Suction-induced hemolysis at various vacuum pressures: implications for intraoperative blood salvage.

BACKGROUND: Suction vacuum pressure (VP) not exceeding 150 torr is recommended during intraoperative blood salvage to minimize hemolysis. When 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 hemorrhage. STUDY DESIGN AND METHODS: This laboratory study was designed to quantitate the hemolysis caused by various VPs in a suction system commonly used for intraoperative blood salvage. For each experiment, a batch of blood with a hematocrit of 30 to 35 percent was prepared by mixing of outdated units of red cells, fresh-frozen plasma, and saline solution. 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 blood before suction and in each aliquot after suction.
RESULTS: Suction of blood mixed with air caused much greater hemolysis than suction of blood alone (p < 0.01 at each VP tested). Raising the VP from 150 to 300 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 from 1.45 +/- 0.50 percent to 2.85 +/- 0.22 percent (p < 0.05) when blood was suctioned with air. With either type of suction, red cell count, hematocrit, and serum potassium did not change significantly throughout 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 blood and air mixing. Increasing the VP above the recommended limit of 150 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 percent, depending on whether air was suctioned with the blood or not. The data support the idea that the lowest VP compatible with a clear surgical field should be used during intraoperative blood salvage and that the suctioning of air should be avoided as much as possible. These data also suggest that, in contrast to current recommendations, suction VP during intraoperative blood salvage can be increased up to 300 torr if required by the rate of bleeding, without causing excessive hemolysis.