Nondepolarizing Neuromuscular Blocking Agents

Neuromuscular blocking medications are an important part of the anesthetic management of many patients undergoing surgery. These drugs act at the neuromuscular junction on postsynaptic acetylcholine receptors. Muscle relaxants can be divided into depolarizing and nondepolarizing categories. Succinylcholine is the only depolarizing neuromuscular blocker used in clinical practice. It has a short onset and duration of action and is associated with several important side-effects. Nondepolarizing muscle relaxants in clinical use are divided into two categories—benzylisoquinolines and steroids. The several medications in this class are varied in their onset, duration of action, metabolism, excretion, and side-effects. Monitoring of muscle relaxation occurs by testing for contraction in response to electrical stimulation. Prolonged paralysis from neuromuscular blockers has a variety of causes, including hypothermia, hepatic dysfunction and atypical enzymes. Reversal of nondepolarizing muscle blockers is often necessary and is done through the use of acetylcholinesterase inhibitors. The side-effects of cholinesterase inhibitors are reduced by using anticholinergic medications that limit the muscarinic effects of increased levels of acetylcholine. An understanding of the appropriate uses, limitations, risks, and monitoring of neuromuscular blocking medications is a fundamental aspect of anesthesiology.