To the Editor:
I read with great interest the publication by Ramsingh et al.,1 which elegantly shows that point-of-care ultrasound examination is considerably more accurate than chest auscultation in discriminating between endotracheal and endobronchial intubation. However, several factors limit the practicality of this technique in routine clinical practice. It requires unrestricted access to neck and thorax and considerable operator experience. All ultrasound examinations were performed by anesthesiologists with at least 4-yr postresidency experience who had previously completed at least 50 whole-body point-of-care ultrasound examinations and at least an additional 25 pulmonary tree and lung expansion ultrasound examinations. Even under the optimal study conditions, it took close to 4 min to complete the ultrasound examination in individual cases. The authors appropriately acknowledge these limitations. However, acknowledgment will not eliminate them.
Somewhat surprisingly, the authors did not make any reference to the 21/23-cm method as a means of assessing endotracheal tube (ETT) position. When using this method, the ETT is positioned at the 21-cm mark in women and at the 23-cm mark in men, measured at the upper incisor teeth or the corner of the mouth. Although this technique is effective in predicting ETT position,2–4 the authors state that using standardized ETT insertion depth is prone to error.1 However, the referenced publication2 does not necessarily support this view. The study population consisted of endotracheally intubated patients admitted to the intensive care unit.2 In the control group (n = 263), position of the ETT was left unchanged. In the study group (n = 304), ETTs were (re)positioned at the 23-cm mark in men and at the 21-cm mark in women, measured at the upper incisor teeth or the upper anterior gums in edentulous patients. The distance between the tip of the ETT and the carina was radiographically determined. In the study group, there were no endobronchial intubations, and in only two patients, the tip of the ETT was between 2 and 3 cm proximal to the carina (0.65%). In the control group, there were seven endobronchial intubations (2.7%); in eight patients, the tip of the ETT was less than 2 cm proximal to the carina (3.0%); and in 20 patients, the tip of the ETT was between 2 and 3 cm proximal to the carina (7.6%).
In a prospective randomized trial, chest auscultation, observation and palpation of chest movements, and check of the ETT tube insertion depth on the centimeter scale basis were used for detecting or excluding endobronchial intubation.4 The position of the ETT was fiberoptically controlled. A maximum of 30 s was allowed to judge the tube position. Of all three tests, checking depth of insertion by the centimeter scale on the ETT was the most accurate. This method showed a sensitivity of 88% (95% CI, 0.75 to 1) and a specificity of 98% (95% CI, 0.39 to 1) for detecting or excluding endobronchial intubation. These values are as good as those obtained by the ultrasound method.1 Importantly, the test results were independent of the anesthesiologist’s experience. Noteworthy, had the 21/23-cm rule been followed, not a single patient would have been endobronchially intubated. However, it would have resulted in a shorter than the recommended safety distance of 2.5 cm between the distal end of the ETT and the carina in 24 of 118 women (20%) and 7 of 42 men (18%). If a 20/22- instead of the 21/23-cm rule had been used, the recommended safety distance would have been achieved in 108 of 118 (92%) women and in all 42 men. The shortest correct intubation depth was 19 cm in 10 women with an average height of 157 cm and a body mass index of 28.4 kg/m2. These findings suggest that in general, using the 20/22-cm rule (with the possible exception of using 19 cm in small women with a higher body mass index) might be safer than using the “traditional” 21/23-cm rule.
The overall evidence suggests that the 21/23-cm method (possibly to be replaced by the 20/22-cm method) allows rapid and reliable assessment of the likelihood of endobronchial intubation without the need for advanced clinical experience and for additional technical equipment and specialized training. The practicing clinician should be aware of a “low-tech” alternative method of assessing the likelihood of endobronchial intubation of equal sensitivity and specificity as the ultrasound method but without its limitations. When next investigating the effectiveness of a technique in assessing the ETT position, it might be more appropriate to choose the 21/23-cm method as the “accepted” standard for comparison rather than chest auscultation.
The author declares no competing interests.