Risk Factors of Hidden Blood Loss in Unilateral Biportal Endoscopic Surgery for Patients with Lumbar Spinal Stenosis

Abstract

Objective

Unilateral biportal endoscopic (UBE) surgery has recently been used as a minimally invasive procedure for the treatment of lumbar spinal stenosis and is associated with less perioperative blood loss. However, perioperative hidden blood loss (HBL) may be neglected during UBE. This study aimed to examine the volume of HBL and discuss the influential risk factors for HBL during unilateral biportal endoscopic surgery.

Methods

From January 2022 to August 2022, 51 patients underwent percutaneous unilateral biportal endoscopic surgery for lumbar spinal stenosis at the Department of Spinal Surgery of the Affiliated Traditional Chinese Medicine Hospital of Southwest Medical University and were enrolled in this study. The data included general indicators (age, sex and body mass index [BMI]), underlying disease (hypertension and diabetes), laboratory test results (prothrombin time [PT], activated partial thromboplastin time [APTT], fibrinogen [Fbg]), and preoperative and postoperative hematocrit and hemoglobin), related imaging parameters (severity of intervertebral disc [IVD] degeneration and soft tissue thickness of the interlaminar approach), number of operated vertebrae and operation time. Total blood loss (TBL) and HBL during surgical procedures were measured via the Gross formula. Influential factors were further analyzed by multivariate linear regression analysis and t‐tests.

Results

The mean HBL was 257.89 ± 190.66 mL for single‐operation patients and 296.58 ± 269.75 mL for two‐operation patients. Patients with lower PT (p = 0.044), deeper tissue thickness (p = 0.047), and diabetes mellitus were determined to have more HBL during UBE. The operation time might also be an important factor (p = 0.047). However, sex (p = 0.265), age (p = 0.771/0.624), BMI (p = 0.655/0.664), APTT (p = 0.545/0.751), degree of degenerated IVD (p = 0.932/0.477), and hypertension (p = 0.356/0.896) were not related to HBL.

Conclusion

This study determined the different influential factors of HBL during UBE. PT, tissue thickness, and diabetes mellitus are the independent risk factors that affect HBL incidence. Long PT may decrease the volume of HBL within a certain range. Tissue thickness and diabetes mellitus can lead to an increased volume of HBL.

Unilateral biportal endoscopic surgery. The skin entry points and target disc were confirmed by plain anteroposterior radiographs to design the optimal operative route. In the left side approach, the insertion point for the endoscope was 1–1.5 cm lateral to the midline in the lower margin of the upper lamina, and the upper margin of the lower lamina was the insertion point for surgical instruments.

Introduction

Lumbar spinal stenosis is a common spinal disease and refers to stenosis of the spinal canal, nerve root canal, or intervertebral foramen caused by bone and soft tissue degeneration. ¹ The space for the thecal sac and nerve roots narrows when mechanical alterations occur within the intervertebral disc; these changes are related to disc herniation and collapse, facet joint hypertrophy, soft‐tissue infolding, and osteophyte formation. ² Most patients present with claudication, back and leg pain, and decreased walking ability. Disease severity significantly affects quality of life and can even cause debilitating results.

Unilateral biportal endoscopic (UBE) surgery is an emerging endoscopic technique that can solve the aforementioned problems to some extent. Over the past few years, UBE has been gradually applied for the treatment of lumbar spinal stenosis. It has the advantages of reduced surgical trauma, improved recovery, and improved cost utility. ³ , ⁴ It takes full advantage of the clear intraoperative view of the surgical field, wide operating range, and complete decompression. Increased accuracy of decompression, less invasion of the spinal cord, and adequate hemostasis can be achieved with good visibility. Postoperative CT scans showed adequate decompression and significant improvement in neurological function.

Previous studies have advocated increased vigilance after surgical procedures to avoid the adverse effects of sustained anemia. The total blood loss during Oblique Lateral Interbody Fusion was always greater than that observed perioperatively. ⁵ The real amount of perioperative blood loss is not equal to the measured volume of blood loss, ⁶ and hidden blood loss (HBL) is often ignored. Hidden blood loss cannot be collected during wound drainage, although it leads to additional loss of blood and results in adverse effects on the prognosis of disease by increasing the incidence of various complications. It is likely to exacerbate decrease in hemoglobin and transfusion requirements, delay wound healing, increase the risk of infection and severe anemia, and prolong the length of hospitalization. ⁷ Therefore, HBL should be considered when performing an operation because HBL has been proven to be associated with postoperative complications and severe anemia. ⁸ However, few articles have reported hidden blood loss in patients treated with UBE. In this study, we collected 51 patients who were diagnosed with lumbar spinal stenosis and underwent UBE retrospectively and aimed to: (i) determine the approximate volume of hidden blood loss; and (ii) analyze the influential risk factors for HBL during UBE including general indicators, underlying diseases, laboratory tests, and related imaging parameters.

Methods and Material

Study Design and Participants

To evaluate the risk factors for HBL in patients who underwent unilateral biportal endoscopic surgery, we recruited 51 consecutive patients who were diagnosed with lumbar spinal stenosis and underwent UBE. The selected patients were treated from January 2022 to August 2022 at the Department of Spinal Surgery of the Affiliated Traditional Chinese Medicine Hospital of Southwest Medical University, China. Inclusion criteria were: (i) patients presenting with neurogenic claudication or bilateral radiculopathy caused by degenerative spinal canal stenosis and confirmed by MRI; and (ii) patients having undergone standard conservative treatments including medications and physical therapies for at least 3 months, such as electrical nerve stimulation, massage, and acupuncture. The exclusion criteria were as follows: (i) previous spine surgery, tumor pathology or infection, trauma, liver disease, or hematologic disease; and (ii) patients who had taken any hemostatic agent, such as tranexamic acid, bone wax, or thrombin, before the operation.

Fifty‐one patients (27 male and 24 female) underwent UBE surgical procedures. The operations were performed by a senior surgeon. This research was approved by the Ethics Committee of the Affiliated Traditional Chinese Medicine Hospital of Southwest Medical University, and informed consent was obtained from all participants (KY2022021‐FS01).

Surgical Procedures of UBE

Patients underwent unilateral biportal endoscopic surgery under general anesthesia at our hospital. The insertion point for the endoscope (endoscopic portal) was located in the lower margin of the upper laminar, while the upper margin of the lower lamina was the insertion point for surgical instruments (instrumental portal). ⁹ The puncture needle was pierced into the interlaminar space so that we could determine the route of surgery under the discographic images(Figure 1). Soft tissue thickness of interlaminar approach was measured as follow (Figure 2). The paravertebral muscles were separated by using a soft tissue separator, and the multifidus muscle was bluntly separated from the surface of the lamina to avoid damaging the paraspinal muscles. Conventional surgical instruments such as bone rongeurs, nucleus pulposus forceps, nerve probes and drills can be used through the working channel. The target area for decompression is generally located at the junction of the spinous process and the lamina. One‐sided hemi‐laminectomy is performed with a drill and a rongeur, and the osteophytes of the articular process can be removed for decompression. The ipsilateral inferior border of the lamina was abraded until the beginning of the ligamentum flavum and the epidural fat was revealed. The extent of cartilage should be conservative, and the facet joint should be preserved as much as possible during the operation. Subsequently, we separated and grasped the proliferated ligamentum flavum with forceps. After adequate decompression of the nerve root was achieved, hemostasis was achieved by electrocoagulation, and the skin incision was sutured.

Fig. 1.

Unilateral biportal endoscopic surgery. The skin entry points and target disc were confirmed by plain anteroposterior radiographs to design the optimal operative route. In the left side approach, the insertion point for the endoscope was 1–1.5 cm lateral to the midline in the lower margin of the upper lamina, and the upper margin of the lower lamina was the insertion point for surgical instruments.

Fig. 2.

Measurement of soft tissue thickness of interlaminar approach. Soft tissue thickness measurements of the interlaminar approach were taken as the distance from the skin to the midpoint of the vertebral plate on the side of the lumbar disc herniation measured by MRI in the axial position.

Clinical Data

The recorded indicators included quantitative variables (age, sex, body mass index [BMI], operation time, Hemoglobin (Hgb)_pre and Hgb_post, hematocrit (Hct)_pre and Hct_post, prothrombin time [PT], activated partial thromboplastin time [APTT] and fibrinogen [Fbg], number of operated vertebrae, degree of degenerated intervertebral disc [IVD], soft tissue thickness of the interlaminar approach) and qualitative variables (hypertension and diabetes mellitus).

Calculation of Hidden Blood Loss

Visible blood loss was generally regarded as the total loss of blood during surgical procedures. However, we usually neglected hidden blood loss. Total blood loss consists of visible and hidden blood loss, and this was the basis for us to estimate the real loss of blood. Hemorrhage causes a temporary decrease in the volume of blood in the circulatory system. Consequently, the vascular filtration pressure decreases, which leads to the transfer of tissue fluid into vessels as a supplement to the circulating blood volume. Moreover, fluid replacement can maintain the effective volume of circulating blood and basic stability. According to these principles, in 1983, Gross proposed a formula for determining the amount of red blood cell loss based on the change in Hct. The formula was proven to be useful in practice when the total amount of rehydration fluid was less than 2000 ml or when the effective circulating blood volume was stable within 24 hours after surgery. No patients received blood transfusions during the period of assessment. Total hemorrhage was evaluated by the volume loss of red blood cells (RBCs) and Hct. ¹⁰ The patients' blood volume (PBV) was calculated by the following formula:

$$\mathsf{PBV}=\mathsf{k}\mathsf{1}\times \mathsf{\text{height}}{\left(\mathsf{m}\right)}^{\mathsf{3}}+\mathsf{k}\mathsf{2}\times \mathsf{\text{weight}}\left(\mathsf{kg}\right)+\mathsf{k}\mathsf{3},$$

where k1 = 0.3669, k2 = 0.03219, and k3 = 0.6041 for males:

$$\mathsf{k}\mathsf{1}=\mathsf{0.3561},\mathsf{k}\mathsf{2}=\mathsf{0.03308},\mathsf{k}\mathsf{3}=\mathsf{0.1833}\mathsf{\text{for females}}.$$

Multiplying the PBV by the D‐value of hematocrit will give the total volume loss of RBC:

$$\mathsf{\text{Total volume loss of}}\mathsf{RBC}\left(\mathsf{L}\right)=\mathsf{PBV}\times \left({\mathsf{Hct}}_{\mathsf{pre}}-{\mathsf{Hct}}_{\mathsf{\text{post}}}\right),$$

$$\mathsf{\text{Hidden blood loss}}\left(\mathsf{mL}\right)=\mathsf{1000}\mathsf{x}\left(\mathsf{\text{total volume loss of}}\mathsf{RBC}/{\mathsf{Hct}}_{\mathsf{\text{mean}}}\right),$$

$$\left[{\mathsf{Hct}}_{\mathsf{\text{mean}}}=\mathsf{1}/\mathsf{\text{2x}}\left({\mathsf{Hct}}_{\mathsf{pre}}+{\mathsf{Hct}}_{\mathsf{\text{post}}}\right)\right].$$

Multiplying the PBV by the D‐value of Hct_pre and Hct_post will yield the total volume loss of RBCs. The lowest postoperative hematocrit level is an essential parameter for calculating the accurate volume of hidden blood loss. The hematocrit value at 3 days after the operation was recorded as Hct_post in previous studies. Here, the lowest hematocrit value observed for five consecutive days following the operation was recorded as the Hct_post so that we could reduce dynamic errors as low as possible by hemodynamic instability. Theoretically, total hemorrhage comprises intraoperative and postoperative blood loss (Figure 3). However, what should be stressed is that visible intraoperative blood loss can be ignored because of the small volume during the UBE procedure. The total blood loss was approximately equal to the volume of HBL and postoperative drainage.

Fig. 3.

Flowchart for the visible volume loss of red blood cell (RBC).

Statistical Analysis

The statistical analysis was performed using SPSS version 22.0 (SPSS, VT, Chicago, IL, USA). A paired sample t‐test was used to compare the differences between the preoperative and postoperative Hct values. One‐way analysis of variance and Pearson correlation analysis were conducted before regression analysis. Multivariate linear regression analysis with full and principal factor models was performed to identify independent factors associated with HBL, including quantitative variables (age, BMI, operation time, postoperative drainage, Fbg, PT, APTT, degree of degenerated IVD, soft tissue thickness of the interlaminar approach, and number of operated vertebrae) and qualitative variables (sex, hypertension, and diabetes mellitus). Statistical significance was defined as p < 0.05 in our study.

Results

HBL of UBE Cannot be Neglected

All patients underwent UBE without transfusion. In total, 51 patients who underwent UBE and met the study criteria were included. The mean age was 58.12 ± 16.49 years (range, 13–81 years). Table 1 shows the demographic data of the patients. There were 45 patients who underwent operation with a single level, and six patients with two levels. The mean HBL was 257.89 ± 190.66 mL for one level and 296.58 ± 269.75 mL for two levels, as shown in Table 2. In addition, the difference between the preoperative and postoperative Hct and Hgb values revealed that HBL could promote the decrease in Hct and Hgb and lead to anemia in Table 3 (p = 0.000, t_Hct = 12.563/t_Hgb = 11.856).

TABLE 1.

Demographic information of patients.

Parameters	Male	Female	Total
Number of patients	27	24	51
Age (years)	56.04 ± 18.52	60.46 ± 13.87	58.12 ± 16.49
Height (cm)	166.44 ± 7.03	155.75 ± 6.17	161.41 ± 8.5
Weight (kg)	64.78 ± 13.43	59.96 ± 8.62	62.51 ± 11.57
BMI kg/m2	23.39 ± 3.65	24.76 ± 3.1	24.03 ± 3.44

Note: Data are mean ± SD.

TABLE 2.

Number of involved levels.

Vertebral levels	Number of patients	Hidden blood loss (mL)
Single	45	257.89 ± 190.66
Double	6	296.58 ± 269.75

Note: Data are mean ± SD.

TABLE 3.

Result of paired samples t test for Hct and Hgb.

	Mean	Std. deviation	Std. error mean	95% Confidence interval of the difference		t	df	p
				Lower	Upper
Hctpre ‐ Hctpost	3.920	2.228	0.312	3.293	4.546	12.563	50	0.000
Hgbpre ‐ Hgbpost	13.529	8.149	1.141	11.237	15.821	11.856	50	0.000

Abbreviations: Hct, hematocrit; Hgb, hemoglobin; pre, preoperative; post, postoperative

*p < 0.05

*Dependent variable: Changes of Hct and Hgb (ml).

Diabetes and PT May Affect HBL

There were no significant differences in these groups with HBL including vertebral level (single/double), sex (male/Female), age (<65 /≥ 65), BMI (< 18.5/18.5–23.9/> 23.9), degree of degenerated IVD (II‐V), tissue thickness (< 5 cm/≥ 5 cm) hypertension, or diabetes mellitus (Ta ≥ 65), BMI (< 18.5/18.5–23.9/> 23.9), degree of degenerated IVD (II‐V), tissue thickness (< 5 cm/≥ 5 cm) hypertension, or diabetes mellitus (Table 4). While, there was a relatively strong positive correlation between diabetes mellitus (r = 0.24, p < 0.05) and HBL, and the correlation between PT (r = −0.32, p < 0.05) and HBL was negative (Table 5).

TABLE 4.

One‐way analysis of variance with HBL.

	Dependent variable*
	F	p
Vertebral level	0.198	0.659
Gender	0.191	0.664
Age	3.504	0.067
BMI	0.017	0.896
Degree of the degenerated IVD	1.180	0.283
Tissue thickness	2.101	0.154
Hypertension	1.481	0.229
Diabetes mellitus	2.974	0.091

Abbreviations: BMI, body mass index; IVD, intervertebral disc.

^*Dependent variable: HBL, Hidden blood loss (mL).

TABLE 5.

Pearson correlation test for HBL coefficients.

	Dependent variable*
	Vertebral level	Gender	Age	Operation time	BMI	PT	APTT	Fbg	Degree of the degenerated IVD	Tissue thickness	Hypertension	Diabetes mellitus	HBL
Vertebral level	1.00	0.14	0.16	0.34	0.22	−0.04	−0.12	0.11	0.25	0.05	0.15	0.21	0.06
Gender	0.14	1.00	0.14	0.22	0.20	−0.07	−0.14	−0.09	0.22	0.04	0.04	0.19	−0.06
Age	0.16	0.14	1.00	0.13	−0.04	−0.05	0.11	0.40	0.52	−0.14	0.49	0.31	0.22
Operation time	0.34	0.22	0.13	1.00	0.34	−0.03	−0.03	−0.04	0.18	0.10	0.09	0.19	−0.25
BMI	0.22	0.20	−0.04	0.34	1.00	−0.11	−0.25	0.02	−0.14	0.40	−0.02	0.22	0.04
PT	−0.04	−0.07	−0.05	−0.03	−0.11	1.00	0.24	0.10	−0.02	0.17	−0.01	−0.18	−0.32
APTT	−0.12	−0.14	0.11	−0.03	−0.25	0.24	1.00	0.43	0.06	−0.07	−0.04	−0.29	−0.11
Fbg	0.11	−0.09	0.40	−0.04	0.02	0.10	0.43	1.00	0.15	0.04	0.32	0.21	0.20
Degree of the degenerated IVD	0.25	0.22	0.52	0.18	−0.14	−0.02	0.06	0.15	1.00	−0.04	0.14	0.14	0.15
Tissue thickness	0.05	0.04	−0.14	0.10	0.40	0.17	−0.07	0.04	−0.04	1.00	−0.16	0.08	0.00
Hypertension	0.15	0.04	0.49	0.09	−0.02	−0.01	−0.04	0.32	0.14	−0.16	1.00	0.59	0.17
Diabetes mellitus	0.21	0.19	0.31	0.19	0.22	−0.18	−0.29	0.21	0.14	0.08	0.59	1.00	0.24

Abbreviations: APTT, activated partial thromboplastin time; BMI, body mass index; IVD, intervertebral disc; PT, prothrombin time.

^*Dependent variable: HBL, Hidden blood loss (mL).

Two Factors Would Increase HBL

Gender (p = 0.265), age (p = 0.771/p = 0.624), BMI (p = 0.655/p = 0.664), APTT (p = 0.545/p = 0.751), degree of degenerated IVD (p = 0.932/p = 0.477), and hypertension (p = 0.356/p = 0.896) were not significantly correlated with HBL both in Tables 6 and 7. Moreover, the PT coefficient was −105.22 (p < 0.05) in Table 7, and the tissue thickness was 9.133 (p < 0.05) in Table 6, which mean that PT value was negatively correlated with HBL and tissue thickness was positively correlated with HBL. As shown in Table 8, the coefficients of the independent variables diabetes mellitus and tissue thickness were 18.921 and 7.158, respectively, indicating that the effect of these two factors on HBL was positive (p < 0.05).

TABLE 6.

Results of multivariate linear regression analysis for whole HBL coefficients.

	Dependent variable*
	Unstandardized		Standardized
	B	SE	β	t	p
(Constant)	−168.469	271.256		−0.621	0.539
Gender	−10.489	9.250	−0.027	−1.134	0.265
Age (years)	0.100	0.342	0.008	0.293	0.771
BMI kg/m2	2.092	4.643	0.036	0.451	0.655
Operation time (min)	−0.028	0.074	−0.009	−0.373	0.711
Vertebral level	−24.656	12.534	−0.040	−1.967	0.058
Tissue thickness (cm)	9.133	4.136	0.040	2.208	0.035
Degree of the degenerated IVD	0.487	5.650	0.002	0.086	0.932
PT	−9.053	6.837	−0.026	−1.324	0.195
APTT	−0.649	1.060	−0.012	−0.612	0.545
Fbg	0.748	3.875	0.004	0.193	0.848
Hypertension	8.827	9.422	0.021	0.937	0.356
Diabetes mellitus	6.204	12.685	0.011	0.489	0.628

Abbreviations: APTT, activated partial thromboplastin time; BMI, body mass index; IVD, intervertebral disc; PT, prothrombin time.

^*Dependent variable: HBL, Hidden blood loss (mL).

TABLE 7.

Results of multiple line regression method for part of HBL coefficients.

	Dependent variable*
	Unstandardized		Standardized
	B	SE	β	t	p
(Constant)	1476.816	753.139		1.961	0.057
Vertebral level	−38.684	91.988	−0.063	−0.421	0.676
Age (years)	1.137	2.299	0.094	0.495	0.624
Operation time (min)	−1.152	0.489	−0.366	−2.357	0.024
BMI kg/m2	4.293	9.812	0.074	0.438	0.664
PT	−105.225	50.438	−0.302	−2.086	0.044
APTT	−2.924	9.150	−0.056	−0.320	0.751
Fbg	25.431	32.055	0.139	0.793	0.432
Degree of the degenerated IVD	31.856	44.340	0.122	0.718	0.477
Tissue thickness (cm)	14.181	35.511	0.062	0.399	0.692
Hypertension	10.646	81.297	0.025	0.131	0.896
Diabetes mellitus	63.966	108.459	0.112	0.590	0.559

Abbreviations: APTT, activated partial thromboplastin time; BMI, body mass index; IVD, intervertebral disc; PT, prothrombin time.

^*Dependent variable: HBL, Hidden blood loss (mL).

TABLE 8.

Results of the optimized regression model.

Model	Dependent variable*
	Unstandardized		Standardized
	B	SE	β	t	p
(Constant)	−51.953	18.636		−2.788	0.008
Diabetes mellitus	18.921	8.785	0.033	2.154	0.037
Tissue thickness (cm)	7.158	3.506	0.031	2.042	0.047

^*Dependent variable: HBL, Hidden blood loss (mL).

Discussion

The Risk Factors of HBL in UBE Perioperatively

Spinal canal stenosis is one of the most common skeletal diseases and can cause severe low back pain and nerve dysfunction in the lower extremities. ¹¹ UBE has been gradually recognized as an effective and safe surgical procedure for the treatment of patients with lumbar spinal stenosis because of its minimal invasiveness, short operation time, minimal intraoperative blood loss, and good postoperative recovery. ¹² , ¹³ While, this study determined that the average HBL was up to 262 mL in UBE, which was significantly greater than the visible blood loss and accounted for approximately 66.3% of the total blood loss. Therefore, variable factors should be controlled during UBE to reduce HBL as much as possible. It is necessary to improve awareness of perioperative HBL and strengthen perioperative monitoring, especially for elderly patients with preoperative anemia. In the present study, it was shown that the volume of hidden blood loss for UBE was obviously greater under general conditions in Table 2. Then, the result of Pearson correlation analysis reveal a relatively strong positive correlation between diabetes mellitus (r = 0.24, p < 0.05) and HBL, and a negative one between PT (r = −0.32, p < 0.05) and HBL. This mean that these two factors could have some impact on HBL during UBE surgery (Table 5). Subsequently, multivariate linear regression analysis further confirmed that PT, tissue thickness, and diabetes mellitus are the independent risk factors that affect HBL incidence (Tables 6 and 7). Tissue thickness and diabetes mellitus are able to increase the volume of HBL during UBE surgery in the treatment of lumbar spinal stenosis (Table 8).

Abnormal PT May Affect HBL

Forty‐five patients with single degenerative levels were determined to have 257.89 ± 190.66 mL of HBL, and six patients with double degenerative levels were determined to have 296.58 ± 269.75 mL HBL. Intuitively, patients who underwent surgery in more segments tended to have more blood loss in the UBE cohort, but there was no significant correlation between vertebral level and HBL (p = 0.058/p = 0.676). We further determined that HBL was not related to sex, age, BMI, or hypertension. However, the Fbg level was found to be an influential factor on perioperative HBL after posterior lumbar fusion surgery. During lumbar vertebral incision and internal fixation surgery, preoperative activation of partial thromboplastin time was proven to increase HBL. ¹⁴ Similarly, our study demonstrated that abnormal PT could cause the HBL and long PT may decrease the volume of HBL within a certain range (p < 0.05).

Tissue Thickness Influences the Volume of HBL

The soft tissue is rich in capillaries, and the tissue bleeds easily after injury. Moreover, the interlaminar approach primarily involves bleeding foci from muscle vessels in the dorsal lamina, which may lead to an increased volume of blood loss in UBE patients. ¹⁵ Tissue thickness was shown to be a positive risk factor for HBL in UBE patients (p < 0.05), which may guide us in the selection of different surgical approaches. The transforaminal approach usually encounters bleeding foci originating from the major branches of the segmental lumbar artery and the emissary veins within the foramen. The interlaminar approach primarily encounters bleeding foci from the muscle vessels in the dorsal lamina, which are believed to be located near the ends of the three main branches. The surgeon should have a comprehensive understanding of the microvascular anatomy in the lumbar spine during endoscopic spinal surgery, so that they can choose the best approach to decrease the volume of HBL as much as possible.

UBE Surgery for Patients with DM Tended to Induce More HBL

Current clinical epidemiological investigations show that DM is closely related to OA. ¹⁶ A comparative study of 148 TKA (total knee arthroplasty) patients revealed that the postoperative drainage rate and total blood loss were greater in the diabetic group than in the nondiabetic group. Moreover, ACT (activated coagulation time) and thrombin generation time (TGT) were greater in the type 2 diabetes group than in the control group (p < 0.05) in a previous study. ACT reflects the TGT (seconds). The greater these values are, the greater the risk of bleeding. However, patients with type 2 diabetes usually tend to be hypercoagulable because of increased levels of coagulation factors VII, VIII, XI, and XII; vascular pseudohemophilic factor (VWF); and fibrinogen in the endogenous coagulation pathway. Diabetic patients have both a high risk of clotting and a tendency to bleed. The results in this research suggested a positive correlation between diabetes incidence and hidden blood loss (p < 0.05). Therefore, for patients with diabetes mellitus, the blood glucose levels should be closely monitored, and normal blood glucose levels should be maintained perioperatively. Control of relevant risk factors, or appropriate management for them would greatly reduce perioperative HBL and TBL.

Therefore, clinicians should strengthen perioperative blood management, take intervention measures, fully assess relevant risk factors before surgery, dynamically monitor blood routine, and timely supplement allogeneic blood for anemic patients to reduce perioperative complications and promote functional recovery after UBE surgery. In addition, tranexamic acid was reported to reduce HBL in posterior lumbar interbody fusion (PLIF) surgery ¹⁷ and safely decrease HBL in patients undergoing intertrochanteric fracture surgery. ¹⁸ Tranexamic acid is a synthetic lysine derivative that reversibly blocks the lysine binding site on the fibrinogen molecule, and is mainly used for a variety of hemorrhages caused by hyperfibrinolysis. ¹⁹ The period from the beginning to 10 h after surgery is the period of hyperfibrinolysis, during which the hemostatic drugs become effective to achieve the best hemostatic effect. ²⁰ Thus, preoperative intravenous tranexamic acid may reduce HBL to some extent.

Limitations and Strengths

The work is the first to analyze the risk factors associated with HBL in UBE surgery. By observing phenomena, collecting cases, compiling statistics and analyzing the data, the conclusions may facilitate to guide the clinical work. In this study, the surgical team was fixed, the surgical and anesthesia methods were the same, and there was no statistically significant difference in comparing the age, height, BMI, and diagnosis of the patients in each group, which relatively reduced the influence of other factors. While, this is a retrospective study, there are some limitations. The number of patients included in the study was small, and there is a possibility of false positives and bias, and further prospective studies with a large number of patients are needed in the future.

Conclusion

The present study determined the different influential factors of HBL during UBE. PT, tissue thickness, and diabetes mellitus are the independent risk factors that affect HBL incidence. Long PT may decrease the volume of HBL within a certain range. Tissue thickness and diabetes mellitus can lead to an increased volume of HBL.

Author Contributions

Sheng Guo, Zhiyong Yu, and Chenglong Wang are co‐first authors and contributed equally to the work. All the authors read and approved the final manuscript.

Funding Information

This work was supported by the Natural Science Foundation of Sichuan Province (2022NSFSC0688), the Nanjing Drum Tower Hospital Talent Introduction Research Initiation Fund (RC2023‐040) and the Research Program of Southwest Medical University (2021ZKMS050).

Conflict of Interest Statement

The authors report no conflicts of interest.

Ethics Statement

This study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the Ethics Committee of Southwest Medical University.