Animal Models and Surgery

Fourteen beagles weighing 9.5 kg to 10.5 kg were prepared for experiments and were purchased from the Laboratory Animal Center of the South Medical University (Guangzhou, China). Propofol (2.0 mg/kg intravenous), pentobarbital (30.0 mg/kg intravenous), and morphine (0.1 mg/kg intravenous) were pre-medicated for inducing general anesthesia. Each animal was then orotracheally intubated in a supine position, with isoflurane (0.5% to 2.0%) inhaled and fentanyl (150 μg/kg, intravenous) administered to maintain anesthesia intra-operatively. A cervical incision was made, with the right internal jugular vein (RIJV) and right common carotid artery (RCCA) carefully dissected. An initial bolus (100 U/kg) of unfractionated heparin was used before cannulation. An activated clotting time (ACT) from 180 to 240 seconds was held and regularly supervised in each experimental circuit. The maintenance dose of heparin was 10 to 50 U/kg/hour. We smoothly cannulated the RCCA and RIJV with the 6-French (Fr) and 8-Fr cannulas (Medtronic Inc., Minneapolis, MN, USA), respectively. To achieve a cardiac output above 80 mL/kg/min, all venous-arterial (V-A) ECMO circuits were maintained with a pump flow rate ranging from 80 to 100 mL/kg/min and with a pump speed from 2500 to 3000 RPM during the experiment. After a-24-hour-observation, the circuit was weaned off and the cannulas were removed. The animals were then extubated with stable hemodynamics.