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Anesthesia implications of Myasthenia Gravis

Anesthesia implications of Myasthenia Gravis. SC 吳彥葶 SC 顏旅君. Brief history. 44 years old man, denied other systemic disease Right eye ptosis and slurred speech for 4 years Myasthenia gravis diagnosed Symptoms fluctuated, 3 times myasthenia crisis.

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Anesthesia implications of Myasthenia Gravis

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  1. Anesthesia implications of Myasthenia Gravis SC 吳彥葶 SC 顏旅君

  2. Brief history 44 years old man, denied other systemic disease Right eye ptosis and slurred speech for 4 years Myasthenia gravis diagnosed Symptoms fluctuated, 3 times myasthenia crisis

  3. This time, progress ocular ptosis and right side diplopia MG with thymoma :Chest CT 2 cm mass in the anterior mediastinum admitted on 92/12/2 for surgery plasmapheresis 4 times operation on 92/12/11.

  4. Neuromuscular Monitoring • Nerve stimulation: Train-of-Four • Site:adductor pollicis muscle (ulnar nerve) • 12/12 9:44 extubation smoothly

  5. Pathophysiology • Autoantibodies against AChR at the neuromuscular junction (NMJ) of skeletal muscles • symptomatic once the number of ACh receptors reduced to 30% of normal • 75% of patients with MG have some degree of thymus abnormality (eg, hyperplasia in 85% , thymoma in 15% ).

  6. Presentation and diagnosis • Weakness increases during the day and improves with rest • Facial muscle weakness:EOM weakness or ptosis • Bulbar muscle weakness: chewing,swallowing • Limb weakness :proximal greater than distal • Some develop respiratory failure • Diagnosis: anticholinesterase test, EMG, anti-AChR antibody

  7. Treatment • Medical: anticholinesterases: pyridostigmine(Mestinon) Immune suppression: corticosteroid, azathioprine, cyclosporine --prevent AChR destruction • Plasmapheresis for severe bulbar symptoms, respiratory compromise (myasthenic crisis) • Thymectomy

  8. Anesthesia considerations—preop evaluation and preparation • Respiratory muscle strength (pulmonary function test) • Protect airway (Clear secretions? Cough?) • Determine the optimal conditions of extubation

  9. Plasmapheresis • Anticholinesterase? • Anxiolytic,sedative,opioid premedication rarely given • small dose benzodiazepine

  10. RESPONSE TO ANESTHETIC DRUGS

  11. Nondepolarizing Neuromuscular Blockers(NDNMB) • MG patient is typically sensitive to NDNMB. • Long acting NDNMB (pancuronium, pipecuronium, doxacuronium) :avoided • Intermediate and short acting: used with careful monitoring. • Single twitch (0.1-1Hz), Train-of-four(2Hz), Tetany(50-100Hz), Double-burst stimulation.

  12. ED95 for vecuronium : 55% of that in normal controls (20g/kg vs. 36g/kg) • Atracurium :58% (0.14mg/kg vs. 0.24mg/kg) • Cisatracurium: more rapid onset ,more marked NM block.

  13. Depolarizing Neuromuscular Blocker (Succinylcholine) • MG patients show resistance to depolarizing agents.( ED95 : 2.6 times of control ) • However ,a case report of MG patient in complete remission: normal sensitivity • MG patients are more likely to develop phase II block , particularly with repeated doses of succinylcholine.

  14. Potent Inhaled Anesthetic Agents • Isoflurane , enflurane: decrease TOF responses • Sevoflurane at 2.5% depresses EMG responses ( T1/Tc at 47%, T4/T1 at 57%). • No work has been reported on the effects of desflurane in MG

  15. Intravenous Anesthetic Agents • Propofol • Anesthetic management using propofol without untoward effects have been described. • Short duration, no effect on NM transmission. • Opioid • do not appear to depress NM transmission in MG muscle. • Central respiratory depression may be a problem. • Use of short-acting opioids : more titratable. Remifentanil (elimination half-life:9.5min)

  16. Etomidate, althesin and ketamine : Reports of uneventful anesthesia.

  17. Interaction with Other Drugs

  18. Regional Anesthesia • Potentiation of NM blockade by local anesthetics has been reported. • Decrease sensitivity of the postjunctional membrane to Ach. • Ester anesthetics, metabolized by cholinesterase, may present particular problems in patients taking anticholinesterases. • Use reduced doses of amide (lidocaine, bupivacaine) to avoid high blood levels.

  19. Anesthesia Management • Several GA techniques have been proposed, none has been proven to be superior. • Use of Muscle Relaxants ? • The use of muscle-relaxants in patients with MG has been associated with • a higher rate of unsuccessful extubation at the end of surgery • longer postoperative mechanical ventilation and hospital stay.

  20. 1)Avoid muscle relaxants. Use inhaled agents both for facilitating intubation and providing relaxation for surgery. • 2)Titrate small doses (10-25% ) of intermediate-acting muscle relaxants . • Reversal? Controversial.

  21. 3)TIVA for the management of myasthenics has been reported. • 4)When possible, many clinicians prefer regional or local anesthesia • Regional techniques- reduce or eliminate the need for muscle relaxants in abdominal surgery.

  22. Postoperative considerations • Closely monitored in ICU where respiratory support can be immediately reinstituted. • Weakness after surgery : a special problem. • Differential diagnosis: • 1.myasthenic crisis • 2. residual effects of anesthetic drugs • 3. nonanesthetic drugs interfering neuromuscular transmission • 4.cholinergic crisis.

  23. Cholinergic crisis:excess of Ach at nicotinic and muscarinic receptors. Usually results from excess anticholinesterases. • Nicotinic overstimulationtwitching, fasciculations, weakness . • When muscarinic effects are obvious , diagnosis is easily made. Antimuscarinics and respiratory support are given.

  24. If anticholinesterases and antimuscarinics has been used, muscarinic symptoms are absent, weakness and fasciculations predominate. • Edrophonium test ,to differentiate this from myasthenic crisis. • Many clinicians prefer to avoid muscle relaxants, or if they do so , they avoid anticholinesterase.

  25. Propofol vs. Sevoflurane Giorgio Della Rocca, Cecilia Coccia, et al. Propofol or sevoflurane anesthesia without muscle relaxants allow the early extubation of myasthenic patients . Canadian Journal of Anesthesia 2003; 50:547-552

  26. Results • Intubating conditions were good in all patients. • Only minimal hemodynamic changes in the propofol group. (mAP decreased 25% compared to the baseline) • Extubation in the operating room .None had to be intubated . • Neuromuscular transmission :minimal changes, more important in the sevoflurane group .Complete recovery at the end of procedure.

  27. Advantages of propofol and sevoflurane. • Propofol obtund airway reflexes and allow a relatively easy intubation in the majority of patients. • The rapid elimination of propofol and the rapid kinetic (low blood gas solubility coefficient) of sevoflurane allowed fast recovery of consciousness, airway reflexes and respiratory function at the end of surgery

  28. Conclusion 1.A very early extubation technique is feasible in myasthenic patients ,either with propofol or sevoflurane general anesthesia without muscle relaxants.

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