Diaphragmatic paralysis

Last revised by Mostafa Elfeky on 23 Nov 2021

Diaphragmatic paralysis (also considered very similar to the term diaphragmatic palsy) can be unilateral or bilateral.

Clinical features are highly variable according to underlying etiological factors:

  • unilateral paralysis: asymptomatic in most of the patients as the other lung compensates
    • may have dyspnea, headaches, fatigue, insomnia and overall breathing difficulty
  • bilateral diaphragmatic palsy can be a medical emergency; they present with severe dyspnea, even with mild exertion

Normally the right dome of the diaphragm is higher in position as compared to the left dome, if the left dome of the diaphragm is elevated (>2 cm) diaphragmatic palsy should be suspected.

Fluoroscopic examination of the diaphragm ("sniff test") is very useful in diagnosing diaphragmatic paralysis. In normal individuals, both hemidiaphragm will descend with inspiration. In cases of unilateral diaphragmatic paralysis, the affected side demonstrates a paradoxical upward movement.

An alternative to fluoroscopy in diagnosing this condition, particularly useful in the pediatric population. Real-time ultrasound is ideal for evaluation of spontaneous respiratory diaphragmatic motion (may require temporary disconnection of the ventilator). This can be performed in the axial plane to compare the two hemidiaphragm simultaneously. Additional coronal or sagittal M-mode can help quantify the degree of movement of each individual hemidiaphragm. Diagnostic criteria include paradoxical movement, excursion of less than 4 mm, and a difference >50% between the excursion of one hemidiaphragm compared to the other.

Bedside ultrasound has been used in a critical care setting for the detection of diaphragmatic dysfunction with a high degree of specificity; the lower limit of normal was defined as 1 cm when observing diaphragmatic craniocaudal excursion in the mid-clavicular line 8. The ability to apply this information and predict the success of weaning a patient from mechanical ventilation tends to be more robust when one measures the contractile nature of the diaphragmatic muscle itself. Medial angulation from a sagittal transducer position in the mid-axillary line allows visualization of the striated, mixed echogenicity band just cephalad to the liver. After placing an M-mode line, one may pause the recording and measure the end-expiratory and end-inspiratory figures, the latter of which should be larger, and calculate a diaphragmatic thickening fraction; values above 30%, indicating no sonographic diaphragmatic dysfunction, have been found to be 71% specific for extubation success 9

The thickening fraction of the intercostal muscles as an index of diaphragmatic dysfunction and the use of accessory muscles has a linear, negative relationship with the calculated thickening index of the diaphragm, although insufficient evidence exists to advocate its routine use at this time. Intercostal thickening fractions >8% have, thus far, been deemed pathologic 10

Patients with unilateral diaphragmatic paralysis do not require treatment. There may be an option for phrenic nerve stimulation in some cases.

On a chest radiograph consider:

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