Written by Chris Thom
Spoon Feed
POCUS shows promise for the newer application of diaphragm ultrasound. Here’s how and when to do it.
If it lives and breathes, you can ultrasound it…
This review highlights POCUS for diaphragmatic function evaluation. The first method to assess function is measurement of diaphragm excursion (DE), which is performed via a low frequency probe placed in the subcostal transverse position between the anterior axillary and mid-clavicular lines (see Figure 1 from the paper below). M-mode is then used to measure the degree of DE during the course of normal respiration, with < 2 cm being a cutoff for abnormal. The second method is the evaluation of diaphragm thickness during expiration. This is performed with a high frequency probe in the coronal plane at the mid-axillary line (see Figure 2 from paper below). The area of apposition of the pleural line with the diaphragm can be identified and the thickness of the diaphragm measured. A cutoff of < 0.2 cm in end expiration is often considered abnormal. Applications reviewed include assessment of neuromuscular disease severity (high correlation has been shown with forced vital capacity, FVC), predicting success of extubation from mechanical ventilation, predicting the failure of non-invasive ventilatory (NIV) support in COPD, assessment of COPD severity and likelihood of recurrent exacerbation, predicting post-operative pulmonary complications, and heart failure assessment.
How will this change my practice?
I personally have not yet employed diaphragm POCUS in my practice. However, this technique will likely have a role in select patient scenarios in the future. Sensitivity and specificity for diaphragmatic dysfunction has been shown to be as high as 93% and 100%, respectively (1). Predicting NIV failure in COPD and having a rapid sonographic correlate to estimate FVC in neuromuscular disease exacerbation could both prove very useful. Hands-on training and repetition will be important to successful measurements, particularly with muscle thickness assessment (2).
Figure 1 –
Figure 2 –
Source
Diaphragmatic ultrasound: approach, emerging evidence, and future perspectives in non-ICU patients. Intern Emerg Med. 2024 Dec 13. doi: 10.1007/s11739-024-03835-w. Epub ahead of print. PMID: 39673007
Additional References
- Merino-Ramirez MA, Bolton CF, Boon AJ, Sorenson EJ, Strommen JA, Watson JC. Sensitivity and specificity of diagnostic ultrasound in the diagnosis of phrenic neuropathy. Neurology. 2015;84(21):2200.
- Garofalo E, Bruni A, Pelaia C, et al. Comparisons of two diaphragm ultrasound-teaching programs: a multicenter randomized controlled educational study. Ultrasound J. 2019;11(1):21.
Editor’s note: In Figures, 1A and 2A, are those pics of Jeremy Boyd’s abs? Flex! ~Clay Smith
