Procedures for measuring and verifying gastric tube placement in newborns: an integrative review

ABSTRACT Objective: to investigate evidence in the literature on procedures for measuring gastric tube insertion in newborns and verifying its placement, using alternative procedures to radiological examination. Method: an integrative review of the literature carried out in the Cochrane, LILACS, CINAHL, EMBASE, MEDLINE and Scopus databases using the descriptors “Intubation, gastrointestinal” and “newborns” in original articles. Results: seventeen publications were included and categorized as “measuring method” or “technique for verifying placement”. Regarding measuring methods, the measurements of two morphological distances and the application of two formulas, one based on weight and another based on height, were found. Regarding the techniques for assessing placement, the following were found: electromagnetic tracing, diaphragm electrical activity, CO2 detection, indigo carmine solution, epigastrium auscultation, gastric secretion aspiration, color inspection, and evaluation of pH, enzymes and bilirubin. Conclusion: the measuring method using nose to earlobe to a point midway between the xiphoid process and the umbilicus measurement presents the best evidence. Equations based on weight and height need to be experimentally tested. The return of secretion into the tube aspiration, color assessment and secretion pH are reliable indicators to identify gastric tube placement, and are the currently indicated techniques.


Introduction
Insertion of Gastric Tube (GT) in Newborns (NB) hospitalized in the Neonatal Intensive Care Unit (NICU) is one of the most commonly performed nursing procedures. It is indicated for gastric decompression, administration of medications, and mainly for feeding the gastric tube process, and despite being a standard procedure for nurses working in the NICU, it is not risk free and involves decisions that may compromise patient safety (1) .
Some of the important aspects to increase safety in using GT in newborns involve care in measuring the insertion length, assessing placement/positioning of the distal end of the tube, and in maintaining its correct positioning (1) . Serious respiratory complications may occur due to bronchopulmonary aspiration of gastric contents or inadequate tube placement reaching the respiratory tract. Intestinal absorption problems and alimentary intolerance related to GT positioning in the pylorus or duodenum can also occur. Moreover, difficulties encountered in the trajectory can cause puncture injuries to the esophagus or respiratory tract (2) . The occurrence of errors in GT placement is very frequent: studies show proportions of 47.5 to 59% inadequate placement between neonatal and pediatric patients (3)(4) .
The nurse's decision-making process during gastric tube procedure begins with the choice of an effective method that has a strong association with measuring the actual tube route from the nostril or oral cavity to the body of the stomach, passing through the entire length of the esophagus (1) .
After choosing the measuring method and performing the insertion, it is necessary to verify that the distal end of the tube has reached the body of the stomach, as well as whether all the distal orifices are within the gastric cavity in order to prevent fluid leakage into the esophagus or duodenum (1) .

Radiological examination of the chest and abdomen
is considered the gold standard verification technique, since it allows visualization of the GT route and the positioning of its distal end. Despite presenting the most reliable result, this technique is costly and is not commonly used in neonatal clinical practice for this reason, as the GT is often replaced, and repeated exposure to radiation can be dangerous (2) . Another limitation is the fact that this test is only effective at the moment it is performed, since tube displacement can happen immediately after (2,5) , thus requiring the use of other techniques to assess tube placement other than radiological examination.
In this integrative review, we sought evidence that may assist nursing assistants in the decisionmaking process regarding gastric tubes in newborns in the NICU, given the importance of always choosing the best health practices aiming at patient safety. Thus, this study aimed to investigate evidence in the literature on procedures for measuring gastric tube insertion in newborns and verifying its placement, using alternative procedures to radiological examination.

Method
This is an integrative review of the literature which seeks to synthesize results from previous studies on the proposed subject (6) . Integrative reviews have the potential to evidence comprehensive understanding of specific issues and to identify gaps in knowledge. This is a very useful method for nurses who are in clinical practice and wish to perform nursing assistance based on scientific evidence (7)(8)(9) .
The steps followed in elaborating this review were: establishing the research question, conducting a literature search, evaluating data, analysing the included studies, interpreting the results and presenting the review (8) .
The guiding question of this study was "What are the procedures for measuring gastric tubes in newborns and for assessing its placement, other than radiological selected studies whose titles addressed the research subject were also investigated.
Article selection was carried out by two researchers independently, and inclusion criteria were: original studies published in-full that address, in the title or abstract, gastric tube measurement procedures and/ or techniques for assessing its placement, and which included newborns in the studied sample; studies published in Portuguese, English or Spanish. Theses and dissertations, pilot studies, review articles, case or experience reports, letters, editorials and publications where the method was not clearly described were excluded. PRISMA recommendations (10) were followed for the study selection, as shown in Figure 1.
A form with the following items was elaborated by the authors for developing the analysis: bibliographic reference, level of evidence, language, country of origin, main researcher's training, database, objective, study design, ethical considerations, subjects, main results, conclusion and limitations. Seven (7) levels of classification were considered to categorize the level of evidence: level 1 -systematic review or meta-analysis of controlled clinical trials; level 2 -well-delineated randomized controlled clinical trial; level 3 -controlled clinical trial without randomization; level 4 -well-delineated cohort or case-control studies; level 5 -systematic review of qualitative and descriptive studies; level 6 -descriptive or qualitative studies; and level 7 -opinion of authorities or experts (11) . The results were analyzed and presented in a descriptive way.
As this is an integrative review, it was not necessary to request approval from the Ethics Committee to carry out the study. We declare no conflicts of interest.   (10) .

Results
The number of publications found in the investigated databases, as well as other sources included in this review are presented in Figure 2.
The 17 articles included in the review were all published in English between 1987 and 2016. The majority of the studies were carried out in the United States (n = 13), the main authors had training in nursing (n = 11) and medicine (n = 6). The included studies were classified into two categories for data analysis: "Methods for measuring gastric tube" and "techniques for assessing gastric tube placement". Characterization of the articles considering the level of evidence is presented in Figure 3.
Rev. Latino-Am. Enfermagem 2017;25:e2908. Other sources List of references from the articles 3 3 * Some publications were repeated in more than one database

Methods for measuring the gastric tube
Among the articles that addressed GT measurement, four were observational studies (13,18,22,27) and two were experimental studies (12,20) , and were mostly published in nursing journals. With regard to ethical aspects, only one article (12) did not report having submitted the study to ethical appreciation. Figure 4 briefly describes each of these studies, addressing the design, objective, population sample, main results and limitations.  (12) .
A method that determines the minimum insertion length of the tube has been specifically developed for low birth weight newborns (<1500g) (13) . Minimum insertion measures proposed in this study are 13cm for newborns weighing less than 750g, 15cm for newborns weighing between 750 and 999g, 16cm for newborns weighing between 1,000 and 1,249g, and 17cm for those In addition to these measurements, two equations are described to estimate the insertion length of the tube: the height-based equation (18,20) and the weightbased formula (22) . According to one of the studies (18) (20) .
Another method described in the literature is the weight-based equation (22) . of poorly placed nasogastric and 60% orogastric tubes.
The lower rates found in orogastric tubes may be related to the fact that the tubes move more when positioned in the oral cavity.
The use of the weight-based formula as an auxiliary method to NEMU in GT insertion was described in another Rev. Latino-Am. Enfermagem 2017;25:e2908.
study (27) , however, the result was lower than expected, with 16% of tubes being incorrectly positioned (above or near the gastroesophageal junction Only one radiologist evaluated the images, and no prospective study was performed for the application of the formula 16 (28) Descriptive Describe the correct positioning rate using the weight-based formula as an auxiliary method 107 NBs || 84% of the tubes were correctly positioned, 12.5% were at the limit and 3.6% were high. Only one radiologist evaluated the images  The diagnostic accuracy tests used in three studies (15,16,24) included in this review were always compared to radiological examination. However, one study (15) evaluated the test accuracy in identifying correctly positioned tubes, and two other studies (16,24) evaluated the accuracy in identifying incorrectly positioned tubes. This prevents the simple comparison of the values between the three studies.
The study that investigated the accuracy of correctly positioned tubes found that the use of pH evaluation along with color evaluation is the safest technique to confirm correct positioning, considering pH <6.0 and translucent greenish and brownish colors (15) .
For studies that performed accuracy tests for incorrect positioning of the tube (16,24) , no placements in the respiratory tract (16,24) , and also because it is possible to detect the presence of CO 2 in the oral cavity, oropharynx, esophagus and stomach (23) . it did not predict tubes positioned in the duodenal portion (16,24) .
The use of the electromagnetic tracing device and evaluating electrical activity in the diaphragm showed good precision and accuracy. The major advantage of these techniques is the possibility of real-time path correction during tube passage, as well as avoiding exposure to radiation, since these procedures are presented as possible substitutes for abdominal radiography. However, the sample of pediatric patients was very reduced, thus making generalizations difficult; also, both techniques are very expensive (19,21) . Electromagnetic device (EMPD**) compared to two radiological examination images Among the pediatric patients, the EMPD** presented 99.4% agreement with the first radiological examination (simple) and 100% with the second (contrast). 19 incorrect positions in the respiratory tract were avoided in the total sample with the use of EMPD**, 4 of them in pediatric patients.
Small sample of pediatric patients. Specific training is required to read the EMPD** result.
12 (23) Experimental; 42 children, between newborns and up to 18 years of age CO 2 detector device 100% accuracy in detecting CO 2 , however CO 2 can be detected outside the airway, for example if the child cries during tube introduction.
Sample selected by convenience. White, green and bronze colors may indicate correct tube placement. Secretion consistency did not prove useful for the positioning assessment.
It was not possible to evaluate Bilirubin and CO 2 , since they did not present variability.
14 (25) Descriptive; 44 newborns Sky blue method for gastric tube exchange Administration of 0.01% indigo carmine solution immediately prior to the exchange procedure. Positioning is considered correct when it is possible to aspirate bluish secretion through the new tube. 94.4% showed a blue solution result.
No comparison was made with another method. The long-term effects of the use of indigo carmine are not known.
15 (26) Descriptive; 54 newborns pH test in situations with and without the use of gastric secretion inhibitors, in fasting and fed newborns Regardless of the use of gastric secretion inhibitors and whether newborns were fasting or not, pH was <5.5 in 90% of cases where the tube was correctly positioned in the radiological evaluation.
Small sample selected by convenience.
17 (28) Descriptive; 63 institutions (1,191 children using gastric or enteral tube, between newborns and up to 14 years) Description of the technique used to verify tube placement, according to the team's responses to the questionnaire First choice techniques in the investigated institutions: inspection of the secretion (n=21), auscultation of the epigastric region (n=18), measurement of the tube (n=8), pH (n=10), X-rays (n=6).
Sample selected by convenience, low reliability of the data collected as they were self-reported by the institutions *Sensitivity; †Specificity; ‡Positive predictive value; §Negative predictive value; ||Investigated the accuracy to determine incorrect positioning; ¶Electrical Activity of the Diaphragm; **Electromagnetic Placement Device; † † Only refers to NBs included in the sample.

Discussion
The first description found in the literature on NEX and NEMU methods dating from 1978 was not included in this review, as it did not clearly present the method described.
In this study, the authors describe using the NEX measure in clinical practice, however, they suspected that it was not a long enough measure, as they were not always able to aspire gastric contents. In order to validate their hypothesis, the authors followed some necropsies (they do not describe how many), and observed that with the NEX method, the distal end of the tube was at the limit of the gastroesophageal junction, and that it was necessary to add a few centimeters to the measurement for the distal end of the tube to reach the body of the stomach. Thus, the authors proposed the NEMU method and observed that the tube was correctly positioned in necropsies using this method (29) .
After this one, other studies have showed the inferiority of the NEX measure compared to the NEMU (12,18,20) . Although the latter also represents a measure that has high variability, the present review indicates that it is the best evidenced method to date to be reproduced in clinical practice.
Equations that use height (18,20) and weight (22,27) to calculate the gastric tube insertion measure seem to reproduce reliable results; however, the absence of experimental studies with such methods impedes them being used as a single reference. Therefore, it is suggested that these equations are only used as a supporting measure in the decision on the tube length to be introduced, at least until studies with new evidence are available.
For the population of NBs below 1,500g, use of the minimum length table of the tube to be introduced can also be indicated as an auxiliary method to avoid positioning above the gastroesophageal junction (13) . It should be noted that this table should only be used for the oral route of insertion.
Verifying GT positioning in NBs is a process that requires nurses' attention due to the unavailability of precise techniques such as electromagnetic tracings or diaphragm electrical activity evaluation, as well as the impossibility of performing a radiological examination at each tube exchange due to the costs and risks involved (1,2) .
Thus (and the findings of this review confirm), nurses must use several strategies simultaneously, with the objective of increasing the safety of the procedure.
The most easily accessible indicator is gastric secretion return to the tube aspiration, which presented good results in the accuracy tests of one of the reviewed studies (24) . Recommendations from international agencies (30-32) also indicate pH (<5.0) evaluation of aspirated secretion as a technique for verifying GT positioning. Other studies (15)(16) suggest that combining pH assessment with secretion coloration (whitish, translucent, greenish or brownish) makes the assessment even safer, since these are the indicators with the best results among the accuracy tests.
The use of gastric shields (histamine-2 receptor antagonists and proton pump inhibitors), as well as continuous infusion of milk formula and the use of sterile water to wash the catheter raise questions about the safety of the aforementioned combined evaluation, since they could increase gastric pH (2) . However, the reviewed studies comparing gastric pH in NBs and infants did not find significant differences between those who received and did not receive these medications, as well as those who were fed continuous infusion, gavage, or those who underwent fasting (2,16,24,26) .
In the absence of gastric secretion return, the risk of improper placement increases. In this situation, nurses may insist on obtaining a sample, performing movement maneuvers with the newborns and injecting air (not more than 2ml). Since it is possible that the tube is in direct contact with the mucosa, these maneuvers can favor its displacement and attainment of secretion.
If it is still not possible to aspirate secretion through the catheter after such maneuvers, the possibility of changing the catheter or performing a radiological examination can be discussed to visualize the path and positioning of the distal end (31) .
The use of abdominal ultrasonography to verify GT placement has been shown to be a useful and effective technique in adults with high sensitivity and specificity; attaining 98.3 and 100%, respectively, when compared with the results of conventional radiological examination (33) . Its use in verifying the location of the end of the GT has been recommended in adult patients instead of radiological examination since it is a simple and fast technique, in addition to the advantage of not exposing the patient to radiation (34)(35) . A study carried out in two intensive care units with 14 neonatal and pediatric patients also demonstrated the efficacy of ultrasound to evaluate jejunal tube placement in these patients (36) .
A pilot study published as a letter (37) , which was not part of this review sample, reports that the use of ultrasonography to verify GT positioning in NBs is not a reliable technique, as it was only possible in one of the 10 cases studied to visualize the distal end of the tube in the stomach. However, all had the gastric position confirmed by the pH test (<5.5) (37) . Considering the small sample size of the cited study and data that contradict promising results in adults, it is necessary to perform more research with ultrasound in NBs.
Despite care for tube maintenance not being the subject of this review, it should be pointed out that monitoring the external length can be used as a supporting measure in maintenance of tube placement and patient safety, especially when dealing with longterm tubes. In the description of an implementation protocol for tube maintenance in NBs (5) and in an integrative review (38) , the authors recommend that the external length should be checked and recorded in the medical record and/or recorded on the tube in a visible manner, always confirming it before use. However, it is relevant to consider that keeping the external length stable does not eliminate the risk of internal displacement.
In this review, it was identified that the procedure of introducing air through the tube and auscultating the epigastric region is the second chosen method of American nurses to confirm gastric positioning (28) , which is also observed in the clinical practice of the authors considering their action and teaching fields. However, literature indicates that it is possible to listen to the air bubbles in the epigastric region, regardless of whether the end of the tube is located in the stomach, esophagus or respiratory tract. Therefore, the use of this technique is discouraged and should be banned (1,16,(29)(30)(31)(32)38) . techniques prior to each GT use (gastric secretion aspiration with pH and color assessment).
Another integrative literature review (38) addressing this subject was found, however, it also included pediatric patients up to 18 years of age. We also found literature reviews (1)(2) that did not present a detailed description of the method and included studies. Thus, the difference in the present integrative literature review was to gather evidence on the methods for measuring and confirming