Blood loss and perioperative transfusions related to surgery for spinal tumors. Relevance of tranexamic acid

External validation of a machine learning prediction model for massive blood loss during surgery for spinal metastases: a multi-institutional study using 880 patients

BACKGROUND CONTEXT

A machine learning (ML) model was recently developed to predict massive intraoperative blood loss (>2,500 mL) during posterior decompressive surgery for spinal metastasis that performed well on external validation within the same region in China.

PURPOSE

We sought to externally validate this model across new geographic regions (North America and Europe) and patient cohorts.

STUDY DESIGN

Multi-institutional retrospective cohort study PATIENT SAMPLE: We retrospectively included patients 18 years or older who underwent decompressive surgery for spinal metastasis across three institutions in the United States, the United Kingdom and the Netherlands between 2016 and 2022. Inclusion and exclusion criteria were consistent with the development study with additional inclusion of (1) patients undergoing palliative decompression without stabilization, (2) patients with multiple myeloma and lymphoma, and (3) patients who continued anticoagulants perioperatively.

OUTCOME MEASURES

Model performance was assessed by comparing the incidence of massive intraoperative blood loss (>2,500 mL) in our cohort to the predicted risk generated by the ML model. Blood loss was quantified in 7 ways (including the formula from the development study) as no gold standard exists, and the method in the development paper was not clearly defined. We estimated blood loss using the anesthesia report, and calculated it using transfusion data, and preoperative and postoperative hematocrit levels.

METHODS

The following five input variables necessary for risk calculation by the ML model were manually collected: tumor type, smoking status, ECOG score, surgical process, and preoperative platelet count. Model performance was assessed on overall fit (Brier score), discriminatory ability (area under the curve (AUC)), calibration (intercept & slope), and clinical utility (decision curve analysis)) for the total validation cohort, and for the North American and European cohorts separately. A sub-analysis, excluding the additional included patient groups, assessed the predictive model's performance with the same inclusion and exclusion criteria as the development cohort.

RESULTS

A total of 880 patients were included with a massive blood loss incidence ranging from 5.3% to 18% depending on the quantification method used. Using the most favorable quantification method, the predictive model overestimated risk in our total validation cohort and scored poorly on overall fit (Brier score: 0.278), discrimination (AUC: 0.631 [95%CI: 0.583, 0.680]), calibration, (intercept: -2.082, [95%CI: -2.285, -1.879]), slope: 0.283 [95%CI: 0.173, 0.393]), and clinical utility, with net harm observed in decision curve analysis from 20%. Similar poor performance results were observed in the sub-analysis excluding the additional included patients (n=676) and when analyzing the North American (n=539) and European (n=341) cohorts separately.

CONCLUSIONS

To our knowledge, this is the first published external validation of a predictive ML model within orthopedic surgery to demonstrate poor performance. This poor performance might be attributed to overfitting and sampling bias as the development cohort had an insufficient sample size, and distributional shift as our cohort had key differences in predictive variables used by the model. These findings emphasize the importance of extensive validation in different geographical areas and addressing biases and pitfalls of ML model development before clinical implementation, as untested models may do more harm than good.

Does Patient Blood Management Affect Outcomes in Metastatic Spine Tumour Surgery? A Review of Current Concepts

STUDY DESIGN

Narrative review.

OBJECTIVE

The spine is the most common site of metastases, associated with decreased quality of life. Increase in metastatic spine tumour surgery (MSTS) has caused us to focus on the management of blood, as blood loss is a significant morbidity in these patients. However, blood transfusion is also not without its own risks, and hence this led to blood conservation strategies and implementation of a concept of patient blood management (PBM) in clinical practise focusing on these patients.

METHODS

A narrative review was conducted and all studies that were related to blood management in metastatic spine disease as well as PBM surrounding this condition were included.

RESULTS

A total of 64 studies were included in this review. We discussed a new concept of patient blood management in patients undergoing MSTS, with stratification to pre-operative and intra-operative factors, as well as anaesthesia and surgical considerations. The studies show that PBM and reduction in blood transfusion allows for reduced readmission rates, lower risks associated with blood transfusion, and lower morbidity for patients undergoing MSTS.

CONCLUSION

Through this review, we highlight various pre-operative and intra-operative methods in the surgical and anaesthesia domains that can help with PBM. It is an important concept with the significant amount of blood loss expected from MSTS.

LEVEL OF EVIDENCE

Not applicable.

Comparison of intraoperative blood loss and perioperative complications between preoperative embolization and nonembolization combined with spinal tumor surgeries: a systematic review and meta-analysis

PURPOSE

The present study aimed to comparatively evaluate intraoperative blood loss (IBL) and perioperative complications between preoperative embolization (PE) and nonembolization (NE) combined with spinal tumor surgeries as well as to determine the subgroup of spinal tumor surgeries suitable for PE.

METHODS

A systematic search in PubMed and EMBASE and an additional search by reference lists of the retrieved studies were undertaken by two reviewers. The mean IBL and perioperative complication rate were employed as the effect size in the general quantitative synthesis through direct calculation. Meta-analysis was performed using standardized mean difference (SMD) and weighted mean difference (WMD) of IBL and the odds ratio (OR) of complications. Heterogeneity was assessed using the I2 statistic.

RESULTS

The reviewers selected 17 published studies for the general quantitative synthesis and meta-analyses. The mean IBL of spinal tumor surgeries was 1786.3 mL in the NE group and 1716.4 mL in the PE group. The mean IBL between the two groups was similar. The pooled WMD and SMD of IBL in spinal tumor surgeries was 324.15 mL (95% CI 89.50-1640.9, p = 0.007) and 0.398 (95% CI 0.114-0.682, p = 0.006), respectively. The reduction of the PE group compared with the NE group for the rates of major complications and major hemorrhagic complications were 7.80% and 5.71%, respectively. The risk of PE-related complications in the PE group was only 1.53% more than in the PE group. The pooled OR of major complications in spinal tumor surgeries was 1.426 (95% CI 0.760-2.674; p = 0.269).

CONCLUSIONS

PE may be suitable for spinal tumor surgeries and some subgroups. From the perspective of complications, PE may also be a feasible option for spinal tumor surgeries.

[Hemostatic disorders in neurosurgical patients: diagnostics and correction]

The authors analyzed the main causes of perioperative hemostatic disorders in neurosurgical patients. The problem of preoperative hemostatic screening, intraoperative and postoperative factors contributing to hemostatic disorders are considered. The authors also discuss the methods for correction of hemostatic disorders.

Use of Tranexamic Acid to Reduce PostOperative Bleeding in Orthopaedic Oncology

Background: Orthopaedic oncology often causes major blood losses that may put at risk patients’ hemodynamic balance and their overall clinical stability. To this date, transfusion therapy still represents the pivotal treatment to counterbalance the reduction in hemoglobin levels which occur after surgery. Although effective, transfusions are expensive and inevitably associated with a number of complications and therefore other solutions, such as procoagulative drugs, could play an important role to prevent massive blood losses.Material and methods: We reviewed the clinical intercourse of 37 patients who underwent major bone resection due to malignant tumors of the lower limb. Cases were divided in two different groups: group G1 consisting of 12 patients treated intraoperatively with tranexamic acid and group G2 which was made of 25 controls.Results: On average, patients treated with tranexamic acid (G1) required transfusion of 3.9 concentrated blood cells units during surgery and 0.9 units during the postoperative course. Other patients (G2), for their part, required on average 3.1 units intraoperatively and 2.1 units postoperatively. No significant difference was found in intraoperative transfusion rate (p=0.402). Instead, postoperative transfusions were significantly less frequent for patients treated with tranexamic acid (p=0.023). None of the 12 patients treated with tranexamic acid had evidence of Deep Vein Thrombosis.Conclusion: Our outcomes indicate that the use of TXA was effective in reducing blood losses also for major surgical interventions in orthopedic oncology.

Antifibrinolytics use during surgery for oncological spine diseases: A systematic review

Background

Data exist of the benefits of antifibrinolytics such as tranexamic acid (TXA) in general spine surgery. However, there are limited data of its use in oncological spine patients.

Methods

A systematic review was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. PubMed, Cochrane, OVID, and Embase databases were searched. Search terms: "tranexamic acid", "aprotinin," "aminocaproic acid," "spine surgery," "spine tumors," and "spine oncology." Included studies were full text publications written in English with patients treated with either agent or who had surgery for oncological spine disease (OSD).

Results

Seven hundred results were reviewed form the different databases, seven were selected. A total of 408 patients underwent spine surgery for OSD and received antifibrinolytics. There was a male predominance (55.2%) and mean age ranged from 43 to 62 years. The most common tumor operated was metastatic renal cancer, followed by breast and lung. Most studies administered TXA as a bolus followed by an infusion during surgery. Median blood loss was of 667 mL (253.3-1480 mL). Patients with TXA required 1-2 units less of transfusion and had 56-63 mL less of postoperative drainage versus no TXA. The median incidence of deep venous thrombosis (DVT) was 2.95% (0-7.9%) and for pulmonary embolism (PE) was 4.25% (0-14.3%). The use of TXA reduced intraoperative blood loss, transfusions and reduced postoperative surgical drainage output compared to no TXA use in patients with OSD.

Conclusion

In this review, we found that TXA may diminish intraoperative blood loss, the need for transfusion and postoperative drainage from surgical drains when used in OSD without major increase in rates of DVT or PE.

Efficacy and Safety of Tranexamic Acid in Cancer Surgery. An Update of Clinical Findings and Ongoing Research

In cancer patients undergoing surgery, tumor biology and anticancer treatments can increase the risk of perioperative bleeding and blood transfusions. Notably, blood transfusions can be potentially associated with an increased risk of life-threatening immune responses, acute lung injury, postoperative infections, and thromboembolism. Moreover, the link between perioperative transfusion and increased risk of cancer recurrence cannot be excluded. On the other hand, cancer patients have an increased risk of thromboembolism due to cancer itself and antineoplastic systemic treatments including chemotherapy and anti-angiogenic drugs. In this complex scenario, effective and safe strategies aimed at the prevention of blood transfusions are warranted. This narrative review addresses the efficacy, and the safety of the synthetic antifibrinolytic agent tranexamic acid (TXA) when used perioperatively in cancer surgery. Although in not oncologic surgery the use of TXA has been extensively studied, in the setting of cancer patients requiring surgery, the evidence is scarce. An overview of the ongoing clinical research is also provided.

Influence of tranexamic acid use on venous thromboembolism risk in patients undergoing surgery for spine tumors

OBJECTIVE

Patients with spine tumors are at increased risk for both hemorrhage and venous thromboembolism (VTE). Tranexamic acid (TXA) has been advanced as a potential intervention to reduce intraoperative blood loss in this surgical population, but many fear it is associated with increased VTE risk due to the hypercoagulability noted in malignancy. In this study, the authors aimed to 1) develop a clinical calculator for postoperative VTE risk in the population with spine tumors, and 2) investigate the association of intraoperative TXA use and postoperative VTE.

METHODS

A retrospective data set from a comprehensive cancer center was reviewed for adult patients treated for vertebral column tumors. Data were collected on surgery performed, patient demographics and medical comorbidities, VTE prophylaxis measures, and TXA use. TXA use was classified as high-dose (≥ 20 mg/kg) or low-dose (< 20 mg/kg). The primary study outcome was VTE occurrence prior to discharge. Secondary outcomes were deep venous thrombosis (DVT) or pulmonary embolism (PE). Multivariable logistic regression was used to identify independent risk factors for VTE and the resultant model was deployed as a web-based calculator.

RESULTS

Three hundred fifty patients were included. The mean patient age was 57 years, 53% of patients were male, and 67% of surgeries were performed for spinal metastases. TXA use was not associated with increased VTE (14.3% vs 10.1%, p = 0.37). After multivariable analysis, VTE was independently predicted by lower serum albumin (odds ratio [OR] 0.42 per g/dl, 95% confidence interval [CI] 0.23-0.79, p = 0.007), larger mean corpuscular volume (OR 0.91 per fl, 95% CI 0.84-0.99, p = 0.035), and history of prior VTE (OR 2.60, 95% CI 1.53-4.40, p < 0.001). Longer surgery duration approached significance and was included in the final model. Although TXA was not independently associated with the primary outcome of VTE, high-dose TXA use was associated with increased odds of both DVT and PE. The VTE model showed a fair fit of the data with an area under the curve of 0.77.

CONCLUSIONS

In the present cohort of patients treated for vertebral column tumors, TXA was not associated with increased VTE risk, although high-dose TXA (≥ 20 mg/kg) was associated with increased odds of DVT or PE. Additionally, the web-based clinical calculator of VTE risk presented here may prove useful in counseling patients preoperatively about their individualized VTE risk.

The Function of Tranexamic Acid to Prevent Hematoma Expansion After Intracerebral Hemorrhage: A Systematic Review and Meta-Analysis From Randomized Controlled Trials

Objectives: The clinical results caused by spontaneous intracerebral hemorrhage (ICH) are disastrous to most patient. As tranexamic acid (TXA) has been proved to decrease the influence of ICH, we conducted this research to explore the function of TXA for the prognosis of ICH compared with placebo.

Methods: We searched MEDLINE, Embase, Cochrane Library, and Clinicaltrials.gov for randomized controlled trials (RCTs) that were performed to evaluate TXA vs. placebo for ICH up to February 2021. The data were assessed by Review Manager 5.3 software. The risk ratio (RR) and mean difference were analyzed using dichotomous outcomes and continuous outcomes, respectively, with a fixed effect model.

Results: We collected 2,479 patients from four RCTs. Then, we took the change of hematoma volume, modified Rankin Scale (mRS), and adverse events as evaluation standard of the treatment for ICH. Through statistical analysis, we found that there is no obvious hematoma expansion effect after the application of TXA (RR = 1.05), and we proceeded the quantitative analysis of percentage change in hematoma volume from baseline, indicating that TXA could inhibit the expansion of hematoma volume (RR = −2.02) compared with placebo. However, according to the outcomes of mRS (0–1, RR = 1.04; 0–2, RR = 0.96), TXA cannot improve neurological functional prognosis. As for the security outcomes—mortality (RR = 1.02), thromboembolic events (RR = 0.99), neurological deterioration (RR = 0.92), infection (RR = 0.86), and craniotomy (RR = 0.41), there seems exist no statistical difference between TXA and placebo.

Conclusions: TXA has an advantage in the aspect of preventing hematoma expansion compared with placebo for ICH, but cannot illustrate the efficacy of TXA in improving neurological functional prognosis, which still needs more researches with large sample sizes. Moreover, for safety, we did not find obvious statistical difference between TXA and placebo.

Resuscitative Endovascular Balloon Occlusion of the Aorta for Blood Control in Lumbar Spine Tumor Resection Surgery: A Technical Note

Objectives

To describe the technique of the aorta balloon occlusion, and evaluate the blood loss in lumbar spine tumor surgery assisted by aortic balloon occlusion, and to observe the balloon‐related complications.

Methods

Six patients with lumbar spine tumor underwent resuscitative endovascular balloon occlusion of the aorta prior to tumor resections in our institution between May 2018 to January 2021. Medical records including demographic, diagnosis, tumor location, surgical approach, intraoperative blood loss, surgical duration, and perioperative balloon‐related complication were evaluated retrospectively.

Results

This series included four males and two females, with a median age of 50 years (range 22 to 69). Of these, three primary tumors were plasmacytoma, giant cell tumor of bone, and osteosarcoma, while recurrence of undifferentiated pleomorphic sarcoma (UPS), recurrence of giant cell tumor of bone (GCT), and metastatic thyroid cancer were diagnosed in cases 1, 6, and 2, respectively. L₂ was involved in cases 1 and 5. L₃ was involved in case 6. L₄ was involved in case 2, 3, and 6. L₅ was involved in case 4. One‐stage total en bloc resection surgery (TES) was accomplished in all patients; of this series, signal anterior approach was conducted in case 1, signal posterior approach was utilized in cases 2, 3, and 6, while combined anterior and posterior approach was performed in cases 4 and 5. The median intraoperative blood loss was 1683 mL and ranged from 400 to 3200 mL with a median surgical duration of 442 min and a range from 210 to 810 min. During the perioperative period, no serious balloon‐related complications occurred.

Conclusions

Endovascular balloon occlusion of the aorta successfully controls intraoperative exsanguination, contributing to a more radical tumor resection and a low rate of tumor cell contamination in lumbar tumor surgery.

Intraoperative blood loss in oncological spine surgery

OBJECTIVE

Intraoperative blood loss in patients undergoing oncological spine surgery poses a major challenge for vulnerable patients. The goal of this study was to assess how the surgical procedure, tumor type, and tumor anatomy, as well as anesthesiological parameters, affect intraoperative blood loss in oncological spine surgery and to use this information to generate a short preoperative checklist for spine surgeons and anesthesiologists to identify patients at risk for increased intraoperative blood loss.

METHODS

The authors performed a retrospective analysis of 430 oncological patients who underwent spine surgery between 2013 and 2018 at the university medical spine center. Enrolled patients had metastatic tumor of the spine requiring surgical decompression of neural structures and/or stabilization including tumor biopsy using an open, percutaneous, and/or combined dorsoventral approach. Patients requiring vertebro- and kyphoplasty or biopsy only were excluded. Statistical analyses performed included a multiple linear regression analysis.

RESULTS

The mean intraoperative blood loss in the study patient cohort was 1176 ± 1209 ml. In total, 33.8% of patients received intraoperative red blood cell transfusions. The statistical analyses showed that tumor histology indicating myeloma, operative procedure length, epidural spinal cord compression (ESCC) score, tumor localization, BMI, and surgical strategy were significantly associated with increased intraoperative blood loss or risk of needing allogeneic blood transfusions. Anesthesiological parameters such as the American Society of Anesthesiologists (ASA) Physical Status classification score were not associated with blood loss. Multiple linear regression analysis demonstrated good predictive value (r = 0.437) for a five-item preoperative checklist to identify patients at risk for high intraoperative blood loss.

CONCLUSIONS

The analyses performed in this study demonstrated key factors affecting intraoperative blood loss and showed that a simple preoperative checklist including these factors can be used to identify patients undergoing surgery for metastatic spine tumors who are at risk for increased intraoperative blood loss.

ABBREVIATIONS

ABT = allogeneic blood transfusion; ASA = American Society of Anesthesiologists; ESCC = epidural spinal cord compression; KW = Kruskal-Wallis; MET = metabolic equivalent of task; RBC = red blood cell.

Challenges and Advances in Managing Thrombocytopenic Cancer Patients

Cancer patients have varying incidence, depth and duration of thrombocytopenia. The mainstay of managing severe chemotherapy-induced thrombocytopenia (CIT) in cancer is the use of platelet transfusions. While prophylactic platelet transfusions reduce the bleeding rate, multiple unmet needs remain, such as high residual rates of bleeding, and anticancer treatment dose reductions/delays. Accordingly, the following promising results in other settings, antifibrinolytic drugs have been evaluated for prevention and treatment of bleeding in patients with hematological malignancies and solid tumors. In addition, Thrombopoeitin receptor agonists have been studied for two major implications in cancer: treatment of severe thrombocytopenia associated with myelodysplastic syndrome and acute myeloid leukemia; primary and secondary prevention of CIT in solid tumors in order to maintain dose density and intensity of anti-cancer treatment. Furthermore, thrombocytopenic cancer patients are often prescribed antithrombotic medication for indications arising prior or post cancer diagnosis. Balancing the bleeding and thrombotic risks in such patients represents a unique clinical challenge. This review focuses upon non-transfusion-based approaches to managing thrombocytopenia and the associated bleeding risk in cancer, and also addresses the management of antithrombotic therapy in thrombocytopenic cancer patients.

A clinical calculator for predicting intraoperative blood loss and transfusion risk in spine tumor patients

BACKGROUND CONTEXT

Surgery for vertebral column tumors is commonly associated with intraoperative blood loss (IOBL) exceeding 2 liters and the need for transfusion of allogeneic blood products. Transfusion of allogeneic blood, while necessary, is not benign, and has been associated with increased rates of wound complication, venous thromboembolism, delirium, and death.

PURPOSE

To develop a prediction tool capable of predicting IOBL and risk of requiring allogeneic transfusion in patients undergoing surgery for vertebral column tumors.

STUDY DESIGN/SETTING

Retrospective, single-center study.

PATIENT SAMPLE

Consecutive series of 274 patients undergoing 350 unique operations for primary or metastatic spinal column tumors over a 46-month period at a comprehensive cancer center OUTCOME MEASURES: IOBL (in mL), use of intraoperative blood products, and intraoperative blood products transfused.

METHODS

We identified IOBL and transfusions, along with demographic data, preoperative laboratory data, and surgical procedures performed. Independent predictors of IOBL and transfusion risk were identified using multivariable regression.

RESULTS

Mean age at surgery was 57.0±13.6 years, 53.1% were male, and 67.1% were treated for metastatic lesions. Independent predictors of IOBL included en bloc resection (p<.001), surgical invasiveness (β=25.43 per point; p<0.001), and preoperative albumin (β=-244.86 per g/dL; p=0.011). Predictors of transfusion risk included preoperative hematocrit (odds ratio [OR]=0.88 per %; 95% confidence interval [CI, 0.84, 0.93]; p<0.001), preoperative MCHgb (OR=0.88 per pg; 95% CI [0.78, 1.00]; p=0.048), preoperative red cell distribution width (OR=1.32 per %; 95% CI [1.13, 1.55]; p<0.001), en bloc resection (OR=3.17; 95%CI [1.33, 7.54]; p=0.009), and surgical invasiveness (OR=1.08 per point; [1.06; 1.11]; p<0.001). The transfusion model showed a good fit of the data with an optimism-corrected area under the curve of 0.819. A freely available, web-based calculator was developed for the transfusion risk model (https://jhuspine3.shinyapps.io/TRUST/).

CONCLUSIONS

Here we present the first clinical calculator for intraoperative blood loss and transfusion risk in patients being treated for primary or metastatic vertebral column tumors. Surgical invasiveness and preoperative microcytic anemia most strongly predict transfusion risk. The resultant calculators may prove clinically useful for surgeons counseling patients about their individual risk of requiring allogeneic transfusion.

Tranexamic Acid Inhibits Hematoma Expansion in Intracerebral Hemorrhage and Traumatic Brain Injury. Does Blood Pressure Play a Potential Role? A Meta-Analysis from Randmized Controlled Trials

BACKGROUND

Tranexamic acid (TXA) is an antifibrinolytic agent, which has shown an effect on reducing blood loss in many diseases. Many studies focus on the effect of TXA on cerebral hemorrhage, however, whether TXA can inhibit hematoma expansion is still controversial. Our meta-analysis performed a quantitative analysis to evaluate the efficacy of TXA for the hematoma expansion in spontaneous and traumatic intracranial hematoma.

METHOD

Pubmed (MEDLINE), Embase, and Cochrane Library were searched from January 2001 to May 2020 for randomized controlled trials (RCTs).

RESULT

We pooled 3102 patients from 7 RCTs to evaluate the efficacy of TXA for hematoma expansion. Hematoma expansion (HE) rate and hematoma volume (HV) change from baseline were used to analyze. We found that TXA led to a significant reduction in HE rate (P = 0.002) and HV change (P = 0.03) compared with the placebo. Patients with moderate or serious hypertension benefit more from TXA. (HE rate: P = 0.02, HV change: P = 0.04) TXA tends to have a better efficacy on HV change in intracerebral hemorrhage (ICH). (P = 0.06) CONCLUSIONS: TXA showed good efficacy for hematoma expansion in spontaneous and traumatic intracranial hemorrhage. Patients with moderate/severe hypertension and ICH may be more suitable for TXA administration in inhibiting hematoma expansion .

Tranexamic acid in Neurosurgery: a controversy indication-review

Tranexamic acid (TXA) is one of the measures indicated to reduce bleeding and the need for volume replacement. However, data on risks and benefits are controversial. This study analyzes the effectivity and risks of using tranexamic acid in neurosurgery. We selected articles, published from 1976 to 2019, on the PubMed, EMBASE, Science Direct, and The Cochrane Database using the descriptors: "tranexamic acid," "neurosurgery," "traumatic brain injury," "subdural hemorrhage," "brain aneurysm," and "subarachnoid hemorrhage." TXA can reduce blood loss and the need for blood transfusion in trauma and spinal surgery. Despite the benefits of TXA, moderate-to-high doses are potentially associated with neurological complications (seizures, transient ischemic attack, delirium) in adults and children. In a ruptured intracranial aneurysm, the use of TXA can considerably reduce the risk of rebleeding, but there is weak evidence regarding its influence on mortality reduction. The TXA use in brain surgery does not present benefit. However, this conclusion is limited because there are few studies. TXA in neurosurgeries is a promising method for the maintenance of hemostasis in affected patients, mainly in traumatic brain injury and spinal surgery; nevertheless, there is lack of evidence in brain and vascular surgeries. Many questions remain unanswered, such as how to determine the dosage that triggers the onset of associated complications, or how to adjust the dose for chronic kidney disease patients.