2026, Number 4
Hemodynamic and ventilatory changes in thoracolumbar surgery. Comparative analysis of two types of intraoperative positioning
Full text
10.35366/123544
Language: Portugu?s
References: 13
Page: 283-293
PDF size: 1541.64 Kb.
ABSTRACT
Introduction: during spinal surgical procedures, proper prone positioning is essential to reduce intra-abdominal pressure and prevent hemodynamic and ventilatory physiological alterations. Material and methods: a randomized observational comparative case-control study was conducted at a national tertiary referral center for spine surgery. Forty-three patients who underwent posterior thoracic and lumbosacral spine surgery over a one-year period were evaluated. Patients were classified according to the spinal segment involved, type of instrumentation, and intraoperative positioning using surgical bolsters. Statistical validity and correlations were assessed using Spearman's Rho. Results: the study population consisted of 36 male and seven female patients, with a mean age of 39.1 ± 21.1 years. The sensitivity phase was based on the evaluation performed by five fellowship-trained spine orthopedic surgeons at this institution. Hemodynamic and ventilatory changes were assessed in the preoperative, intraoperative, and postoperative periods in patients undergoing posterior thoracolumbar instrumentation, using bolster configuration (longitudinal vs transverse) as the primary variable. 18 patients were positioned using longitudinal bolsters and 25 using transverse bolsters. Significant hemodynamic differences were identified between bolster configurations, with greater intraoperative blood loss observed in patients positioned with transverse bolsters compared with longitudinal bolsters (Spearman's Rho, p = 0.025). Additionally, a strong positive correlation was observed between tranexamic acid administration and reduced intraoperative blood loss, with a 99% confidence level (Spearman's Rho, p < 0.01). Ventilatory changes were also identified, with higher intraoperative FiO2 requirements in patients positioned with transverse bolsters compared with longitudinal bolsters (p = 0.030). Discussion: based on the available literature, there are no comparable studies directly evaluating these variables, limiting positive or negative comparisons. Therefore, this study establishes a clinically relevant precedent for future research. Conclusion: longitudinal bolster positioning is associated with reduced intraoperative blood loss and lower oxygen requirements. Tranexamic acid administration decreases intraoperative bleeding in both groups, with a greater hemodynamic benefit observed when combined with longitudinal bolster positioning.INTRODUCTION
Prone positioning is commonly used to access the thoracic, lumbar, and sacral segments of the spine. Therefore, appropriate setup of the operating table and the positioning accessories employed are essential not only to ensure patient comfort but also to prevent hemodynamic and ventilatory physiological alterations.
The prone position induces a physiological adaptation in response to sustained pressure exerted on the anterior thoracic and abdominal walls. This continuous, moderate-intensity pressure is transmitted to the inferior vena cava, resulting in significant redistribution of venous blood toward the vertebral venous system. In clinical practice, surgeons frequently prioritize optimal exposure of the anatomical area to be addressed, potentially overlooking the associated hemodynamic and ventilatory consequences of patient positioning.
The most commonly used bolster configurations during prone positioning are longitudinal and transverse; however, current literature lacks sufficient evidence to establish which configuration is physiologically superior.
As it is a common practice in our national surgical and economic environment, the aim is to document the existence of hemodynamic and ventilatory changes related to the placement of soft positioners based on 15 cm high rolls of fabric and thereby set a precedent for future research of greater scope.
The vertebral venous system is anatomically connected to the thoracic region through the spinal canal and to the abdominal and pelvic regions via intercostal, lumbar, and other venous pathways. Oscar Batson was a pioneer in experimental studies involving non-human primates, demonstrating that in the presence of inferior vena cava occlusion, non-arterial venous return from the lower extremities tends to be redirected toward the vertebral venous system. This system thereby functions as an auxiliary venous drainage pathway, known as the Batson vertebral venous plexus (Figure 1).1
In patients with an elevated body mass index, adoption of the prone surgical position alters respiratory mechanics due to reduced thoracic expansion, thereby requiring higher tidal volumes and increased oxygen concentrations. It has been documented that elevated vertebral venous pressure may result in decreased spinal cord arterial pressure, consequently exposing the patient to a higher risk of neurological injury.2,3
Several strategies for operating table positioning have been proposed, including the so-called Muslim prayer position, kneeling position, and flexed positioning. These configurations result in marked flexion of the spine, hips, and knees, potentially leading to vascular and neural compromise at these levels. Consequently, multiple positioning devices have been developed to facilitate safe prone positioning during spine surgery, such as the Canadian frame, Relton-Hall frame, Andrews table, and Wilson frame (Figure 2). In resource-limited settings where such devices are unavailable, alternative positioning adaptations are commonly employed, including the use of two longitudinal or two transverse bolsters, depending on the surgical modality and the surgeon's experience (Figure 3).1
Several studies have demonstrated aortic mobilization and displacement associated with patient repositioning from the supine to the prone position, further influenced by the placement of anterior thoracic and abdominal supports. A thorough understanding of the physiological dynamics experienced by the patient during repositioning and padding is therefore essential for adequate surgical preparation and operative planning, as it allows identification of the potential risk of aortic and inferior vena cava displacement.4
Related studies have also reported that sustained pressure on the skin surface during prolonged surgical procedures predisposes patients to pressure-related injuries, including pressure ulcers and peripheral nerve injuries, with an incidence ranging from 5 to 66% among surgically treated patients.5
The Relton-Hall frame concentrates pressure on the anterior thoracic and abdominal walls at four specific points, thereby increasing the risk of cutaneous ulcer formation. This scenario may differ when using the Wilson frame, Andrews table, or the genupectoral position (Figure 4), which allow more adequate exposure of the thoracic and lumbar segments. However, the use of these positioning devices does not eliminate the occurrence of intraoperative physiological alterations or postoperative complications.6
Spine surgeons must remain aware of intraoperative patient positioning to mitigate potentially harmful pressure on vulnerable structures, with particular attention to intra-abdominal organs. These conditions may systematically affect the patient, increasing the risk of intraoperative bleeding and ventilatory disturbances.7
Reports in the literature have described cases of sudden arrhythmia occurring after prone positioning when using the Jackson table, with thoracic compression considered the most likely underlying cause.7
Comparative analyses between the Jackson surgical table and the Wilson frame have shown that, although both devices require prone positioning and may increase intra-abdominal pressure, they are also associated with hemodynamic alterations, including pressure-dependent reductions in renal microvascular and macrovascular blood flow. Despite these findings, no significant differences in the incidence of acute kidney injury have been identified between positioning systems.8
In awake patients, hypotension induced by repositioning from the supine to the prone position is usually counteracted by baroreceptor activation and sympathetic nervous system responses. In contrast, surgically anesthetized patients exhibit reduced activation of these compensatory mechanisms following anesthetic induction, predisposing them to posture-related hypotension. This hemodynamic alteration may secondarily increase pressure within the thoracic and inferior vena cava systems, potentially triggering severe complications such as intraoperative hemorrhage, spinal cord ischemia, postoperative visual loss, and activation of the Bezold-Jarisch reflex.9-11
From a ventilatory standpoint, increased intra-abdominal pressure results in cephalad displacement of the diaphragm, leading to increased pulmonary vascular resistance and reduced respiratory compliance. These changes increase the risk of pulmonary atelectasis and are associated with variations in stroke volume, pulse pressure variation, and corrected flow time. Such physiological alterations appear to be attenuated when convex supports with minimal angulation are used during prone positioning.12,13
MATERIAL AND METHODS
A randomized observational comparative case–control study was conducted in patients undergoing thoracolumbar surgical instrumentation between November 2022 and November 2023.
Inclusion criteria: a) Patients with vertebral fractures involving the thoracic and lumbosacral segments. b) Patients undergoing thoracolumbar spine instrumentation surgery in the prone position. c) Age ≥ 18 years. d) Both sexes.
Exclusion criteria: a) Patients with a prior diagnosis of cardiovascular or pulmonary disease. b) Patients requiring anterior instrumentation or procedures involving spinal segments other than the thoracolumbar or lumbosacral region.
A non-probabilistic consecutive case sampling technique was used. Sample size calculation was performed using the formula for comparative observational studies described by Hulley et al., considering the proportion of patients presenting thoracic and lumbar spine fractures with an expected total margin of error of ± 0.2.
Patients were stratified according to the spinal segment involved and the type of instrumentation performed. A comprehensive registry of collected variables was created (Table 1), which included parameters recorded during the preoperative, intraoperative, and postoperative periods.
The analysis was conducted in three phases:
Sensitivity phase. This phase was based on the evaluation performed by five fellowship-trained orthopedic spine surgeons affiliated with this institution. Hemodynamic and ventilatory changes were assessed in the preoperative, intraoperative, and postoperative periods, using 15 cm high fabric positioning rolls between the surgical table and the patient (longitudinal with anatomical reference at the superior anterior iliac spine to the outer third of the clavicle vs transverse which are placed parallel at the level of the fifth intercostal space, and over both iliac crests respectively exceeding 5 cm the edge on each side of the patient's body) as the primary reference. Postoperative records and anesthesiology charts were reviewed.
Consistency phase. To analyze ventilatory and hemodynamic changes throughout the surgical period, standard monitoring parameters recorded by the anesthesiology and nursing teams were utilized. For comparative purposes, identical parameters were obtained at admission to the operating room and again in the post-anesthesia care unit.
Statistical analysis. Data were recorded in an Excel database and subsequently analyzed using IBM SPSS Statistics version 25. Descriptive statistics were reported using measures of central tendency and dispersion. Statistical significance was defined as a p value < 0.05. Correlation validity was assessed by measuring patient variability using the Pearson correlation coefficient.
RESULTS
A total of 43 patients undergoing posterior thoracic and lumbosacral spine surgery were evaluated over a one-year period in the spine surgery department. The cohort consisted of 36 male and 7 female patients, with a mean age of 39.1 ± 21.1 years. 18 patients were positioned using a longitudinal bolster configuration, whereas 25 patients were positioned using transverse bolsters.
The analysis demonstrated a p value of 0.025 (< 0.05), leading to rejection of the null hypothesis and acceptance of the research hypothesis. These findings provide evidence of an association between bolster configuration (longitudinal vs transverse) and intraoperative blood loss. The correlation coefficient was 0.341, indicating a low positive correlation between these variables (Table 2).
These findings indicate that hemodynamic changes do occur between longitudinal and transverse bolster positioning in patients undergoing posterior thoracolumbar surgical approaches, with greater intraoperative blood loss observed in the transverse bolster configuration compared with the longitudinal configuration (Figure 5).
As this is a public institution with limited economic resources, the routine application of tranexamic acid is not standardized. Therefore, we report results in the group with and without its use, correlating the use of longitudinal and transverse rolls as the main objective of the study. The calculated p-value was < 0.01, with a Spearman's rho correlation coefficient of 0.663, indicating a strong direct association between intraoperative blood loss and the administration of tranexamic acid (Table 3).
In conclusion, it can be stated with 99% confidence that there is a strong positive association between the administration of tranexamic acid and a reduction in intraoperative blood loss as an independent variable. This association, when combined with the longitudinal placement of rolls, significantly reduces bleeding in patients undergoing thoracolumbar spine surgery (Figure 6).
A p value of 0.030 (< 0.05) was obtained, leading to rejection of the null hypothesis and acceptance of the research hypothesis. These results provide evidence of an association between bolster configuration (longitudinal vs transverse) and inspiratory oxygen fraction (FiO2), with a correlation coefficient of 0.331, indicating a low positive correlation between these variables (Table 4).
These findings indicate that ventilatory changes occur according to bolster positioning in patients undergoing posterior thoracolumbar surgical approaches, with higher intraoperative oxygen requirements observed in patients positioned with transverse bolsters compared with those positioned with longitudinal bolsters (Figure 7).
A p value > 0.05 was obtained, indicating no significant association between bolster configuration and preoperative, intraoperative, or postoperative mean arterial pressure (Table 5).
DISCUSSION
Based on a review of the literature, no comparable studies were identified that would allow direct positive or negative comparison of our findings. The study population comprised 43 patients (36 male and seven female), with a mean age of 39.1 ± 21.1 years. Of these, 18 patients were positioned using longitudinal bolsters and 25 using transverse bolsters. Hemodynamic and ventilatory changes associated with repositioning from the supine to the prone position were analyzed.
The differences observed were statistically significant, as demonstrated by Spearman's rho correlation analysis (p < 0.05), showing reduced intraoperative blood loss in patients positioned with longitudinal bolsters compared with transverse bolsters, as well as lower oxygen requirements, positively improving the combination of longitudinal rolling with the use of tranexamic acid.
The mean body mass index in patients positioned with transverse bolsters was 25.7, compared with 26.1 in those positioned with longitudinal bolsters; however, no statistically significant association was identified between body mass index and the final outcomes of our study, as a limitation, we found that this may vary in higher degrees of obesity or in morbid obesity since the positioners would have to change the height and have limitations in releasing intra-abdominal pressure secondarily.
Tranexamic acid use was analyzed, both independently and in combination with a bolster configuration, this is a limitation and could potentially bias our study since we lack the financial resources to apply it uniformly to all our patients. In other words, intraoperative blood loss was evaluated regardless of bolster positioning, as well as specifically in patients who received tranexamic acid while controlling for longitudinal versus transverse bolster placement. This approach allowed a more precise assessment of the additive effect of tranexamic acid on intraoperative bleeding reduction.
Important limitations of this study include the fact that it is only one reference center, the uncontrolled variable of the use of tranexamic acid in a unified manner in all cases, and secondarily, that it is subdivided into study groups depending on the body mass index, which is a main factor in intra-abdominal pressure and possible ventilatory and hemodynamic complications.
CONCLUSIONS
Patients undergoing posterior thoracolumbar spine surgery with longitudinal bolster positioning experienced lower intraoperative blood loss and reduced oxygen requirements. Additionally, patients who received tranexamic acid demonstrated decreased intraoperative bleeding, with the greatest reduction observed when tranexamic acid administration was combined with longitudinal bolster positioning.
This study has limitations due to its single-center design and the lack of standardized routine use of tranexamic acid due to cost constraints. However, it represents one of the first analyses to address this cost-effective intraoperative positioning strategy, commonly used in public and private institutions in Mexico. Therefore, it sets a relevant precedent for future national and international research conducted in spinal surgery centers, suggesting the expansion of subgroups with different body mass indices to observe whether the results become less significant as abdominal circumference increases.
REFERENCES
AFFILIATIONS
1 Fellow in Advanced Spine Surgery. Hospital de Traumatología y Ortopedia "Dr. y General Rafael Moreno Valle" (HTO-RMV). Mexico.
2 Chief of Spine Surgery Department, HTO-RMV.
3 Attending Spine Surgeon, HTO-RMV.
4 Anesthesiologist, HTO-RMV.
5 Chief of the Minimally Invasive Center, Spine Surgery - Orthopedics Puebla. Mexico.
ORCID:
6 0009-0008-9905-7416
7 0009-0000-8800-971X
8 0009-0009-5726-9346
9 0000-0003-4710-896X
10 0009-0009-7401-3297
11 0009-0009-9543-6889
12 0009-0003-2227-1725
13 0000-0003-4159-0222
Conflict of interests: the authors declare no conflict of interests.
EVIDENCE LEVEL
II-3CORRESPONDENCE
Omar Marroquín-Herrera, MD, MSc. E-mail: dr.omarmhspine@gmail.comReceived: January 26, 2026. Accepted: April 2, 2026