Diaphragm ultrasound is an emerging, revolutionary bedside tool that provides a safe, accurate, and noninvasive approach to comprehensively evaluate the anatomy and function of the respiratory muscle pump, with widespread and crucial applications in ICUs and clinics.
The two primary measurements are diaphragm excursion (DE) and thickness and diaphragm thickening fraction (DTF). DE is typically measured in the subcostal area at the midclavicular line or anterior axillary line using a phased-array or curvilinear transducer in M-mode. It visualizes diaphragm movement over time during tidal respiration, deep breathing, and sniffing and correlates with lung inspiratory volumes.1 Diaphragm thickness is assessed in the zone of apposition at the midaxillary line 0.5 to 2 cm below the costophrenic angle, typically around the eighth or ninth intercostal space, with a high-frequency linear probe. It views the diaphragm as a hypoechoic muscle layer between the parietal pleura and the peritoneum.1,2 The DTF is calculated as the percentage inspiratory increase in thickness and reflects both the work of breathing and contractile activity.2
Diaphragm ultrasound has several clinical applications. Indices like thickness, DTF, and DE have been extensively studied for predicting successful weaning and liberation from mechanical ventilation.3,4 However, significant heterogeneity across studies makes a general conclusion somewhat challenging.3–5 DTF of less than 20% to 30% or DE of less than 2 cm with deep inspiration is useful in diagnosing diaphragm dysfunction (DD).6,7 Ultrasound outperforms traditional techniques like fluoroscopy in diagnosing DD.1 Furthermore, it helps assess muscle atrophy, which is linked to prolonged mechanical ventilation, through tracking changes in diaphragm size.2 In respiratory diseases, such as COPD and neuromuscular disorders, it predicts noninvasive ventilation (NIV) success, assesses air trapping, and evaluates rehabilitation effects.7,8 In an emergent setting, it can be used to predict NIV failure in community-acquired pneumonia.9
Current limitations to widespread adoption of this practice include operator dependence and difficulty visualizing the left hemidiaphragm. To address this, there is a recent effort to standardize the measurement technique.10 Future advancements include advanced techniques to enable more detailed tissue analysis, such as tissue Doppler imaging, speckle tracking ultrasound, and ultrasound shear wave elastography.11–13
References
1. Aarab Y, Flatres A, Garnier F, et al. Shear wave elastography, a new tool for diaphragmatic qualitative assessment: a translational study. Am J Respir Crit Care Med. 2021;204(7):797-806. doi:10.1164/rccm.202011-4086OC
2. Santana PV, Cardenas LZ, de Albuquerque ALP, de Carvalho CRR, Caruso P. Diaphragmatic ultrasound: a review of its methodological aspects and clinical uses. J Bras Pneumol. 2020;46(6):e20200064. doi:10.36416/1806-3756/e20200064
3. Tuinman PR, Jonkman AH, Dres M, et al. Respiratory muscle ultrasonography: methodology, basic and advanced principles and clinical applications in ICU and ED patients-a narrative review. Intensive Care Med. 2020;46(4):595-605. doi:10.1007/s00134-019-05892-8
4. Turton P, ALAidarous S, Welters I. A narrative review of diaphragm ultrasound to predict weaning from mechanical ventilation: where are we and where are we heading? Ultrasound J. 2019;11(1):2. doi:10.1186/s13089-019-0117-8
5. Zambon M, Greco M, Bocchino S, Cabrini L, Beccaria PF, Zangrillo A. Assessment of diaphragmatic dysfunction in the critically ill patient with ultrasound: a systematic review. Intensive Care Med. 2017;43(1):29-38. doi:10.1007/s00134-016-4524-z
6. Parada-Gereda HM, Tibaduiza AL, Rico-Mendoza A, et al. Effectiveness of diaphragmatic ultrasound as a predictor of successful weaning from mechanical ventilation: a systematic review and meta-analysis. Crit Care. 2023;27(1):174. doi:10.1186/s13054-023-04430-9
7. Yamada T, Minami T, Yoshino S, et al. Diaphragm ultrasonography: reference values and influencing factors for thickness, thickening fraction, and excursion in the seated position. Lung. 2024;202(1):83-90. doi:10.1007/s00408-023-00662-2
8. Minami T, Manzoor K, McCool FD. Assessing diaphragm function in chest wall and neuromuscular diseases. Clin Chest Med. 2018;39(2):335-344. doi:10.1016/j.ccm.2018.01.013
9. Hernandez-Voth A, Sayas Catalan J, Corral Blanco M, et al. Long-term effect of noninvasive ventilation on diaphragm in chronic respiratory failure. Int J Chron Obstruct Pulmon Dis. 2022;17:205-212. doi:10.2147/COPD.S171134
10. Chu SE, Lu JX, Chang SC, et al. Point-of-care application of diaphragmatic ultrasonography in the emergency department for the prediction of development of respiratory failure in community-acquired pneumonia: a pilot study. Front Med (Lausanne). 2022;9:960847. doi:10.3389/fmed.2022.960847
11. Haaksma ME, Smit JM, Boussuges A, et al. EXpert consensus On Diaphragm UltraSonography in the critically ill (EXODUS): a Delphi consensus statement on the measurement of diaphragm ultrasound-derived parameters in a critical care setting. Crit Care. 2022;26(1):99. doi:10.1186/s13054-022-03975-5
12. Fritsch SJ, Hatam N, Goetzenich A, et al. Speckle tracking ultrasonography as a new tool to assess diaphragmatic function: a feasibility study. Ultrasonography. 2022;41(2):403-415. doi:10.14366/usg.21044
13. Soilemezi E, Savvidou S, Sotiriou P, Smyrniotis D, Tsagourias M, Matamis D. Tissue Doppler imaging of the diaphragm in healthy subjects and critically ill patients. Am J Respir Crit Care Med. 2020;202(7):1005-1012. doi:10.1164/rccm.201912-2341OC
