Outline the aetiology, clinical manifestations and treatment of phrenic nerve palsy after cardiac surgery.
Aetiology: potential contributing factors include difficult dissection, internal mammary artery dissection, excessive retraction (sternum/pericardium), use of topical cooling (eg. slush) and haematoma from internal jugular venipuncture
Clinical manifestations: Can be unilateral (esp. left) or less common bilateral. Usually manifest by respiratory difficulties. Patient may not be able to be weaned from mechanical ventilation, or may have significant post-operative requirements for respiratory support. Persistent collapse and/or pneumonia may develop. Clinical examination may reveal decreased movement on affected side, decreased breath sounds (± signs of collapse/consolidation), significant dullness to percussion, with absence of normal tidal percussion. Radiological investigations confirm elevated hemidiaphragm (&/or collapse/consolidation), which moves paradoxically on sniff test (fluoroscopy).
Treatment: usually expectant for underlying lesion. Supportive care plus specific treatment of complications (eg. aggressive physiotherapy, non-invasive ventilatory support).
There are a few ways to damage the phrenic nerve during cardiac surgery:
- Sever it completely (hence difficult dissection makes it more likely)
- Put pressure on it accidentally (hence excessive retraction is to blame)
- Topical cardiac cooling (the icy slush causes a neuropraxia)
- IJ haematoma
The clinical manifestations will be unequal chest expansion, atelectasis on the affected side, an elevated hemidiaphragm on CXR, and difficult ventilation/weaning.
With inspiration, the paralysed diaphragm paradoxically retracts upwards.
Management is supportive. One has no choice but to continue ventilator support until it resolves. Diaphragmatic plication may be considered in persisting symptomatic diaphragmatic palsy.
Wilcox, Pearce, et al. "Phrenic nerve function and its relationship to atelectasis after coronary artery bypass surgery." CHEST Journal 93.4 (1988): 693-698.