What is the management and treatment of a phrenic (phrenic nerve) sign?

Management and Treatment of Phrenic Nerve Dysfunction

The management of phrenic nerve dysfunction should focus on identifying the underlying cause and implementing appropriate interventions to restore diaphragmatic function, with diaphragm pacing being the primary treatment option for suitable candidates.

Diagnostic Evaluation

• Comprehensive evaluation of phrenic nerve function requires both radiographic and pulmonary function testing, as well as electrodiagnostic assessment to quantify nerve deficit and determine the extent of denervation atrophy 1
• The fluoroscopic sniff test is a highly accurate (95.9%) and reliable diagnostic tool for evaluating phrenic nerve function, with excellent sensitivity (90.9%) and specificity (100%) 2
• Phrenic nerve stimulation techniques, including electrical stimulation (ES) and magnetic stimulation (MS), provide objective assessment of diaphragm function independent of patient effort 3
• Measurement of twitch transdiaphragmatic pressure (Pdi,tw) following phrenic nerve stimulation provides a specific index of diaphragm strength 3

Treatment Options

Diaphragm Pacing

• Diaphragm pacing generates breathing using the patient's own diaphragm as the respiratory pump and is considered optimal for ventilatory support during wakefulness in carefully selected patients 3

• The system consists of battery-operated external transmitters that generate pulses transmitted via external antennae to subcutaneously implanted receivers connected to platinum phrenic nerve electrodes 3

• Bilateral implantation of phrenic nerve electrodes and diaphragm pacer receivers is recommended to achieve optimal ventilation 3

• Key benefits include:

  • Portability and freedom from mechanical ventilator during daytime use 3
  • Ability to participate in supervised age-appropriate activities while receiving assisted ventilation 3

• Important considerations for diaphragm pacing:

  • Patient selection criteria include no or mild intrinsic lung disease, non-obese status, and intact phrenic nerve-diaphragm axis 3
  • Conservative use is typically recommended (12-15 hours per day) 3
  • Patients still require continuous monitoring with pulse oximetry and PETCO2 3
  • Patients who require 24-hour ventilatory support should have an alternate form of ventilation for part of the day 3

Potential Complications and Management

• Obstructive apnea can occur during sleep with diaphragm pacing due to lack of synchronous upper airway skeletal muscle contraction 3

  • This can be managed by adjusting pacer settings to lengthen inspiratory time and/or decrease the force of inspiration 3

• Long-term electrical stimulation may cause histopathological changes in the phrenic nerve:

  • Focal areas of demyelination ranging from swelling to total myelin removal with fibrosis 4
  • These changes appear to be related to electrode application technique rather than the electrical stimuli themselves 4

• Pneumothorax is a potential complication during phrenic nerve procedures, particularly in patients with thin necks 5

Surgical Options

• Phrenic nerve reconstruction has become a standard surgical treatment for diaphragm paralysis due to phrenic nerve injury 1

  • This approach aims to restore functional diaphragmatic activity rather than static repositioning of the diaphragm (diaphragm plication) 1
  • A multidisciplinary approach at specialty referral centers is required for optimal outcomes 1

• For complete surgical resection of thymic tumors (which may affect the phrenic nerve), the standard approach involves complete surgical resection from the phrenic nerve to phrenic nerve laterally 3

Special Considerations

• Patients with cardiac pacemakers can safely use diaphragm pacers as long as the cardiac pacemaker is bipolar, minimizing potential electromagnetic interference with the bilateral monopolar phrenic nerve electrodes 3

• For patients who rely on diaphragm pacing:

  • It is mandatory to have a backup diaphragm pacer transmitter already set based on physiologic study 3
  • Spare antennae should be available in the home as these components frequently break 3
  • The second transmitter can be set to deliver optimal settings for exercise, allowing different settings for school versus physical activities 3

• Implantable phrenic nerve stimulation is being investigated as a potential alternative approach for treating central sleep apnea in heart failure patients 3

Follow-up Care

• After diaphragm pacer implantation, extensive experience in pacer management is required for biannual then annual comprehensive in-hospital evaluation 3
• The goal with diaphragm pacing is to minimize electrical stimulation while providing optimal ventilation and oxygenation 3