Multiple sequential insults cause post-pump syndrome

Background. We hypothesize that post-pump syndrome (PPS) following cardiopu lmonary bypass (CPB) can be caused by multiple minor insults and that the m echanism of PPS is a priming and subsequent activation of polymorphonuclear (PMN) leukocytes. In this study extensive pathophysiologic and morphometri c assessment was undertaken in a porcine model of sequential insult PPS. Methods. Pigs were anesthetized, placed on a ventilator, instrumented for m easurements of hemodynamic function, and separated into five groups: (1) Co ntrol (n = 4)-surgery only, (2) CPB (n = 4)-placed on femoral-femoral hypot hermic (28 degrees C) bypass for 1 h, (3) LPS (n 6)-underwent sham CPB foll owed by infusion of low dose endotoxin [E. coli lipopolysaccharide (LPS-1 m u g/kg)], (4) Heparin + protamine + LPS (HP + LPS, n = 4)-were heparinized without CPB for 1 h, following which protamine and LPS were infused and (5) CPB + LPS (n = 8)-subjected to both CPB and LPS. Results. Only CPB + LPS resulted in acute respiratory distress typical of P PS as indicated by a significant decrease in PaO2 and increase in intrapulm onary shunt fraction (p < 0.05). CPB + LPS significantly increased tissue d ensity and the number of sequestered monocytes and PMNs (p < 0.05) above al l other groups. Alveolar macrophages (AM) increased equally in all groups r eceiving LPS. Conclusions. CPB primes the inflammatory system causing pulmonary PMN seque stration without lung injury. Exposure to an otherwise benign dose of endot oxin results in activation of the sequestered PMNs causing PPS. This study confirms that PPS can be caused by multiple minor insults. (Ann Thorac Surg 1999;67:978-85) (C) 1999 by The Society of Thoracic Surgeons.