Bayesian methodology for the design and interpretation of clinical trials in critical care medicine: a primer for clinicians

Design and Execution of Clinical Trials in the Cardiac Intensive Care Unit

Clinical practice in the contemporary cardiac intensive care unit (CICU) has evolved significantly over the last several decades. With more frequent multisystem organ failure, increasing use of advanced respiratory support, and the advent of new mechanical circulatory support platforms, clinicians in the CICU are increasingly managing patients with complex comorbid disease in addition to their high-acuity cardiovascular illnesses. Here, the authors discuss challenges associated with traditional trial design in the CICU setting and review novel clinical trial designs that may facilitate better evidence generation in the CICU.

Bayesian methods: a potential path forward for sepsis trials

BACKGROUND

Given the success of recent platform trials for COVID-19, Bayesian statistical methods have become an option for complex, heterogenous syndromes like sepsis. However, study design will require careful consideration of how statistical power varies using Bayesian methods across different choices for how historical data are incorporated through a prior distribution and how the analysis is ultimately conducted. Our objective with the current analysis is to assess how different uses of historical data through a prior distribution, and type of analysis influence results of a proposed trial that will be analyzed using Bayesian statistical methods.

METHODS

We conducted a simulation study incorporating historical data from a published multicenter, randomized clinical trial in the US and Canada of polymyxin B hemadsorption for treatment of endotoxemic septic shock. Historical data come from a 179-patient subgroup of the previous trial of adult critically ill patients with septic shock, multiple organ failure and an endotoxin activity of 0.60-0.89. The trial intervention consisted of two polymyxin B hemoadsorption treatments (2 h each) completed within 24 h of enrollment.

RESULTS

In our simulations for a new trial of 150 patients, a range of hypothetical results were observed. Across a range of baseline risks and treatment effects and four ways of including historical data, we demonstrate an increase in power with the use of clinically defensible incorporation of historical data. In one possible trial result, for example, with an observed reduction in risk of mortality from 44 to 37%, the probability of benefit is 96% with a fixed weight of 75% on prior data and 90% with a commensurate (adaptive-weighting) prior; the same data give an 80% probability of benefit if historical data are ignored.

CONCLUSIONS

Using Bayesian methods and a biologically justifiable use of historical data in a prior distribution yields a study design with higher power than a conventional design that ignores relevant historical data. Bayesian methods may be a viable option for trials in critical care medicine where beneficial treatments have been elusive.

IV Vitamin C in Adults With Sepsis: A Bayesian Reanalysis of a Randomized Controlled Trial

OBJECTIVES

The Lessening Organ Dysfunction with Vitamin C trial showed a harmful effect of vitamin C on 28-day death or persistent organ dysfunction. To maximize interpretation, we present a post hoc Bayesian reanalysis.

DESIGN

Bayesian reanalysis of a randomized placebo-controlled trial.

SETTING

Thirty-five ICUs.

PATIENTS

Adults with proven or suspected infection, vasopressor support, and no more than 24 hours of ICU admission.

INTERVENTIONS

Patients were allocated to receive either vitamin C (50 mg/kg of body weight) or placebo every 6 hours for up to 96 hours.

MEASUREMENTS AND MAIN RESULTS

The primary outcome was the composite of death or persistent organ dysfunction (i.e., vasopressor use, invasive mechanical ventilation, or new renal replacement therapy) at 28 days. We used Bayesian log-binomial models with random effects for hospital site and varying informative prior beliefs for the effect of vitamin C to estimate risk ratios (RRs) with 95% credible intervals (Crls) in the intention to treat population (vitamin C, 435 patients; placebo, 437 patients). Using weakly neutral priors, patients allocated to vitamin C had a higher risk of death or persistent organ dysfunction at 28 days (RR, 1.20; 95% Crl, 1.04-1.39; probability of harm, 99%). This effect was consistent when using optimistic (RR, 1.14; 95% Crl, 1.00-1.31; probability of harm, 98%) and empiric (RR, 1.09; 95% Crl, 0.97-1.22; probability of harm, 92%) priors. Patients allocated to vitamin C also had a higher risk of death at 28 days under weakly neutral (RR, 1.17; 95% Crl, 0.98-1.40; probability of harm, 96%), optimistic (RR, 1.10; 95% Crl, 0.94-1.30; probability of harm, 88%), and empiric (RR, 1.05; 95% Crl, 0.92-1.19; probability of harm, 76%) priors.

CONCLUSIONS

The use of vitamin C in adult patients with proven or suspected infection and vasopressor support is associated with high probability of harm.

Use of Pharmacologic Prophylaxis Against Venous Thromboembolism in Hospitalized Injured Children

Despite a practice management guideline and risk prediction model for venous thromboembolism (VTE), pediatric-specific evidence on pharmacologic prophylaxis is lacking. In a retrospective study, we characterized receipt of prophylaxis and explored its effectiveness in hospitalized injured patients below 18 years old using data from the Trauma Quality Improvement Program. Concordance of receipt of prophylaxis with guideline and predicted risk of VTE was estimated using κ statistic. Effectiveness was explored using cohorts matched based on the risk prediction model. A total of 11,165 (6.2%) of 180,932 patients received prophylaxis. Those who received prophylaxis were more commonly post-pubertal and more severely injured. Receipt of prophylaxis was fairly concordant with the guideline (κ=0.32) and predicted risk of VTE (κ=0.29). Receipt of prophylaxis was associated with higher rates of VTE likely due to confounding by indication. Low molecular weight heparin seemed more effective against VTE than unfractionated heparin (incidence rate ratio: 0.52; 95% confidence interval: 0.36, 0.75), but less effective when received ≥72 hours after admission to the hospital. We showed that hospitalized injured children did not commonly receive prophylaxis. We also showed that prophylaxis may be effective in hospitalized injured children, but it needs to be proven definitively in a randomized clinical trial.

Bayesian statistics in anesthesia practice: a tutorial for anesthesiologists

This narrative review intends to provide the anesthesiologist with the basic knowledge of the Bayesian concepts and should be considered as a tutorial for anesthesiologists in the concept of Bayesian statistics. The Bayesian approach represents the mathematical formulation of the idea that we can update our initial belief about data with the evidence obtained from any kind of acquired data. It provides a theoretical framework and a statistical method to use pre-existing information within the context of new evidence. Several authors have described the Bayesian approach as capable of dealing with uncertainty in medical decision-making. This review describes the Bayes theorem and how it is used in clinical studies in anesthesia and critical care. It starts with a general introduction to the theorem and its related concepts of prior and posterior probabilities. Second, there is an explanation of the basic concepts of the Bayesian statistical inference. Last, a summary of the applicability of some of the Bayesian statistics in current literature is provided, such as Bayesian analysis of clinical trials and PKPD modeling.

A Research Agenda for Precision Medicine in Sepsis and Acute Respiratory Distress Syndrome: An Official American Thoracic Society Research Statement

Background: Precision medicine focuses on the identification of therapeutic strategies that are effective for a group of patients based on similar unifying characteristics. The recent success of precision medicine in non-critical care settings has resulted from the confluence of large clinical and biospecimen repositories, innovative bioinformatics, and novel trial designs. Similar advances for precision medicine in sepsis and in the acute respiratory distress syndrome (ARDS) are possible but will require further investigation and significant investment in infrastructure. Methods: This project was funded by the American Thoracic Society Board of Directors. A multidisciplinary and diverse working group reviewed the available literature, established a conceptual framework, and iteratively developed recommendations for the Precision Medicine Research Agenda for Sepsis and ARDS. Results: The following six priority recommendations were developed by the working group: 1) the creation of large richly phenotyped and harmonized knowledge networks of clinical, imaging, and multianalyte molecular data for sepsis and ARDS; 2) the implementation of novel trial designs, including adaptive designs, and embedding trial procedures in the electronic health record; 3) continued innovation in the data science and engineering methods required to identify heterogeneity of treatment effect; 4) further development of the tools necessary for the real-time application of precision medicine approaches; 5) work to ensure that precision medicine strategies are applicable and available to a broad range of patients varying across differing racial, ethnic, socioeconomic, and demographic groups; and 6) the securement and maintenance of adequate and sustainable funding for precision medicine efforts. Conclusions: Precision medicine approaches that incorporate variability in genomic, biologic, and environmental factors may provide a path forward for better individualizing the delivery of therapies and improving care for patients with sepsis and ARDS.

Efficacy of Early Prophylaxis Against Catheter-Associated Thrombosis in Critically Ill Children: A Bayesian Phase 2b Randomized Clinical Trial

OBJECTIVES

We obtained preliminary evidence on the efficacy of early prophylaxis on the risk of central venous catheter-associated deep venous thrombosis and its effect on thrombin generation in critically ill children.

DESIGN

Bayesian phase 2b randomized clinical trial.

SETTING

Seven PICUs.

PATIENTS

Children less than 18 years old with a newly inserted central venous catheter and at low risk of bleeding.

INTERVENTION

Enoxaparin adjusted to anti-Xa level of 0.2-0.5 international units/mL started at less than 24 hours after insertion of central venous catheter (enoxaparin arm) versus usual care without placebo (usual care arm).

MEASUREMENTS AND MAIN RESULTS

At the interim analysis, the proportion of central venous catheter-associated deep venous thrombosis on ultrasonography in the usual care arm, which was 54.2% of 24 children, was significantly higher than that previously reported. This resulted in misspecification of the preapproved Bayesian analysis, reversal of direction of treatment effect, and early termination of the randomized clinical trial. Nevertheless, with 30.4% of 23 children with central venous catheter-associated deep venous thrombosis on ultrasonography in the enoxaparin arm, risk ratio of central venous catheter-associated deep venous thrombosis was 0.55 (95% credible interval, 0.24-1.11). Including children without ultrasonography, clinically relevant central venous catheter-associated deep venous thrombosis developed in one of 27 children (3.7%) in the enoxaparin arm and seven of 24 (29.2%) in the usual care arm (p = 0.02). Clinically relevant bleeding developed in one child randomized to the enoxaparin arm. Response profile of endogenous thrombin potential, a measure of thrombin generation, was not statistically different between trial arms.

CONCLUSIONS

These findings suggest the efficacy and safety of early prophylaxis that should be validated in a pivotal randomized clinical trial.

Does team leader gender matter? A Bayesian reconciliation of leadership and patient care during trauma resuscitations

OBJECTIVE

Team leadership facilitates teamwork and is important to patient care. It is unknown whether physician gender-based differences in team leadership exist. The objective of this study was to assess and compare team leadership and patient care in trauma resuscitations led by male and female physicians.

METHODS

We performed a secondary analysis of data from a larger randomized controlled trial using video recordings of emergency department trauma resuscitations at a Level 1 trauma center from April 2016 to December 2017. Subjects included emergency medicine and surgery residents functioning as trauma team leaders. Eligible resuscitations included adult patients meeting institutional trauma activation criteria. Two video-recorded observations for each participant were coded for team leadership quality and patient care by 2 sets of raters. Raters were balanced with regard to gender and were blinded to study hypotheses. We used Bayesian regression to determine whether our data supported gender-based advantages in team leadership.

RESULTS

A total of 60 participants and 120 video recorded observations were included. The modal relationship between gender and team leadership (β = 0.94, 95% highest density interval [HDI], -.68 to 2.52) and gender and patient care (β = 2.42, 95% HDI, -2.03 to 6.78) revealed a weak positive effect for female leaders on both outcomes. Gender-based advantages to team leadership and clinical care were not conclusively supported or refuted, with the exception of rejecting a strong male advantage to team leadership.

CONCLUSIONS

We prospectively measured team leadership and clinical care during patient care. Our findings do not support differences in trauma resuscitation team leadership or clinical care based on the gender of the team leader.

Trial Design in Critical Care Nutrition: The Past, Present and Future

The specialty of nutrition in critical care is relatively modern, and accordingly, trial design has progressed over recent decades. In the past, small observational and physiological studies evolved to become small single-centre comparative trials, but these had significant limitations by today’s standards. Power calculations were often not undertaken, outcomes were not specified a priori, and blinding and randomisation were not always rigorous. These trials have been superseded by larger, more carefully designed and conducted multi-centre trials. Progress in trial conduct has been facilitated by a greater understanding of statistical concepts and methodological design. In addition, larger numbers of potential study participants and increased access to funding support trials able to detect smaller differences in outcomes. This narrative review outlines why critical care nutrition research is unique and includes a historical critique of trial design to provide readers with an understanding of how and why things have changed. This review focuses on study methodology, population group, intervention, and outcomes, with a discussion as to how these factors have evolved, and concludes with an insight into what we believe trial design may look like in the future. This will provide perspective on the translation of the critical care nutrition literature into clinical practice.

Clinical trials in critical care: can a Bayesian approach enhance clinical and scientific decision making?

Recent Bayesian reanalyses of prominent trials in critical illness have generated controversy by contradicting the initial conclusions based on conventional frequentist analyses. Many clinicians might be sceptical that Bayesian analysis, a philosophical and statistical approach that combines prior beliefs with data to generate probabilities, provides more useful information about clinical trials than the frequentist approach. In this Personal View, we introduce clinicians to the rationale, process, and interpretation of Bayesian analysis through a systematic review and reanalysis of interventional trials in critical illness. In the majority of cases, Bayesian and frequentist analyses agreed. In the remainder, Bayesian analysis identified interventions where benefit was probable despite the absence of statistical significance, where interpretation depended substantially on choice of prior distribution, and where benefit was improbable despite statistical significance. Bayesian analysis in critical care medicine can help to distinguish harm from uncertainty and establish the probability of clinically important benefit for clinicians, policy makers, and patients.

Typology of Published Randomized Controlled Trials Investigating Initial Ventilation Strategy in Critically Ill Patients With Acute Respiratory Failure: A Methodologic Review

BACKGROUND

Randomized controlled trials (RCTs) in patients with hypoxemic acute respiratory failure (ARF) often failed to show survival benefits and resulted in varying clinical end points.

RESEARCH QUESTION

This methodologic review was conducted of published RCTs on ARF, with a careful attention to whether the study results were positive or negative.

STUDY DESIGN AND METHODS

MEDLINE, Cochrane Central Register of Controlled Trials, and Web of Science were searched for published RCTs in adult patients with ARF between January 1995 and December 2019. The objective was to investigate sources of heterogeneity and factors associated with a positive RCT (ie, with a significant difference on the primary end point). To determine the importance of the primary end point choice, end points were classified as follows: (1) respiratory event end points (corresponding to modification of the ventilation support); (2) physiologic/clinical end points (corresponding to oxygenation or clinical parameters); and (3) mortality. The Cochrane risk-of-bias tool was used to assess study quality.

RESULTS

Seventy-four RCTs were included (57% were single-center RCTs) comparing mainly oxygenation/ventilation strategies (95%) in patients with various ARF causes (62%); studies were stopped prematurely in 20% of the trials. A standardized management of ARF was observed in 24 (32%) trials. Twenty-two distinct primary end points have been used, the first of which were those based on respiratory events (44 RCTs [49%]), namely intubation in 76% of the cases. Physiologic/clinical end points have been used in 21 trials (29%) and mortality in nine (12%). Overall, 42 (57%) RCTs were positive, 52% in studies with respiratory event end points, 76% in studies with physiologic/clinical end points, and 33% in studies with mortality end points. Adjusted for study quality (Cochrane risk-of-bias tool), factors associated with a positive RCT included clinically based primary end points (OR, 8.40; 95% CI, 1.35-65.79), the use of standardized ARF management (OR, 4.55; 95% CI, 1.02-22.88), and single-center trials (OR, 3.85; 95% CI, 1.25-13.11).

INTERPRETATION

The typology of published RCTs in patients with ARF could be used to frame future trial designs in this field and guide clinicians and researchers toward optimal research transfer to the bedside.

The Statistical Curriculum Within Randomized Controlled Trials in Critical Illness

OBJECTIVES

Incomplete biostatistical knowledge among clinicians is widely described. This study aimed to categorize and summarize the statistical methodology within recent critical care randomized controlled trials.

DESIGN

Descriptive analysis, with comparison of findings to previous work.

SETTING

Ten high-impact clinical journals publishing trials in critical illness.

SUBJECTS

Randomized controlled trials published between 2011 and 2015 inclusive.

INTERVENTIONS

Data extraction from published reports.

MEASUREMENTS AND MAIN RESULTS

The frequency and overall proportion of each statistical method encountered, grouped according to those used to generate each trial's primary outcome and separately according to underlying statistical methodology. Subsequent analysis compared these proportions with previously published reports. A total of 580 statistical tests or methods were identified within 116 original randomized controlled trials published between 2011 and 2015. Overall, the chi-square test was the most commonly encountered (70/116; 60%), followed by the Cox proportional hazards model (63/116; 54%) and logistic regression (53/116; 46%). When classified according to underlying statistical assumptions, the most common types of analyses were tests of 2 × 2 contingency tables and nonparametric tests of rank order. A greater proportion of more complex methodology was observed compared with trial reports from previous work.

CONCLUSIONS

Physicians assessing recent randomized controlled trials in critical illness encounter results derived from a substantial and potentially expanding range of biostatistical methods. In-depth training in the assumptions and limitations of these current and emerging biostatistical methods may not be practically achievable for most clinicians, making accessible specialist biostatistical support an asset to evidence-based clinical practice.

Epidemiology of Lower Extremity Deep Venous Thrombosis in Critically Ill Adolescents

OBJECTIVE

To determine the epidemiology of lower extremity deep venous thrombosis (DVT) in critically ill adolescents, which currently is unclear.

STUDY DESIGN

We performed a multicenter, prospective, cohort study. Adolescents aged 13-17 years who were admitted to 6 pediatric intensive care units and were anticipated to receive cardiopulmonary support for at least 48 hours were eligible, unless they were admitted with DVT or pulmonary embolism or were receiving or anticipated to receive therapeutic anticoagulation. While patients were in the unit, serial sonograms of the lower extremities were performed, then centrally adjudicated. Bayesian statistics were used to leverage the similarities between adults and adolescents.

RESULTS

A total of 88 adolescents were enrolled, from whom 184 lower extremity sonograms were performed. Of these, 9 adolescents developed DVT, with 1 having bilateral DVT. The frequency of DVT was 12.4% (95% credible interval: 6.1%, 20.1%), which ranged from 6.3% to 19.8% with a variability of 41.0% across units. All cases of DVT occurred in adolescents who received invasive mechanical ventilation (frequency: 16.5%; 95% credible interval 8.1%, 26.6%). DVT was associated with femoral central venous catheterization (OR 15.44; 95% credible interval 1.62, 69.05) and severe illness (OR for every 0.1 increase in risk of mortality 3.11; 95% credible interval 1.19, 6.85). DVT appears to be associated with prolonged days on support.

CONCLUSIONS

Our findings highlight the similarities and differences in the epidemiology of DVT between adults and adolescents. They support the conduct and inform the design of a trial of pharmacologic prophylaxis in critically ill adolescents.

Effect sizes in ongoing randomized controlled critical care trials

Background

An important limitation of many critical care trial designs is that they hypothesize large, and potentially implausible, reductions in mortality. Interpretation of trial results could be improved by systematic assessment of the plausibility of trial hypotheses; however, such assessment has not been attempted in the field of critical care medicine. The purpose of this study was to determine clinicians’ views about prior probabilities and plausible effect sizes for ongoing critical care trials where the primary endpoint is landmark mortality.

Methods

We conducted a systematic review of clinical trial registries in September 2015 to identify ongoing critical care medicine trials where landmark mortality was the primary outcome, followed by a clinician survey to obtain opinions about ten large trials. Clinicians were asked to estimate the probability that each trial would demonstrate a mortality effect equal to or larger than that used in its sample size calculations.

Results

Estimates provided by individual clinicians varied from 0% to 100% for most trials, with a median estimate of 15% (IQR 10–20%). The median largest absolute mortality reduction considered plausible was 4.5% (IQR 3.5–5%), compared with a median absolute mortality reduction used in sample size calculations of 5% (IQR 3.6–10%) (P = 0.27).

Conclusions

For some of the largest ongoing critical care trials, many clinicians regard prior probabilities as low and consider that plausible effects on absolute mortality are less than 5%. Further work is needed to determine whether pooled estimates obtained by surveying clinicians are replicable and accurate or whether other methods of estimating prior probability are preferred.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-017-1726-x) contains supplementary material, which is available to authorized users.

Updating Evidence for Using Hypothermia in Pediatric Severe Traumatic Brain Injury: Conventional and Bayesian Meta-Analytic Perspectives

OBJECTIVE

To evaluate clinical trials of hypothermia management on outcome in pediatric patients with severe traumatic brain injury using conventional and Bayesian meta-analyses.

DATA SOURCES

Screening of PubMed and other databases to identify randomized controlled trials of hypothermia for pediatric severe traumatic brain injury published before September 2016.

STUDY SELECTION

Four investigators assessed and reviewed randomized controlled trial data.

DATA EXTRACTION

Details of trial design, patient number, Glasgow Coma Scale score, hypothermia and control normothermia therapy, and outcome of mortality were collated.

DATA SYNTHESIS

In conventional meta-analysis, random-effects models were expressed as odds ratio (odds ratio with 95% credible-interval). Bayesian outcome probabilities were calculated as probability of odds ratio greater than or equal to 1. In seven randomized controlled trials (n = 472, patients 0-17 yr old), there was no difference in mortality (hypothermia vs normothermia) with pooled estimate 1.42 (credible-interval, 0.77-2.61; p = 0.26). Duration of hypothermia (24, 48, or 72 hr) did not show difference in mortality. (Similar results were found using poor outcome.) Bayesian analyses of randomized controlled trials ordered by time of study completed recruitment showed, after the seventh trial, chance of relative risk reduction of death by greater than 20% is 1-in-3. An optimistic belief (0.90 probability that relative risk reduction of death > 20% hypothermia vs normothermia) gives a chance of relative risk reduction of death by greater than 20% of 1-in-2.

CONCLUSIONS

Conventional meta-analysis shows the null hypothesis-no difference between hypothermia versus normothermia on mortality and poor outcome-cannot be rejected. However, Bayesian meta-analysis shows chance of relative risk reduction of death greater than 20% with hypothermia versus normothermia is 1-in-3, which may be further altered by one's optimistic or skeptical belief about a patient.

Bayes to the Rescue: Continuous Positive Airway Pressure Has Less Mortality Than High-Flow Oxygen

OBJECTIVES

The merits of high-flow nasal cannula oxygen versus bubble continuous positive airway pressure are debated in children with pneumonia, with suggestions that randomized controlled trials are needed. In light of a previous randomized controlled trial showing a trend for lower mortality with bubble continuous positive airway pressure, we sought to determine the probability that a new randomized controlled trial would find high-flow nasal cannula oxygen superior to bubble continuous positive airway pressure through a "robust" Bayesian analysis.

DESING, SETTING, PATIENTS, AND INTERVENTIONS

Sample data were extracted from the trial by Chisti et al, and requisite to "robust" Bayesian analysis, we specified three prior distributions to represent clinically meaningful assumptions. These priors (reference, pessimistic, and optimistic) were used to generate three scenarios to represent the range of possible hypotheses. 1) "Reference": we believe bubble continuous positive airway pressure and high-flow nasal cannula oxygen are equally effective with the same uninformative reference priors; 2) "Sceptic on high-flow nasal cannula oxygen": we believe that bubble continuous positive airway pressure is better than high-flow nasal cannula oxygen (bubble continuous positive airway pressure has an optimistic prior and high-flow nasal cannula oxygen has a pessimistic prior); and 3) "Enthusiastic on high-flow nasal cannula oxygen": we believe that high-flow nasal cannula oxygen is better than bubble continuous positive airway pressure (high-flow nasal cannula oxygen has an optimistic prior and bubble continuous positive airway pressure has a pessimistic prior). Finally, posterior empiric Bayesian distributions were obtained through 100,000 Markov Chain Monte Carlo simulations.

MEASUREMENTS AND MAIN RESULTS

In all three scenarios, there was a high probability for more death from high-flow nasal cannula oxygen compared with bubble continuous positive airway pressure (reference, 0.98; sceptic on high-flow nasal cannula oxygen, 0.982; enthusiastic on high-flow nasal cannula oxygen, 0.742). The posterior 95% credible interval on the difference in mortality identified a future randomized controlled trial would be extremely unlikely to find a mortality benefit for high-flow nasal cannula oxygen over bubble continuous positive airway pressure, regardless of the scenario. Interpreting these findings using the "range of practical equivalence" framework would recommend rejecting the hypothesis that high-flow nasal cannula oxygen is superior to bubble continuous positive airway pressure for these children.

CONCLUSIONS

For children younger than 5 years with pneumonia, high-flow nasal cannula oxygen has higher mortality than bubble continuous positive airway pressure. A future randomized controlled trial in this population is unlikely to find high-flow nasal cannula oxygen superior to bubble continuous positive airway pressure.

Prevention of Hospital-Acquired Venous Thromboembolism in Children: A Review of Published Guidelines

Venous thromboembolism, which includes deep venous thrombosis and pulmonary embolism, is a potentially preventable condition in children. In adults, pharmacologic prophylaxis has been shown to significantly reduce the incidence of venous thromboembolism in distinct patient cohorts. However, pediatric randomized controlled trials have failed to demonstrate the efficacy of pharmacologic prophylaxis against thrombosis associated with central venous catheters, the most important risk factor for venous thromboembolism in children. Despite the lack of supporting evidence, hospital-based initiatives are being undertaken to try to prevent venous thromboembolism in children. In this study, we sought to review the published guidelines on the prevention of venous thromboembolism in hospitalized children. We identified five guidelines, all of which were mainly targeted at adolescents and used various risk-stratification approaches. In low-risk children, ambulation was the recommended prevention strategy, while mechanical prophylaxis was recommended for children at moderate risk and pharmacologic and mechanical prophylaxis were recommended for the high-risk group. The effectiveness of these strategies has not been proven. In order to determine whether venous thromboembolism can be prevented in children, innovative clinical trial designs are needed. In the absence of these trials, guidelines can be a source of valuable information to inform our practice.

Bayesian approach to the assessment of the population-specific risk of inhibitors in hemophilia A patients: a case study

Background

Developing inhibitors is a rare event during the treatment of hemophilia A. The multifacets and uncertainty surrounding the development of inhibitors further complicate the process of estimating inhibitor rate from the limited data. Bayesian statistical modeling provides a useful tool in generating, enhancing, and exploring the evidence through incorporating all the available information.

Methods

We built our Bayesian analysis using three study cases to estimate the inhibitor rates of patients with hemophilia A in three different scenarios: Case 1, a single cohort of previously treated patients (PTPs) or previously untreated patients; Case 2, a meta-analysis of PTP cohorts; and Case 3, a previously unexplored patient population – patients with baseline low-titer inhibitor or history of inhibitor development. The data used in this study were extracted from three published ADVATE (antihemophilic factor [recombinant] is a product of Baxter for treating hemophilia A) post-authorization surveillance studies. Noninformative and informative priors were applied to Bayesian standard (Case 1) or random-effects (Case 2 and Case 3) logistic models. Bayesian probabilities of satisfying three meaningful thresholds of the risk of developing a clinical significant inhibitor (10/100, 5/100 [high rates], and 1/86 [the Food and Drug Administration mandated cutoff rate in PTPs]) were calculated. The effect of discounting prior information or scaling up the study data was evaluated.

Results

Results based on noninformative priors were similar to the classical approach. Using priors from PTPs lowered the point estimate and narrowed the 95% credible intervals (Case 1: from 1.3 [0.5, 2.7] to 0.8 [0.5, 1.1]; Case 2: from 1.9 [0.6, 6.0] to 0.8 [0.5, 1.1]; Case 3: 2.3 [0.5, 6.8] to 0.7 [0.5, 1.1]). All probabilities of satisfying a threshold of 1/86 were above 0.65. Increasing the number of patients by two and ten times substantially narrowed the credible intervals for the single cohort study (1.4 [0.7, 2.3] and 1.4 [1.1, 1.8], respectively). Increasing the number of studies by two and ten times for the multiple study scenarios (Case 2: 1.9 [0.6, 4.0] and 1.9 [1.5, 2.6]; Case 3: 2.4 [0.9, 5.0] and 2.6 [1.9, 3.5], respectively) had a similar effect.

Conclusion

Bayesian approach as a robust, transparent, and reproducible analytic method can be efficiently used to estimate the inhibitor rate of hemophilia A in complex clinical settings.