Plasma Exchange Regimen in Myasthenic Crisis
For myasthenic crisis, administer 5 plasma exchange sessions over 5 days (or up to 7 sessions over 14 days), with each session exchanging 1.5 liters of plasma (20-25 ml/kg, representing 0.5-0.6 plasma volumes per session). 1, 2
Standard Treatment Protocol
Immediate initiation of plasma exchange is indicated for patients in myasthenic crisis with respiratory compromise requiring hospitalization, severe generalized weakness (Grade 3-4), or bulbar dysfunction threatening airway protection. 1, 3
Plasma Exchange Dosing Regimen
- Perform 5 sessions over 5 days as the standard protocol 1
- Exchange volume: 1.5 liters of plasma per session (equivalent to 20-25 ml/kg body weight or 0.5-0.6 plasma volumes) 2
- Alternative extended regimen: 7 exchanges over 14 days can be used in severe cases 4
- Sessions are typically performed at 2-3 day intervals 5
Clinical Context and Monitoring
Plasma exchange should be initiated alongside high-dose corticosteroids (methylprednisolone 1-2 mg/kg/day IV or prednisone 1-1.5 mg/kg/day orally) and requires ICU-level monitoring with frequent pulmonary function assessments. 1, 3
- Monitor negative inspiratory force (NIF) and vital capacity (VC) frequently during treatment 1
- Apply the "20/30/40 rule" to assess respiratory failure risk: VC <20 ml/kg, maximum inspiratory pressure <30 cmH₂O, or maximum expiratory pressure <40 cmH₂O 1
- Perform daily neurological evaluations throughout the treatment course 1
Alternative to Plasma Exchange
IVIG (2 g/kg total dose over 5 days at 0.4 g/kg/day) is equally effective as plasma exchange and may be preferred when plasma exchange is contraindicated, not feasible, or in pregnant women. 6, 1, 2
- Sequential therapy (plasma exchange followed by IVIG) provides no additional benefit and should be avoided 6
- Both modalities demonstrate equivalent clinical efficacy in reducing myasthenia scores and achieving stable clinical status 2
Critical Medication Management During Treatment
Immediately discontinue medications that worsen myasthenia gravis before initiating plasma exchange: β-blockers, IV magnesium (absolutely contraindicated), fluoroquinolones, aminoglycosides, and macrolide antibiotics. 1, 3
- When using cyclophosphamide, administer the infusion after the plasma exchange session 4
- When using rituximab, hold plasma exchange for 48-72 hours after rituximab infusion to prevent antibody removal 4
- Discontinue or withhold pyridostigmine in intubated patients 1
Expected Clinical Response
Most patients demonstrate significant clinical improvement within 7-14 days, with mean myasthenia scores decreasing substantially and patients achieving stable clinical status (Oosterhuis Classes 1-2). 2, 7
- Uniform, significant improvement occurs in the majority of patients, including successful extubation of intubated patients 7
- 3-5 treatment sessions using the low plasma volume dosage (20-25 ml/kg) are adequate to improve clinically relevant symptoms significantly in most patients 2
- Substantial reduction of acetylcholine receptor antibodies is documented after each session 2
Safety Considerations
Plasma exchange carries risks including hemodynamic shifts, coagulation disorders, electrolyte imbalances, and line-related bacteremia, requiring careful monitoring and expertise in apheresis procedures. 4
- Immunoadsorption demonstrates fewer adverse events (10 total with 1 serious adverse event) compared to plasma exchange (16 total with 7 serious adverse events) and may be considered as an equally effective alternative 2
- Plasma exchange requires specialized equipment and expertise, often necessitating transfer to tertiary academic centers 4