PURPOSE: This study is divided into 2 parts, an experimental study to establish a technique of extracorporeal circulation with low oxygen partial pressure and a clinical study to show the feasibility in humans. MATERIAL AND METHODS: Experimental surgery with extracorporeal circulation was performed in 20 dogs divided into 2 groups of ten. In group I, cannulation was done first in the superior vena cava, then in the inferior vena cava, keeping normal heartbeat and breathing, controlled by a respirator and pure oxygen. After passing through a heat exchanger, the blood of each vena cava was injected in the femoral artery. Blood samples from the aorta were taken above the diaphragm in every 30 minutes to check gasometric values. In group II, the right atrium was drained and half of the blood injected in the pulmonary artery with another pump and picked up through the left ventricle to the reservoir that also works as a heat exchanger. The mixed blood (50% arterial and 50% venous) was re-injected by another pump in the arterial circulation. The heart was maintained fibrillating and the breathing controlled by the respirator. In the clinical study, 40 patients were divided into 2 groups of 20 each. In group A the patients were bypassed in the conventional manner, that is, compressed air and oxygen in the oxigenator with high arterial pO2. In group B, pure oxygen was used in the membrane oxigenator and venous-arterial shunt, performed between 40% to 50%. RESULTS: In both groups, from a physiologic point of view there was shunting of 50% of venous blood to the arterial circulation and arterial blood flow was maintained high (around 100 ml\kg\min). It was observed that the arterial pO2 in both groups remained between 50 and 100 mmHg and venous saturation between 50 and 70%. All animals woke up at end of the experiment. In the clinical study, the arterial pO2 was a low 60 mmHg. Comparison of the clinical results showed there was no mortality difference between both groups, but in the group B, with the low pO2 and venous-arterial shunt, the post-operative bleeding was significantly smaller, having been used three times less blood and no need to use the blender.
Extracorporeal circulation; Blood pressure; Oxygen; Venae cavae; Pulmonary artery; Oxygenators, membrane
