Diaphragmatic Ultrasound in Adults: Image Acquisition and Interpretation

Point-of-care ultrasound has been rapidly advancing in recent years. However, protocols for diaphragm assessment remain challenging due to a lack of agreement on guidelines, poor inter-operator reliability, and more complex knobology. We aim to address this by providing a technique to screen for diaphragm dysfunction that is simple, quick, high yield and reproducible.

We combine two straightforward POCUS techniques. One, a qualitative evaluation of hemidiaphragm motion, and two, a novel quantitative assessment of excursion of the zone of apposition. This protocol is reliable, reproducible by different clinicians, and can be quickly mastered compared to other more complex protocols, such as dome of diaphragm excursion and diaphragmatic thickening.

Our protocol enables feasible and reliable assessment of diaphragm dysfunction, allowing for high quality research to be conducted and the risk of bias to be minimized. This protocol is also versatile and can be used in multiple different clinical settings, such as evaluation of the diaphragm in critically ill patients on mechanical ventilation, screening for phrenic nerve dysfunction in the perioperative setting, and monitoring neurologic diseases to name a few. Given the novelty of this protocol, future studies should be conducted to validate this technique by comparing its accuracy to established gold standards.

In addition, future studies can apply this protocol in clinical settings to correlate findings with patient outcomes. To begin, position the patient in a semi-recumbent position on the examination table. For the probe, select a low frequency transducer with a frequency less than or equal to five megahertz, such as a curvilinear or sector array probe.

Apply ultrasound coupling gel to the probe and select the abdominal preset on the ultrasound machine. For right hemidiaphragm assessment, place the probe on the right flank at the fifth to seventh intercostal space along the mid axillary line, aligning the beam with the coronal plane of the body. Adjust the probe, slide, fan, or rock as needed until the diaphragm is centered in the view and the liver or spleen, diaphragm, spine, and super diaphragmatic space are all clearly visible.

Instruct the patient to take a slow vital capacity breath in and out. Click the Acquire button to capture a short clip during patient respiration. Now, visually assess diaphragmatic excursion, categorizing it as either grossly intact, grossly absent, or indeterminate.

To assess the zone of opposition or ZOA excursion, select a high frequency linear transducer with a frequency greater than 10 to 13 megahertz. After applying ultrasound coupling gel to the probe, select the lung or musculoskeletal preset on the ultrasound machine. Place the probe at the mid axillary line at the level of the eighth or ninth intercostal spaces with the probe indicator pointing cephalad towards the patient's head.

Angle the beam perpendicular to the chest wall and center the axis so that the rib interspace is centered with cranial and caudal ribs visible at the screen's edges. Set the depth and adjust the gain to make the diaphragm or pleural line visibly distinct from surrounding structures. To measure the end inspiratory location, instruct the patient to breathe in fully and hold their breath for four seconds or as long as comfortable.

During the breath hold, follow the pleural line caudally until the point where the pleural line is visible in only a part of the rib interspace and the rest contains the diaphragm at a similar depth. Adjust the probe positioning as needed to center the view on the ZOA with subcutaneous tissue above and a rib on either side of the screen. Using a non-permanent skin marker, draw a line on the patient perpendicular to the transducer's long axis to mark the interspace where the ZOA is found.

Ask the patient to exhale and resume normal breathing. After repeating the measurement, take the average of the two measurements to determine the final value of the end inspiration location of the ZOA. To measure the end expiratory location, instruct the patient to breathe in fully, then exhale completely and hold their breath for four seconds or as long as comfortable.

Slide the probe cranially to locate the end expiratory location of the ZOA. After centering the view on the ZOA, mark the interspace using a skin marker as performed earlier. Now ask the patient to resume normal breathing.

Repeat and take the average of the two measurements. Finally, measure the distance between the averaged end inspiratory and end expiratory skin markings using a ruler in centimeters. Record this distance as the maximal diaphragmatic excursion.