This was a retrospective observational study. Ethics approval was obtained from the institution medical research ethics committee (MREC ID No.: 202057–8602), and waiver of informed consent was granted due to the retrospective study design. AIS patients who underwent an elective single-staged PSF surgery under general anaesthesia at a tertiary university hospital over a period of 18 months (2018 until 2019) were identified retrospectively. Patients who received a single bolus of 30 mg/kg TXA (Group A) and a bolus of 30 mg/kg followed by continuous infusion of 10 mg/kg/h of TXA (Group B) until the end of surgery were included in the analysis. Decision on TXA dosing regimen was at the discretion of the treating anaesthesiologist, and doses other than the two described above were excluded. Patients aged between 10 and 21 years diagnosed with idiopathic scoliosis, with American Society of Anaesthesiologists (ASA) physical status I–II, preoperative haemoglobin > 10 g/dL, platelet count > 150,000 µ/L, and normal coagulation profile were eligible for inclusion.

Exclusion criteria were patients with severe haematological disorder, severe cardiac disease, or severe restrictive pulmonary disease, received anticoagulants and antiplatelet within 14 days prior to operation, and those who had preoperative serum creatinine > 200 µmol/L or serum aspartate aminotransferase > 100 IU/L.

In addition, only patients who adhered to the anaesthetic and surgical protocol were included together with complete information on estimated total surgical blood loss, pre- and postoperative haemoglobin levels, international normalised ratio (INR), activated partial thromboplastin time (aPTT), and fibrinogen values.

The patients received either total intravenous anaesthesia with target-controlled infusion (TCI) of propofol and remifentanil targeting a bispectral index of 40–60 or volatile anaesthetic desflurane with TCI remifentanil aiming a minimum alveolar concentration of 0.6 to 0.8. Intravenous TXA was administered either as a single bolus of 30 mg/kg at induction or as a bolus followed by continuous infusion of 10 mg/kg/h until the end of surgery. Patient monitoring includes invasive blood pressure, heart rate, oxygen saturation, and electrocardiogram. The lower limit of mean arterial pressure (MAP) during exposure was 60 mmHg, whilst during and after correction, the MAP was maintained above 75 mmHg. Cell salvage was used in all patients in which the harvested blood was reinfused when blood loss exceeded 20% of total blood volume or at the end of surgery. The transfusion trigger for allogenic blood transfusion was when haemoglobin level dropped below 8 g/dL.

All the surgeries were performed by the two senior surgeons (K. M. K., C. Y. W. C.) utilizing a dual attending surgeon strategy. Alternate-level pedicle screw instrumentation was performed for all patients. At the proximal and distal foundation levels, three to four pedicle screws were inserted. Posterior releases consisted of facetectomies with excision of the inferior articular processes. No posterior column osteotomies were performed. Fusion was augmented using local autogenous bone graft. All patients had subfascial drains inserted prior to closure which was initially clamped during the immediate postoperative period. On postoperative day 1, the drain was subsequently released to drain up to a maximum of 200 mL. The drain was then removed, and no further drainage was performed.

Data of baseline characteristics including age, sex, height, weight, and body blood volume, as well as baseline operative details such as number of vertebral levels fused, Cobb’s angle, number of screws, duration of surgery, and skin incision length, were collected. Data on estimated total intraoperative and postoperative (from surgical drain) blood loss, blood volume harvested from cell salvage system, and number of allogenic packed cell transfusion were retrieved along with laboratory data (haemoglobin, INR, aPTT, fibrinogen levels) at following time points: T1, pre-operation; T2, post-operation 0 h; and T3, post-operation 48 h. Data on complication rates (seizure, thrombotic event) were gathered.

This was a retrospective exploratory analysis. Hence, a priori sample size calculation was not performed. All patients who fulfilled the eligibility criteria between December 2018 and September 2019 were included in the analysis.

Baseline characteristics, operative data, intraoperative blood loss, and laboratory values were compared between Groups A and B. For categorical variables, chi-square test was performed. For continuous variables, independent Student t-test was used for normally distributed data, whilst Mann–Whitney U-test was used for non-normally distributed data. All statistical analyses were performed using SPSS version 22 (IBM Corporation, NY, USA). A two-sided p < 0.05 was considered statistically significant. Multiplicity adjustment was not performed due to the exploratory nature of this study.