A Comparative Analysis of 4-, 12-, and 24-hour Intervals of Drain Clamping Reduces Postoperative Blood Loss Following Posterior Spinal Surgery in Adolescent Idiopathic Scoliosis: A Prospective Randomized Controlled Trial

Abstract

Study Design

The study was designed as a prospective randomized controlled trial.

Background

Posterior spinal fusion for adolescent idiopathic scoliosis (AIS) is frequently associated with substantial blood loss, often requiring blood transfusion. To reduce postoperative blood loss, drain clamping is considered a viable technique to enhance hemostasis; however, the optimal time intervals for applying postoperative drain clamping remain uncertain.

Aims

The aim of the study is to analyze and compare the volume of postoperative blood loss following 4-, 12-, and 24-hour drain clamping intervals in AIS patients undergoing posterior spinal fusion.

Materials and Methods

Patients diagnosed with AIS who underwent posterior spinal surgery between 2021 and 2024 were recruited for the study. The patients were allocated in a 1:1:1 ratio to 4-, 12-, or 24-hour intervals of drain clamping. The primary outcome was cumulative drain output until removal. Secondary outcomes included intraoperative blood loss, blood loss per fused level, transfusion rate, postoperative change in hemoglobin, Cobb angle correction, and complications. Analyses followed the intention-to-treat principle.

Results

Ninety patients were enrolled in this study. Mean cumulative drain output was 1,374 ± 339.8 mL in the 4-hour interval group, 1,325 ± 467.6 mL in the 12-hour interval group, and 1,472 ± 286.3 mL in the 24-hour interval group (p = 0.30). Intraoperative blood loss (p = 0.47), blood loss per fused level (p = 0.54), and transfusion rates (p = 0.63) were comparable. No hematomas, surgical site infections, or delayed wound healing were observed up to 24 months. Minor complications included one case of adhesive bandage irritation (12-hour interval group) and two cases of superficial wound dehiscence (24-hour interval group).

Conclusion

Drain clamping at 4-, 12-, or 24-hour intervals did not significantly alter postoperative blood loss or transfusion requirements. A 4-hour interval drain clamping appears sufficient, balancing hemostatic benefit with safety.

Keywords

blood loss - spinal surgery - adolescent idiopathic scoliosis - drain clamping - clamping intervals

Introduction

Adolescent idiopathic scoliosis (AIS) affects 1 to 3% of children aged 10 to 16 years and is characterized by a three-dimensional spinal deformity with coronal, sagittal, and axial components. Surgical intervention is generally indicated for progressive curves exceeding 40°, with the goals of halting progression, restoring balance, and improving quality of life.[1] [2] [3]

Posterior spinal fusion for AIS, although effective, is frequently associated with significant intraoperative and postoperative blood loss. Transfusion may be required, with risks associated with immunologic reaction, alloimmunization, and transfusion-transmitted infections.[4] [5] Various blood conservation strategies, including antifibrinolytic therapy, hypotensive anesthesia, intraoperative cell salvage, and hemodilution, have been employed to reduce transfusion rates.[6] [7] [8]

Postoperative drainage management remains controversial. Closed suction drains are widely used to prevent hematoma formation, which can impede wound healing and increase the risk of infection. However, immediate drainage may promote excessive postoperative blood loss. Temporary drain clamping can provide a tamponade effect, enhancing hemostasis, yet the optimal duration remains undefined. Evidence from joint arthroplasty supports short-interval clamping, but data specific to pediatric spinal deformity surgery are lacking.[9] [10] [11] [12]

This study aimed to compare 4-, 12-, and 24-hour drain-clamping intervals in AIS patients undergoing posterior spinal fusion, with the hypothesis that prolonged clamping would not confer additional benefit over short clamping in reducing postoperative blood loss.

Materials and Methods

After institutional review board approval, patients diagnosed with AIS who underwent posterior spinal deformity correction with fusion and instrumentation at our institution between 2021 and 2024 were enrolled in this study. Exclusion criteria included congenital, juvenile, infantile, neuromuscular, or adult scoliosis, as well as revision or anterior procedures. Written informed consent was obtained from all participants and their guardians.

Randomization and Allocation Concealment

Patients were assigned to one of three study groups: 4-hour, 12-hour, or 24-hour drain-clamping intervals, using a 1:1:1 allocation ratio. The allocation was achieved through permuted block randomization with variable block sizes of 6 and 9 to mitigate the predictability of the allocation. The randomization sequence was generated electronically by Sealed Envelope Ltd. (2024). Allocation concealment was maintained using sequentially numbered, opaque, and sealed envelopes prepared by an independent statistician uninvolved in patient recruitment or outcome assessment. These envelopes were only opened by the circulating nurse at the time of wound closure to determine group assignment.

Perioperative Protocol

All scoliosis surgeries conducted at our institution were meticulously planned and executed by an experienced spine deformity surgeon (T.P.), with assistance from two spine fellows. To optimize intraoperative conditions and minimize blood loss, patients were positioned in the prone position on a radiolucent Jackson table with the abdomen free of external compression, thereby reducing intra-abdominal pressure and subsequent epidural venous engorgement. This positioning strategy diminishes venous back-pressure, enhances venous return, and facilitates operative hemostasis. An intravenous dose of tranexamic acid (10 mg/kg) was administered 30 minutes prior to incision, without a maintenance infusion, in conjunction with intraoperative blood pressure control to maintain a mean arterial pressure between 55 and 65 mm Hg throughout the procedure.

Following exposure, partial facetectomies were performed across the affected segments to increase spinal flexibility and facilitate fusion. Instrumentation involved the placement of hooks, pedicle screws, and a rod system via a freehand technique. Correction maneuvers included rod derotation, differential rod contouring, direct vertebral rotation, and compression-distraction techniques. In cases of residual deformity, in situ rod contouring was employed to optimize correction. Wound closure was preceded by the insertion of a 10-Fr closed-suction drain via a subfascial approach. All procedures were performed under intraoperative neuromonitoring and image guidance using a C-arm.

Drain and Transfusion Protocols

Drains were clamped immediately after closure and released to continuous suction after the assigned interval (4, 12, or 24 hours). Removal criteria were output <100 mL/24 h or postoperative day 3. Allogeneic transfusion was indicated for hemoglobin <8 g/dL, or 8 to 9 g/dL with symptomatic anemia (tachycardia, hypotension unresponsive to fluids, or ischemic symptoms).

Outcomes Measurement

The demographic and radiographic data of the patient population encompassed several variables, including sex, age, body mass index (BMI), Lenke's curve type, and pre- and postoperative major Cobb angle measurements. Additional variables comprised the number of instrumented levels (fusion segments), preoperative hemoglobin and hematocrit values, intraoperative blood loss, total blood loss prior to the drainage removal, and the duration of the surgical procedure. These data were collected systematically and thoroughly analyzed.

Primary endpoint: cumulative postoperative drain output (mL) from the time of wound closure until the drain is removed. Secondary endpoints included intraoperative blood loss (mL), blood loss per fused level (mL/level), transfusion rate (%), postoperative hemoglobin change (g/dL), changes in the major coronal Cobb angle and percentage correction, length of hospital stay (days), and complications such as hematoma, surgical site infection, delayed wound healing, among others. Complications were systematically evaluated at 1-, 3-, 6-, 12-, and 24-month follow-up intervals.

Statistical Analysis

The sample size was determined using an a priori power calculation for a fixed-effects, one-way Analysis of Variance (ANOVA) to assess three independent groups stratified by drain clamping at 4-, 12-, and 24-hour intervals. The analysis employed G*Power software (test family: F-tests; statistical test: ANOVA: fixed effects, omnibus, one-way). Parameters were configured at a two-sided significance level of α = 0.05 and a power (1–β) of 0.80. Considering the pilot nature of this study and the lack of prior comparative data, a moderate effect size (Cohen's f = 0.25) was assumed in accordance with established guidelines.

Statistical analyses were executed using SPSS version 29.0 (IBM, Armonk, New York, United States). Continuous variables are expressed as means ± standard deviations, whereas categorical variables are presented as percentages. One-way ANOVA was applied to compare parametric data across the three groups, while the Kruskal–Wallis test was used for non-parametric data. Differences in categorical variables among the groups were analyzed with Pearson's Chi-square test. A p-value of less than 0.05 was deemed to indicate statistical significance.

Protocol Deviations

Minor deviations from the protocol were prospectively documented. These included variations in drain management (e.g., incomplete clamping due to loose fixation), small timing discrepancies (e.g., unintentional clamp release before the assigned interval, delayed initiation of clamping, or clamp release beyond the assigned interval). Minor recording errors, such as incomplete hourly drain volume documentation, but with complete cumulative output, were also categorized as protocol deviations. These deviations were deemed minor because they did not compromise capture of the primary endpoint (cumulative drain output), which was complete for all patients.

Results

Participant Flow and Baseline Characteristics

In this study, 116 patients were initially evaluated. Ninety patients met the inclusion criteria and were randomly allocated into equal groups, as illustrated in the CONSORT flowchart ([Fig. 1]). Baseline demographic and clinical characteristics, including sex, age, weight, height, BMI, preoperative major coronal Cobb angle, fusion level, preoperative hemoglobin and hematocrit levels, and surgical duration, were comparable among all groups ([Table 1]).

Fig. 1 The CONSORT flowchart of the study. CONSORT, CONsolidated Standards of Reporting Trials.

Table 1 Demographic data among three groups

	4-h interval of drain-clamping group (n = 30)	12-h interval of drain-clamping group (n = 30)	24-h interval of drain-clamping group (n = 30)	p-Value
Age (y)	16.1 ± 3.7	15.1 ± 1.8	15.3 ± 1.3	0.23
Sex				0.53
Female	29 (96.7%)	26 (89.7%)	27 (90%)
Male	1 (3.3%)	4 (10.3%)	3 (10%)
Weight (kg)	46.3 ± 6.3	47.8 ± 12.4	44.8 ± 5.5	0.43
Height (cm)	158.7 ± 5.5	160.1 ± 8.6	159.5 ± 7.5	0.75
BMI (kg/m2)	18.4 ± 2.5	18.0 ± 2.9	18.2 ± 2.9	0.87
Lenke's curve type
Type 1	11	13	8
Type 2	2	0	0
Type 3	3	0	4
Type 4	1	1	0
Type 5	12	14	11
Type 6	1	2	7
Preoperative major Cobb angle (degree)	52.4 ± 10.4	51.1 ± 15.4	49.5 ± 10.0	0.07
Instrumented level (fusion segments), IQR	10 [9,11]	11 [6,12]	11 [9,12]	0.69
Preoperative hemoglobin level (g/L)	12.2 ± 1.3	12.8 ± 1.6	12.3 ± 0.8	0.20
Preoperative hematocrit level (%)	36.8 ± 3.4	38.6 ± 4.1	37.0 ± 2.2	0.09
Duration of surgery (min)	173 ± 28.1	216 ± 60.4	218 ± 39.6	0.07

Abbreviation: BMI, body mass index.

Blood Loss and Transfusion Rate

The analysis of intraoperative blood loss, total blood loss prior to drain removal, blood loss per fusion segment, and the intraoperative blood transfusion rate is presented in [Table 2]. No statistically significant differences were detected among the three groups for intraoperative blood loss (p = 0.47), total blood loss prior to drain removal (p = 0.30), blood loss per fusion segment (p = 0.54), and the intraoperative transfusion rate (p = 0.63) ([Figs. 2] and [3]).

Table 2 Comparative analysis of pre-and postoperative parameters among the three groups

	4-h interval of drain-clamping group (n = 30)	12-h interval of drain-clamping group (n = 30)	24-hour interval of drain-clamping group (n = 30)	p-Value
Intraoperative blood loss (mL), IQR	600 [475, 700]	600 [300, 700]	500 [300, 612]	0.47
Total blood loss prior to drain removal (mL)	1,374 ± 339.8	1,325 ± 467.6	1,472 ± 286.3	0.30
Blood loss per fusion segment (mL)	143.1 ± 39.7	141.1 ± 51.7	153.9 ± 30.0	0.54
Postoperative major Cobb angle (degree)	9.9 ± 6.5	12.6 ± 8.5	8.9 ± 5.4	0.06
Change in Pre- and postoperative major Cobb angle (%)	81.0 ± 12.2	75.0 ± 13.9	81.5 ± 10.8	0.07
Intraoperative transfusion rate (%)	8 (26.7%)	11 (37.9%)	9 (30.0%)	0.63
Complication rates (%)	0 (0%)	1 (3.3%)	2 (6.7%)	0.54

Abbreviation: IQR, interquartile range.

Fig. 2 The mean total blood loss in the closed suction drain at 4-, 12-, and 24-hour intervals in the drain clamping group.

Fig. 3 The mean blood loss in closed suction drains per fusion segment level in the 4-, 12-, and 24-hour interval drain-clamping groups.

Outcomes and Complication Rates

The postoperative major Cobb angle and the percentage change in the preoperative and postoperative major Cobb angles, as well as complication rates among the three groups, are detailed in [Table 2]. No statistically significant differences were observed in the postoperative major Cobb angle (p = 0.06) or in the percentage change of the preoperative and postoperative major Cobb angles (p = 0.07) ([Fig. 4]). During the 12-hour interval of drain clamping, one case of adhesive bandage irritation was recorded (3.3%). In the 24-hour drain-clamping group, two cases (6.7%) of superficial wound dehiscence were noted 1 week following the procedure. Importantly, follow-up assessments conducted at 1, 3, 6, 12, and 24 months postoperatively revealed no drain-related complications, including surgical site infection, hematoma, or delayed wound healing, across the three groups.

Fig. 4 The difference between the preoperative major Cobb angle and the postoperative major Cobb angle.

Protocol adherence was predominantly exemplary. Minor deviations were infrequent and evenly distributed across the study cohort as described in [Table 3]. Most notably, comprehensive primary outcome data were acquired from all participants, thus permitting the inclusion of all 90 subjects in the intention-to-treat (ITT) analysis.

Table 3 Minor deviations from the protocol among the three groups

	4-h interval of the drain-clamping group	12-h interval of the drain-clamping group	24-h interval of the drain-clamping group
Incomplete clamping due to loose fixation (Replace within 15 min)	0/30 (0%)	0/30 (0%)	1/30 (3.3%)
Unintentional clamp release before the assigned interval (<30 min)	0/30 (0%)	1/30 (3.3%)	2/30 (6.6%)
Delayed initiation of clamping (<10 min)	0/30 (0%)	0/30 (0%)	0/30 (0%)
Clamp release beyond the assigned interval (<30 min)	1/30 (3.3%)	1/30 (3.3%)	0/30 (0%)

Discussion

AIS surgery is a significant procedure that can result in considerable blood loss during the intraoperative and postoperative periods, especially during the bone resection procedure, which is typically performed to facilitate increased spinal flexibility. This procedure can result in significant bleeding, which is often necessary for blood transfusion. The blood transfusion can lead to various complications, such as immunological reactions or disease transmission. Several strategies have been implemented to reduce the need for blood transfusions, including the application of hypotensive anesthesia, the utilization of hemostatic agents, the practice of hemodilution, the use of bipolar sealing devices, and the establishment of preoperative screening protocols.[8] Fox et al reported that the use of hypotensive anesthesia, by maintaining systolic blood pressure within the range of 75 to 85 mm Hg during the procedure, can significantly reduce intraoperative blood loss in a cohort of 19 patients diagnosed with Duchenne muscular dystrophy who underwent posterior corrective spinal deformity surgery.[9] In addition, Verma et al indicated that the implementation of antifibrinolytic therapies during scoliosis surgery demonstrates significant efficacy in managing postoperative bleeding and decreases the necessity for postoperative blood transfusions.[10] Copley et al reported that the application of the hemodilution method could significantly decrease the requirement for blood transfusions to 37%, in contrast to the non-hemodilution group, which experiences a transfusion rate as high as 79%.[11]

Drain clamping is one of the effective methods employed to minimize postoperative blood loss by providing additional time for the clotting mechanism to develop. By clamping the drain, a closed space is established, facilitating the tamponade effect, which aids in hemostasis. In contrast, postoperative hematoma represents a significant complication in the majority of spinal surgeries that can adversely affect neurological outcomes if not addressed promptly. Moreover, postoperative hematoma is correlated with an increased risk of surgical site infection.[12] As a result, the implementation of an open suction drain has been established as a standard practice to reduce the risk of postoperative hematoma formation. However, in pediatric and adolescent scoliosis surgeries, the procedure rarely necessitates decompression to access neural structures; hence, applying a drain clamp is deemed sufficiently safe. However, a consensus has not been reached regarding defining an optimal time interval for drain clamping. In studies related to joint replacement surgery, the practice of drain clamping is routinely employed to reduce postoperative blood loss.

The comparison of 4-, 12-, and 24-hour clamping protocols was specifically tailored to evaluate both the biological dynamics of postoperative bleeding and the practical considerations in perioperative management of AIS patients. Typically, active bleeding following posterior spinal fusion predominantly occurs within the initial 6 to 8 hours, after which drainage mainly consists of low-pressure serosanguinous fluid.[13] [14] Extending clamping beyond this physiological period is hypothesized to improve tamponade; however, clinical evidence supporting this remains sparse. By assessing these widely adopted intervals, our study seeks to determine whether prolonged clamping reduces postoperative blood loss and the requirement for blood transfusions in AIS surgery.

In this study, an ITT approach was adopted, ensuring that all 90 randomized patients were analyzed in their originally assigned groups. This preserved the benefits of randomization and reflects real-world practice, in which minor deviations are inevitable. The protocol deviations observed did not compromise the collection of the primary endpoint, which was complete for all patients. By transparently reporting these deviations and maintaining an ITT framework, we minimized potential bias due to attrition and enhanced the external validity of our findings.

Although our study reported only a few minor complications (one case of adhesive bandage irritation in the 12-hour group and two cases of superficial wound dehiscence in the 24-hour group), no instances of hematoma, deep surgical site infection, or delayed wound healing were observed during the follow-up period, which lasted up to 24 months. Concerns regarding the potential for increased infection or hematoma with prolonged drain clamping are valid and have been raised in the orthopedic literature. Zamora-Navas et al demonstrated that prolonged drain duration beyond 24 hours may increase the risk of bacterial colonization and subsequent infection. In contrast, studies in total knee arthroplasty have shown that shorter clamping intervals, such as 4 hours, can provide sufficient hemostatic benefit without elevating the risk of hematoma formation.[15] [16] [17] [18] Our findings are consistent with these reports, suggesting that short-interval clamping (4 hours) is safe and effective in posterior spinal fusion for AIS.

The study acknowledged certain limitations. It used a single-center design and had a modest sample size, thereby limiting the ability to exclude rare adverse events. Larger, multicenter studies with extended surveillance periods are necessary to more precisely delineate the safety profile of extended drain clamping within this patient population.

In conclusion, postoperative drain clamping at 4-, 12-, and 24-hour intervals demonstrated no significant differences in postoperative blood loss, transfusion requirements, or complication rates following posterior spinal fusion for AIS. This study indicates that a 4-hour interval of drain clamping is sufficient and safe, potentially optimizing postoperative protocols without compromising outcomes.

Conflict of Interest

None declared.

Authors' Contributions

All authors contributed to the study's conception and design. T.P., S.S., and W.R. did the material preparation, data collection, and analysis. T.P. wrote the first draft of the manuscript and all authors commented on the previous versions of the manuscript. All authors read and approved the final manuscript. T.P., W.R., S.S., P.K., K.T., C.P., and S.K. conducted the study design, manuscript writing, and editing, approved the version to be published, and agreed to be accountable for all aspects of work.

Ethical Approval

The study was approved by the Ethics Committee of Lerdsin Hospital.

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Publication History

Article published online:
14 January 2026