In-vitro evaluation of the hemolytic effects of augmented venous drainage

Augmentation of venous drainage with either kinetic-assisted drainage (KAVD) or vacuum-assisted (VAVD) has been used clinically in order to overcome added venous resistance due to smaller venous cannulae or tubing. This in-vitro study evaluates the extent of hemolysis and sub-lethal red blood cell membrane damage than occurs with augmented (kinetic or vacuum) when compared to conventional gravity drainage. Four trials were conducted using each test circuit. The circuits were primed with 6 liters of fresh heparinized bovine blood, which was diluted to a hematocrit of 32% and was recirculated at 5 L/min for 8 hours. Hemolysis was determined by the change in plasma free-hemoglobin (Hb), hematocrit, and potassium at two hour intervals. The red cell osmotic fragility index was used to quantify the sub-lethal red blood cell membrane damage and was also measured every two hours. After 8 hours, the mean +/- SD of the plasma free-Hb were: 96.27 +/- 69.45 mg/dl for gravity, 83.87 +/- 48.14 mg/dl for vacuum-assist, and 134.45 +/-83.78 mg/dl for kinetic-assist. Two-hour increases in the plasma free-Hb revealed the following median values (mg/dL/2 h): 16.90 for gravity, 13.75 for vacuum-assist, and 19.40 for kinetic-assist. Analysis of the two-hour increases in plasma free-Hb with Kruskal-Wallis One-Way ANOVA did not reveal a significant difference among the groups. After 8 hours, the red cell osmotic fragility test results at the 0.55% sodium chloride concentration were compared. The medians of the percent hemolysis were 52.67% for gravity, 49.8% for vacuum-assist, and 57.2% for kinetic-assist. Analysis with the Kruskal-Wallis Wallis One-Way ANOVA did not reveal a significant difference among the groups. Therefore, there is no significant increase in hemolysis or sub-lethal red blood cell membrane damage associated with the use of augmented venous drainage.