues relate to levels of high resistance to the colorimetric testing device from small bore EGTs, and the presence of secretions or lubricant at the distal end of the tube leading to occlusion of the EGT (Gilbert 2012). In a recent meta–analysis by Chau 2011 both capnography and capnometry were evaluated in confirming EGT position in adults. This study concluded that there was strong evidence available to support their use for this purpose, with a sensitivity ranging from 0.88 to 1.00 and specificity of 0.95 to 1.00.
Due to different risk factors for tube misplacement (Creel 2007) and disparity in gastric aspirate pH levels (Gilbertson 2011), results from adult studies cannot conclusively be generalised to the paediatric population. Additionally, the meta-analysis included auscultation of air as an acceptable reference standard, despite this having been established as an unsafe EGT placement verification procedure (National Patient Safety Agency 2011a), alongside several methodological limitations. Therefore, a systematic review of CO₂ detection for testing EGT placement in children is required to identify and critically evaluate the current evidence base, address the identified limitations of the available literature and to definitively establish the diagnostic test accuracy of this new application of an existing clinical technology.