THE PATHOPHYSIOLOGY OF CARDIOPULMONARY BYPASS - THE RISKS AND BENEFITS OF HEMODILUTION

To summarize, the clinical studies evaluating pulmonary function after cardiopulmonary bypass are compromised by transfusion practices. Those studies in which there was a high postoperative colloid osmotic pressure in the crystalloid group showed no significant positive effect with colloid supplements when compared with the colloid supplemented group. In those studies that showed low colloid osmotic pressures in the crystalloid group, there was an increase in lung water and some negative changes in gas exchange when compared with the colloid prime group. Hemodilution has been shown to cause increased extracellular fluid in the heart, gastrointestinal tract, liver, and musculoskeletal systems resulting in increased total body water after surgery. There is no clearly documented morbidity related to interstitial edema of the internal organs, muscles, or subcutaneous tissues. One can only speculate if the postoperative ileus, effusions, and general fatigue following cardiopulmonary bypass might be in part related to interstitial edema related to hemodilution.