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1703 Onset of respiration after delivery by Caesarean section and the vagina

Our previous work has shown that babies born by C section requiring resuscitation rarely achieve a functional residual capacity (FRC) immediately, unlike those born by vaginal delivery. As these differences could be due either to asphyxia or the mode of delivery, we have measured the first spontaneous breath in 21 babies born vaginally, measuring intrathoracic pressure with a micro pressure transducer on a 6fg catheter, and thoracic volume change on a pneumotachograph, from the time the baby's head was delivered on the perineum until regular respiration had commenced. We compared the results with data obtained on 12 babies born by C section, commencing measurements as soon as the baby's head was delivered through the uterine incision. Those delivered vaginally experienced prolonged squeeze of up to 237cm H2O, compared to a transient pressure of 113cm H2O on passage through the uterine scar. Inspiratory pressures and volumes were similar for the two groups, but only five of those born by C section had an FRC after the first breath, compared to 20 of the 21 vaginal deliveries. Opening pressures were rarely seen in either group. We conclude that passage down the birth canal does aid lung expansion at birth.