What is the management approach for diaphragmatic dysfunction or phrenic nerve injury in the Cardiovascular Intensive Care Unit (CVICU)?

Management of Diaphragmatic Dysfunction/Phrenic Nerve Injury in CVICU

Non-invasive ventilation (NIV) should be the first-line ventilatory support for patients with diaphragmatic dysfunction or phrenic nerve injury in the CVICU, as it is well-tolerated and extubation from invasive mechanical ventilation may be difficult in these patients. 1

Diagnostic Assessment

• Diaphragmatic ultrasound is recommended as a bedside tool to assess diaphragmatic function, particularly in patients being weaned from mechanical ventilation 2
• Transdiaphragmatic pressure (Pdi) measurement requires simultaneous recordings of esophageal and gastric pressures to assess diaphragmatic contribution to breathing 2
• Phrenic nerve stimulation techniques (electrical or magnetic) provide objective assessment of diaphragm function independent of patient effort 3
• A negative gastric pressure to transdiaphragmatic pressure ratio (Pga/Pdi) indicates severe diaphragmatic dysfunction or paralysis 2

Acute Management Algorithm

Initial Respiratory Support

• Initiate NIV promptly in patients with diaphragmatic dysfunction showing signs of respiratory distress or hypercapnia 1
• Avoid excessive oxygen administration in isolation as it can worsen hypercapnia; target oxygen saturation of 88-92% in adults or above 92% for children 1
• Monitor CO2 levels closely with transcutaneous monitoring or arterial blood gases 1
• Consider controlled ventilation modes as patient triggering may be ineffective 1

Monitoring and Escalation Criteria

• Maintain low threshold for enhanced monitoring and critical care input if any of the following are present 1:

  • Hypoxemia (saturations <95%)
  • Hypercapnia (>45 mmHg/6 kPa)
  • Elevated respiratory rate
  • Signs of respiratory fatigue

• Warning signs requiring immediate intervention include 1:

  • Difficulty achieving adequate oxygenation
  • Rapid desaturation during breaks from NIV
  • Presence of bulbar dysfunction with more profound hypoxemia

Ventilation Settings

• For patients with neuromuscular disease (NMD), use low levels of pressure support 1
• Apply PEEP in the range of 5-10 cmH2O to increase residual volume and reduce oxygen dependency 1
• Consider volume control (or volume assured) modes when high inflation pressures are required 1

Special Considerations

Invasive Mechanical Ventilation

• If NIV fails, do not delay intubation unless escalation to invasive mechanical ventilation is not desired by the patient or deemed inappropriate 1
• In the setting of single organ respiratory failure with diaphragmatic dysfunction, the prospects of recovery are good and invasive ventilation should be considered when NIV is unsuccessful 1
• Plan extubation carefully and perform in a specialist center with NIV and mechanical insufflator-exsufflator (MI-E) support available following extubation 1

Weaning Considerations

• Diaphragmatic dysfunction is a major cause of weaning failure 2
• Before initiating weaning, ensure the precipitant cause of respiratory failure is treated, pH is normalized, and chronic hypercapnia is corrected 1
• Physiotherapy treatment is recommended before and after extubation to reduce weaning duration and risk of extubation failure 1
• Consider prophylactic NIV after extubation for patients at high risk of reintubation 1

Advanced Treatment Options

• For persistent bilateral diaphragmatic dysfunction, consider referral for evaluation of diaphragm pacing 3, 4
• Diaphragm pacing generates breathing using the patient's own diaphragm as the respiratory pump and may be optimal for ventilatory support during wakefulness in carefully selected patients 3
• For unilateral diaphragmatic paralysis causing significant symptoms, surgical plication of the diaphragm may be considered 5, 6
• Phrenic nerve reconstruction combined with diaphragm pacing may offer greater functional recovery than pacing alone in bilateral diaphragmatic dysfunction 4

Long-term Management

• Following an episode of acute hypercapnic respiratory failure, nocturnal NIV should usually be continued pending discussion with a home ventilation service 1
• Advance care planning, particularly around the potential future use of invasive mechanical ventilation, is recommended in patients with progressive neuromuscular disease 1
• Ensure an individualized emergency healthcare plan is in place and discussed with the patient and family for future hospital admissions 1

Pitfalls and Caveats

• Patients with diaphragmatic dysfunction may not display typical signs of respiratory distress such as labored breathing and accessory muscle use 1
• Incorrect placement of the gastric balloon in the lower esophagus can mimic severe diaphragmatic dysfunction when measuring transdiaphragmatic pressure 2
• Recruitment of abdominal muscles during expiration followed by sudden relaxation at inspiration can also mimic diaphragmatic dysfunction 2
• Senior staff should be involved in decision-making, in conjunction with home mechanical ventilation specialists, especially when the appropriateness of invasive mechanical ventilation is questioned 1