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Abstract & Commentary
Source: Hsieh KS, et al. Secondary confirmation of endotracheal tube position by ultrasound image. Crit Care Med 2004; 32:S374-377.
Verification of endotracheal tube placement in the airway following intubation is critical in the emergent setting. In addition to auscultation and other clinical assessments, new techniques for tube confirmation include measurement of end-tidal carbon dioxide (CO2) and use of the esophageal detector device. However, each of these methods has limitations, and thus, multiple methods of real-time confirmation are recommended.
Investigators studied the utility of ultrasonography to verify correct placement of the endotracheal tube in patients cared for in a pediatric intensive care unit (ICU). During a six-month study period, they studied 59 patients who were intubated for either cardiopulmonary arrest or impending respiratory failure. Ultrasound imaging was performed using a portable machine with 2-D and M-mode scanning and tranducer frequencies varying from 2.5 to 7.5 MHz. Several scanning windows were utilized, primarily the subxiphoid window with a wide scanning angle (70-85°) to allow visualization of both sides of the diaphragm. Operators assessed diaphragmatic movement to confirm tube placement. If both sides of the diaphragm moved toward the abdomen during positive ventilation and toward the chest during exhalation, then the tube was determined to be placed correctly. Opposite movement indicated esophageal placement. Asymmetric movement of the left and right sides of the diaphragm indicated tube placement in a mainstem bronchi.
The authors report that this ultrasound technique correctly identified two esophageal intubations as well as eight right mainstem bronchus intubations. Because confirmation was performed real-time at the bedside, the investigators reported that these misplacements were corrected rapidly without difficulty. Moreover, for the right mainstem intubations, the endotracheal tubes were withdrawn a small distance until bilateral equal motion of the diaphragm could be seen clearly on ultrasound. Subsequently, the authors report that their ultrasound technique confirmed all 59 intubations.
They conclude that ultrasound imaging of diaphragm motion allows a useful, quick, noninvasive, real-time anatomic method for assessment and confirmation of endotracheal tube position.
Commentary by Ted Chan, MD, FACEP
Bedside ultrasonography performed by the ED physician is becoming more common for many indications. This study is an interesting report on using ultrasound as another means of verifying endotracheal tube placement rapidly at the bedside. Whereas others have attempted to actually visualize the upper airway during intubation with limited success,1 this study uses ultrasound to visualize the diaphragm to assess airway control.
The authors report excellent success with their approach, even suggesting that real-time ultrasound can provide gross tuning for correcting mainstem intubations. However, a number of limitations should be kept in mind when considering this study. First, the total number of patients was small, and a much larger study is needed to confirm ultrasonography’s applicability in this setting. Second, the gold standard to determine correct tube location is not clear in this study, which could have affected the results. Third, the study population was limited to patients in a pediatric ICU; it is not clear how well this technique would perform in adults, particularly those with greater soft tissue, which may interfere with sonographic imaging. Finally, as this technique is based on diaphragmatic movement, it is not clear if there could be differences in assessing motion in patients who are paralyzed compared with those who are spontaneously breathing when intubated.
This concept is intriguing, but more study is needed. Although it is unlikely that ultrasonography will become the single gold-standard method for verifying tube placement any time soon, it could add to our current armamentarium of methods for intubation confirmation.
Dr. Chan, Associate Clinical Professor of Medicine, Emergency Medicine, University of California, San Diego, is on the Editorial Board of Emergency Medicine Alert.
1. Ma G, et al. Using ultrasound to visualize and confirm endotracheal intubation. Acad Emerg Med 1999;6:515.