Effects of cyanosis and hypothermic circulatory arrest on lung function inneonatal lambs

Background. Lung function is often impaired after cardiac surgery and cardi opulmonary bypass (CPB), particularly in chronically cyanotic patients. Thi s study aimed to evaluate lung function in a surgically created chronic cya notic neonatal lamb model after CPB and deep hypothermic circulatory arrest (DHCA) and to assess the role of nitric oxide (NO) in the pathogenesis of increased pulmonary vascular resistance. Methods. A chronic cyanosis model was surgically created in 7 lambs (4.7 +/ - 0.8 days old) by anastomosing the pulmonary artery (PA) to the left atriu m (LA). Another 7 lambs underwent a sham operation (control). One week late r, the animals underwent shunt takedown and CPB with 90 minutes of DHCA at 18 degrees C. Cardiac index (CI), pulmonary vascular resistance index (PVRI ), lung dynamic compliance (C-dym), alveolar-arterial oxygen difference (Aa DO(2)), left atrial plasma nitrate/nitrite (NO metabolites) levels, and pul monary cGMP production (concentration difference between LA and PA) were me asured before CPB and at 1 and 2 hours after reperfusion. Results. The cyanosis model consistently produced significantly lower arter ial oxygen tension (34.8 +/- 2.3 vs 93.1 +/- 8.8 torr in control, p < 0.001 ) and Qp/Qs (0.6 +/- 0.1 vs 1.0 +/- 0.0 in control, p < 0.001) than control s. Postoperative PVRI was significantly lower in the cyanosis group than in controls, although CPB with DHCA significantly elevated PVR in both cyanot ic and control animals. There were no significant differences in AaDO(2) an d C-dyn after CPB between groups. The level of NO metabolites did not chang e before or after CPB in either cyanotic or acyanotic animals. NO metabolit e levels tended to be higher in the cyanotic animals (p = 0.08). There was no significant difference in pulmonary cGMP production between both groups. Conclusions. These findings suggest that CPB with DHCA, per se, does not af fect NO production in cyanotic or acyanotic neonatal lambs but causes incre ased PVR in both groups. Chronic cyanosis does not result in reduced pulmon ary function after CPB with DHCA, and is associated with lower PVR. The mec hanism may involve an increased NO production in cyanotic animals. (C) 1999 by The Society of Thoracic Surgeons.