SUCTION-INDUCED HEMOLYSIS AT VARIOUS VACUUM PRESSURES - IMPLICATIONS FOR INTRAOPERATIVE BLOOD SALVAGE

Background: Suction vacuum pressure (VP) not exceeding 150 torr is rec ommended during intraoperative blood salvage to minimize hemolysis. Wh en the suction provided by this VP becomes inadequate because of brisk bleeding, an alternative high-VP suction should be used and the blood discarded. This approach often results in the salvage of only a small fraction of the blood shed during surgery complicated by large hemorr hage. Study Design and Methods: This laboratory study was designed to quantitate the hemolysis caused by various VPs in a suction system com monly used for intraoperative blood salvage. For each experiment, a ba tch of blood with a hematocrit of 30 to 35 percent was prepared by mix ing of outdated units of red cells, fresh-frozen plasma, and saline so lution. Aliquots of this blood were suctioned at VPs of 150, 200, 250, and 300 torr, either without (6 experiments) or with (4 experiments) maximal air entrainment. Total hemoglobin, hematocrit, red cell count, plasma-free hemoglobin, and serum potassium were measured in the bloo d before suction and in each aliquot after suction. Results: Suction o f blood mixed with air caused much greater hemolysis than suction of b lood alone (p < 0.01 at each VP tested). Raising the VP from 150 to 30 0 torr increased hemolysis from 0.14 +/- 0.20 percent (mean +/- SD) to 0.32 +/- 0.21 percent (p < 0.05) when blood alone was aspirated and f rom 1.45 +/- 0.50 percent to 2.85 +/- 0.22 percent (p < 0.05) when blo od was suctioned with air. With either type of suction, red cell count , hematocrit, and serum potassium did not change significantly through out the range of VPs tested. Conclusion: Hemolysis was found to depend on the VP applied and, to a much greater extent, on the amount of blo od and air mixing. Increasing the VP above the recommended limit of 15 0 torr was not associated with inordinate hemolysis. Even when a VP as high as 300 torr was used, hemolysis ranged between 0.3 and 3.0 perce nt, depending on whether air was suctioned with the blood or not. The data support the idea that the lowest VP compatible with a clear surgi cal field should be used during intraoperative blood salvage and that the suctioning of air should be avoided as much as possible. These dat a also suggest that, in contrast to current recommendations, suction V P during intraoperative blood salvage can be increased up to 300 torr if required by the rate of bleeding, without causing excessive hemolys is.