Suxamethonium

Suxamethonium - The only depolarising neuromuscular blocker available in the UK. It has a rapid onset of action (45–60 s) and a short duration of action (5 min). Breakdown is dependent on plasma pseudocholinesterase. It is best to keep the ampoule in the fridge to prevent a gradual loss of activity due to spontaneous hydrolysis.

Uses
Agent of choice for:
• rapid tracheal intubation as part of a rapid sequence induction
• for procedures requiring short periods of tracheal intubation, e.g. cardioversion
• management of severe post-extubation laryngospasm unresponsive to gentle positive pressure ventilation

Contraindications
History of malignant hyperpyrexia (potent trigger)
Hyperkalaemia (expect a further increase in K+ level by 0.5–1.0 mmol/l)
Patients where exaggerated increase in K+ (>1.0 mmol/l) are expected:
• severe burns
• extensive muscle damage
• disuse atrophy
• paraplegia and quadriplegia
• peripheral neuropathy, e.g. Guillain–Barre´

Administration
As a rapid sequence induction: 1.0–1.5 mg/kg IV bolus, after 3 min pre-oxygenation with 100% O2 and a sleep dose of induction agent Apply cricoid pressure until tracheal intubation confirmed. Intubation possible within 1 min. Effect normally lasting <5 min Repeat dose of 0.25–0.5 mg/kg may be given. Atropine or glycopyrollate should be given at the same time to avoid bradycardia/asystole

How not to use suxamethonium
In the conscious patient
By persons not trained to intubate the trachea

Adverse effects
Malignant hyperpyrexia
Hyperkalaemia
Transient increase in IOP and ICP
Muscle pain
Myotonia
Bradycardia, especially after repeated dose

Cautions
Digoxin (may cause arrhythmias)
Myasthenia gravis (resistant to usual dose)
Penetrating eye injury ( IOP may cause loss of globe contents)
Prolonged block in:
• patients taking aminoglycoside antibiotics, magnesium
• myasthenic syndrome
• pseudocholinesterase deficiency (inherited or acquired)

Organ failure
Hepatic: prolonged apnoea (reduced synthesis of pseudocholinesterase)