A novel systematic ABC approach to Diaphragmatic Evaluation (ABCDE)
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KeywordsAcoustic Window Anterior Axillary Line Pleural Line Diaphragmatic Paralysis Diaphragmatic Muscle
To the Editor,
Experience with US-guided regional anesthesia suggests that a systematic approach using readily identifiable landmarks can be valuable for facilitating an effective block. Using a similar systematic approach, we offer a simple method for consistently and readily identifying diaphragmatic muscle thickening using B-mode US. Our ABC Diaphragm Evaluation (ABCDE) approach involves first placing a high-frequency, linear US probe (e.g., 10-15 MHz) at the anterior axillary line just below the level of the nipple (Figure). One can observe recognizable landmarks between the two ribs, such as movement of the pleura (lung sliding) on top of the diaphragm muscle during breathing. By moving the probe in a caudal direction along the axillary line, one can identify diaphragmatic muscle thickening for evaluations caudal to the pleural line because the diaphragm is no longer hidden under the pleura during inspiration (see Video 1: spleen side and Video 2: liver side).
Several distinct features are evident when using this ABCDE method with the US probe in the longitudinal plane. First, the image of the pleural edge moves caudally during normal respiration. Second, the pleura can be visualized as it slides just above the diaphragm, helping to distinguish the diaphragmatic muscle from the intercostal muscles. Lastly, diaphragmatic thickening can be observed just inferior to the edge of the pleura as the scan moves caudally. Seeking specific acoustic windows of the liver or spleen, which is often difficult, is thus unnecessary. Indeed, the success rate with the ABCDE method is the same on each side because the diaphragm is assessed directly via the intercostal space, without requiring the liver or spleen for US windows (see attached videos as Electronic Supplementary Material).
It is important to note that pleural (i.e., lung) movement does not guarantee spontaneous diaphragmatic contraction and movement. This is because pleural motion can be generated by paradoxical movement caused by the contralateral lung and diaphragm. Moreover, the change in the diaphragm thickening ratio [thickness at inspiration − thickness at expiration]/thickness at expiration) reflects muscle effort (28-96% change in healthy individuals vs −35% to 5% change in those with diaphragmatic paralysis).4,5
In summary, we believe that this novel ABC Diaphragm Evaluation approach may help anesthesiologists easily and quickly learn and remember how to identify the diaphragmatic muscle using US for rapid clinical diagnosis and monitoring.
Conflicts of interest
Dr. Tsui is supported by a Clinical Scholar Award from the Alberta Heritage Foundation for Medical Research (AHFMR). Dr. Tsui’s research is supported by the Canadian Anesthesia Research Foundation.
Supplementary material 1 (MP4 7326 kb)
Supplementary material 2 (MP4 7330 kb)