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Canadian Journal of Anesthesia 52:213 (2005)
© Canadian Anesthesiologists' Society, 2005

Correspondence

Are non-depolarizing neuromuscular blocking agents innocuous for the neonates?

Joanne Guay, MD FRCPC

Montreal, Quebec

To the Editor:

I read with interest the article1 written by Dr. Littleford and was glad to see she did not make the statement commonly found in most textbooks that the administration of a neuromuscular relaxant does not affect Apgar or neurobehavioural scores. Partial residual curarization of the neonate can occur when clinical doses of a non-depolarizing neuromuscular blocking agent is used during a Cesarean section despite umbilical vein concentrations lower than the known neonatal EC50 for that specific agent.2 In one randomized double-blind study, at 15 min of life, the proportion of neonates with an abnormal neurobehavioural adaptive capacity score was higher in the group whose mothers received an ED90 dose of atracurium (14/25) than in the group whose mothers received an ED95 dose of d-tubocurarine (6/21; P < 0.05).2 The difference was seen in the active tone category (mode score 7 vs 9; P = 0.02) and was statistically significant for active contraction of the neck extensors (mode score 1 vs 2; P = 0.01).2

Since the umbilical vein to maternal vein (UV/MV) ratio of non-depolarizing neuromuscular blocking agents varies from 7 to 26% and fetal concentrations will increase with higher injected doses and with longer injection-to-delivery interval for drugs with a high molecular weight, when total avoidance of these drugs before clamping of the umbilical cord is not feasible, using the lowest possible dose of an agent with a low UV/MV ratio and short duration of action appears to be the safest choice.3

References

1 Littleford J. Effects on the fetus and newborn of maternal analgesia and anesthesia: a review. Can J Anesth 2004; 51: 586–609.[Abstract/Free Full Text]

2 Perreault C, Guay J, Gaudreault P, Cyrenne L, Varin F. Residual curarization in the neonate after caesarean section. Can J Anaesth 1991; 38: 587–91.[Abstract/Free Full Text]

3 Guay J, Grenier Y, Varin F. Clinical pharmacokinetics of neuromuscular relaxants in pregnancy. Clin Pharmacokinet 1998; 34: 483–96.[Medline]


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REPLY
Judith Littleford
CJA 2005 52: 213-214. [Full Text]  




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