Epidural anaesthesia is initiated in Primigravida at 38 weeks gestation, with a bolus of 15mg of Bupivacaine. Within few minutes, fetal heart rate monitoring shows variable decelerations. If scalp pH reveals fetal acidosis, compared with a normal pH, the anaesthetic absorbed by fetus will be present in
Local anaesthetics, being basic drugs become more ionized at low fetal pH. Ionized molecules are thus trapped on fetal side of circulation.
Lower concentration, most in ionized form
Higher concentration, most in ionized form
Higher concentration, most in unionized form
Unchanged concentration, equal fraction of ionized and nonionized