What are the primary recommendations for pulmonary care in a patient with myasthenia gravis (MG) requiring respiratory support?

Pulmonary Care in Myasthenia Gravis

Respiratory Monitoring and Crisis Recognition

Patients with myasthenia gravis require systematic pulmonary function monitoring using the "20/30/40 rule" to identify imminent respiratory failure: vital capacity <20 ml/kg, maximum inspiratory pressure <30 cmH₂O, or maximum expiratory pressure <40 cmH₂O warrant immediate ICU admission and preparation for elective intubation. 1

Key Monitoring Parameters

• Measure forced vital capacity (FVC) and negative inspiratory force (NIF) regularly, especially in patients with bulbar symptoms or Grade 3-4 disease, as these predict need for mechanical ventilation 2, 1
• Perform daily neurological evaluations during acute exacerbations to assess progression of weakness 2
• Use the single breath count test as a bedside supplement to formal FVC measurements for continuous monitoring 1
• Monitor for worsening dysphagia, dysarthria, and diplopia as these bulbar symptoms often precede respiratory compromise 2, 3

Management of Myasthenic Crisis with Respiratory Failure

Immediate Interventions

• Admit to ICU immediately when FVC falls below 20 ml/kg or NIF drops below 30 cmH₂O, before emergent respiratory arrest occurs 1
• Consider noninvasive positive-pressure ventilation (NIPPV) first, as this has been successful even in patients with bulbar weakness and can avoid intubation 4
• Proceed to elective intubation if NIPPV fails or if patient cannot protect airway due to severe bulbar dysfunction 1, 4

Pharmacological Crisis Management

• Initiate plasmapheresis (preferred) or IVIG 2 g/kg over 5 days (0.4 g/kg/day) as rapid immunomodulation for Grade 3-4 myasthenic crisis 2, 1
• Start high-dose corticosteroids concurrently: methylprednisolone 1-2 mg/kg/day IV or prednisone 1-1.5 mg/kg/day orally 2, 1
• Discontinue or withhold pyridostigmine in intubated patients during crisis, as acetylcholinesterase inhibitors should be avoided in acute respiratory failure 1, 4

Critical Medication Avoidance

Strictly avoid medications that worsen neuromuscular transmission and can precipitate respiratory crisis:

• β-blockers, IV magnesium, fluoroquinolone antibiotics, aminoglycoside antibiotics, and macrolide antibiotics must be avoided as they interfere with neuromuscular junction function 2, 3, 1
• Avoid depolarizing paralytics entirely if intubation is necessary; use reduced doses of nondepolarizing agents instead 4
• Do not use corticosteroids initially in acute crisis until after IVIG or plasmapheresis is started, despite their role in maintenance therapy 4

Aggressive Respiratory Therapy Protocol

Implement intensive respiratory interventions to reduce pulmonary complications, as aggressive treatment correlates with shorter mechanical ventilation duration and reduced pneumonia/atelectasis rates (46% vs. 91% in less aggressive protocols). 5

Specific Interventions

• Frequent suctioning to clear secretions, particularly in patients with bulbar weakness who cannot protect their airway 5
• Intermittent positive-pressure breathing (IPPB) treatments to prevent atelectasis 5
• Chest physiotherapy and bronchodilator treatments as needed based on lung injury severity 5
• Adjust respiratory intervention intensity based on lung injury score and forced vital capacity measurements 5

Staged Management by Disease Severity

Grade 1 (Ocular Only)

• No specific pulmonary monitoring required unless symptoms progress 2
• Pyridostigmine 30 mg orally three times daily, titrating to maximum 120 mg four times daily 2, 3

Grade 2 (Mild Generalized Weakness)

• Baseline pulmonary function testing with NIF and VC to establish monitoring parameters 2, 3
• Add corticosteroids (prednisone 1-1.5 mg/kg/day) if pyridostigmine provides insufficient control 2, 3
• Avoid IVIG for chronic maintenance as it is not indicated for stable Grade 2 disease 2

Grade 3 (Severe Weakness)

• Frequent pulmonary function monitoring with serial FVC and NIF measurements 2, 1
• Hospitalize for close observation as respiratory decompensation can occur rapidly 2
• Initiate IVIG or plasmapheresis along with high-dose corticosteroids 2

Grade 4 (Respiratory Failure)

• Immediate intubation and mechanical ventilation for life-threatening respiratory failure 2
• ICU-level monitoring with continuous respiratory assessment 2, 1
• Aggressive immunotherapy with plasmapheresis or IVIG plus IV corticosteroids 2, 1

Prevention of Respiratory Complications

Infection Control

• Treat respiratory tract infections aggressively, as they are the most common precipitant of myasthenic crisis 4, 6
• Consult neurology for antibiotic selection to avoid contraindicated agents that worsen MG 3
• Monitor urinary tract infections closely as they can also trigger respiratory decompensation 1

Patient Education

• Teach patients to recognize early respiratory symptoms: increased shortness of breath, difficulty clearing secretions, weak cough, orthopnea 2, 6
• Instruct immediate medical attention for any significant increase in muscle weakness or respiratory symptoms 2
• Educate about medication avoidance to prevent iatrogenic crisis 2, 3

Special Considerations

Pregnancy

• IVIG may be preferred over plasmapheresis in pregnant women with myasthenic crisis due to fewer monitoring requirements 2

Neonatal Myasthenia

• Transient respiratory muscle weakness in newborns from maternal antibodies may rarely require ventilatory support 6

Long-term Ventilation

• Do not use NIPPV for preventive purposes in stable patients, as studies show increased mortality with prophylactic nocturnal ventilation 7