Proper use and interpretation of diaphragmatic ultrasonography
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KeywordsPleural Line Diaphragmatic Paralysis Diaphragmatic Muscle Diaphragm Thickness Diaphragmatic Function
To the Editor,
We read with interest the technical description by El-Boghdadly et al. 1 regarding the utility of ultrasound scanning as part of the assessment of diaphragmatic function after brachial plexus blockade. We are appreciative of their admission regarding the novelty of our previously described ABCDE plus sniff technique2 and their decision to emulate it as part of their attempt “to further simplify diaphragm ultrasonography” by “using simple surface marking”. Unfortunately, their description neglects the importance of the systematic “step by step” approach we outlined. They also incorrectly claim that gross caudal movement of the pleural line can reliably be used to detect diaphragmatic paralysis. To appreciate the pros and cons of each approach more fully, however, it is important to show clearly where one technique ends and the other begins.
Although not cited in their article, the basis for our use of the sniff test and El-Boghdadly et al.’s use of surface markings primarily stem from the original concept of the “ABCDE” approach,3 a mnemonic aid for locating ideal scanning sites to evaluate the diaphragm via intercostal windows rather than hepatic or splenic windows. It involves placing the ultrasound probe at the (A)nterior axillary line just below the level of the nipple, identifying pleural/lung sliding during (B)reathing, and moving the probe in a (C)audal direction along the axillary line until the (D)iaphragm can be identified and (E)valuated. This mnemonic method utilizes step-by-step landmarking of readily recognizable features, such as lung sliding or movement of the pleural line, to locate the diaphragmatic muscle, which is the primary area of interest. It seems that El-Boghdadly et al. intended to describe a new technique of their own by eliminating these systematic steps from the ABC approach - advocating only probe placement at ribs 7-8 (right) or ribs 8-9 (left). By following this course, however, they may have unknowingly reported a technique with a starting location similar to that described by Sarwal et al. 4
We recently performed a pilot study7 that showed that the newly described ABCDE approach provided easy visualization of lung sliding and the diaphragmatic muscle itself. Furthermore, we showed that there was no relation between changes in diaphragmatic thickness and the distance of lung sliding by surface marking. The implication of this observation is that lung sliding or pleural line movement distance recorded by surface marking cannot reliably predict diaphragm thickness changes or vice versa. Thus, cephalad or caudal displacement of the pleural reflection should serve only as an aid for locating the diaphragm, not for assessing its function.
The authors greatly thank Dr. C. Prabhakar, Department of Anesthesia, University of British Columbia for sharing his experiences and expertise as well as ultrasound images on this topic.
Conflicts of interest
This submission was handled by Dr. Hilary P. Grocott, Editor-in-Chief, Canadian Journal of Anesthesia.
- 7.Halliday S, Horne S, Tsui BC. Diaphragm thickness and its relationship to lung sliding using the abc approach to diaphragmatic evaluation: a feasibility study in patients undergoing ultrasound-guided brachial plexus blocks. Spring 2016 Abstract Titles: ASRA 41st Annual Regional Anesthesiology and Acute Pain Medicine Meeting March 31-April 2, 2016 New Orleans, LA. Reg Anesth Pain Med 2016; 41: 632-52.Google Scholar