O2 extraction ratio (ER) and cytokine production during cardiopulmonary bypass (CPB)

Introduction. During CPB, blood contact whit foreign surfaces activates biohumoral cascade, leading to systemic inflammatory response (SIRS), and the VO2-DO2 dependency becomes pathologic when ER>0.4. Patients with high post-operative VO2 after elective cardiac surgery have higher circulating levels of endotoxin, TNF, IL6 and a more severe post-perfusion syndrome. This study investigates whether a pathologic DO2-VO2 dependency may occur during CPB, despite of adequate perfusion and usual hemodilution, Methods: 60 patients undergoing hypothermie (30°C) CPB for selective coronary artery bypass grafting were studied. 2 L of Ringer's lactate solution primed the circuit, keeping Ht=24,8±3% without hemotransfusion, pump flow rates of 2.2 to 2.4 L/min/m2 BSA were maintained, cold blood anterograde/retrograde cardioplegia was used. Arterial and venous blood gases, Ht, DO2, VO2, ER (i.e. VO2/DO2=Da-vO2/CaO2) were measured/calculated every 30 min during CPB. In 11 patients, venous blood was sampled after 30 and 60 min of CPB, at the end and 24 h after CPB. Using phytohemoagglutinin (PHA) as mitogen and peripheral blood mononuclear cells (PBMC) isolated from blood samples, cytokine (TNFα, IL6,IL 8) production was measured: Results. 256 measurements were performed. A ER[removed]0.4 (G-II) in 73 (28.5%), despite no significant differences among Ht values. In G-I, VO2=0.29 DO2+1.35 (r=0.59, p<0.001), in G-II; VO2=0.45 DO2+5.58 (r= 0.71, p[removed]0.4, i.e. a pathological DO2-VO2 dependency seems more frequent when tissue energy demand is higher. The correlation between VO2I and DO2I is higher if ER[removed]0.4. Citokine production during CPB (TNFα=720±166 pg/ml, IL6=6.06±1.7 ng/ml, IL8=35.8±2.8 ng/ml) is not correlated with energy request and mediator activation. DO2-VO2 dependency occurs more frequently when VO2 is high, and with ER is a method to assess and manage metabolic impairment.