Carbon dioxide detection for diagnosis of inadvertent respiratory tract placement of enterogastric tubes in children

  • Protocol
  • Diagnostic

Authors

  • Fiona Smith,

    Corresponding author
    1. Faculty of Health, Life & Social Sciences, Edinburgh Napier University, School of Nursing, Midwifery and Social Care, Edinburgh, UK
    • Fiona Smith, School of Nursing, Midwifery and Social Care, Faculty of Health, Life & Social Sciences, Edinburgh Napier University, Sighthill Campus, Edinburgh, EH11 4BN, UK. f.smith@napier.ac.uk.

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  • Agi Holland,

    1. Faculty of Health, Life & Social Sciences, Edinburgh Napier University, School of Nursing, Midwifery and Social Care, Edinburgh, UK
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  • Kay Penny,

    1. Edinburgh Napier University, School of Management, Edinburgh, UK
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  • Marie Elen,

    1. Faculty of Health, Life & Social Sciences, Edinburgh Napier University, School of Nursing, Midwifery and Social Care, Edinburgh, UK
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  • Deborah McGirr

    1. Faculty of Health, Life & Social Sciences, Edinburgh Napier University, School of Nursing, Midwifery and Social Care, Edinburgh, UK
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Abstract

This is the protocol for a review and there is no abstract. The objectives are as follows:

To determine the diagnostic accuracy of capnometry and capnography for detecting respiratory EGT placement in children compared to the reference standard.

Background

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).

Index test(s)

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.

Clinical pathway

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.

Rationale

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.

Objectives

To determine the diagnostic accuracy of capnometry and capnography for detecting respiratory EGT placement in children compared to the reference standard.

Methods

Criteria for considering studies for this review

Types of studies

We will include studies which compare the diagnostic accuracy of CO₂ detection for EGT placement in the respiratory tract with the reference standard, and those which evaluate the diagnostic accuracy of CO₂ detection for differentiating between respiratory and gastrointestinal tube placement, in children. We will include both prospective and retrospective cross sectional studies. We will include diagnostic case control studies as the performance of the index test needs to be determined using within patient comparison of the reference standard. CO₂ detection may be assessed by either capnometry or capnography.

As a patient may have more than one EGT per admission, the unit of analysis for the review will be defined as one EGT tube checking procedure. One EGT tube checking procedure will be defined as testing occasions in which one index test and one reference test are completed simultaneously.

Participants

Children (as defined by the trialists) who are undergoing EGT placement in any care setting for any reason.

Index tests

The index test evaluated in this review is CO₂ detection by either capnometry or capnography against the reference standard.

Target conditions

We will include studies if the aim of the diagnostic test was to confirm EGT placement or diagnose inadvertent respiratory placement, or both, in children.

Reference standards

The reference standard is either radiographic or direct visualisation of EGT placement.

Search methods for identification of studies

Electronic searches

We will search the following databases:

  1. The Cochrane Register of Diagnostic Test Accuracy Studies (latest issue);

  2. Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, latest issue) (Appendix 1);

  3. MEDLINE (Appendix 2);

  4. EMBASE (Appendix 3);

  5. CINAHL (Appendix 4);

  6. Medion database.

Searching other resources

We will not limit the search by language or publication status. We will contact manufacturers of colorimetric capnometers (e.g. Easycap and Easycap II Nellcor-Puritan Bennet) and capnographs (e.g. Ohmeda 5250 RGM monitor division of British Oxygen Company) that have been used within trials to identify any published, unpublished or ongoing studies which meet the inclusion criteria. We will review conference proceedings from the British Association for Parenteral and Enteral Nutrition (BAPEN), European Society of Parenteral and Enteral Nutrition (ESPEN), American Society of Parenteral and Enteral Nutrition (ASPEN), Australian Society of Parenteral and Enteral Nutrition (AUSPEN), South African Society of Parenteral and Enteral Nutrition (SASPEN) and the Latin American Federation for Parenteral and Enteral Nutrition (FELANPE) will be handsearched for relevant studies. We will also search the abstracts of the Neonatal Society’s scientific meetings (from 2001 to present). Where appropriate the authors of abstracts will be contacted to identify further studies deemed worthy of review. We will screen reference lists within relevant studies to identify any further potential papers worthy of review (Horsley 2011).

Data collection and analysis

Selection of studies

We will undertake the systematic review using the methods outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011) and the Cochrane Handbook for Systematic Reviews of Diagnostic Test Accuracy (Deeks 2010). Two authors (FS and ME) will independently examine the titles and abstracts identified by the search strategy to remove any duplicate records and obviously irrelevant reports. We will retrieve and evaluate the full text versions of potentially relevant studies identified by at least one author. Two authors (FS and ME) will independently assess each study to determine if they meet the eligibility criteria outlined above in the section Criteria for considering studies for this review. We will resolve any disagreements by discussion between the authors (FS, ME and DM), with a further author (AH) acting as arbiter. We will provide details of both included and excluded studies in the respective tables of the review.

Data extraction and management

FS and AH will extract data independently utilising a standardised data extraction form. We will resolve any disagreements by discussion between the authors (FS and AH), with a further author (ME) acting as arbiter. The data extraction form will include the following:

  • author, year of publication and journal/source of study;

  • study design;

  • total study population;

  • age range of participants;

  • total number of ventilated and spontaneously breathing participants;

  • total number of number of orogastric and nasogastric tubes;

  • reference standard (either radiographic or direct visualisation of EGT placement);

  • performance of reference standard (negative or positive confirmation of respiratory placement);

  • index test (either capnography or colorimetric capnometry);

  • performance of index test (negative or positive confirmation of respiratory placement);

  • QUADAS-2 items (i.e. the recognised quality assessment tool for diagnostic test accuracy studies).

We will use the statistical package within Review Manager software (RevMan 5.2), utilising double data entry with two authors (AH and FS) to control and correct data entry errors.

Assessment of methodological quality

We will assess the risk of bias of included studies using QUADAS-2 tool for assessing risk of bias and applicability as outlined by Whiting 2011 and recommended by the Cochrane Diagnostic Test Accuracy Group (Wisniewski 2012). The qualities assessed are described in detail in Appendix 5.

For each item in the quality assessment, a description of how the study addressed the issue will be included and a judgement entered of 'low', 'high' or 'unclear' for an overall risk of bias for each domain and 'low', 'high' and 'unclear' overall concern for domains one, two and three. We will include an Assessment of methodological quality table which will detail all of the judgements made for all included studies in the review. Assessment of methodological quality will be carried out by the two authors (FS and AH) independently. We will resolve any disagreements by discussion between the authors, with a further author (ME) acting as arbiter.

Statistical analysis and data synthesis

We will extract data of diagnostic performance from each primary study and construct 2 x 2 tables of true positive cases, false positive cases, true negative cases and false negative cases. We anticipate that data will be binary categorisation for all studies due to the nature of the diagnosis under investigation (either gastric placement or not); therefore, no threshold for positivity is required.

We will calculate sensitivity and specificity with a 95% confidence interval (CI) for each study. We will present the individual study results graphically using forest plots and the receiver operating characteristic (ROC) space.

We will use the bivariate random-effects approach as described by Reitsma 2005 for the meta-analysis of the pairs of sensitivity and specificity. The bivariate approach preserves the two-dimensional nature of the data by analysing pairs of sensitivity and specificity jointly, incorporating any correlation that might exist between the two measures using a random-effects model. Explanatory variables may also be added to the bivariate model to investigate how these variables affect sensitivity and specificity separately. Study level covariates exploring the effects of mechanical ventilation, size of tube and conscious level will be added to the analysis. We will categorise these covariates as:

  1. mechanical ventilation: ventilated or not;

  2. tube size: small bore (6 Fr or below) or not (8 Fr or above);

  3. conscious level: impaired or not.

The bivariate mean estimates of sensitivity and specificity will also be presented graphically along with their corresponding 95% confidence ellipses.

We will use the Proc NLMIXED procedure available within the statistical software package, SAS Inc., to carry out the bivariate random-effects analyses.

Investigations of heterogeneity

Heterogeneity in test accuracy is likely to arise due to differences in study characteristics. We will investigate this in the first instance using exploratory analysis and visual inspection of forest plots of sensitivities and specificities, and through visual inspection of the pairs of sensitivity and 1-specificity for each study, plotted in 'ROC space'. Study characteristics to be compared include the 'test type' (i.e. capnography or capnometry) and also:

  1. whether the patients are mechanically ventilated or not;

  2. whether the bore of the feeding tube is small (6 Fr and below) or not (8 Fr and above);

  3. whether the patients' conscious level is impaired or not.

Subject to an adequate sample size of at least 10 included studies, heterogeneity will be further investigated by adding study level covariates to the hierarchical model to identify factors associated with diagnostic test accuracy. The aforementioned binary categorical covariates will be considered for inclusion in the model.

Sensitivity analyses

We will use sensitivity analysis to explore the effect of age (for example, neonate and teenager) and study inclusion eligibility (clear study eligibility for review inclusion or dubious) on the primary analysis. We will also use sensitivity analysis to restrict studies with a superior form of index test (capnography), reference test (chest x-ray or direct visualisation) and blinding (the index test was interpret without knowledge of the outcome of the reference test) and studies at a low risk of verification bias (i.e. with predetermined criteria for chest x-ray interpretation). These covariates will be incorporated in the bivariate model to examine the effect of potential sources of bias across subgroups of studies.

Acknowledgements

We gratefully acknowledge the support provided by Edinburgh Napier University and Racquel Simpson at the Upper Gastrointestinal and Pancreatic Diseases Review Group for designing the search strategies.

Appendices

Appendix 1. CENTRAL (OvidSP) search strategy

  1. Intubation, Gastrointestinal/

  2. Enteral Nutrition/

  3. ((nasal or nose or nasoenteral or nasogastric) adj2 (cannula* or tube* or tubal or intubation)).tw.

  4. ((enteral or enteric) adj2 (feed* or nutrition)).tw

  5. (Feeding adj2 (tube* or tubal)).tw

  6. Ryle* tube.tw.

  7. ((fine bore or small bore) adj2 tube*).tw.

  8. or/1-7

  9. capnography/

  10. (capnograph* or capnogram*).tw.

  11. capnomet*.tw.

  12. ((carbon dioxide or CO2) adj3 (detect* or monitor* or measur* or concentrat* or estimat* or waveform*)).tw.

  13. or/9-12

  14. 8 and 13

Appendix 2. MEDLINE (OvidSP) search strategy

  1. Intubation, Gastrointestinal/

  2. Enteral Nutrition/

  3. ((enteral or enteric) adj2 (feed* or nutrition)).tw

  4. ((nasal or nose or nasoenteral or nasogastric) adj2 (cannula* or tube* or tubal or intubation)).tw.

  5. (Feeding adj2 (tube* or tubal)). tw

  6. Ryle* tube.tw.

  7. ((fine bore or small bore) adj2 tube*).tw.

  8. or/1-7

  9. capnography/

  10. (capnograph* or capnogram*).tw.

  11. capnomet*.tw.

  12. ((carbon dioxide or CO2) adj3 (detect* or monitor* or measur*or concentrat* or estimat* or waveform*)).tw.

  13. or/9-12

  14. 8 and 13

Appendix 3. EMBASE (OvidSP) search strategy

  1. nasogastric tube/

  2. ((nasal or nose or nasoenteral or nasogastric) adj2 (cannula* or tube* or tubal or intubation)).tw.

  3. ((fine bore or small bore) adj2 tube*).tw

  4. enteric feeding/

  5. ((enteral or enteric) adj2 (feed* or nutrition)).tw

  6. feeding apparatus/

  7. (Feeding adj2 (tube* or tubal)).tw

  8. Ryle* tube.tw.

  9. Nose Feeding/

  10. or/1-9

  11. capnography/

  12. (capnograph* or capnogram*).tw.

  13. capnomet*.tw.

  14. capnograph/ or capnometer/

  15. ((carbon dioxide or CO2) adj3 (detect* or monitor* or measur* or concentrat* or estimat* or waveform*)).tw.

  16. or/11-15

  17. 10 and 16

Appendix 4. CINAHL search strategy

Search ID# Search Terms
S15S9 AND S14
S14S10 OR S11 OR S12 OR S13
S13((carbon dioxide or CO2) N3 (detect* or monitor* or measur* or concentrat* or estimat* or waveform*))
S12capnomet*
S11(capnograph* or capnogram*)
S10(MH "Capnography")
S9S1 OR S2 OR S3 OR S4 OR S5 OR S6 OR S7 OR S8
S8(MH "Enteral Feeding Pumps") OR (MH "Feeding Tube Care+")
S7((fine bore or small bore) N2 tube*)
S6Ryle* tube*
S5(Feeding N2 (tube* or tubal))
S4((nasal or nose or nasoenteral or nasogastric) N2 (cannula* or tube* or tubal or intubation))
S3((enteral or enteric) N2 (feed* or nutrition))
S2(MH "Enteral Nutrition")
S1(MH "Nasoenteral Tubes") OR (MH "Intubation, Gastrointestinal")

Appendix 5. Study quality assessment details

Domain 1: Patient selection

  • Risk of bias: Could the selection of patients introduced bias?

Signalling question 1: Was a consecutive or random sample of patients enrolled?
Signalling question 2: Was a case-control design avoided?
Signalling question 3: Did the study avoid inappropriate exclusions?

Certain conditions may make the passage of an EGT more difficult, such as anatomical variation of the larynx and pharynx and altered physiology of swallowing (Der Kureghian 2011). We will classify as "yes" those studies that excluded patients in whom it was difficult to insert an EGT; those studies which did not exclude such patients shall be classified as "no"; and where this information is unclear we shall classify those studies as "unclear".

Applicability: Are there concerns that the included patients and the setting do not match the review question?

The inclusion criteria for this review outline studies for inclusion in which the patients are considered to require an EGT passed for any reason. Therefore, we anticipate that all the studies in the review will be judged as "low" concern.

Domain 2: Index test

  • Risk of bias: Could the conduct or interpretation of the index test have introduced bias?

Signalling question 1: Were the index test results interpreted without knowledge of the results of the reference standard?
Signalling question 2: If a threshold was used, was it pre-specified?

We will classify the studies as "no" if the index test results were interpreted without knowledge of the reference standard; "yes" if the index tests were interpreted with knowledge of the reference standard results; and "unclear" if this information is not clear.

Applicability: Are there concerns that the index test, its conduct or interpretation differ from the review question?

The detection of carbon dioxide by capnometry or capnography for determining EGT placement is an inclusion criteria for this review, so we anticipate that all studies will be classified as "low" concern.

Domain 3: Reference standard

  • Risk of bias: Could the reference standard, its conduct or its interpretation have introduced bias?

Signalling question 1: Is the reference standard likely to correctly classify the target condition?

We will classify the studies as "yes" if the criteria for correct EGT placement were the currently acceptable standards of placement verification (outlined in Reference standards); "no" if the criteria for verification of placement were by any other method; and "unclear" if this information is not clear.
We will classify the studies as "yes" if the reference test results were interpreted without knowledge of the index test; "no" if the reference standard was interpreted with knowledge of the index test results; and "unclear" if this information is not clear.

Applicability: Are there concerns that the target condition as defined by the reference standard does not match the question?

The target condition is the confirmation of EGT placement in the stomach, which may be aided by the use of pre-specified diagnostic criteria for chest x-ray interpretation (Lamont 2011). The threshold at which an x-ray is interpreted as positive (i.e. EGT in the stomach) may, therefore, be different depending on whether the interpretation was based on the individual clinician's interpretation or according to clear diagnostic criteria. We will classify those studies who used clear diagnostic criteria for chest x-ray interpretation as "low" concern; "high concern" for those not using clear diagnostic criteria or where the interpretation was based on the individual clinician's interpretation; and "unclear" concern if this information is not clear.

Domain 4: Flow and timing

  • Risk of bias: Could the patient flow have introduced bias?

Signalling question 1: Was there an appropriate interval between the index test and reference standard?
Signalling question 2: Did all patients receive the same reference standard?
Signalling question 3: Were all patients included in the analysis?

If an EGT is correctly inserted and initial gastric placement is confirmed, continual assessment is still required as any routine activity (e.g. vomiting, coughing, retching) can cause tube displacement (Simons 2012). Therefore, any delay in testing may influence results. However, we have set an arbitrary time delay between tests in line with the American Association of Critical Care Nurses 2009 who recommend tube location to be checked at four-hourly intervals. We will classify the study as "yes" if the delay is less than four hours; "no" if the delay is four hours or more; and "unclear if the information is unclear.
We will classify the study as "yes" if all patients had the same reference standard; "no" if the reference standard was different; and "unclear" if this information is unclear.
Uninterpretable results may be present (e.g. unclear chest x-ray, blocked EGT preventing gas flow required for capnography/capnometry). Additionally, withdrawals from the study may be present. We will classify the study as "yes" if uninterpretable results were reported and the study had no withdrawals or the withdrawals were unlikely to affect the results; "no" if uninterpretable results were not reported or there were withdrawals that were likely to affect the results, or both; and "unclear" if this information is not clear.

Contributions of authors

Conceiving the review: Agi Holland (AH) and Fiona Smith (FS)
Designing the review: AH, FS and Kay Penny (KP)
Co-ordinating the review: FS
Data collection for the review: FS, ME and DM
Designing search strategies: Racquel Simpson, Cochrane Upper Gastrointestinal and Pancreatic Diseases Review Group Trials Search Co-ordinator
Undertaking searches: FS and ME
Screening search results: FS and ME
Organising retrieval of papers: AH and DM
Screening retrieved papers against inclusion criteria: FS, ME and AH
Appraising the quality of the papers: FS, ME and AH
Extracting data from papers: AH and FS
Writing to authors of papers for additional information: DM
Providing additional data about papers: AH
Obtaining and screening data on unpublished papers: FS and AH
Entering data into RevMan 5.2: AH and FS
Analysis of data: FS, AH and KP
Interpretation of data: FS, AH and KP
Providing a clinical perspective: ME and DM
Writing the review: FS, AH, KP, ME, DM
Securing funding for the review: AH and FS
Performing various work that was the foundation of the current study: AH and FS

Declarations of interest

None known.

Sources of support

Internal sources

  • Edinburgh Napier University, UK.

External sources

  • No sources of support supplied

Ancillary