Muscle Relaxants and Neuromuscular Blockade

Muscle relaxants are a group of anesthetic adjuncts administered to improve relaxation of skeletal muscles during surgical or diagnostic procedures. The term neuromuscular blocking agents (NMBAs) is a cumbersome but descriptive name that refers to the fact that this class of drugs produce their effects by action at the neuromuscular junction. A prime indication for the use of NMBAs in human practice is tracheal intubation during induction of anesthesia. All NMBAs exert their effects at the neuromuscular junction or motor endplate. The classic interaction of a NMBA such as d-tubocurarine or atracurium and the cholinergic receptor involves a competitive binding of the drug to the receptor, thus inhibiting the coupling of nerve action potential transmission with muscular contraction. The NMBAs are quaternary ammonium compounds designed to mimic the quaternary nitrogen atom of ACh. Most animals can be intubated relatively easily without paralysis, and muscle relaxation caused by inhalant anesthetic agents is adequate for most procedures.