Studies on HBL after orthopedic surgery have mostly focused on total hip arthroplasty (THA), total knee arthroplasty (TKA), and ALIF/PLIF surgery 18. In a work on anterior/posterior lumbar fusion surgery (ALIF/PLIF), HBL was approximately 40% of TBL 12,18. Chen et al. 19 reviewed and analyzed of the patients undergoing conventional posterior open approach, the average HBL was 382 ± 153.8mL; and the average HBL of patients undergoing percutaneous approach was 240.0 ± 65.1mL. In our study, a substantial amount of HBL (164.00 ± 112.02ml, 40.65% of TBL) occurred after MIPTSF., the obtained amount was much greater than that of visible intraoperative blood loss. Some studies suggest that for patients undergoing total hip replacement, HBL is positively correlated with changes in BMI, blood transfusion, incision length, preoperative and postoperative HCT, and negatively correlated with age 20. Nevertheless, there have been no previous studies regarding the influential factors correlated to the HBL during the MIPTSF of AO type A1-A3 thoracolumbar fractures. In this study, we investigated and identified the risk factors of HBL following this surgery by multivariate linear regression analysis. The results proposed that the TBL, percentage of vertebral height loss, percentage of vertebral height restoration, numbers of fractured vertebrae, and numbers of fixed vertebral segments were positive independent risk factors for HBL.
Our statistical analysis showed that the patients who had massive TBL suffered from more HBL than those who have little TBL. TBL was the independent risk factor, which may have to do with PBV, because TBL is calculated by multiplying PBV by changes of HCT and subtracting the IBL according to the Gross formula 15,which might relate to the patient’s weight and height. However, BMI had not been identified as a risk factor in our study, although body mass index was also calculated by weight and height. Based on collected data in our study, it was easy to find that HBL is directly related to a large amount of blood loss.
HBL during orthopedic surgery is generally accepted as being due to blood infiltration into tissue compartments and loss due to hemolysis 21,22. Our study found that the percentage of vertebral height loss and the percentage of vertebral height restoration were correlated with HBL. Vertebra involves cancellous bone, and its blood supply is abundant. The expansion of vertebral cavity will cause internal bleeding. The recovery of fractured vertebral body height may lead to enlarged cavity, and the space around vertebral body may be enlarged. We suspect that the blood would seep into these fracture spaces, leading to an increase in HBL 23. Vertebral cavity and muscle space also provide storage cavity for HBL.
In our study, the numbers of fractured vertebrae and numbers of fixed vertebral segments were positively related to HBL, as Chen et al. guessed 19. A previous study proposed that he number of fractured vertebrae was the risk factor of HBL in percutaneous kyphoplasty surgery 24. Ju et al. held that ALIF was associated with substantial perioperative HBL, and the inclusion of L4/5 in the procedure were significant risk factors for increased blood loss 18. However, we found that the number of fixed segments was an independent risk factor for hidden blood loss, and the fracture level was not included in our data. We will further explore the relationship between fracture level and hidden blood loss in the future.
Our previous studies had shown that muscle thickness is also an independent risk factor for hidden blood loss in spinal surgery 25, thicker muscle may be associated with larger penetrable tissue compartments, allowing blood to ooze into the tissue cavity 26. Jiang et al. 27 found that posterior cervical soft tissue was positively correlated with both TBL and HBL in the expansive open-door laminoplasty (EOLP). But the muscle thickness or subcutaneous fat thickness was not clarified as a risk factor in this study. We think that this might be related to the less muscle damage caused by minimally invasive surgery. Therefore, we still need to further study the relationship between muscle thickness and HBL in the setting of spine surgery.
Excessive blood loss can increase the possibility of blood transfusion, which is associated with transfusion reactions, anaphylactic reaction, infections and delayed recovery 28. Furthermore, excessive blood loss can prolong the hospitalization time and increase the use of medication 29. The TBL, percentage of vertebral height loss, percentage of vertebral height restoration, numbers of fractured vertebrae, and numbers of fixed vertebral segments should be correctly understood before operation to ensure the safety of patient treatment.