What are the signs, symptoms, treatment, and management of phrenic nerve injury in the Cardiovascular Intensive Care Unit (CVICU)?

Phrenic Nerve Injury in CVICU: Signs, Symptoms, Treatment, and Management

Phrenic nerve injury in the CVICU most commonly presents as hemidiaphragmatic paralysis with symptoms including dyspnea, orthopnea, and sleep-disordered breathing, requiring prompt diagnosis and management through respiratory support and potential surgical intervention if recovery does not occur within 3-6 months. 1, 2, 3

Pathophysiology and Etiology

• Phrenic nerve injury during cardiac surgery can occur through direct trauma, traction, thermal injury, and is more common during redo operations and concurrent Cox-maze procedures 2
• Common mechanisms of injury include hypothermia during cardioplegia, mechanical trauma during internal mammary artery harvesting, and direct surgical manipulation 4
• Injury is more frequently observed following specific procedures such as systemic-pulmonary artery anastomosis, ligation of persistent ductus arteriosus, and atrial septectomy 5

Signs and Symptoms

• Hemidiaphragmatic paralysis presenting as immobility or elevation of the diaphragm on imaging 2
• Exertional dyspnea and orthopnea, particularly when lying flat 3
• Sleep-disordered breathing and nocturnal desaturation 3
• Respiratory distress with increased work of breathing 2
• Difficulty weaning from mechanical ventilation 6
• Paradoxical abdominal motion during inspiration (abdominal paradox) 7
• In bilateral phrenic nerve injury, patients may develop oxygen dependency or ventilator dependency 3

Diagnostic Evaluation

• Chest X-ray showing elevated hemidiaphragm on the affected side 2, 8
• Diaphragmatic ultrasound at bedside to assess diaphragmatic function, particularly during weaning from mechanical ventilation 6
• Fluoroscopy to confirm paradoxical movement of the affected hemidiaphragm 8
• Phrenic nerve stimulation techniques (electrical or magnetic) to provide objective assessment of diaphragm function independent of patient effort 1, 6
• Measurement of twitch transdiaphragmatic pressure (Pdi,tw) following phrenic nerve stimulation to specifically assess diaphragm strength 1
• Negative gastric pressure to transdiaphragmatic pressure ratio indicating severe diaphragmatic dysfunction or paralysis 6

CVICU Management Algorithm

Acute Management

1. Initial Respiratory Support:

   • Initiate non-invasive ventilation promptly in patients showing signs of respiratory distress or hypercapnia 6
   • Consider controlled ventilation modes as patient triggering may be ineffective 6
   • Target oxygen saturation of 88-92% in adults to avoid worsening hypercapnia 6
   • Monitor CO2 levels closely with transcutaneous monitoring or arterial blood gases 6

2. For Patients Requiring Mechanical Ventilation:

   • Apply positive end-expiratory pressure (PEEP) to improve oxygenation 5
   • If non-invasive ventilation fails, do not delay intubation unless escalation is not desired by the patient 6

Weaning Considerations

• Ensure the precipitant cause of respiratory failure is treated and pH is normalized before initiating weaning 6
• Implement physiotherapy treatment before and after extubation to reduce weaning duration 6
• Consider prophylactic non-invasive ventilation after extubation for patients at high risk of reintubation 6
• Plan extubation carefully and perform in a specialized setting with non-invasive ventilation support available 6

Treatment Options

Conservative Management

• Most adult patients can be managed conservatively with respiratory support 2
• Most phrenic nerve injuries will recover within 3-6 months if the nerve is not transected 2
• Physiotherapy and respiratory muscle training 6
• Nocturnal non-invasive ventilation for patients with sleep-disordered breathing 6

Surgical Interventions

• Diaphragmatic Plication:

  • Consider early diaphragmatic plication in younger patients who fail to wean from mechanical ventilation 2
  • Particularly beneficial in very young infants to reduce morbidity 5
  • Involves surgically flattening and fixing the paralyzed diaphragm to prevent paradoxical movement 8

• Phrenic Nerve Reconstruction:

  • Safe and effective alternative to diaphragm plication in properly selected patients 3
  • Increasingly becoming a standard surgical treatment for diaphragm paralysis 3
  • Requires a multidisciplinary approach at specialty referral centers 3

• Diaphragm Pacing:

  • Consider for long-term management in selected patients 1
  • System consists of battery-operated external transmitters that generate pulses transmitted via external antennae 1
  • Patient selection criteria include no or mild intrinsic lung disease, non-obese status, and intact phrenic nerve-diaphragm axis 1

CVICU-Specific Tips

• Identify patients at high risk for phrenic nerve injury (redo operations, extensive dissection) and monitor diaphragm function closely post-operatively 2, 4
• Implement preventive strategies during surgery, including careful pericardial incision and visual identification of the nerve during dissection 2
• For patients with unilateral diaphragm paralysis, positioning with the affected side up can improve ventilation-perfusion matching 3
• Monitor for complications such as atelectasis, pneumonia, and respiratory failure, which occur in approximately 79% of patients with phrenic nerve injury 5
• Ensure an individualized emergency healthcare plan is in place for future hospital admissions 6
• For patients with cardiac pacemakers requiring diaphragm pacing, ensure the cardiac pacemaker is bipolar to minimize potential electromagnetic interference 1