What is hemidiaphragmatic paresis?

Hemidiaphragmatic Paresis: Definition, Diagnosis, and Management

Hemidiaphragmatic paresis refers to weakness or partial paralysis of one side of the diaphragm, which can significantly impair respiratory function and lead to decreased pulmonary function by 25-50%. 1

Definition and Pathophysiology

• Hemidiaphragmatic paresis represents a decrease in the strength of one side of the diaphragm, while complete paralysis is an extreme form of this weakness 2
• It can result from abnormalities anywhere along the neuromuscular axis, most frequently arising from diseases affecting the phrenic nerves or from myopathies affecting the diaphragm itself 2
• The condition can cause a 25-50% decrease in pulmonary function, significantly affecting respiratory mechanics 1, 3

Clinical Presentation

• Common symptoms include dyspnea (particularly on exertion), orthopnea, and respiratory distress 2, 4
• Physical examination may reveal rapid, shallow breathing or paradoxical inward motion of the abdomen during inspiration 2
• Patients may report difficulty breathing when lying flat (86% experience dyspnea) 1
• The condition can be asymptomatic for years before becoming symptomatic in later stages 1

Diagnostic Approach

Initial Imaging

• Chest X-ray (anteroposterior and lateral views) is recommended as the first diagnostic study for patients with suspected diaphragmatic dysfunction 1
• Suspicious findings include abnormal lucency, hemidiaphragm elevation, or deviation of the mediastinum 1
• Normal chest radiographs have been reported in 11-62% of cases with diaphragmatic injuries or uncomplicated diaphragmatic hernias 1

Secondary Imaging

• CT scan with contrast enhancement of the chest and abdomen is recommended if chest X-ray is abnormal or symptoms persist 1
• Fluoroscopy can be used for functional assessment following chest radiography or CT to evaluate diaphragmatic motion 1
• Ultrasonography is highly valuable for dynamic assessment of diaphragm function:
  • Can detect paradoxical movement during respiration 1, 4
  • M-mode ultrasonography can identify absence of movement during quiet breathing and paradoxical movement during voluntary sniffing 4, 5
  • Has high sensitivity and specificity for diagnosing neuromuscular disorders of the diaphragm 1

Confirmatory Testing

• Diagnosis of diaphragmatic weakness is confirmed by a reduction in maximal static transdiaphragmatic pressure (Pdimax) 2, 1
• The diagnosis of diaphragmatic paralysis is confirmed by the absence of a compound diaphragm action potential on phrenic nerve stimulation 2
• The ratio of inspiratory gastric pressure swings to transdiaphragmatic pressure (Pga/Pdi) can assess diaphragmatic contribution to tidal effort 1
  • A negative Pga/Pdi ratio indicates severe diaphragmatic dysfunction and represents paradoxical abdominal motion 1

Common Causes

• Phrenic nerve injury during medical procedures:
  • Cardiac procedures like atrial fibrillation ablation 4
  • Regional anesthesia techniques such as interscalene brachial plexus blocks (occurs in up to 100% of conventional approaches) 3, 6
  • Supraclavicular nerve blocks (34% incidence of complete hemidiaphragmatic paralysis) 5
• Traumatic diaphragmatic injury:
  • Blunt trauma (3-8% of all traumatic diaphragmatic hernias) 1
  • Penetrating trauma (65% of traumatic diaphragmatic hernias) 1
• Neurological disorders affecting the phrenic nerve 2
• Myopathies affecting the diaphragm muscle 2

Clinical Implications

• Reduced respiratory function with 25-27% decrease in forced vital capacity and forced expiratory volume 3, 6
• Impaired ability to clear secretions and increased risk of atelectasis 3
• Potential for respiratory failure in patients with pre-existing pulmonary disease 3
• May contribute to sleep apnea, particularly of the central type 1

Management Considerations

• Treatment depends on underlying cause and severity of symptoms 2
• For iatrogenic causes (like post-anesthesia), modified approaches can reduce incidence:
  • Extrafascial approach for interscalene blocks reduces incidence to 17% versus 46% with conventional intrafascial approach 6
  • Infraclavicular approach for brachial plexus blockade has significantly lower risk (3%) compared to supraclavicular approach (34%) 5
• Caution is advised when performing procedures with high risk of diaphragmatic paresis in patients with respiratory compromise 3
• Patients with hemidiaphragmatic paresis should be monitored for respiratory complications, especially those with pre-existing pulmonary disease 3

Pitfalls and Caveats

• Diagnosis is often missed due to nonspecific symptoms and failure to perform appropriate diagnostic tests 2
• Incorrect placement of the gastric balloon in the lower esophagus during pressure measurements can mimic severe diaphragmatic dysfunction 1
• Recruitment of abdominal muscles during expiration followed by sudden relaxation at the beginning of inspiration can also mimic diaphragmatic dysfunction 1
• The condition may be misdiagnosed as pneumonia or bronchiolitis, especially following viral illness 1