Archives of Academic Emergency Medicine. 2021; 9(1): e68 REV I EW ART I C L E Screening Performance Characteristics of Ultrasonogra- phy in Confirmation of Endotracheal Intubation; a Sys- tematic Review and Meta-analysis Mehrdad Farrokhi1∗, Bardia Yarmohammadi2, Amir Mangouri3, Yasaman Hekmatnia4, Yaser Bahramvand5, Moein Kiani6, Elham Nasrollahi5, Milad Nazari-Sabet7, Niusha Manoochehri-Arash8, Maria Khurshid9 †, Shima Mosalanejad10, Vida Hajizadeh11, Reza Amani-Beni12, Masoumeh Moallem13, Maryam Farahmandsadr14 1. Eris Research Institute, Tehran, Iran. 2. School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran. 3. Department of Vascular and Endovascular Surgery, Sina Hospital, Tehran University of Medical Sciences, Tehran, Iran. 4. Islamic Azad University, Sari Branch, School of Medicine, Sari, Iran. 5. School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran. 6. School of Medicine, Zanjan University of Medical Sciences, Zanjan, Iran. 7. Department of General Surgery, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran. 8. Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran. 9. Department of Internal Medicine, Berkshire Medical Center, Pittsfield, Massachusetts, USA. 10.Department of Internal Medicine, Faculty of Medicine, Tehran Medical Sciences, Islamic Azad University, Tehran, Iran. 11.School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran. 12.School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran. 13.Department of Emergency Medicine, School of Medicine, Tehran Medical Sciences Branch, Islamic Azad University, Tehran, Iran. 14.School of Medicine, Jahrom University of Medical Sciences, Jahrom, Iran. Received: August 2020; Accepted: September 2021; Published online: 26 October 2021 Abstract: Introduction: Recent studies have suggested that point-of-care ultrasonography can be used for confirming the placement of endotracheal tube. This systematic review and meta-analysis aimed to investigate the sensitivity and specificity of ultrasonography for confirming endotracheal tube placement. Methods: In this meta-analysis, systematic search of the previous published papers investigating the diagnostic accuracy of ultrasonography for confirmation of endotracheal tube placement was performed. Seven electronic databases, including PubMed, Scopus, Google Scholar, EBSCO, EMBASE, Web of Science, and Cochrane Database were searched up to July 2021, for all relevant articles published in English on this topic. Meta-DiSc version 1.4 software was used for sta- tistical analysis. Results: The estimated pooled sensitivity and specificity of ultrasonography for confirmation of endotracheal tube location were 0.98 (95% CI: 0.98–0.99) and 0.94 (95% CI 0.91–0.96), respectively. The pooled positive likelihood ratio and negative likelihood ratio were 5.94 (95% CI 4.41–7.98) and 0.03 (95% CI: 0.02-0.04), respectively. The diagnostic odds ratio of ultrasonography was 281.47 and the area under hierarchical summary receiver operating characteristic (HSROC) revealed an appropriate accuracy of 0.98. Conclusion: Ultrasonog- raphy has high diagnostic accuracy and can be used as a promising tool for confirmation of endotracheal tube placement, especially in critically ill patients or when capnography is not available, or its result is equivocal. Keywords: Airway management; intubation; meta-analysis; sensitivity and specificity; ultrasonography Cite this article as: Farrokhi M, Yarmohammadi B, Mangouri A, Hekmatnia Y, Bahramvand Y, Kiani M, Nasrollahi E, Nazari-Sabet M, Manoochehri-Arash N, Khurshid M, Mosalanejad S, Hajizadeh V, Amani-Beni R, Moallem M, Farahmandsadr M. Screening Performance Char- acteristics of Ultrasonography in Confirmation of Endotracheal Intubation; a Systematic Review and Meta-analysis. Arch Acad Emerg Med. 2021; 9(1): e68, https://doi.org/10.22037/aaem.v9i1.1360. ∗Corresponding Author: Mehrdad Farrokhi; Eris Research Institute, Tehran, Iran. Email: dr.mehrdad.farrokhi@gmail.com, Phone Number: This open-access article distributed under the terms of the Creative Commons Attribution NonCommercial 3.0 License (CC BY-NC 3.0). Downloaded from: http://journals.sbmu.ac.ir/aaem M. Farrokhi et al. 2 1. Introduction Securing a definitive airway in critically ill patients is a nec- essary procedure performed in intensive care unit (ICU), out of hospital, and in the emergency department (ED) settings. Direct assessment of the endotracheal tube passage through the cords is commonly performed via primary localization, followed by a confirming method (1, 2). However, direct vi- sualization of endotracheal tube passing through the cord may be misleading during difficult intubations, which may lead to esophageal intubation in emergency cases. Unrec- ognized esophageal intubations are associated with catas- trophic consequences such as neurological complications or death. Therefore, different techniques are often used to con- firm the appropriate placement of endotracheal tube, but not all of them are all of them are not reliable enough to con- firm the tracheal intubation (3, 4). It has been suggested that both clinical evaluations and confirmatory methods in- cluding auscultation, chest expansion following ventilation, bronchoscopy, chest X-ray, capnography, and end-tidal car- bon dioxide (ETCO2) assessment should be used to confirm the location of endotracheal tube. In this regard, ETCO2 has not been suggested for patients with cardiac arrest or em- bolism. Similarly, capnography has some limitations, includ- ing low reliability in patients with embolism or cardiac ar- rest, or recent bag-valve-mask use (5-7). Due to the above- mentioned limitations, combined with growing application of ultrasound by emergency medicine (EM) physicians and ease of use of point-of-care ultrasonography, many studies have been performed to assess the reliability of ultrasonogra- phy for approving the placement of endotracheal tube. How- ever, most of these investigations had small sample sizes with different gold standards, resulting in conflicting findings. Ac- cumulating lines of evidence have recently suggested that point-of-care ultrasonography can be used as an adjunct for confirming the placement of endotracheal tube, especially in critical situations such as cardiac arrest or when other con- firmation methods are not available (8-10). However, be- fore approval of ultrasonography as a promising technique for confirmation of endotracheal tube placement, it is nec- essary to pool the results of previously published studies. Therefore, in this systematic review and meta-analysis, we aimed to assess the screening performance characteristics of ultrasonography in confirmation of endotracheal tube place- +989384226664. † Corresponding Author: Maria Khurshid; Department of Internal Medicine, Berkshire Medical Center, Pittsfield, Massachusetts, USA. Email: drmkhur- shid@yahoo.com. ment. 2. Methods 2.1. Data Sources and Searches We performed a systematic search of the previous published papers investigating the diagnostic accuracy of ultrasonog- raphy for confirmation of endotracheal tube placement. We searched PubMed, Scopus, Google Scholar, EBSCO, EMBASE, Web of Science, and Cochrane Databases from inception to July 2021. The systematic search was carried out using medi- cal subject heading (MeSH) terms for ”ultrasonography” and ”intubation”. In this regard, we used ”sono”, ”sonography”, ”ultrasonography”, ”ultrasound”, ”endotracheal intubation”, ”esophageal intubation”, and ”intubation”. Our search had no restrictions with respect to location of study or publica- tion date. Furthermore, in this meta-analysis, we only as- sessed human studies. 2.2. Selection Criteria In this meta-analysis we included studies investigating the diagnostic accuracy of bedside ultrasound to confirm endo- tracheal tube placement following emergency or elective in- tubation in adult subjects. The included studies were re- quired to compare the findings of ultrasonography with a gold standard technique, such as fiberoptic bronchoscopy or capnography, for confirmation of endotracheal tube place- ment. Retrospective design studies, case reports, case series, and reviews were excluded and clinical trials, case-control or cohort design studies were included in this study. Investi- gations performed using mannequins, cadavers, or pediatric patients were excluded from the study. Two independent reviewers (M.F and B.Y) assessed the studies according to the above-mentioned criteria and any discrepancy between them was resolved by a third reviewer (M.K). In order to avoid possible duplicates, we searched the first author’s name, as well as the place and the period of the subjects’ enrolment. In the case of different versions of the same study, only the most recent was considered. 2.3. Data Extraction Data were extracted by two reviewers and included char- acteristics of the studies (the first author, publication date, sample size, male percentage, mean age of participants, and location of intubation), ultrasonic technique, transducer type, percentage of esophageal intubation, gold standard for confirmation of endotracheal tube placement, and diagnos- tic accuracy parameters of ultrasonography (number of true positive, true negative, false positive, and false negative). The process of data extraction was performed by two investiga- tors independently and finally, inconsistencies regarding in- cluded studies were resolved by a third reviewer. This open-access article distributed under the terms of the Creative Commons Attribution NonCommercial 3.0 License (CC BY-NC 3.0). Downloaded from: http://journals.sbmu.ac.ir/aaem 3 Archives of Academic Emergency Medicine. 2021; 9(1): e68 2.4. Data Synthesis Meta-DiSc version 1.4 software and Comprehensive Meta- Analysis software version 3 were used for statistical analysis. The heterogeneity among the included studies was investi- gated using Q-statistic and I2 index. If the value of I2 was higher than 50% or P-value was less than 0.10, the random model was used to estimate the sensitivity and specificity of ultrasonography for confirmation of endotracheal tube placement. Alternatively, if the value of I2 was less than 50% and P-value was higher than 0.10, the sensitivity and speci- ficity of ultrasonography were calculated using fixed model. Egger’s test and funnel plot were used to evaluate publication bias. 3. Results 3.1. Search Results Figure 1 summarizes the flow of studies in this review ac- cording to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) recommendations. A total of 9542 studies were identified in our preliminary search. After removal of 1682 duplicates, abstracts of the remaining 7860 studies were assessed by two independent reviewers (M.F and B.Y). The full-text of 142 articles were evaluated for eli- gibility and 107 article were excluded according to the exclu- sion criteria. Finally, 33 articles evaluating 2840 patients were included in our meta-analysis. 3.2. Characteristics of Included Studies The characteristics of the 33 included studies are summa- rized in table 1. Studies were performed between 2007 and 2020, with the sample sizes ranging from 19–150 subjects. Most of the included studies were performed in Iran (seven studies). Twenty-nine studies were prospective observa- tional studies and 4 were controlled trials. Five studies were conducted in ICUs, 10 were performed in operating rooms, and 18 were carried out in EDs. The prevalence of esophageal intubation was estimated to be 8.4% (95% CI: 6.5-10.8; Figure 2). 3.3. Publication Bias and Quality Assessment Assessment of publication bias based on Egger’s test showed that there was a statistically significant publication bias (P<0.01). Moreover, the funnel plot of included studies re- vealed significant asymmetry (Figure 3). Quality assessment of the included studies was performed using QUADAS-2 tool (Table 2). 3.4. Diagnostic Accuracy Indices The estimated pooled sensitivity and specificity of ultra- sonography for confirmation of endotracheal tube location were 0.98 (95% CI: 0.98–0.99) and 0.94 (95% CI 0.91–0.96), re- spectively (Figure 4 and Figure 5). The pooled positive like- lihood ratio and negative likelihood ratio were 5.94 (95% CI 4.41–7.98) and 0.03 (95% CI: 0.02-0.04), respectively (Figure 6 and Figure 7). Furthermore, the diagnostic odds ratio of ultrasonography was 281.47 (95% CI: 168.91–469.06) (Figure 8). The area under hierarchical summary receiver operating characteristic curve (HSROC) revealed an appropriate accu- racy of 0.98 (Figure 9). Subgroup analysis based on trans- ducer type and location of intubation (ICU or ED, or oper- ating room) showed acceptable sensitivity and specificity. 4. Discussion The results showed that the estimated pooled sensitivity and specificity of ultrasonography for confirmation of endotra- cheal tube location were 0.98 and 0.94, respectively. The di- agnostic odds ratio of ultrasonography was 281.47 and the area under HSROC revealed an appropriate accuracy of 0.98. Our findings confirm the efficacy of ultrasonography as an adjunct for assessment of endotracheal tube location during intubation. It should be noted that these results are impor- tant since capnography has been considered to have low ac- curacy, especially in subjects with critical conditions. Simi- larly, ultrasonography has been approved by advanced car- diac life support guidelines as an adjunct for capnography to confirm endotracheal tube placement (11). Furthermore, most confirmatory techniques need some ventilation, which is associated with higher rates of aspiration and gastric dis- tention in cases with wrong location of endotracheal tube (5, 12). On the other hand, ultrasonography does not in- crease risk of aspiration or gastric distention and has some advantages including being available in different locations, noninvasive, and rapid for confirmation of endotracheal tube placement. In a similar study, Adhikari et al. (13) have per- formed a systematic search in different databases to iden- tify studies evaluating efficacy of ultrasonography for con- firmation of endotracheal tube placement. Their systematic search yielded 5 eligible studies. In this study, the authors es- timated 91% sensitivity (95% CI, 74% to 97%) and 97% speci- ficity (95% CI, 89%to 99%) for ultrasonography, which are lower than those found in our study. In another study, a systematic search was carried out in EM- BASETM, MEDLINE, LILACS, The Cochrane Library, Kore- aMed, OpenGrey, and the World Health Organization Inter- national Clinical Trials Registry from their inception to 2014, which yielded 11 studies with 969 patients (14). They re- ported pooled sensitivity and specificity of ultrasonography in confirming the placement of the tube as 0.98 and 0.98, re- spectively. Although their estimated pooled sensitivity was similar to that found in our study, their pooled specificity was higher than ours. These differences can partially be ex- This open-access article distributed under the terms of the Creative Commons Attribution NonCommercial 3.0 License (CC BY-NC 3.0). Downloaded from: http://journals.sbmu.ac.ir/aaem M. Farrokhi et al. 4 plained by the difference in the number of included studies, sample sizes of patients, and also causes of patient hospital- ization. Although our findings confirmed the efficacy of ultrasonog- raphy as a promising adjunct for confirmation of endotra- cheal tube placement, it should be noted that there are some significant limitations for ultrasonography. First, the efficacy of ultrasonography is dependent on the operator and ultra- sonography by different operators may result in different ul- trasonographic image qualities and decisions. Therefore, ul- trasonography operators must obtain necessary skills before performing ultrasonography for confirmation of endotra- cheal tube location. Furthermore, ultrasonography cannot be performed easily in situations where there is only one op- erator, because that operator may be the technician perform- ing endotracheal intubation. Therefore, in these cases, the static techniques is superior to dynamic technique. More- over, the placement of ultrasonographic transducer on the trachea when a tube is entering the trachea may be associ- ated with a more difficult intubation as it might deviate its path. In this regard, it has been suggested that the pressure of transducer on trachea should be reduced by ultrasonogra- phy operator to prevent deviation of endotracheal tube dur- ing intubation. If ultrasonography increases the risk of dif- ficult intubation, the procedure should be performed using static technique. From another point of view, ultrasonog- raphy may be difficult for some intubations including cases with different airway anatomy, neck edema, cervical collar, subcutaneous emphysema, and neck masses. Unlike ultra- sonography, capnography requires four to five ventilations to confirm the location of endotracheal tube placement, so ul- trasonography is faster than capnography. However, the ef- ficacy of capnography is not dependent on the experience of operator and training does not affect the accuracy of this method (15). It is now well established that ultrasonography has several strong points for confirmation of endotracheal tube loca- tion. Deviation of endotracheal tube into the esophagus can be easily identified before initiation of ventilation because ultrasonography is carried out in real time during intuba- tion. Since ultrasonography has an appropriate specificity for identification of esophageal intubation, this method can be used in cases with indefinite result of capnography to reduce the total number of intubation attempts. Furthermore, ultra- sonography does not interfere with chest compression and intubation can be performed during cardiopulmonary resus- citation. However, further studies with larger sample sizes using appropriate gold standards are required to establish ul- trasonography as a promising diagnostic test for assessment of endotracheal tube location. 5. Limitations Different methods of confirmation were used as gold stan- dard to indicate sensitivity and specificity of sonography for confirmation of endotracheal tube placement. 6. Conclusion The results showed that ultrasonography has high diagnostic accuracy and can be used as a promising tool for confirma- tion of endotracheal tube placement, especially in critically ill patients or when capnography is not available, or its result is equivocal. 7. Declarations 7.1. Acknowledgments The authors thank all those who contributed to this study. 7.2. Conflict of Interest None. 7.3. Funding/Support None. 7.4. Authors’ contribution All authors contributed to study design, data collection, writ- ing draft of study. 7.5. Data Availability Not applicable. References 1. 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This open-access article distributed under the terms of the Creative Commons Attribution NonCommercial 3.0 License (CC BY-NC 3.0). Downloaded from: http://journals.sbmu.ac.ir/aaem 7 Archives of Academic Emergency Medicine. 2021; 9(1): e68 Table 1: Characteristic of studies included in the meta-analysis Author Year Sample Size Location Mean Age Male (%) Ultrasonic Technique Transducer Type Esophageal Intubation (%) Gold Standard Chowdhury et al. (3) 2020 120 OR 39.02 28 Dynamic Linear 4.1 CAP+A Chen et al. (1) 2020 118 ICU 71.5 60.2 Dynamic NR 10.2 DV+FB Men et al. (16) 2019 68 OR 60.4 54 Static Curvilinear 17.6 A+FB Patil et al. (17) 2019 91 ICU NR NR Dynamic Linear 2 CAP Afzalimoghadam et al. (18) 2019 90 ED 59.2 58.9 Dynamic Linear 3.3 CAP Zamani et al. (19) 2018 100 ED 57.5 73 Dynamic Linear 6 CAP Kad et al. (20) 2018 100 OR NR NR Static Linear 2 A et al. (21) 2018 40 ICU 55.7 65 Dynamic Curvilinear 10 FB Inangil et al. (22) 2018 50 OR 42.9 56 Dynamic Linear 6 CAP Arya et al. (23) 2018 75 ICU 63.4 55.3 Dynamic Linear 16 CAP Arafa et al. (24) 2018 107 OR 41.4 63.6 Dynamic Linear 7.5 CAP Zamani et al. (25) 2017 150 ED 58.5 56 Static Linear 11.3 O+AS+DV+A Yang et al. (26) 2017 93 OR 53.5 46 Static Linear 9.7 CAP+A Thomas et al. (27) 2017 100 ED 50.8 59 Static Linear 5 CAP Rahmani et al. (28) 2017 75 ED 61.1 62.7 Dynamic Linear 0 DV Masoumi et al. (8) 2017 100 ED 64.5 65 Static Curvilinear 6 CAP Lahham et al. (9) 2017 72 ED 57.7 56.9 Dynamic Linear 4.2 CAP Abhishek et al. (5) 2017 100 OR 38.9 NR Static Linear 5 CAP Khosla et al. (29) 2016 20 ICU 70.5 100 Static Linear 0 CAP+A Karacabey et al. (a) (10) 2016 85 ED 67.2 NR Dynamic Linear 38.2 CAP Karacabey et al. (b) (10) 2016 30 ED NR NR Dynamic Linear NR CAP Abbasia et al. (30) 2015 120 ED 50 61.5 Dynamic/Static Linear 11.7 DV+A+CAP Sun et al. (31) 2014 96 ED 68.8 67.6 Dynamic Curvilinear 7.3 CAP+A Hoffman et al. (32) 2014 101 ED 58 NR Dynamic/Static Linear 10 DV+CAP Saglam et al. (33) 2013 69 ED NR NR Static Linear 7.2 CAP Hosseini et al. (34) 2013 57 ED 59 60 Static Curvilinear 21 DV+A+O Chou et al. (a) (35) 2013 89 ED 69.9 69 Dynamic Curvilinear 7.6 CAP+A Adi et al. (36) 2013 107 ED NR NR Static Linear 5.6 CAP Noh et al. (37) 2012 19 ED NR NR Dynamic Linear 15.7 CAP Mulsu et al. (38) 2011 150 OR 40.5 50.7 Dynamic Linear 50 CAP+A Chou et al. (b) (39) 2011 83 ED 67.6 54.5 Static Curvilinear 15.7 CAP Chou et al. (c) (39) 2011 29 ED NR NR Static Curvilinear 10.3 CAP Park et al. (40) 2009 30 ED 59.6 56.7 Dynamic Linear 10 CAP+A Werner et al. (41) 2007 66 OR 38.9 21.2 Dynamic Linear 57.6 DV+CAP Milling et al. (42) 2007 40 OR 52.5 17.5 Dynamic Curvilinear 12.5 CAP+A OR: operation room; ICU: intensive care unit; ED: emergency department; NR: not reported; CAP: capnography; A: auscultation; DV: direct visualization; FB: fiberoptic bronchoscopy. This open-access article distributed under the terms of the Creative Commons Attribution NonCommercial 3.0 License (CC BY-NC 3.0). Downloaded from: http://journals.sbmu.ac.ir/aaem M. Farrokhi et al. 8 Table 2: Quality assessment of the included studies using QUADAS-2 tool Study RISK OF BIAS APPLICABILITY CONCERNS Patient selection Index test Reference standard Flow & timing Patient selection Index test Reference standard Chowdhury et al. © © © © © © © Chen et al. © © © © © © © Men et al. © © © © © © © Patil et al. © © © © © © © Afzalimoghadam et al. © © © © © © © Zamani et al. © © © © © © © Kad et al. © © © © © © © Kabil et al. © © © © © © © Inangil et al. © © © © © © © Arya et al. © © © © © © © Arafa et al. © © © © © © © Zamani et al. ? © © © © © © Yang et al. © © © © © © © Thomas et al. © ? © © © © © Rahmani et al. © © © © © © © Masoumi et al. ? © © © © © © Lahham et al. ? © © © © © © Abhishek et al. ? © © © © © © Khosla et al. © © © © © © © Karacabey et al. (a) © © © © © © © Karacabey et al. (b) © © © © © © © Abbasia et al. § © © © © © © Sun et al. © © © ? © © © Hoffman et al. ? © © © © © © Saglam et al. § © © © © © © Hosseini et al. © © © © © © © Chou et al. (a) ? © © © © © © Adi et al. ? © © © © © © Noh et al. ? © © ? © © © Mulsu et al. © © © © © © © Chou et al. (b) ? © © © © © © Chou et al. (c) ? © © © © © © Park et al. ? © © © © © © Werner et al. ? © © © © © © Milling et al. ? © © © © © © ©: Low Risk; §: High Risk; ?: Unclear Risk This open-access article distributed under the terms of the Creative Commons Attribution NonCommercial 3.0 License (CC BY-NC 3.0). Downloaded from: http://journals.sbmu.ac.ir/aaem 9 Archives of Academic Emergency Medicine. 2021; 9(1): e68 Figure 1: PRISMA flowchart of the literature search and selection of studies that reported accuracy of ultrasonography for confirmation of endotracheal placement. This open-access article distributed under the terms of the Creative Commons Attribution NonCommercial 3.0 License (CC BY-NC 3.0). Downloaded from: http://journals.sbmu.ac.ir/aaem M. Farrokhi et al. 10 Figure 2: Forest plot of prevalence of esophageal intubation. This open-access article distributed under the terms of the Creative Commons Attribution NonCommercial 3.0 License (CC BY-NC 3.0). Downloaded from: http://journals.sbmu.ac.ir/aaem 11 Archives of Academic Emergency Medicine. 2021; 9(1): e68 Figure 3: Publication bias of the included studies for analysis of the rate of esophageal intubation confirmed using ultrasonography. This open-access article distributed under the terms of the Creative Commons Attribution NonCommercial 3.0 License (CC BY-NC 3.0). Downloaded from: http://journals.sbmu.ac.ir/aaem M. Farrokhi et al. 12 Figure 4: Forest plot of the overall sensitivity of ultrasonography for confirmation of endotracheal tube placement. This open-access article distributed under the terms of the Creative Commons Attribution NonCommercial 3.0 License (CC BY-NC 3.0). Downloaded from: http://journals.sbmu.ac.ir/aaem 13 Archives of Academic Emergency Medicine. 2021; 9(1): e68 Figure 5: Forest plot of the overall specificity of ultrasonography for confirmation of endotracheal tube placement. This open-access article distributed under the terms of the Creative Commons Attribution NonCommercial 3.0 License (CC BY-NC 3.0). Downloaded from: http://journals.sbmu.ac.ir/aaem M. Farrokhi et al. 14 Figure 6: Forest plot of the overall positive likelihood ratio of ultrasonography for confirmation of endotracheal tube placement. This open-access article distributed under the terms of the Creative Commons Attribution NonCommercial 3.0 License (CC BY-NC 3.0). Downloaded from: http://journals.sbmu.ac.ir/aaem 15 Archives of Academic Emergency Medicine. 2021; 9(1): e68 Figure 7: Forest plot of the overall negative likelihood ratio of ultrasonography for confirmation of endotracheal tube placement. This open-access article distributed under the terms of the Creative Commons Attribution NonCommercial 3.0 License (CC BY-NC 3.0). Downloaded from: http://journals.sbmu.ac.ir/aaem M. Farrokhi et al. 16 Figure 8: Forest plot of the overall diagnostic odds ratio (OR) of ultrasonography for confirmation of endotracheal tube placement. This open-access article distributed under the terms of the Creative Commons Attribution NonCommercial 3.0 License (CC BY-NC 3.0). Downloaded from: http://journals.sbmu.ac.ir/aaem 17 Archives of Academic Emergency Medicine. 2021; 9(1): e68 Figure 9: Hierarchical summary receiver-operating characteristic curve (HSROC) indicating accuracy of ultrasonography for confirmation of endotracheal tube placement. This open-access article distributed under the terms of the Creative Commons Attribution NonCommercial 3.0 License (CC BY-NC 3.0). Downloaded from: http://journals.sbmu.ac.ir/aaem Introduction Methods Results Discussion Limitations Conclusion Declarations References