Suxamethonium Aponea

Pathophysiology

  • Suxamethonium (succinylcholine) is a depolarising neuromuscular blocking agent

  • Normally metabolised by plasma cholinesterase (pseudocholinesterase/butyrylcholinesterase)

  • Suxamethonium aponea occurs due to:

    • Deficiency in plasma cholinesterase quantity or quality

    • Most commonly caused by genetic variants leading to atypical cholinesterase

    • Results in prolonged paralysis (hours instead of minutes)

Clinical Presentation

  • Unexpected prolonged paralysis after succinylcholine administration

  • Failure to resume spontaneous respiration after short surgical procedures

  • Continued flaccid paralysis beyond expected duration (>10-15 minutes)

  • Patient remains conscious but unable to move, breathe, or communicate

  • Vital signs typically stable (if ventilation maintained)

  • Anxiety and psychological distress once sedation wears off

At-Risk Populations

  • Genetic variants (autosomal recessive inheritance pattern):

    • Homozygous atypical gene (1:3,000 patients)

    • Heterozygous atypical gene (1:25 patients)

  • Family history of prolonged paralysis after anaesthesia

  • Certain ethnic populations with higher prevalence of atypical genes

  • Patients with:

    • Liver disease (decreased cholinesterase production)

    • Malnutrition

    • Pregnancy (particularly third trimester)

    • Burns (acute phase)

    • Uraemia/renal failure

    • Certain medications:

      • Organophosphates

      • Echothiophate eye drops

      • Cyclophosphamide

      • Metoclopramide

      • Oral contraceptives

      • Certain MAO inhibitors

Diagnosis

  • Clinical suspicion based on unexpectedly prolonged paralysis

  • Timing: paralysis persisting >15-30 minutes after succinylcholine

  • Exclusion of other causes of prolonged paralysis:

    • Residual non-depolarising blockade

    • Respiratory centre depression

    • Electrolyte abnormalities

    • Hypothermia

    • Acid-base disturbances

Neuromuscular Transmission (NMT) Monitoring Findings

  • Characteristic pattern:

    • No fade on train-of-four (TOF) stimulation

    • No post-tetanic facilitation

    • All four twitches equally suppressed

    • Gradual recovery of all twitches simultaneously

  • Differs from non-depolarising blockade (which shows fade)

  • Very slow recovery of twitch height over hours

Management

  • Immediate measures:

    • Continue mechanical ventilation

    • Maintain sedation/anesthesia until recovery

    • Reassure patient if awake

    • Inform surgical team

  • Supportive care:

    • Maintain normothermia

    • Monitor ventilation and oxygenation

    • Provide adequate sedation and analgesia

    • Consider transfer and ICU admission for prolonged cases

  • No specific antidote/reversal agent available

  • Fresh frozen plasma (FFP) may be considered in severe cases (provides functional cholinesterase)

  • Avoid repeated doses of succinylcholine

Recovery and Follow-up

  • Continue ventilation until full recovery of neuromuscular function

  • Monitor with NMT until TOF ratio >0.9

  • Document in medical records as significant anaesthetic complication

  • Refer patient for testing to confirm diagnosis

  • Genetic counselling for patient and family

  • Medical alert bracelet recommended

  • Inform patient about implications for future anaesthetics

Testing for Cholinesterase Deficiency

  • Dibucaine number:

    • Measures inhibition of enzyme by dibucaine

    • Normal: 70-80% inhibition

    • Heterozygous: 40-60% inhibition

    • Homozygous atypical: 10-30% inhibition

  • Fluoride number:

    • Similar test using sodium fluoride

    • Helps differentiate variants

  • Plasma cholinesterase activity level

  • Genetic testing for butyrylcholinesterase gene mutations

  • Testing should be delayed 6-8 weeks after event (acute phase may have falsely low levels)

  • First-degree relatives should be tested

Future Anesthetic Considerations

  • Avoid succinylcholine in confirmed cases

  • Use non-depolarizing neuromuscular blockers if needed

  • Consider alternative airway management techniques

  • Always have NMT monitoring available

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