It is well known that when considering perioperative transfusion strategies, patients' anemia degree, coagulation function, age, cardiopulmonary compensatory function, basal metabolic rate, and other factors are all factors to be considered[1, 4, 18, 19]. However, blood loss is clearly one of the most important factors when developing transfusion strategies. Despite the growing interest and recognition of HBL as an important parameter in perioperative blood loss, it is still underestimated by most orthopaedic surgeons. It was previously reported that mean HBL was 337 ml, which was 46.8% of TBL following posterior cervical open-door laminoplasty (EOLP). Carreon, L. Y. et al. had reported that HBL for patients underwent two or three-level posterior lumbar decompression and fusion ranging from 678-1267ml and averaged 42.3% of estimated blood loss. Unexpectedly, our result demonstrated that a substantial amount of HBL (469.5 ± 195.3ml, 57.6 % of TBL) frequently occurred following UBE surgery, which was quite larger than expected. It is however unclear what the risk factors are in UBE surgery. In this work, we retrospectively analyzed clinical information from 134 patients who underwent UBE surgery to screen and identify risk factors of HBL by multiple linear regression.
Previous literature findings have shown advanced age to be a risk factor in posterior lumbar fusion, which was similar to the results of our study[23, 24]. One possible explanation was that the elderly had poor compensatory capacity of the cardiovascular system and insufficient self-regulation because of vascular sclerosis. Another possible reason is that bleeding is more likely to infiltrate into the tissue spaces in the elderly due to muscle wastage and hypercoagulable state.
A previous study has suggested that ASA classification was an independent risk factor of HBL in anterior cervical fusion surgery[25, 26]. Meanwhile, author suggested that patients with ASA III have a much greater HBL than those in ASA I and II. Therefore, some noted that higher ASA classification facilitated the identification of high-risk people who require blood transfusion in spine fusion surgery. Our study also arrived at similar conclusions. In the UBE surgery, the higher the ASA classification, the greater HBL in the patient[14, 27]. In contrast to patients with ASA I, those with ASA II to IV generally have poor general condition and more comorbid underlying disease. Especially, the poor tolerance of surgery and anesthesia in some patients leads to a poorer coagulation system function than in lower grade patients, resulting in more HBL.
The results of the multiple linear regression analysis indicated that PBV was one of the independent risk factors for HBL. It is noteworthy that PBV was calculated following the formula of Nadler et al. BMI was one of the parameters in the calculation of PBV, however, in our investigation, BMI was not identified as a risk factor. Further validation is needed with a large sample study. Another notable finding was that TBL was also identified as an independent risk factor of HBL. This might be because of the fact that the TBL was calculated by changes of Hct according to the Gross formula. In the present study, patients with high total blood loss also had high occult blood loss, which was similar to previous studies. Another notable finding was that postoperative Hct and Hct loss were identified as independent factors rather than postoperative Hb and Hb loss. Despite these findings, significant difference in Hct and Hb levels were observed between the pre- and postoperative group using the Student’s t test. According to published reports, perioperative hemodilution and fluid overload might be the important explanations for more Hct change[5, 30]. Therefore, this could possibly account for different significances between Hct- and Hb-related indexes in multiple linear regression analysis.
In this work, we found that patients' fibrinogen levels were negatively correlated with HBL. Fibrinogen is an inflammatory protein that gets converted to fibrin in the presence of thrombin and directly influences the platelet adhesion and activation[31, 32]. Zhou et at. have reported a retrospective clinical study of HBL-related risk factors in a sample size of 137 patients undergoing MIS-TLIF surgery, in which fibrinogen levels were negatively associated with HBL, which is similar to our findings.
Zhou et al. reported a retrospective clinical study of HBL-related risk factors in a sample size of 137 patients undergoing MIS-TLIF surgery, in which fibrinogen levels were negatively associated with HBL, which is similar to our findings. However, some studies draw an inconsistent conclusion. Another study demonstrated that fibrinogen level was a positive influential factor. Explanations might be as follows. In general, patients with higher fibrinogen levels are in a hypercoagulable state. According to their report, the patient underwent posterior lumbar fusion (PLF) after placement of drainage tube and the drainage volume was recorded. We know that the postoperative drainage volume should be subtracted when calculating HBL, so the drainage volume became the key to the problem. In their study patients with high fibrinogen levels were in a hypercoagulable state and bleeding could clot in the lacunes or dead space, a decrease in postoperative drainage was observed, resulting in HBL that was exaggerated. In contrast, no drains were placed in our investigation. Therefore, all postoperative hemorrhage was considered as HBL. It has already been mentioned that patients with higher fibrinogen levels are prone to thrombus formation and stop bleeding. This is not difficult to conclude that fibrinogen levels are a positive influence factor in HBL.
Our study demonstrated that operative time and number of fusion levels were independent risk factors for perioperative HBL in UBE surgery. Several prior studies have also suggested that number of fusion levels is a predictor of blood transfusion in spinal surgery[33, 34].
In addition to that, we suggest that surgery involving multiple fusion levels enlarges the manipulation space and that implantation of more instruments facilitates movement of more red blood cells into the tissue space. When more levels are fused, the bleeding of the vertebral cancellous bone surface significantly increases. Anatomically, the management of hemorrhage in the lumbar spine with rich blood supply, especially the spinal venous plexus, is tricky[11, 35, 36]. And UBE surgery relies on continuous, large amounts of saline irrigation with certain pressure, resulting in more difficulty in adequate hemostasis intraoperatively[11, 37].
Overall, in order to reduce HBL during the perioperative period of UBE surgery, we believe that blood routine examination before and after operation is necessary, which is able to clarify whether the patient has anemia or a tendency toward anemia. At the same time, the surgical team should also focus on patient age, ASA classification, PBV, TBL, and fibrinogen level to carefully assess whether a patient is at increased risk of postoperative bleeding. Given that UBE surgery is currently less practiced in China, further refinement of surgical technique, adequate intraoperative hemostasis, and shorter operation time are necessary in the future.
There are some limitations to the present study that should be addressed. Although this was a multicenter study, the study was the relatively small number of patients, and the fact that the analysis was performed retrospectively and not in a blinded fashion. Beyond that, according to prior studies, we found no consistent opinion on when to remove the drainage tube. Based on our clinical experience, we removed the drainage tube when the drainage volume was < 50 mL in 24 hours. The timing of drain removal may influence the outcome of HBL, which warrants further investigation. Finally, most patients were from local sites only, so the findings need to be subjected to further validation, especially relevant studies from different regions and countries.