Onset of respiration in infants delivered by cesarean section.

We studied the ventilatory parameters and the pattern of breathing including the onset of respiration in 20 healthy infants immediately after cesarean-section delivery. In eight of the infants further measurements were obtained at 60 min of life. The pattern of breathing immediately after delivery is very irregular with a marked tendency to keep the lung inflated mainly through interruptions of expiration. After the first expiration some air remains in the lung representing the formation of functional residual capacity (FRC). FRC obtained with the first breath is proportional to the previous inspired volume and is the largest contribution towards the full establishment of FRC. Tidal volume and FRC of the first breath are similar to that reported in babies delivered vaginally, which suggests that the forces required for lung inflation are similar in the two groups of infants. The first breath tends to be deeper and slower and has a longer expiratory time than subsequent breaths. At 60 min of life the respiratory pattern becomes more regular, tidal volume is further decreased, and respiratory frequency is increased through a reduction of expiratory time.