Muscle relaxants in infants and children.

In the first 2 years of life there is physical and biochemical maturation of the neuromuscular junction of man. With this maturation there is an increase in the neuromuscular reserve (margin of safety) of the infant and a change in the contractile properties of skeletal muscle. On a weight basis neonates and young infants are resistant to both depolarizing and non-depolarizing muscle relaxants; when dosage is calculated on the basis of surface area neonates and young infants are not resistant to succinylcholine, but appear sensitive to non-depolarizing relaxants. Variation in extracellular fluid volume probably explains these differences in apparent resistance. Data relating recovery of neuromuscular transmission to plasma or tissue bath concentrations of dTc are conflicting. Awareness of the clinical response of neonates and infants to muscle relaxants and awareness of the non-neuromuscular blocking properties of relaxants in infants and children permits the use of these anesthetic adjuncts in patients of any age.