Observations of 3-Hydroxy-N-Methylmorphinan Hydrobromide (Dromoran®) on Fetal Respiratory Movements of the Rabbit. ∗

Abstract

Discussion and Summary

Dromoran® passes without difficulty across the placental barrier and produces a decrease in the rate of respiratory movements of the fetuses. This passage across the placental barrier might be expected in view of the general principle stated by Needham(8) that the placental barrier is freely passed by practically all substances of low molecular weight. Thus in obstetrical analgesia one can assume that the agent will pass the placental barrier and the best analgesic will be one which will have high analgesic potency in the mother and a minimal effect on fetal respiration activity. The final evaluation of an analgesic must therefore be made under clinical conditions where the analgesic property can be evaluated in the patient. The doses of Dromoran® used in these experiments were much higher than would be used for human patients and there is no doubt but what satisfactory analgesia in humans can be obtained with lower doses. The question of whether these doses depress the respiratory function of the baby can be answered by clinical observation only with difficulty. On the basis of the parallelism shown in the rabbit experiments between the response of the maternal respiration rate and the rate of fetal respiratory movement it would appear safe to assume that if, in the human mother, respiratory function was depressed there would almost certainly be a corresponding effect on the respiratory function of the baby. Thus an obstetrician might make use of changes in the maternal respiration rate as an index to the respiratory function of the baby.