ANNALS OF EMERGENCY MEDICINE
Systematic Review Snapshot TAKE-HOME MESSAGE During emergency intubations, transtracheal ultrasonography can be used to assess endotracheal tube placement before conﬁrmation with capnography. METHODS DATA SOURCES MEDLINE, EMBASE, the Cochrane Library, and Trip database were searched in the English language, whereas KoreaMed and Literature in the Health Sciences in Latin America and the Caribbean System were searched in the other languages from inception to September 2014. OpenGrey and the World Health Organization Clinical Trials Registry were searched for unpublished literature and ongoing studies. Bibliographies and related abstract links were also explored.
Can Transtracheal Ultrasonography Be Used to Verify Endotracheal Tube Placement? EBEM Commentators
Michael Gottlieb, MD John Bailitz, MD Department of Emergency Medicine Cook County Hospital Chicago, IL
Results Table. Sensitivity and speciﬁcity of transtracheal ultrasonography for determining intubation. Outcome Measure Pooled data Emergency intubations
Sensitivity (95% CI)
Speciﬁcity (95% CI)
Number of Studies (Number of Patients)
0.98 (0.97–0.99) 0.98 (0.97–0.99)
0.98 (0.95–0.99) 0.94 (0.86–0.98)
11 (969) 8 (713)
CI, Conﬁdence interval.
STUDY SELECTION Studies evaluating the accuracy of transtracheal ultrasonography in conﬁrming endotracheal tube placement were assessed by 2 study authors and a nonauthor subject expert, with disagreement resolved by consensus. Only studies assessing living adult humans and using capnography as the criterion standard were included. DATA EXTRACTION AND SYNTHESIS Study quality was assessed with the QUADAS-2 tool. Data were arranged into 22 tables to calculate both pooled and emergency situation sensitivities and speciﬁcities, with corresponding 95% conﬁdence intervals. Heterogeneity was assessed with both a Cochran Q test and inconsistency index.
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Twelve studies met the inclusion criteria, with 1 excluded because of difﬁculty computing zero in the contingency table. Of the remaining 11 studies (including 969 intubations), 3 examined the accuracy in elective intubations and 8 assessed the accuracy in emergency intubations. Transtracheal ultrasonography was performed by emergency medicine residents in 6 studies, attending emergency physicians in 2 studies, and nonemergency physicians in 2 studies; 1 study did not describe the ultrasonographer level of training. The majority of the studies were judged to be at a low risk of bias, with strong applicability ratings according to the QUADAS-2 assessment tool. Only 2
of the included studies were considered to be at high risk of bias isolated to patient selection, and 1 was deemed to be at high risk of bias isolated to the reference test. Sensitivity and speciﬁcity were very high for the pooled data, with a slight decrease in speciﬁcity for the subgroup analysis that included only emergency intubations (Table). The Cochran Q and inconsistency index indicated minimal to moderate variation across the studies.
Commentary Conﬁrmation of proper placement of an endotracheal tube is essential because unrecognized esophageal Volume 66, no. 4 : October 2015
Systematic Review Snapshot
intubation can lead to disastrous consequences. Numerous methods of endotracheal tube conﬁrmation have been described in the literature, with varying degrees of accuracy. The widely recognized 2010 advanced cardiac life support guidelines recommend the use of quantitative capnography as the criterion standard to conﬁrm endotracheal tube placement.1 However, capnography has multiple limitations, including false positives with hypopharyngeal endotracheal tube placement, false negatives with cardiac arrest, and the requirement for multiple ventilations before conﬁrmation.2,3 Additionally, quantitative capnography is not available in all emergency departments. As a result, there has been increased research into the use of ultrasonography to visually conﬁrm endotracheal tube placement. This systematic review reported a sensitivity of 98% and a speciﬁcity of 94% among emergency intubations. By comparison, a large meta-analysis of combined colorimetric capnometry and capnography demonstrated a sensitivity of 93% and a speciﬁcity of 97%.2 Although the meta-analysis summarized in this snapshot is smaller than the combined colorimetric capnometry and capnography studies, there are signiﬁcant implications for the emergency physician. Most emergency physicians are familiar with ultrasonography, and transtracheal ultrasonography appears to be a relatively simple
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technique to add to their armamentarium. Moreover, it is faster than capnography and does not require ventilations to assess tube placement.4 The procedure involves placing a linear transducer horizontally across the tracheal cartilage and assessing dynamic passage of the endotracheal tube through the trachea or visualization of a “second trachea” next to the trachea, signifying the presence of the endotracheal tube in the esophagus. This may be supplemented with transthoracic ultrasonography, but the latter requires ventilations for conﬁrmation.5,6 One limitation of this study was the use of capnography as the reference standard, which has imperfect sensitivity and speciﬁcity.2,7,8 Future studies could beneﬁt from a more deﬁnitive conﬁrmatory test, such as direct visualization with a video laryngoscope or bronchoscopy. Despite 98% sensitivity, there were 4 undetected esophageal intubations, which have potentially disastrous consequences if not identiﬁed. Other potential limitations of using transtracheal ultrasonography include delays because of machine warm-up, interoperator variability, and the need for a second provider to perform the ultrasonography during the intubation attempt. Transtracheal ultrasonography demonstrates acceptable accuracy for initial endotracheal tube placement, but further randomized trials are required before it can replace
capnography for endotracheal tube conﬁrmation. Editor’s Note: This is a clinical synopsis, a regular feature of the Annals’ Systematic Review Snapshot (SRS) series. The source for this systematic review snapshot is: Das SK, Choupoo NS, Haldar R, et al. Transtracheal ultrasound for veriﬁcation of endotracheal tube placement: a systematic review and meta-analysis. Can J Anaesth. 2015;62:413-423. 1. Neumar RW, Otto CW, Link MS, et al. Part 8: adult advanced cardiovascular life support: 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation. 2010;122(18 suppl 3):S729-S767. 2. Li J. Capnography alone is imperfect for endotracheal tube placement conﬁrmation during emergency intubation. J Emerg Med. 2001;20:223-229. 3. Takeda T, Tanigawa K, Tanaka H, et al. The assessment of three methods to verify tracheal tube placement in the emergency setting. Resuscitation. 2003;56:153-157. 4. Pfeiffer P, Rudolph SS, Børglum J, et al. Temporal comparison of ultrasound vs. auscultation and capnography in veriﬁcation of endotracheal tube placement. Acta Anaesthesiol Scand. 2011;55:1190-1195. 5. Park SC, Ryu JH, Yeom SR, et al. Conﬁrmation of endotracheal intubation by combined ultrasonographic methods in the emergency department. Emerg Med Australas. 2009;21:293-297. 6. Saglam C, Unlüer EE, Karagöz A. Conﬁrmation of endotracheal tube position during resuscitation by bedside ultrasonography. Am J Emerg Med. 2013;31:248-250. 7. Anton WR, Gordon RW, Jordan TM, et al. A disposable end-tidal CO2 detector to verify endotracheal intubation. Ann Emerg Med. 1991;20:271-275. 8. Bozeman WP, Hexter D, Liang HK, et al. Esophageal detector device versus detection of end-tidal carbon dioxide level in emergency intubation. Ann Emerg Med. 1996;27:595-599.
Michael Brown, MD, MSc, Alan Jones, MD, and David Newman, MD, serve as editors of the SRS series.
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