Corresponding author: Anastasia Ivanova, Tsivyan Novosibirsk Research Institute of Traumatology and Orthopedics, 17 Frunze St., Novosibirsk 630091, Russia; Email:
the end of spinal surgery does not mean cessation of the patient’s blood loss due to the impossibility of achieving complete hemostasis in the area of tissue damage. Various types of postoperative wound drains are used to remove the wound output. Although the drains are commonly used after spinal surgery, their effectiveness remains controversial.^{[1, 2]} The decision of whether to apply drainage and what type of placement and management of postoperative drains to use is often based on the surgeon’s preference rather than evidencebased medicine.^{[3–6]} The volume of postoperative blood loss can be equal to or even exceed that of the intraoperative blood loss.^{[7–10]} However, the question of what factors determine the volume of blood loss in the postoperative period remains open.
The predictors of massive postoperative blood loss during surgical correction of scoliosis in adolescents are believed to be the following: the body mass index, preoperative platelet count, the severity of spinal deformity, the number of fusion levels and screws placed, osteotomy surgeries, volume of intraoperative infusion of crystalloids and colloids, and transfusions of donor blood components.^{[8, 11, 12]}
Maintaining an adequate oxygen capacity of the blood is known to be the key to successful postoperative rehabilitation of a patient. In this regard, underestimation of the significance of drain loss can significantly affect the postoperative state of patients who underwent the surgery for idiopathic scoliosis (IS). Therefore, increasing the patient’s safety level is tightly associated with prediction, adequate assessment, and correction of both intraoperative and postoperative blood loss.^{[13–15]} Analyzing the available scientific sources on the topic, we did not come across a single publication proposing options for predicting the postoperative blood loss .
Taking into account different opinions about the effect of spinal osteotomies on drain loss, we proposed the following null hypothesis: spinal osteotomies have no significant effect on the postoperative blood loss.
The objective of the study was to find the significant predictors of postoperative blood loss in surgery for idiopathic scoliosis.
in this retrospective study, we analyzed the data for 140 adolescent IS patients who received surgical treatment for spinal deformities at Novosibirsk Research Institute of Traumatology and Orthopedics n.a. Y.L. Tsivyan in 2016–2017. The inclusion criteria were IS, age of 11–18 years, and first dorsal fusion with pedicle screw fixation (
The research was conducted in full compliance with the ethical laws (extract from the minutes of the Biomedical Ethics Committee No. 006/11 dated 25.03.2011 and No. 005/17 dated 03.03.2017).
All statistical analyses were performed using the RStudio software (version 1.3.959 – © 2009–2020 RStudio, Inc., USA,
Descriptive characteristics are presented as median [first quartile; third quartile] (MED [Q1; Q3]) for numerical data and as percentage for categorical data. To statistically test the hypotheses about the equality of numerical characteristics of sample distributions in the compared groups, the unpaired MannWhitney U test was used: the distribution bias was calculated by obtaining a 95% confidence interval for the bias. Twotailed Fisher’s exact test was used to compare categorical data.
Pairwise relationships between parameters were identified by calculating the Spearman’s correlation coefficient. The relationship between the parameters and postoperative blood loss was analyzed using univariate and multivariate linear regression models.
Statistical hypotheses were tested at a critical level of significance of
The main parameters in the groups are presented in
Distribution of main parameters between the groups



Age, years  15 [13; 16]  14 [13; 17]  0 [1; 1]  0.933 
Height, cm  161 [154.5; 167.5]  160 [155; 165]  0 [3; 4]  0.857 
Body weight, kg  50 [44; 56]  48 [44; 59]  2 [6; 2]  0.358 
Surgery duration, min  175 [152.5; 200]  155 [150; 185]  10 [0; 25]  0.058 
Number of 
7 [5; 12]  5 [4; 7]  2 [1; 3]  <0.001* 
Intraoperative blood loss, ml  550 [400; 670]  450 [350; 500]  100 [0; 150]  0.009* 
Intraoperative blood loss, % of 
15 [11; 21]  12 [10; 15]  3 [1; 5]  <0.001* 
* statistically significant difference.
As can be seen in
Sixtytwo percent of group 1 patients underwent twolevel osteotomy, 32% and 6% of patients had three and fourlevel osteotomy, respectively. The vast majority of patients were females: women were 86.4% and 78.4% in groups 1 and 2, respectively (
Analysis of postoperative drainage loss demonstrated that blood loss volume was the highest on the first day of the postoperative period and amounted to 300 [200; 350] ml in group 1 and 250 [200; 350] ml in group 2 (
Total postoperative blood loss in groups



Total drainage blood loss volume, ml  700 [600; 850]  650 [550; 800]  50 [0; 130]  0.104 
Total drainage blood loss volume, % of 
20.4 [17.1; 23,8]  17.9 [14.6; 21.5]  2.7 [0.6; 4.7]  0.010* 
* statistically significant difference.
As can be seen in
Calculation of Spearman’s correlation coefficient (
The univariate linear regression models made it possible to establish the most significant predictors determining the drainage blood loss volume expressed in % of CBV in group 1: patient’s weight (coefficient: −0.361, 95% CI [−0.48; −0.24],
An average negative correlation of drainage blood loss volume as % of CBV with patient’s body weight (
Assessment of perioperative blood loss (intraoperative + postoperative) did not show any significant differences between the groups in blood loss expressed both in ml and % of CBV: 1250 [1050; 1450] ml in group 1; 1100 [950; 1250] ml in group 2 (
Construction of univariate linear regression models allowed us to identify significant predictors of perioperative blood loss in ml in group 1: patient’s body weight (coefficient: 6.98, 95% CI [0.26; 13.7],
Since we found statistically significant differences between the groups in the drainage blood loss volume as % of CBV, we decided to conduct a statistical analysis of the data for the entire sample of patients to confirm or exclude the effect of spinal osteotomies on the value of postoperative blood loss.
Analysis of the entire sample of patients revealed a weak positive correlation of drainage blood loss volume with surgery duration (
Linear regression models for the general sample of patients







Sex  −0.96 [−3.9; 21.9]  0.521  
Age  −0.3 [−0.7; 0.2]  0.293  
Body weight  −0.3 [−0.4; −0.2]  <0.001*  −0.235 [−0.33; −0.14]  <0.001* 
Height  −0.1 [−0.2; 0]  0.056  
Intraoperative blood loss, ml  0.0 [0; 0.01]  0.196  
Intraoperative blood loss, % of CBV  0.3 [0.2; 0.5]  <0.001*  0.198 [0.06; 0.34]  0.006* 
Surgery duration  −0.0 [−0.1; 0.0]  0.110  
Number of 
0.00 [−0.3; 0.3]  0.849  
Spinal osteotomies  3.4 [−1.1; 5.8]  0.005* 
* – statistically significant difference.
As can be seen from the data presented in
where * are coefficients for a multivariate linear regression model and IBL is intraoperative blood loss in % of CBV.
Having estimated the boundaries of the interval for random discharges, we obtained the following formulas for:
The upper limit of the estimated drainage blood loss volume in % of CBV:
The lower limit of the estimated drainage blood loss volume in % of CBV:
The total
Since intergroup comparison showed significant difference in the number of
Comparison of parameters between the groups after





Age, years  15 [13; 17]  14.5 [13.75; 17]  0 [1; 1]  0.641 
Height, cm  161 [155; 168.25]  160.5 [155; 165.75]  2 [2; 6]  0.457 
Body weight, kg  50 [45; 56]  49 [44; 59]  0 [−6; 3]  0.875 
Surgery duration, min  160 [140; 180]  157.5 [150; 185]  −5 [−15; 10]  0.664 
Number of 
5 [4; 7]  5 [4; 7]  0 [−1; 1]  0.544 
Intraoperative blood loss, ml  450 [387.5; 562.5]  450 [387.5; 512.5]  0 [−50; 70]  0.540 
Intraoperative blood loss, % of CBV  11.709 [10.48; 7.46]  12.005 [10.39; 15.1]  0.45 [−1.16; 2.3]  0.582 
Total drain blood loss volume  205 [200; 285]  245 [187.5; 277.5]  0 [−50; 50]  0.868 
Perioperative blood loss, ml  1160 [1000; 1262.5]  1125 [972.5; 1262.5]  50 [−50; 150]  0.323 
Perioperative blood loss, % of CBV  32.86 [29.08; 37.85]  30.81 [26.21; 35.11]  2.34 [−0.95; 5.62]  0.131 
Sex  f – 31 (86.1 %) m – 5 (13.9 %)  f – 28 (77.8 %) m – 8 (22.2 %)  0.541  
Number of SmithPetersen osteotomies  2 – 23 (63.9 %) 3 – 13 (36.1 %) 
awareness of predictors determining the volume of postoperative blood loss during surgical correction of IS is an important aspect of personalized patient management which increases safety after completion of the surgical stage of treatment. The data we obtained on the value of postoperative and perioperative blood loss during surgical correction of IS, as well as relationships revealed both in the groups and in the general sample of patients, are quite consistent with the data presented by other authors.^{[8, 11, 16, 17]} However, there are some differences in the literature data on this issue, which is most likely due to the fact that the authors consider heterogeneous preoperative and intraoperative parameters as factors influencing the volume of postoperative blood loss.
In particular, a strong correlation between drainage blood loss volume and intraoperative blood loss was reported by Gubin et al.^{[11]}, while patient’s body weight was not considered a significant factor. Guay et al.^{[18]} studied IS patients and concluded that the number of fused segments is a key factor in predicting intraoperative and total (intraoperative + postoperative) blood loss. The authors also noted that no factor considered alone could adequately predict postoperative bleeding.
The data presented by Choi et al.^{[19]} are the closest to our study. This is because the authors analyzed the effect of Ponte osteotomies in addition to other preoperative and intraoperative parameters on postoperative blood loss in 50 patients with IS who underwent dorsal correction of spinal deformity with
The univariate regression analysis revealed the following predictors of drainage loss: patient’s body weight −0.3 [−0.4; −0.2] (
It is interesting to note that the correlation analysis showed that body weight and the drainage blood loss volume expressed in % of CBV negatively correlate with each other. We assume that the greater the patient’s body weight is, the more severe the tissue damage in the fusion area is, which is associated with a high level of tissue factor released to the bloodstream. This circumstance causes a pronounced activation of the hemostasis system and, thus, affects the drainage blood loss volume. Further research aimed at studying the perioperative functional state of the hemostatic system in a specific category of patients will make it possible to confirm this assumption.
The positive side of the presented research is that the defined inclusion and exclusion criteria determined the homogeneity of the study sample. However, the work has limitations: the study sample was not sufficiently large, which could affect the power of the statistical relationship. Moreover, we measured only visible postoperative blood loss, which is evaluated directly, and did not take into account possible occult bleeding. However, the decision to use this approach to assess the postoperative blood loss was a conscious choice, since drain output is known to have a low hematocrit^{[9]}, and the proposed formula for calculating the predicted drainage blood loss volume considers the loss of blood with hematocrit level similar to the one of circulating blood, thus minimizing possible design errors. We re commend performing calculations using the formula for the upper limit of the estimated drainage blood loss volume in practice. The proposed model for assessing the volume of postoperative blood loss is certainly not universal. The value of determination coefficient R^{2} in our multivariate model, which equals 0.25, suggests that there are other factors besides the identified ones that affect postoperative blood loss. The search for these factors in future studies can make certain adjustments to the created mathematical model for predicting drainage blood loss volume.
The study established the most significant predictors determining the volume of postoperative blood loss in surgery for idiopathic scoliosis: body weight and intraoperative blood loss expressed in % of CBV. A model for predicting the volume of postoperative blood loss was created based on the identified parameters. This model will optimize the material and technical support for the treatment associated with transfusion during the perioperative period.