Low-flow cardiopulmonary bypass produces greater pulmonary dysfunction than circulatory arrest

Background. Deep hypothermic circulatory arrest (DHCA) is used during the repair of congenital heart disease in neonates. However, because of concern about neurologic injury after DHCA, there is increasing use of continuous deep hypothermic low-flow cardiopulmonary bypass (DHCPB). This study examines the effects of DHCPB versus DHCA on pulmonary dynamics in 1-week-old piglets (weight range, 2.5 to 3.5 kg). Methods. Animals were placed on CPB (37°C) at 100 mL · kg^-1 · min^-1, cooled to 18°C, and then assigned to one of two groups: DHCPB (n = 7), 25 to 50 mL · kg^-1 · min^-1 DHCPB for 90 minutes; or DHCA (n = 8), DHCA for 90 minutes. Animals were rewarmed to 37°C, weaned from CPB, and observed for 30 minutes. Static pulmonary compliance and pulmonary vascular resistance index were assessed before CPB, 5 minutes after CPB, and 30 minutes after CPB. Results. There was greater impairment of static pulmonary compliance after DHCPB compared with 90 minutes of DHCA. There was a trend toward higher pulmonary vascular resistance index in the DHCPB group; however, significance was not reached. Conclusions. Deep hypothermic low flow cardiopulmonary bypass produces greater pulmonary dysfunction than DHCA, manifested by decreased static pulmonary compliance. If DHCPB is used in place of DHCA in congenital heart operations, close attention to ventilatory and fluid management is mandatory in the postoperative period to prevent further worsening of pulmonary dysfunction.