Troubleshooting the rat model of cardiopulmonary bypass: effects of avoiding blood transfusion on long-term survival, inflammation and organ damage

Abstract

Introduction: Rat models of cardiopulmonary bypass (CPB) have been used to examine the mechanisms of associated organ damage and to test intervention strategies. However, these models only partly mimic the clinical situation, because of the use of blood transfusion and arterial inflow via the tail artery. Thus a model using arterial inflow in the aorta and a miniaturized CPB circuit without need of transfusion was validated by examining intra-procedure characteristics, mortality and the effects of CPB on biomarkers of inflammation and cerebral injury during 5days follow-up.

Methods: Male Wistar rats (n=95) were anesthetized with isoflurane (2.5%) and fentanyl/midazolam during CPB. Animals were assigned to Control (n=6), Sham (n=40) or normothermic CPB (n=49) groups. Both Sham and CPB were cannulated in the aorta via the left carotid artery and in the right common jugular vein for access into the right heart. Extracorporeal circulation (ECC) was instituted for 60min only in CPB at a flow rate of 120mLkg(-1)min(-1) employing a CPB circuit of 15ml primed with 6% hydroxyethyl starch 60mgml(-1) solution. Rats were sacrificed at either 1h or 1, 2 or 5days after Sham or weaning from CPB. Plasma IL-6 and s100Beta levels were measured and blood cell counts were performed.

Results: Mortality in CPB animals (3 out of 49) and Sham (4 out of 40) did not differ (chi-square=0.46, dF=1, P>0.5). Compared to baseline (1.87±0.46∗10^9cells/L), Sham procedure (cannulation and anesthesia) significantly increased blood neutrophil count at the end of the period matching ECC (6.34±2.36∗10^9cells/L, P<0.05). CPB induced neutrophilia which persisted during 24h recovery. Also, CPB caused a rapid and prominent increase in plasma IL-6 from the first hour of the postoperative period (~1200pg/ml) with continuation (50-90pg/ml) up to 5th day of recovery. S100Beta levels were above detection level only in 3 out of 42 samples from CPB animals.

Discussion: Our rat model of CPB without homologous blood transfusion produces a reproducible and reliable systemic inflammatory response, with low mortality rates on long term follow up. The model more closely mimics the human situation in respect to arterial inflow site and avoidance of blood transfusion. Thus, our CPB model is suitable to study its influence on systemic inflammation, ischemia-reperfusion injury, microcirculation and vascular dysfunction in vivo, and to evaluate potential therapeutic interventions.