1. Correct Answer: D. Paradoxical diaphragmatic movement

Rationale: The craniocaudal excursion of the posterior third of the diaphragm can be assessed by imaging the subcostal region between the midclavicular and anterior axillary lines, with the transducer directed medially, cranially, and posteriorly. The diaphragm is the echogenic curvilinear structure located between the liver in the near field and lung in the far field. Diaphragm dysfunction can be detected with a high degree of specificity. There is better correlation between the inspired volume and diaphragmatic movement in the supine position compared to sitting or standing. Paradoxical movement is more pronounced in the supine position as compensatory expiration by the abdominal wall is reduced. In diaphragmatic dysfunction, compensatory contraction from the inspiratory muscles of the rib cage and neck causes the weakened diaphragm to move in a cephalad direction, as illustrated in these images with the movement of the diaphragm away from the transducer during inspiration (Figure 58.1A).

Diaphragm dysfunction arising from phrenic nerve injury could occur during cardiothoracic surgery, neck surgery, or mechanical trauma. Forced vital capacity is reduced by 30% of the predicted value in unilateral hemidiaphragmatic paralysis, and further reduced by 75% in bilateral paralysis.

1. Houston JG, Morris AD, Howie CA, Reid JL, McMillan N. Technical report: quantitative assessment of diaphragmatic movement—a reproducible method using ultrasound. Clin Radiol. 1992;46(6):405-407.

2. Kokatnur L, Rudrappa M. Diaphragmatic palsy. Diseases. 2018;6:E16.

3. McCool FD, Manzoor K, Minami T. Disorders of the diaphragm. Clin Chest Med. 2018;39(2):345-360.

4. Sarwal A, Walker FO, Cartwright MS. Neuromuscular ultrasound for evaluation of the diaphragm. Muscle Nerve. 2013;47(3):319-329.

5. Umbrello M, Formenti P. Ultrasonographic assessment of diaphragm function in critically ill subjects. Respir Care. 2016;61(4):542-555.

2. Correct Answer: A. Ventilator weaning should proceed based on the degree of diaphragmatic excursion.

Rationale: The right and left hemidiaphragms can be imaged through the liver and spleen windows, respectively, to assess the degree of craniocaudal excursion. This M-mode image illustrates an excursion of nearly 3 cm. Normal diaphragmatic excursion in adults has been reported to range from 1.9 to 9 cm, with various correction factors for age, sex, weight, and height proposed by different studies. Although currently there are no uniform guidelines for defining diaphragmatic dysfunction and adjusting for baseline characteristics, an excursion of less than 1 cm is widely agreed upon as indicative of diaphragm dysfunction.

This image shows a pleural effusion with atelectasis and an additional assessment of the size of the effusion should be considered. However, the narrow pleural separation shown in this image alone does not reveal an effusion of significant size to support proceeding immediately to a chest tube.

1. Boussuges A, Gole Y, Blanc P. Diaphragmatic motion studied by m-mode ultrasonography: methods, reproducibility, and normal values. Chest. 2009;135(2):391-400.

2. Sarwal A, Walker FO, Cartwright MS. Neuromuscular ultrasound for evaluation of the diaphragm. Muscle Nerve. 2013;47(3):319-329.

3. Weerakkody Y, Reddy U, et al. Diaphragmatic paralysis. Radiopaedia. Accessed September 5, 2019. https://radiopaedia.org/articles/diaphragmatic-paralysis-1?lang=us.

3. Correct Answer: D. The degree of diaphragmatic thickening in layer B predicts weaning success.

Rationale: When weaning from mechanical ventilation, ultrasound assessment of the diaphragm has been applied to help predict extubation failure. A linear array transducer placed along the anterior axillary line at the intercostal spaces between the seventh and ninth ribs provides images at the zone of apposition to enable assessment of diaphragm thickness and echogenicity. Diaphragm thickness varies with inspiratory effort and level of contraction. The diaphragm (Layer B) is visualized as the hypoechoic layer of muscle in-between two hyperechoic connective tissue layers (the parietal pleura and peritoneum), deep to the intercostal muscles (Layer A). M-mode echocardiography in this image shows a dynamic increase in diaphragm thickness from 0.18 to 0.25 cm during inspiration, giving a thickening fraction of 39%. A thickening fraction above 30% is indicative of normal diaphragm contractility and has been found to predict extubation success with 71% specificity.

While various studies have identified different thresholds for thickening fraction in predicting ventilator weaning failure, a thickening fraction of less than 20% is widely agreed upon as indicative of diaphragm weakness. The absence of thickening correlates well with invasive measurements of transdiaphragmatic pressure and enables the diagnosis of diaphragm paralysis with high sensitivity and specificity.

1. Harper CJ, Shahgholi L, Cieslak K, Hellyer NJ, Strommen JA, Boon AJ. Variability in diaphragm motion during normal breathing, assessed with B-mode ultrasound. J Orthop Sports Phys Ther. 2013;43:927-931.

2. Matamis D, Soilemezi E, Tsagourias M, et al. Sonographic evaluation of the diaphragm in critically ill patients. Technique and clinical applications. Intensive Care Med. 2013;39(5):801-810.

3. Sarwal A, Walker FO, Cartwright MS. Neuromuscular ultrasound for evaluation of the diaphragm. Muscle Nerve. 2013;47(3):319-329.

4. Summerhill EM, El-Sameed YA, Glidden TJ, McCool FD. Monitoring recovery from diaphragm paralysis with ultrasound. Chest. 2008;133(3):737-743.

4. Correct Answer: C. There is appropriate diaphragmatic thickening

Rationale: These B-mode images illustrate diaphragm thickening at the intercostal space along the anterior axillary line at the zone of apposition, where the diaphragm contacts the rib cage. In these images, the rib is on the right (Figure 58.10, marked by *). During inspiration, the diaphragm is seen “peeling away” from the chest wall as it increases in thickness (option C). While there is insufficient evidence to support routine evaluation of the intercostal muscles in assessing respiratory function, an intercostal thickening fraction of greater than 8% is suggestive of a pathologic respiratory pattern.

1. Matamis D, Soilemezi E, Tsagourias M, et al. Sonographic evaluation of the diaphragm in critically ill patients. Technique and clinical applications. Intensive Care Med. 2013;39(5):801-810.

5. Correct Answer: D. DT = (0.28 – 0.25)/0.25 = 0.12, indicating impaired DT

Rationale: Identification of diaphragm dysfunction with ultrasonography has been found to be predictive of extubation failure. Diaphragm atrophy and weakness develop in the first few days of mechanical ventilation and critical illness, and are exacerbated by the use of paralytic agents and steroids. Diaphragm thickness has been correlated with the strength of the diaphragm and muscle shortening, but not with endurance or fatigability. Good association has been found between the thickening fraction and transdiaphragmatic pressure measurements. The thickening fraction is defined as:

(End-Inspiratory Thickness – End-Expiratory Thickness) ÷ End-Expiratory Thickness

Thresholds for predicting extubation failure vary between studies. However, the consensus is that a thickening fraction of less than 0.2 indicates diaphragm dysfunction.

1. Gottesman E, McCool FD. Ultrasound evaluation of the paralyzed diaphragm. Am J Respir Crit Care Med. 1997;155(5):1570-1574.

2. Matamis D, Soilemezi E, Tsagourias M, et al. Sonographic evaluation of the diaphragm in critically ill patients. Technique and clinical applications. Intensive Care Med. 2013;39(5):801-810.