[The origin of non-emulsified fat during autotransfusions in elective hip surgery]

In addition to hemodilution and preoperative blood donations, mechanical intraoperative autotransfusion (MAT) is an important method of preventing or minimizing the transfusion of homologous blood in operations with major blood loss. Using cell separators allows most of the problems of MAT to be solved, but the processed red cell concentrates of patients having hip joint replacement contain fat. Due to the high risk of fat embolism during bone surgery, as well as other circulatory problems, it is of interest whether the infusion of up to 15 ml of fat does not expose patients to an even higher risk. This study aimed to research the pathogenesis of fat embolism and possibly support one of the existing theories. METHODS. Semiquantitative oil measurement: in 45 cases with first insertion of hip joint prosthesis and 16 cases with change of prosthesis MAT was used intra- and postoperatively. For comparison, 10 patients with aortic aneurysm repair were checked for fat as well. In these cases MAT was only used intraoperatively. After the red cell concentrate was processed there was a time lag of 10 min to allow better sedimentation of fat. At the end of retransfusion 50 ml of blood were saved. They were then separated into 10-ml plastic tubes, centrifuged, and fat content was measured using a mm-scale. The results were transformed to ml by means of a previously determined calibration. Analogous to hematocrit values, it was thus possible to establish a lipocrit for these patients. In another 16 cases of hip surgery we carried out cholesterol/triglyceride investigations in red cell concentrates, and in 5 cases analysis of the fatty acids by gas chromatography was performed. RESULTS. The lack of an emulsifier causes biochemical analysis of cholesterol-triglyceride levels to be impossible. Therefore, triglycerides and cholesterol in MAT blood were below normal levels although a high quantity of fat could be seen in the blood. No oil was found in any of the patients in the vascular surgical group. There were 61 patients in the orthopedic group; no oil was found in 34.4%, we found 1-2 ml in 16.4%, and in 49.2% there was more than 2 ml of oil. With regard to age, sex, weight, height, and deviation from Broca index no significant difference in lipocrit could be seen. Differences in lipocrit were observed depending on the type of operation (i.e. new insertion/change of hip prosthesis), these were not significant possibly due to the small number of patients undergoing a change of prosthesis. The more MAT blood was transfused, the more significant were the rises in lipocrit level. The rinsing solution itself (1000 ml NaCl 0.9% with heparin 30,000 IU) does not influence the oil concentrations. Gas chromatography revealed that there was more than 40% oleic acid and 20% palmitic acid. Combined with linoleic acid, this comprised 4/5 of the total amount of oil (Table 3)...