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Infants
Area of Science:
- Anesthesiology and Pharmacology
- Pediatric Physiology
Background:
- Neuromuscular junction maturation occurs during the first two years of life.
- Infant skeletal muscle contractile properties and neuromuscular reserve change with maturation.
Purpose of the Study:
- To analyze infant response to muscle relaxants.
- To understand factors influencing drug resistance and sensitivity in neonates and infants.
Main Methods:
- Review of existing data on neuromuscular blocking agents in infants.
- Analysis of dosage calculations based on weight versus surface area.
- Consideration of extracellular fluid volume's role.
Main Results:
- Infants show resistance to muscle relaxants on a weight basis, but sensitivity on a surface area basis for non-depolarizing agents.
- Extracellular fluid volume variations likely explain apparent resistance differences.
- Conflicting data exists regarding neuromuscular transmission recovery and drug concentrations.
Conclusions:
- Understanding infant responses and non-neuromuscular effects of relaxants is crucial.
- Muscle relaxants can be safely used in pediatric patients of all ages.
- Clinical response and pharmacokinetic data guide safe anesthetic adjunct use.
Abstract:
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.