What are the indications for Non-Invasive Ventilation (NIV) in patients with myasthenia gravis?

NIV Indications for Myasthenia Gravis

NIV should be initiated in myasthenia gravis patients with impending or established myasthenic crisis who have respiratory compromise but have not yet developed severe hypercapnia (PCO2 <45 mmHg), as this approach can prevent intubation in approximately 58% of cases and significantly reduce ventilation duration, ICU stay, and pulmonary complications. 1

Primary Indications for NIV in Myasthenia Gravis

NIV is indicated for acute or acute-on-chronic hypercapnic respiratory failure due to neuromuscular disease, including myasthenia gravis. 2 The specific clinical scenarios where NIV should be considered include:

• Impending myasthenic crisis with declining respiratory function but before severe decompensation occurs, as early intervention prevents the need for intubation 1
• Acute respiratory failure in myasthenic crisis as the initial ventilatory support method, which successfully avoided intubation in 58% of episodes in the highest quality study 1
• Post-extubation respiratory support to prevent reintubation after invasive mechanical ventilation, which was successful in preventing reintubation in 3 of 10 patients in one series 3
• Chronic nocturnal ventilatory support in treatment-refractory myasthenia gravis patients with sleep-disordered breathing and daytime respiratory symptoms 4

Predictors of NIV Success

The decision to attempt NIV versus proceeding directly to intubation should be guided by specific clinical parameters:

• PCO2 ≤45 mmHg at NIV initiation is the single strongest predictor of NIV success; PCO2 >45 mmHg predicts NIV failure and need for intubation (P=0.04) 1
• APACHE II score <6 independently predicts NIV success in myasthenic crisis 5
• Serum bicarbonate <30 mmol/L (indicating lesser metabolic compensation for respiratory acidosis) independently predicts NIV success 5
• Absence of severe bulbar dysfunction is critical, as bulbar dysfunction makes NIV delivery difficult or impossible and increases failure risk 2

Contraindications and Warning Signs

NIV should not be attempted or should be discontinued in favor of intubation when:

• Severe bulbar dysfunction is present, as this makes NIV delivery impossible and significantly increases aspiration risk 2
• PCO2 exceeds 45 mmHg, which strongly predicts NIV failure 1
• Deteriorating consciousness level occurs, requiring immediate consideration of intubation 6
• Copious respiratory secretions are present that cannot be adequately cleared 2
• Rapid desaturation during NIV breaks suggests impending failure and need for HDU/ICU placement 2

Initial NIV Settings and Interface Selection

• Begin with IPAP 8-12 cmH2O and EPAP 3-5 cmH2O using bilevel positive airway pressure (BiPAP) mode 6
• Patients with neuromuscular disease typically require low levels of pressure support compared to other conditions 2
• Use a full-face mask initially in the acute setting, transitioning to nasal mask after 24 hours as the patient improves 2, 6
• Have multiple mask sizes and types available to optimize fit and minimize air leaks 6

Monitoring and Assessment of Response

• Obtain arterial blood gases at 1-2 hours to assess PaO2, PaCO2, and pH improvement 6
• Expect clinical improvement by 4-6 hours; lack of progress indicates likely NIV failure and need for intubation 6
• Monitor for difficulty achieving adequate oxygenation or rapid desaturation during NIV breaks, which are important warning signs of deterioration in neuromuscular disease 2
• Senior staff should be involved in decision-making, particularly when experience with neuromuscular disease is limited 2

Outcomes and Benefits

The evidence demonstrates substantial benefits of NIV in myasthenia gravis:

• Mean BiPAP duration of 4.3 days in patients who successfully avoided intubation 1
• Initial BiPAP treatment was the only variable associated with decreased ventilation duration (P<0.007) compared to immediate intubation 1
• Reduced pulmonary complications, with lower rates of atelectasis and pneumonia (46% vs 91% in historical controls) when aggressive respiratory management is employed 7
• Shorter ICU and hospital lengths of stay compared to patients requiring immediate intubation 1

Critical Pitfalls to Avoid

• Do not delay NIV initiation in patients with declining respiratory function who meet criteria, as the therapeutic window is narrow 1
• Do not use NIV as a substitute for intubation when invasive ventilation is clearly more appropriate, particularly in patients with severe bulbar dysfunction or hypercapnia >45 mmHg 2, 1
• Do not underestimate the impact of bulbar dysfunction, as communication difficulties and aspiration risk make NIV delivery extremely challenging 2
• Anticipate sudden deterioration in neuromuscular disease patients, as decline can be very rapid 2

Extubation Considerations

For myasthenia gravis patients being weaned from invasive mechanical ventilation:

• Maximal expiratory pressure (PEmax) ≥40 cmH2O is a strong predictor of successful extubation 5
• Assess cough effectiveness and sputum load before extubation, as poor cough strength leading to sputum impaction is the most common cause of extubation failure (61.5% of failures) 5
• Consider NIV as post-extubation support to prevent reintubation, particularly in patients with borderline respiratory parameters 3
• Upper airway patency and bulbar function must be carefully evaluated prior to extubation 2