What is the recommended inpatient monitoring protocol for a patient with myasthenia gravis, including respiratory function (forced vital capacity and negative inspiratory force), neurological exam, vital signs, laboratory tests, and medication management?

Inpatient Monitoring Protocol for Myasthenia Gravis

Patients with myasthenia gravis require ICU-level monitoring with frequent respiratory function assessments (every 4-6 hours initially), continuous cardiorespiratory monitoring, and neurological examinations at least every 2 hours, particularly those with generalized weakness or bulbar symptoms. 1, 2

Respiratory Function Monitoring

The "20/30/40 rule" must guide your assessment and escalation decisions:

• Measure forced vital capacity (FVC) and negative inspiratory force (NIF) every 4-6 hours initially 2, 3

• Critical thresholds requiring immediate intubation preparation:

  • FVC <20 ml/kg 2, 3
  • Maximum inspiratory pressure (NIF) <30 cmH₂O 2, 3
  • Maximum expiratory pressure <40 cmH₂O 2, 3

• Supplementary bedside assessment: Single breath count test - have the patient take a deep breath and count at two numbers per second while exhaling; counting to ≥25 correlates with normal respiratory muscle function 2

• Do NOT rely on pulse oximetry or arterial blood gases as early indicators - these may remain normal until respiratory failure is imminent 2

• Consider end-tidal CO₂ monitoring as an optional early warning tool 2

Neurological Examination

Perform focused neurological assessments every 2 hours minimum, evaluating:

• Bulbar function: dysphagia, dysarthria, facial weakness, drooling 4
• Ocular signs: ptosis, extraocular movement abnormalities 4
• Proximal muscle strength: ability to lift arms, climb stairs, neck flexion 4
• Fatigability: worsening weakness with repetitive movements 4, 5
• Reflexes should remain normal - abnormal reflexes suggest alternative diagnosis 5
• Sensation should be intact - sensory deficits point away from MG 5

Vital Signs and Cardiorespiratory Monitoring

Continuous monitoring is mandatory for patients with generalized MG or those at risk of crisis:

• Continuous pulse oximetry and cardiac telemetry 1, 2
• Blood pressure and heart rate every 2-4 hours 1
• Temperature monitoring to detect infections - respiratory infections are the most common trigger for myasthenic crisis 3, 6

Laboratory Tests

Initial comprehensive workup:

• Serologic testing: acetylcholine receptor (AChR) antibodies, anti-striated muscle antibodies 4, 2
• If AChR negative: muscle-specific kinase (MuSK) and lipoprotein-related protein 4 (LRP4) antibodies 4, 2
• Cardiac evaluation: troponin to assess for myocardial involvement 4
• Inflammatory markers: CPK, aldolase, ESR, CRP to evaluate for concurrent myositis 2
• Infection screening: urinalysis, chest X-ray, blood cultures if febrile 3, 6

Ongoing monitoring:

• Daily electrolytes - particularly if on corticosteroids or immunotherapy 2
• Magnesium levels - hypomagnesemia requires neurology consultation before any IV magnesium administration (which is otherwise absolutely contraindicated) 2

Medication Management

IMMEDIATELY discontinue these medications that worsen MG:

• β-blockers 4, 3
• IV magnesium (absolutely contraindicated) 4, 2, 3
• Fluoroquinolones 4, 2, 3
• Aminoglycosides 4, 2, 3
• Macrolide antibiotics 4, 2, 3

Pyridostigmine management:

• Discontinue or withhold in intubated patients 2, 3, 5
• For non-intubated patients with stable symptoms: continue at 30-120 mg orally every 4-6 hours (maximum 600 mg daily) 2
• IV conversion if needed: 30 mg oral = 1 mg IV pyridostigmine or 0.75 mg neostigmine IM 2

Avoid corticosteroids initially in acute crisis - wait until after plasmapheresis or IVIG is initiated 5

Level of Care Determination

ICU admission criteria:

• Any patient meeting the 20/30/40 rule thresholds 2, 3
• Progressive bulbar symptoms with aspiration risk 4, 7
• Myasthenic crisis (respiratory failure requiring ventilatory support) 2, 3, 6

Intermediate care/step-down unit criteria:

• Patients with progressive neuromuscular dysfunction requiring cardiorespiratory monitoring but without altered sensorium 1
• Stable patients requiring neurologic assessment no more frequently than every 2 hours 1

Minimum monitoring duration: 24 hours in ICU, HDU, or recovery unit even after apparent stabilization 2

Critical Pitfalls to Avoid

• Do not wait for hypoxemia or hypercapnia to escalate care - respiratory failure in MG can progress rapidly once these appear 2
• Never use depolarizing paralytics (succinylcholine) if intubation is required - use reduced doses of non-depolarizing agents instead 5, 8
• Do not perform edrophonium testing in crisis - avoid all acetylcholinesterase inhibitors during acute decompensation 5
• Respiratory infections are the most common trigger (found in 60-70% of cases) - aggressive infection screening and treatment is essential 3, 6, 7
• 30-40% of myasthenic crises have no identifiable trigger - absence of obvious precipitant should not delay treatment 6