Anaesthetic management of myasthenia gravis (MG)

1. Preoperative assessment and optimisation

• Defer elective surgery until MG is clinically stable or optimally controlled, in discussion with the neurologist.
• Establish disease severity:
  • Ocular vs generalized MG
  • Bulbar symptoms: dysphagia, dysarthria, weak cough, aspiration or choking
  • Respiratory symptoms, exercise tolerance, previous myasthenic crisis or ventilation
  • Current treatment and daily pyridostigmine dose
• Look for associated conditions, especially thymoma, thyroid disease and other autoimmune disease. Review chest imaging if a mediastinal mass is possible.
• For major surgery or respiratory/bulbar involvement, obtain baseline respiratory function, especially FVC/vital capacity.
• Continue pyridostigmine and usual corticosteroids/immunosuppressants on the morning of surgery. If a long procedure causes a missed dose, weakness may become evident at emergence.
  Miller's Anesthesia, 10e, p. 4204-4205.
• In poorly controlled MG, urgent surgery, or marked bulbar/respiratory weakness, neurologic optimisation with IVIG or plasma exchange may be needed before surgery.
• Discuss possible postoperative ventilation with high-risk patients.

2. Choice of anaesthetic technique

Regional/local anaesthesia

• Preferred where feasible because it avoids airway manipulation and neuromuscular blockers.
• Use sedation sparingly, with continuous observation for hypoventilation or upper-airway obstruction.
• Avoid techniques likely to impair breathing:
  • High neuraxial block in patients with poor respiratory reserve
  • Interscalene brachial plexus block, if phrenic nerve palsy would be poorly tolerated
  • Bilateral blocks associated with diaphragmatic dysfunction

General anaesthesia

• Short-acting agents and careful titration are preferred.
• Propofol with a short-acting opioid can permit tracheal intubation in selected patients without a neuromuscular blocking drug (NMBD).
• Volatile anaesthetics such as sevoflurane or desflurane provide muscle relaxation, but MG patients are more sensitive to their neuromuscular depressant effects. Barash, Cullen, and Stoelting’s Clinical Anesthesia, 9e, p. 3256.
• Maintain normothermia, good analgesia, and avoid factors that precipitate weakness: infection, pain, hypothermia/hyperthermia, electrolyte disturbance, missed MG medication, and residual paralysis.

3. Neuromuscular blockers

4. Drugs to avoid or use cautiously

• Magnesium, including magnesium-containing antacids or IV magnesium
• Aminoglycosides
• Fluoroquinolones
• Macrolides and ketolides, especially telithromycin
• Beta-blockers
• Procainamide and some antiarrhythmics
• Calcium-channel blockers
• Large doses of IV lidocaine, especially alongside NMBDs
• Excess sedatives, opioids, and respiratory depressants

5. Emergence and postoperative care

• Aim for fully awake extubation only after:
  • Adequate spontaneous tidal volume and respiratory rate
  • Strong cough and airway reflexes
  • Good head lift/limb strength compared with baseline
  • No bulbar weakness or excessive secretions
  • Quantitative TOF ratio >0.9, ideally >0.95 in this high-risk group
• Use multimodal analgesia to reduce opioid requirement.
• Observe in PACU for longer than usual. Patients with severe/bulbar MG, abnormal respiratory function, major surgery, or any concern about weakness should receive monitored or ICU care.
• Early signs of respiratory deterioration: rapid shallow breathing, weak cough, dysphagia/drooling, altered voice, paradoxical breathing, rising CO₂, or hypoxaemia. Miller's Anesthesia, 10e, p. 4206-4207.

6. Distinguish postoperative crises

• Myasthenic crisis: worsening weakness, weak cough, respiratory failure, often with little secretion excess. Treat with respiratory support, neurologic input, and usually IVIG or plasma exchange.
• Cholinergic crisis: rare; weakness plus muscarinic excess: salivation, lacrimation, bronchospasm, bradycardia, diarrhoea, vomiting, sweating, miosis. Stop further anticholinesterase, give atropine or glycopyrrolate, and provide ventilatory support. Miller's Anesthesia, 10e, p. 4206-4207.

Short exam summary

Anaesthetic management of Parkinsonism / Parkinson disease - 10 marks

Introduction

1. Preoperative management

A. Assessment

• Determine severity: tremor, rigidity, bradykinesia, dyskinesia, “on-off” phenomena, ability to lie still.
• Ask specifically for:
  • Dysphagia, sialorrhoea, reflux, choking or recurrent aspiration
  • Dyspnoea, stridor, weak cough, sleep apnoea
  • Orthostatic dizziness/syncope and urinary dysfunction
  • Dementia, hallucinations, delirium, depression
• Review coexisting cardiac, pulmonary and autonomic disease.
• Check all drugs and the exact timing of the usual levodopa dose.
• For patients with deep-brain stimulation (DBS), identify device type and involve neurology/device personnel. Protect the device from electromagnetic interference.

B. Continue anti-parkinsonian drugs

• Do not abruptly stop levodopa or dopamine agonists.
• Give the usual morning dose with a sip of water, preferably close to induction. Levodopa has a short half-life of about 1-3 hours.
• Interruption for more than 6-12 hours can cause severe rigidity, impaired ventilation, fever, autonomic instability, and a Parkinsonism-hyperpyrexia syndrome resembling neuroleptic malignant syndrome.
  Barash, Cullen, and Stoelting’s Clinical Anesthesia, 9e, p. 1854.

• Carbidopa/levodopa: commonly 25/100 mg orally three times daily initially, but perioperatively continue the patient’s individual prescribed dose and schedule.
• If prolonged fasting is expected, use enteral levodopa through a tube whose tip is beyond the stomach when appropriate. A historical review suggests administering the patient’s usual oral levodopa about 20 minutes before induction and repeating doses about every 2 hours when clinically necessary (perioperative review).
• If enteral administration is impossible, discuss with neurology:
  • Rotigotine patch: available as 2, 4, 6 or 8 mg/24 h patches; maintenance range 4-24 mg/24 h.
  • Apomorphine SC: 2-8 mg for an established patient’s “off” episode. It should be initiated only with specialist guidance because it can cause severe nausea and hypotension.
    Harrison’s Principles of Internal Medicine, 22e, p. 1923-1929.

2. Premedication

• Avoid or use minimal benzodiazepine sedation because elderly patients may develop confusion, respiratory obstruction, or delayed recovery.
• Give aspiration prophylaxis where indicated.
• If an anticholinergic is required, glycopyrrolate 0.1-0.2 mg IV is preferable to atropine/scopolamine because it does not cross the blood-brain barrier.
• Correct dehydration and treat postural hypotension before induction.

3. Choice of anaesthesia

Regional anaesthesia

• Patient remains conscious, permitting assessment of tremor and neurological status.
• Avoids airway manipulation, general anaesthetic drugs, and delayed reintroduction of oral medication.
• Useful in patients who need frequent dopaminergic dosing.

• Severe tremor, rigidity, dyskinesia, anxiety, or inability to cooperate can make regional anaesthesia unsuitable.
• Sedation must be light and titrated.

General anaesthesia

• Either volatile-based anaesthesia or TIVA may be used.
• Propofol is usually suitable for induction, commonly 1-2 mg/kg IV, but titrate down in frail elderly or hypovolaemic patients. It may occasionally cause dyskinesia but suppresses tremor and has an antiemetic effect.
• Use a short-acting opioid cautiously. Avoid rapid large boluses of fentanyl or alfentanil because they can cause rigidity/dystonic reactions.
• Volatile agents including isoflurane, sevoflurane and desflurane have no consistent adverse Parkinson-specific interaction, but may worsen hypotension.
  Barash, Cullen, and Stoelting’s Clinical Anesthesia, 9e, p. 1855.

Airway

• Treat as increased aspiration risk if there is dysphagia, reflux, retained secretions, or severe bulbar dysfunction.
• Consider a cuffed tracheal tube and rapid-sequence induction when aspiration risk is high.
• Extubate only when fully awake, with intact cough, airway reflexes and adequate ventilation.

4. Intraoperative management

A. Autonomic dysfunction

• Parkinsonism may cause orthostatic hypotension, labile blood pressure and impaired compensatory responses.
• Anti-parkinsonian drugs and volatile agents may aggravate hypotension.
• Ensure adequate hydration, use slow positional changes, and monitor BP closely.
• Treat hypotension initially with fluids if appropriate, then use titrated vasopressors:
  • Phenylephrine 50-100 micrograms IV bolus, repeated as needed, or infusion.
  • Norepinephrine 2-8 micrograms/min IV infusion, titrated in severe/refractory hypotension.
• Avoid excessive indirect sympathomimetics where a patient is on MAO-B inhibitors; responses may be unpredictable.

B. Neuromuscular blockers

• Use standard agents as indicated, but ensure complete reversal.
• Residual weakness, rigidity, poor cough and aspiration can produce postoperative pulmonary complications.
• Use quantitative neuromuscular monitoring and extubate only after full recovery.

C. DBS precautions

• If a DBS is present, document baseline function.
• Turn stimulation off only in coordination with the managing team if electrosurgery interference is anticipated.
• Prefer bipolar cautery where possible; keep the current path away from the device and intracranial leads.
• Reactivate and confirm device function postoperatively.

5. Drugs to avoid

Antiemetic

• Preferred: ondansetron 4 mg IV near the end of surgery.
• Alternative: dexamethasone 4-8 mg IV at induction, if not contraindicated.
• Avoid dopamine-blocking antiemetics listed above. Ondansetron does not block dopamine receptors, though monitor for serotonin toxicity when combined with MAO-B inhibitors or multiple serotonergic drugs.

6. Postoperative management

• Restart oral levodopa/carbidopa immediately once safe swallowing is established.
• If oral intake is not possible, arrange an enteral or specialist-approved non-oral dopaminergic strategy.
• Provide opioid-sparing multimodal analgesia, pulmonary physiotherapy, early mobilisation, and aspiration precautions.
• Monitor for:
  • Hypoventilation, upper-airway obstruction and aspiration pneumonia
  • Hypotension
  • Delirium, hallucinations and agitation, which may appear 24-72 hours after surgery
  • Acute rigidity, hyperthermia, dysautonomia or raised CK suggesting withdrawal-related Parkinsonism-hyperpyrexia syndrome.

Conclusion