Although techniques for the perioperative management of patients under open heart surgery with extracorporeal circulation have been established in human, the use of the heart-lung machine to correct heart disease has not been accepted in the veterinary practice, especially in dogs. The most common congenital heart defects in dogs are aortic stenosis (35%), pulmonic stenosis (20%), ventricular septal defect (12%), patent ductus arteriosus (11%), mitral valve dysplasia (8%), tricuspid valve dysplasia (7%) and tetralogy of Fallot (0,6%). However, for most cardiac operations the use of a heart lung machine (HLM) is necessary. The deleterious effects after CPB are haemolysis, low cardiac output, renal failure, cerebral dysfunction, post-perfusion respiratory insufficience. Since the highest sensitivity to HLM-induced insults is found in the brain, we focused on cerebral alterations to optimize HLM for the use in small animals.
Materials and methods
Piglets (n=54, 7-10kg, 3-4 weeks old) were submitted to extracorporeal circulation (ECC) at 25, 50 or 100% of the standard flow rate for 60 min of cardioplegic cardiac arrest. Body temperature was kept at either 18, 25 and 38°C. Routine hemodynamic and functional parameters were measured online until 4 hours of reperfusion. Immunohistology was used to qualify heat shock protein HSP70 level in hippocampus; HPLC was used to quantify jugular venous blood malondialdehyde (MDA) levels as ischemic markers.
Reduced ECC flow led to significant reduction of mean arterial pressure by 79%, reduction of jugular venous saturation by 47%, reduction of carotid blood blow by 92%, Tissue oxygenation index was reduced by 25% while serum lactate was increased by 350%. All these changes were significantly enhanced in the 38°C versus 25°C or 18°C groups. There was a significant increase in HSP70 and MDA in the 25 and 50% flow groups.
It is possible to use ECC in pigs. A reduction in global blood flow during ECC leads to significant biochemical changes in the hippocampus. The lowest cerebral impairment was achieved at 18-25°C with not more than 50% blood flow reduction.