Transplacental Distribution of Atracurium, Laudanosine and Monoquaternary Alcohol During Elective Caesarean Section

Abstract

Maternal venous (MV), umbilical venous (UV) and umbilical arterial (UA) blood samples were obtained for assay of atracurium, laudanosine and monoquaternary alcohol concentrations in 22 healthy patients undergoing elective Caesarean section under general anaesthesia. At delivery (at a mean time of 8.2 min after atracurium 0.3 mg kg-1), the mean UV concentrations were 103 ng ml-1 (range 44-189 ng ml-1) for atracurium, 26 ng ml-1 (range 6-60 ng ml-1) for laudanosine and 59 ng ml-1 (range 21-148 ng ml-1) for monoquaternary alcohol. The ratios of UV:MV, UA:MV and UA:UV blood concentrations were related positively to time since injection of atracurium for all three substances (P less than 0.01 in each instance). The UV:MV ratio at delivery was greatest for laudanosine: mean 19.4% (range 1-35%), compared with 7% (range 2-21%) for atracurium and 10% (range 0-15%) for monoquaternary alcohol. These low values confirm that, although atracurium crosses the placental barrier and its metabolites may be found in the fetus, the drug is safe to use during Caesarean section.

In reply

“…9 Laudanosine has aroused concern because of possible excitement and seizure activity in the newborn, but the low concentrations observed confirm that the drug can be safely used in caesarean section. 10 Moreover, there are no clinical reports of complications related to laudanosine in the newborn. Sensitivity to laudanosine in humans is not known.…”

Anaesthesia for fetal surgery

“…Virtually every organ system in the mother undergoes physiological changes during pregnancy (26,27,28). Those changes of particular importance to the anaesthesiologist are well known and include alterations in the gastrointestinal, pulmonary, cardiovascular and central nervous systems.…”

“…Respiratory alterations during pregnancy are of particular significance to the anaesthesiologist (26–28). Minute ventilation is increased by 50% and oxygen consumption is increased to a lesser degree by the end of the first trimester.…”

“…Supine hypotension syndrome can occur in pregnant patients from compression of the inferior vena cava by the gravid uterus (26–32). This compression can lead to a marked decrease in systemic venous return, as well as an increase in uterine venous pressure, and thus a decrease in uterine perfusion pressure, placing the fetus at risk for hypoxia.…”

Pharmacokinetic Optimisation of General Anaesthesia in Pregnancy

“…For continuation of neuromuscular block, drugs with rapid elimination such as vecuronium (Dailey et al 1984) and atracurium (Flynn et al 1984;Shearer et al 1991) are more attractive than older drugs which are eliminated more slowly (Agoston et al 1992). At caesarean section, clearance of vecuronium was greater (Dailey et al 1984) and onset of action was faster, but the duration of action was prolonged (Baraka et al 1992) compared with that in nonpregnant women.…”