Emergency Management of Myasthenic Crisis
For a patient with myasthenia gravis in myasthenic crisis with respiratory failure, immediately secure the airway with intubation, initiate mechanical ventilation, admit to ICU, and start plasmapheresis (preferred) or IVIG 2 g/kg over 5 days along with high-dose corticosteroids (methylprednisolone 1-2 mg/kg/day IV), while withholding all acetylcholinesterase inhibitors including pyridostigmine. 1
Immediate Airway and Respiratory Management
Intubate early and electively before emergent respiratory arrest occurs in any patient meeting the "20/30/40 rule": FVC <20 ml/kg, NIF <30 cmH₂O, or maximum expiratory pressure <40 cmH₂O. 1, 2 Do not wait for hypoxemia or hypercapnia to develop—these are late findings and respiratory failure can progress rapidly once they appear. 2
- Use orotracheal intubation as the preferred approach for securing the airway. 3
- Avoid depolarizing paralytics (succinylcholine) entirely; if paralysis is necessary, use reduced doses of nondepolarizing agents. 4
- Initiate mechanical ventilation immediately upon intubation; noninvasive positive-pressure ventilation (BiPAP/CPAP) may be attempted first in patients not yet meeting intubation criteria but showing progressive weakness, even with bulbar involvement. 4
- Hyperventilate with 100% oxygen at high flow rates (2-3 times normal minute volume) to address potential hypercapnia. 1
Critical Medication Management
Immediately discontinue pyridostigmine and all other acetylcholinesterase inhibitors in intubated patients with myasthenic crisis. 5, 1, 4 Continuing these agents during crisis increases oropharyngeal secretions and can worsen respiratory muscle weakness. 6, 4
Stop all medications known to exacerbate myasthenia gravis: 5, 1, 7
- β-blockers
- Intravenous magnesium (absolutely contraindicated)
- Fluoroquinolones
- Aminoglycosides
- Macrolide antibiotics
Avoid corticosteroids initially in the emergency department during acute crisis, as they can transiently worsen weakness before providing benefit. 4 However, once the patient is stabilized in the ICU with secured airway, initiate high-dose corticosteroids (methylprednisolone 1-2 mg/kg/day IV or prednisone 1-1.5 mg/kg/day). 1
Acute Immunotherapy
Plasmapheresis is preferred over IVIG for myasthenic crisis with respiratory failure, as it may be more effective in this severe setting. 1, 3 If plasmapheresis is unavailable or contraindicated, administer IVIG 2 g/kg IV over 5 days (0.4 g/kg/day). 5, 1
- Begin immunotherapy immediately upon ICU admission; early treatment can achieve clinical improvement within days and may prevent intubation if started before complete respiratory decompensation. 8
- Do not administer plasmapheresis immediately after IVIG, as plasmapheresis will remove the immunoglobulin. 5
- Consider rituximab if the patient is refractory to IVIG or plasmapheresis. 5
ICU Monitoring and Supportive Care
Admit to ICU with continuous cardiorespiratory monitoring for a minimum of 24 hours, though median duration of mechanical ventilation is 12-14 days. 2, 8
Respiratory function assessment: 1, 2
- Measure FVC and NIF every 4-6 hours initially
- Use single-breath count test (patient counts aloud at ~2 numbers/second; ≥25 correlates with normal respiratory strength) as a rapid bedside screen
- Do not rely on pulse oximetry or arterial blood gases as early indicators—they remain normal until failure is imminent
Establish invasive monitoring: 2
- Insert arterial line for continuous blood pressure monitoring and frequent blood gas sampling
- Place central venous line for medication administration and fluid management
- Insert urinary catheter to monitor output
Laboratory evaluation: 5, 1, 2
- Troponin (screen for myocardial involvement)
- CPK, aldolase, ESR, CRP (assess for concurrent myositis)
- Electrolytes, renal and hepatic function, coagulation studies
- Arterial blood gases
- Daily electrolyte panels during treatment
Neurological examination every 2 hours assessing bulbar function (dysphagia, dysarthria, facial weakness), ocular signs (ptosis, extraocular movements), proximal muscle strength, and fatigability. 2
Identify and Treat Precipitating Factors
Aggressively screen for and treat infections, as they trigger 60-70% of myasthenic crises. 2 Obtain: 2
- Urinalysis and urine culture (urinary tract infections are common triggers)
- Chest radiograph
- Blood cultures if febrile
Prevent aspiration pneumonia: 8, 3
- Place small-bore duodenal feeding tube (more comfortable and lower aspiration risk than nasogastric tubes)
- Initiate supportive enteral feeding once bowel sounds present
- Implement aggressive pulmonary toilet with suctioning, chest physiotherapy, and bronchodilator treatments as needed
Common Pitfalls to Avoid
Do not perform edrophonium (Tensilon) testing in a patient with suspected myasthenic crisis and respiratory compromise. 6, 4 If the patient is in cholinergic crisis (overtreated), edrophonium will worsen oropharyngeal secretions and respiratory muscle weakness; testing should only occur after respiratory exchange is secured and the patient is stable. 6
Do not delay intubation waiting for "objective" respiratory failure on blood gases—clinical assessment using the 20/30/40 rule is superior for timing intervention. 1, 2
Do not use high-dose corticosteroids as monotherapy without concurrent plasmapheresis or IVIG in acute crisis; steroids alone can initially worsen weakness. 4
Recognize that 15-20% of myasthenic crises occur as the first manifestation of previously undiagnosed myasthenia gravis. 8 Maintain high clinical suspicion in any patient presenting with rapidly progressive flaccid weakness, bulbar symptoms, and respiratory failure without sensory deficits or autonomic involvement.
Prognosis and Duration
Median duration of mechanical ventilation is 12-14 days under appropriate treatment, though 20% remain ventilated after 1 month due to complications. 8 Mortality is 2-5% (some series report up to 16%), with deaths almost never caused by the crisis itself but by comorbidities and complications. 8 The lifetime risk of crisis recurrence is approximately 30%. 8