This patient's presentation suggests unilateral diaphragmatic paralysis likely due to phrenic nerve injury during cardiac surgery. The phrenic nerves originate from C3-C5 to innervate the diaphragm on each side. Unilateral diaphragmatic paralysis is more common than bilateral paralysis and is usually due to the following:
Patients with unilateral diaphragmatic paralysis and no underlying lung disease are usually asymptomatic at rest but can develop dyspnea with exertion. Patients with underlying lung disease may report dyspnea at rest, orthopnea, or sleep-disordered breathing.
Chest x-ray usually reveals elevated hemidiaphragm. However, this can be missed in some postoperative patients due to other changes (eg, pleural effusions, infiltrates, atelectasis). Diagnosis is confirmed by asking patients to sniff forcefully under fluoroscopy (sniff test). The normal diaphragm moves downward during inspiration and the paralyzed side has paradoxical upward movement.
Spirometry shows a restrictive defect (low forced vital capacity), but the normal decrease of <10% in the supine position is exacerbated and may fall > 50%. This results from the cephalad displacement of the abdominal viscera. Patients may also have supine hypoxemia, but hypercarbia is rare in the absence of lung disease.
Asymptomatic patients with unilateral diaphragmatic paralysis do not require treatment. Many patients with mild-to-moderate dyspnea may improve spontaneously within 1-2 years. However, those with significant impairment may benefit from ipsilateral surgical diaphragmatic plication.