The medical records of 153 patients with ASD who underwent correction surgery at Seirei Sakura Citizen Hospita between January 2012 and October 2021 were reviewed retrospectively. The study included patients who underwent thoracolumbosacral fusion at ≥4 levels [6] and excluded two patients who underwent this procedure at <4 levels. Ultimately, 151 cases were included.

The institutional review board of Seirei Sakura Citizen Hospital approved the study protocol, including the review of patient records (no., 2020007). The study was performed in accordance with the ethical standards of the 1964 Declaration of Helsinki and its later amendments. All patients provided informed consent for their data to be included in studies submitted for publication.

Autologous blood was collected between 35 and 6 days preoperatively. Specifically, 400 mL of autologous blood was collected weekly, and 400–1,600 mL of autologous blood was collected as requested by the surgeon. However, autologous donation was avoided in patients with anemia (hemoglobin [Hb] <10 g/dL) or suspected bacteremia.

Deformity correction was performed in all patients using transforaminal lumbar interbody fusion, lateral lumbar interbody fusion (LLIF), or grade 1–5 osteotomy with cancellous allografts and autografts [9–12]. Then, the conventional open approach in posterior surgery was routinely selected for the release of facet joints and bone grafts. The number of fusion levels and correction techniques are determined at the discretion of the attending surgeons. Two-staged surgery is selected in cases requiring anter-posterior combined surgery or grade ≥3 osteotomies [13]. Tranexamic acid (TXA) is routinely administered intraoperatively (loading dose of 1,000 mg, followed by continuous infusion of 10 mg/kg/hr) [14–18], and surgeries are simultaneously performed by two attending surgeons in posterior surgery since May 2017 [1,19,20]. Bleeding episodes were controlled using conventional methods, such as cautery, manual compression, or suturing; microporous polysaccharide hemospheres, including Arista (Bard Davol Inc., Warwick, UK); and oxidized cellulose, such as Surgicel (Ethicon Inc., Raritan, NJ, USA). When these agents cannot control the bleeding, gelatin-thrombin-based hemostatic agents, such as Floseal (Baxter Healthcare Corp., Deerfield, IL, USA) or Surgiflo (Ethicon Inc.), have been used since October 2014. The cell-saver system is used in posterior surgery, and all surgeries were performed by the same team of four experienced spine surgeons.

All patients underwent general anesthesia by a single anesthesiologist and received forced-air warming blankets (Bair Hugger System; 3M, St. Paul, MN, USA). Controlled hypotension was maintained by the intravenous administration of nicardipine with a target decrease in mean blood pressure of 90±10 mm Hg. The cell-saver system was used in all cases, and the need for intraoperative transfusion was determined according to the surgical criterion of Hb level <8 g/dL. Preoperative autologous or cell-saver blood was selected first. Subsequently, allogeneic RBCs, platelets, or fresh-frozen plasma was transfused.

All patients received similar postoperative management. A drainage tube was used at the surgical site postoperatively, which was removed 2 days postoperatively. Postoperative transfusion was performed when the Hb level was <7 g/dL. Patients were occasionally transfused when their Hb level was 7–8 g/dL, and bleeding continued from the drainage tube with or without mean arterial pressure of <90 mm Hg and/or urine output <0.5 mL/kg/hr.

Baseline data, including age at surgery, sex, blood type, body mass index (defined as weight/height squared [kg/m²]), American Society of Anesthesiologists’ (ASA) physical status [21], and preoperative Hb level (g/dL) immediately before surgery at admission, were retrospectively investigated. The preoperative use of anticoagulants or antiplatelets and nonsteroidal anti-inflammatory drugs (NSAIDs), number of patients who received allogeneic RBC transfusion, and amount of autologous blood donation were also investigated. Surgical factors, such as instrumented fusion levels, total operative duration, and need for grade ≥3 osteotomies, LLIF, and pelvic fixation were collected. Hypothermia was defined as a decrease in the core temperature <36°C at least once during surgery [22]. The use of TXA and simultaneous exposure and gelatin-thrombin-based hemostatic agents was also investigated. Preoperative and postoperative (1 week postoperatively) global spine alignment parameters, including the sagittal vertical axis (SVA), pelvic incidence (PI), thoracic kyphosis, lumbar lordosis (LL), and PI–LL, were assessed on lateral whole-spine radiographs [23]. Intraoperative and postoperative estimated blood losses (EBLs) from the drainage tube at the surgical site from immediately to 2 days postoperatively were investigated. The % estimated blood volume (%EBV) was calculated using the following formula: EBL/weight (mL/kg). Perioperative (intraoperatively to 2 days operatively) use and amount of allogeneic RBC transfusion were investigated.

Continuous and categorical variables were analyzed using Student t-test and Fisher’s exact test, respectively. Patients were categorized into the transfusion and non-transfusion groups according to the use of allogeneic RBC transfusion. Baseline characteristics, surgical factors, and global spine alignment parameters were compared between the two groups. Spearman’s rank-order correlation was conducted to assess collinearity. Factors with a correlation coefficient of ≥0.5 were excluded in the multivariate analysis. A stepwise multivariate logistic regression analysis was conducted to identify predictors of the need for allogeneic RBC transfusion. Odds ratios (ORs) are reported with 95% confidence intervals (CIs). A p-value <0.05 was considered significant in the tests of statistical inference. Furthermore, a post hoc power analysis was reported, and all analyses were performed using IBM SPSS Statistics for Windows ver. 25.0 (IBM Corp., Armonk, NY, USA).

Intraoperative and postoperative EBLs were 994.2±754.5 mL (range, 25–3,810 mL) and 801.3±491.6 mL (range, 0–2,610 mL), respectively. Seventy-one patients (47.0%) received perioperative allogeneic RBC transfusions. The mean amount of allogeneic RBC transfused in these patients was 1,763.4±1,042.7 mL. Age was significantly higher (p=0.024), the number of patients and units of preoperative autologous blood transfused were significantly lower (p<0.001), and preoperative Hb level was significantly lower (p=0.025) in the transfusion group than in the non-transfusion group (Table 1).

The preoperative PI–LL was significantly higher (p=0.021) and grade ≥3 osteotomies (p<0.001) was significantly more common in the transfusion group than in the non-transfusion group (Table 2). Conversely, the use of TXA and simultaneous exposure were significantly less common (p<0.001), total operative duration was significantly longer (p<0.001), and intraoperative and postoperative EBLs (p<0.001) were significantly greater in the transfusion group than in the non-transfusion group (Table 3).

Spearman’s rank-order correlation revealed collinearity factors, including LLIF and grade ≥3 osteotomies (r=0.53, p<0.001). EBL demonstrated collinearity with fusion levels, use of TXA and simultaneous exposure, and surgical time (r=0.41, −0.51, and 0.55; p<0.001). The ASA physical status showed collinearity with the preoperative use of anticoagulants or antiplatelets (r=0.46, p<0.001). PI–LL also correlated with other global spine parameters, including the SVA, PI, and LL (r=0.72, 0.61, and 0.84; p<0.001). Therefore, LLIF, EBL, preoperative use of anticoagulants or antiplatelets, SVA, PI, and LL were excluded from the multivariate analysis. In the stepwise multivariate logistic regression analyses with 16 potential predictors (age, sex, body mass index, ASA physical status, blood type, hypothermia, preoperative autologous blood donation, preoperative Hb, preoperative use of NSAIDs, preoperative PI–LL, grade ≥3 osteotomies, pelvic fixation, fusion levels, TXA and simultaneous exposure use, gelatin-thrombin-based hemostatic agent use, and total operative duration), the absence of TXA and simultaneous exposure use (OR, 26.3; 95% CI, 7.6–90.9; p<0.001), absence of autologous blood donation (OR, 21.2; 95% CI, 4.4–100.0; p<0.001), and longer operative duration (OR, 1.6; 95% CI, 1.3–1.9; p<0.001) were independent risk factors for allogeneic RBC transfusion (Table 4).

A post hoc power analysis showed that this study had the power to detect differences (autologous donated blood, 0.998; use of TXA and simultaneous exposure, 1; and total operative duration, 1). In the periodical comparison of intraoperative EBLs and number of patients with allogeneic RBC transfusion, the intraoperative EBL ranged from 741 to 1,472 mL. The proportion of patients receiving allogeneic RBC transfusion ranged from 39% to 79% before the use of TXA and simultaneous exposure from 2012 to 2017; however, the intraoperative EBL ranged from 475 to 866 mL. Conversely, the proportion of patients with allogeneic RBC transfusion ranged from 9% to 17% after TXA and simultaneous exposure between 2018 and 2021 (Fig. 1).

Four and two patients in the transfusion and non-transfusion groups experienced wound infections, respectively (p=0.707). Cardiovascular events including deep venous thrombosis (n=2), pulmonary embolism (n=1), stroke (n=1), and ischemic colitis (n=1) occurred in five patients in the RBC transfusion group, and pulmonary embolism (n=1) and acute celiac artery compression syndrome (n=1) developed in two patients in the non-transfusion group [24] (p=0.254). The incidence of wound infection and cardiovascular events was not different between the RBC transfusion and non-transfusion groups.