Activation of the plasma kallikrein-kinin system in respiratory distress syndrome.

Components of the plasma kallikrein-kinin and fibrinolytic systems together with antithrombin III were measured the first days postpartum in 13 premature babies with severe respiratory distress syndrome (RDS). Seven of the patients received a single dose of porcine surfactant (Curosurf) as rescue treatment. Nine premature babies without lung disease or any other complicating disease served as controls. There were no differences in prekallikrein values between surfactant treated and non-treated RDS babies during the first 4 d postpartum. The controls had, however, significantly higher prekallikrein values than the RDS babies already at the first day of age (mean +/- SD 32 +/- 8% in controls versus 22 +/- 6 and 21.5 +/- 5% in the treated and nontreated RDS groups, respectively). Plasma kallikrein activities did not differ between RDS and control patients. Plasma kallikrein inhibition values, which increased steadily in all groups, were lower in the RDS babies treated with surfactant than in controls at d 2 and 4. The degree of degradation of plasma high molecular weight kininogen was measured in RDS patients treated with surfactant and was significantly higher when compared with controls at d 1, demonstrating an increased proteolysis of kininogen to kinin early in RDS. There were no differences in plasminogen and plasmin values between RDS and control babies. This study shows that the plasma kallikrein-kinin system is activated in RDS. This system as well as the fibrinolytic system does not seem to be influenced by rescue instillation of a single dose of porcine surfactant into the lungs of premature babies with RDS.