Massive pulmonary infarction during total cardiopulmonary bypass in unanesthetized spontaneously breathing lambs

We provided total cardiopulmonary support for 1-18 hours in unanesthetized tethered lambs by peripheral vascular cannulation, using a roller pump and the spiral membrane lung. Respirations were allowed to remain spontaneous and unaided. A Swan-Ganz catheter was placed for retrograde pulmonary artery blood flow sampling. Within a few minutes following induced ventricular fibrillation the PCO2 of sampled blood flowing retrograde through the lungs fell below 10 mm Hg, the PO2 rose to near 150 mm Hg, the pH rose to above 7.8, and the glucose level fell to less than 20 mg %. All of these values later gradually shifted, approaching mixed venous blood values within minutes. After 1-18 hrs of perfusion the animals went into shock and were sacrificed. At autopsy, the lungs of animals breathing room air were beefy and hemorrhagic. In lambs that were "breathing" CO2 enriched air the retrograde pulmonary artery blood pH and PCO2 was usually maintained close to the mixed venous blood values. The observed pulmonary changes were considerably less abnormal, and the microscopic abnormalities were at times nonexistent. We believe the integrity of pulmonary blood flow is vital to the survival of the lungs as a functioning organ. Cessation of total forward pulmonary blood flow (unlike partial cardiopulmonary bypass), combined with spontaneous pulmonary ventilation, rapidly leads to massive, pulmonary infarctions, shock, and death.