Proteolytic enzyme levels during cardiopulmonary bypass

Pulmonary damage resembling "shock lung" is frequently seen following cardiopulmonary bypass. In many of these cases a rise in the plasma level of proteolytic enzymes has been observed. In order to establish whether changes in plasma proteinase activity occur as a result of cardiopulmonary bypass per se, or whether hemodilution and surgical tissue destruction may be responsible, three groups of animals were studied. Control dogs were anesthetized, heparinized, and transfused rapidly with Ringer's lactate to a hematocrit of less than 30%. In the second group hemodilution was combined with a sham thoracotomy. The third group was perfused for 90 minutes on total cardiopulmonary bypass at flow rates between 60 and 95 ml/kg/min using a roller pump and an infant bubble oxygenator. Serum beta-glucuronidase and acid phosphatase activity was measured by spectrophotometry immediately after anesthesia and at fixed time intervals during the experimental procedure, as well as on the second and third postoperative days. It was found that beta-glucuronidase increased 78.2 +/- 6.6% during extracorporeal circulation, while acid phosphatase rose 46.3 +/- 4.2%. Increases in enzyme activity were significantly greater in the perfused group when compared with the sham-operated and the control groups. The results suggest that the postperfusion lung syndrome may be attributable in part to proteinase release caused by blood/material interaction within the extracorporeal circuit.