Neuromuscular Blocking Drugs

Neuromuscular Blocking Drugs

• Primary Uses:
  • Perform tracheal intubation.
  • Facilitate ventilation.
  • Provides optimal surgical operating conditions.

• Neuromuscular Junction:
  • Presynaptic Axon of terminal motor junction
  • Neuromuscular Synaptic junction vesicles
  • Sarcolemmz Muscle fiber
  • Synaptio cleft
  • Mitochondrion
  • Postsynaptic membrane
  • Myofibrils
  • Capiilary

• Table 9-1. Depolarizing and nondepolarizing muscle relaxants.

Depolarizing	Short-acting	Nondepolarizing	Short-acting	Intermediate-acting	Long-acting
Succinylcholine	Mivacurium	Atracurium	Cisatracurium	Vecuronium	Rocuronium

Depolarizing (Succinycholine)

• Adverse Effects:
  • Cardiac dysrhythmias: sinus bradycardia, and even asystole.
  • Hyperkalemia. (burns, RF, muscular dystrophies & paraplegia)
  • A transient increase in intraocular pressure.
  • Increase in intracranial & intragastic pressure.
  • Myalgia: abdomen, back, and neck.
  • Histamine release.
  • Dual block.
  • Succinylcholine apnea Low levels of plasma cholinesterase (severe liver or kidney disease)
  • Anaphylaxis.
  • Malignant hyperthermia (MH).

Nondepolarizing Blockers

• Mechanism of Action: They act by competitively blocking the binding of ACh to its receptors.
• Characteristics:
  • Absence of fasciculations.
  • Reversal by AChE inhibitors.

ATRACURIUM

• Advantages:
  • Widely used and have an intermediate onset and duration of action.
  • Histamine release.
  • Metabolism is by ester hydrolysis in the plasma.

CISATRACURIUM

• Advantages:
  • Metabolism is by ester hydrolysis in the plasma.
  • Relatively slow onset of action.
  • Does not release histamine.

ROCURONIUM

• Advantages:
  • Intubating conditions can be achieved in 60-90 seconds after an induction dose of 0.6 mg/Kg. Increasing the dose to 1.2 mg/kg shortens the time can be used for rapid sequence induction when Suxamethonium is contraindicated.
  • Histamine is not released.

Anticholinesterases (Neostigmine)

• Mechanism of Action: They inhibit the action of the acetylcholinesterase enzyme at the NMJ by increasing the concentration of Ach at NMJ.
• Clinical Tests: The ability to lift the head from the bed for 5 seconds.
• Dosage: Intravenous injection at a dose of 0.05 mg/kg (maximum 5mg).
• Adverse Effects: To minimize adverse effects such as bradycardia, miosis, GI upset, nausea, bronchospasm, increased sweating, salivation & bronchial secretions, an antimuscarinic such as glycopyrronium 0.01 mg/kg or atropine 0.02 mg/kg must be administered along with the anticholinesterase.

Sugammadex Sodium

• Mechanism of Action: Selective reversal of neuromuscular blockade (NMB) induced by rocuronium or vecuronium in adults undergoing surgery.
• Advantages: Can be used in pediatric.

Peripheral Nerve Stimulator

• Uses:
  • Check the depth of neuromuscular blockade.
  • Determine that neuromuscular blockade is reversed.
  • At least 3 twitches on a train of four should be detected before attempting reversal.

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