Positive end expiratory pressure (PEEP) and right to left shunting in immature goats.

Immature fetal goats were exteriorized by caesarean section and catheters were placed in a pulmonary vein (PV), carotid artery (CA), femoral artery (FA), and the main pulmonary artery (PA). The goats were ventilated at 7.5 and 15 cm H20 positive end expiratory pressure (PEEP) between control periods at 0 PEEP. Right to left shunting (Qs/Qt) was calculated for three anatomic sites: lung, foramen ovale, and ductus arteriosus, and for two summation shunts: preductal and total. Total Qs/Qt increased in 8 of 14 animals at 7.5 cm H2O PEEP and in 7 of 12 animals at 15 cm H2O PEEP. Intrapulmonary shunting increased in only one experiment. The increase in total Qs/Qt resulted from elevated extrapulmonary shunting, always including the ductus arteriosus. The variation in response to PEEP was from animal to animal and not from one level to another within one animal. Changes in total Qs/Qt on PEEP did not correlate with the size of control Qs/Qt at any site.