Suxamethonium (Scoline) Apnoea Dr S Spijkerman

Pathophysiology Suxamethonium is broken down by pCE Inherited abnormal genetic variant of pCE (autosomal recessive) Prolonged apnoea after a standard dose of suxamethonium Several variations: normal pCE enzyme gene = E1U. E1a (a = abnormal) (E1uE1a) recovery time from suxamethonium < 30 minutes (E1aE1a) recovery time from suxamethonium >2 hours 3. E1f (the fluoride pCE) 4. E1s (silent) → little pCE activity →recovery from suxamethonium can take >> 3 hours. NB: Mivacurium is also broken down by pCE and should be avoided in these patients.

Acquired causes of decreased pCE activity (NB: These causes prolong the effect of suxamethonium by minutes and not by hours like the inherited types) Pregnancy (dilutional effect due to increased water component) Newborns (dilutional effect and immature liver, thus decreased pCE synthesis) Liver diseases Malnutrition Severe hypothyroidism Plasmapheresis  

Clinical presentation Prolonged apnoea and inability to move after standard dose of suxamethonium Patient may be aware, thus may present with tachycardia, hypertension  

DDx delayed awakening: Drugs Benzodiazepine premedication Opioid overdose intra-operatively Insufficient reversal of nondepolarising muscle relaxants Suxamethonium apnoea Failure to discontinue anaesthetic vapour Pre-operative alcohol intoxication Endocrine Severe hypothyroidism Hypoglycaemia Diabetic keto-acidosis (DKA), hyper osmotic nonketotic coma (HONK) Addison’s crisis

DDx (cont) Electrolyte disturbances Hyponatraemia Hypocalcaemia Hypermagnesaemia (magnesium sulphate treatment etc) Acid-base disturbances Hypercapnoea (“Carbon dioxide narcosis”) – due to hypoventilation Hypocapnoea (no drive for breathing) – due to hyperventilation Hypothermia   Intra- operative complications Cerebro-vascular incident Myocardial infarction Undiagnosed muscle diseases

Treatment of scoline apnoea Treat apnoea Mechanical ventilation until normal muscle strength returns Prevent awareness Continue anaesthesia with inhalant or sedate well with benzodiazepines Exclude differential diagnosis See table 3 Fresh frozen plasma/whole blood Contains pCE and will speed recovery BUT risk of infections like HIV too high, thus NOT recommended Recombinant pCE Very expensive. Cheaper to treat symptomatically Confirm scoline apnoea pCE activity dibucaine or fluoride number If scoline apnoea confirmed Council patient and family members Medic alert bracelet for patient Test family members

Dibucaine is a local anaesthetic that inhibits the activity of pCE Dibucaine is a local anaesthetic that inhibits the activity of pCE. The normal gene is inhibited by 80% (dibucaine number = 80%), atypical gene by 20% (dibucaine number = 20%) and heterozygous gene by 40-60% (dibucaine number = 40- 60%). In the same way a fluoride number can be determined