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1.  An Economic Evaluation of Venous Thromboembolism Prophylaxis Strategies in Critically Ill Trauma Patients at Risk of Bleeding 
PLoS Medicine  2009;6(6):e1000098.
Using decision analysis, Henry Stelfox and colleagues estimate the cost-effectiveness of three venous thromboembolism prophylaxis strategies in patients with severe traumatic injuries who were also at risk for bleeding complications.
Background
Critically ill trauma patients with severe injuries are at high risk for venous thromboembolism (VTE) and bleeding simultaneously. Currently, the optimal VTE prophylaxis strategy is unknown for trauma patients with a contraindication to pharmacological prophylaxis because of a risk of bleeding.
Methods and Findings
Using decision analysis, we estimated the cost effectiveness of three VTE prophylaxis strategies—pneumatic compression devices (PCDs) and expectant management alone, serial Doppler ultrasound (SDU) screening, and prophylactic insertion of a vena cava filter (VCF)—in trauma patients admitted to an intensive care unit (ICU) with severe injuries who were believed to have a contraindication to pharmacological prophylaxis for up to two weeks because of a risk of major bleeding. Data on the probability of deep vein thrombosis (DVT) and pulmonary embolism (PE), and on the effectiveness of the prophylactic strategies, were taken from observational and randomized controlled studies. The probabilities of in-hospital death, ICU and hospital discharge rates, and resource use were taken from a population-based cohort of trauma patients with severe injuries (injury severity scores >12) admitted to the ICU of a regional trauma centre. The incidence of DVT at 12 weeks was similar for the PCD (14.9%) and SDU (15.0%) strategies, but higher for the VCF (25.7%) strategy. Conversely, the incidence of PE at 12 weeks was highest in the PCD strategy (2.9%), followed by the SDU (1.5%) and VCF (0.3%) strategies. Expected mortality and quality-adjusted life years were nearly identical for all three management strategies. Expected health care costs at 12 weeks were Can$55,831 for the PCD strategy, Can$55,334 for the SDU screening strategy, and Can$57,377 for the VCF strategy, with similar trends noted over a lifetime analysis.
Conclusions
The attributable mortality due to PE in trauma patients with severe injuries is low relative to other causes of mortality. Prophylactic placement of VCF in patients at high risk of VTE who cannot receive pharmacological prophylaxis is expensive and associated with an increased risk of DVT. Compared to the other strategies, SDU screening was associated with better clinical outcomes and lower costs.
Please see later in the article for Editors' Summary
Editors' Summary
Background
For patients who have been seriously injured in an accident or a violent attack (trauma patients), venous thromboembolism (VTE)—the formation of blood clots that limit the flow of blood through the veins—is a frequent and potentially fatal complication. The commonest form of VTE is deep vein thrombosis (DVT). “Distal” DVTs (clots that form in deep veins below the knee) affect about half of patients with severe trauma; “proximal” DVTs (clots that form above the knee) develop in one in five trauma patients. DVTs cause pain and swelling in the affected leg and can leave patients with a painful condition called post-thrombotic syndrome. Worse still, part of the clot can break off and travel to the lungs where it can cause a life-threatening pulmonary embolism (PE). Distal DVTs rarely embolize but, if untreated, half of patients who present with a proximal DVT will develop a PE, and 2%–3% of them will die as a result.
Why Was This Study Done?
VTE is usually prevented by using heparin, a drug that stops blood clotting, but clinicians treating critically ill trauma patients have a dilemma. Many of these patients are at high risk of serious bleeding complications so cannot be given heparin to prevent VTE. Nonpharmacological ways to prevent VTE include the use of pneumatic compression devices to keep the blood moving in the legs (clots often form in patients confined to bed because of the sluggish blood flow in their legs), repeated screening for blood clots using Doppler ultrasound, and the insertion of a “vena cava filter” into the vein that takes blood from the legs to the heart. This last device catches blood clots before they reach the lungs but increases the risk of DVT. Unfortunately, no-one knows which VTE prevention strategy works best in trauma patients who cannot be given heparin. In this study, therefore, the researchers use decision analysis (the systematic evaluation of the most important factors affecting a decision) to estimate the costs and likely clinical outcomes of these strategies.
What Did the Researchers Do and Find?
The researchers used cost and clinical data from patients admitted to a Canadian trauma center with severe head/neck and/or abdomen/pelvis injuries (patients with a high risk of bleeding complications likely to make heparin therapy dangerous for up to two weeks after the injury) to construct a Markov decision analysis model. They then fed published data on the chances of patients developing DVT or PE, and on the effectiveness of the three VTE prevention strategies, into the model to obtain estimates of the costs and clinical outcomes of the strategies at 12 weeks after the injury and over the patients' lifetime. The estimated incidence of DVT at 12 weeks was 15% for the pneumatic compression device and Doppler ultrasound strategies, but 25% for the vena cava filter strategy. By contrast, the estimated incidence of PE was 2.9% with the pneumatic compression device, 1.5% with Doppler ultrasound, but only 0.3% with the vena cava filter. The expected mortality with all three strategies was similar. Finally, the estimated health care costs per patient at 12 weeks were Can$55,334 and Can$55,831 for the Doppler ultrasound and pneumatic compression device strategies, respectively, but Can$57,377 for the vena cava filter strategy; similar trends were seen for lifetime health care costs.
What Do These Findings Mean?
As with all mathematical models, these findings depend on the data fed into the model and on the assumptions included in it. For example, because data from one Canadian trauma unit were used to construct the model, these findings may not be generalizable. Nevertheless, these findings suggest that, although VTE is common among patients with severe injuries, PE is not a major cause of death among these patients. They also suggest that the use of vena cava filters for VTE prevention in patients who cannot receive heparin should not be routinely used because it is expensive and increases the risk of DVT. Finally, these results suggest that, compared with the other strategies, serial Doppler ultrasound is associated with better clinical outcomes and lower costs.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1000098.
The US National Heart Lung and Blood Institute provides information (including an animation) on deep vein thrombosis and pulmonary embolism
MedlinePlus provides links to more information about deep vein thrombosis and pulmonary embolism (in several languages)
The UK National Health Service Choices Web site has information on deep vein thrombosis and on embolism (in English and Spanish)
The Eastern Association for the Surgery of Trauma working group document Practice Management Guidelines for the Management of Venous Thromboembolism in Trauma Patients can be downloaded from the Internet
doi:10.1371/journal.pmed.1000098
PMCID: PMC2695771  PMID: 19554085
2.  Does dalteparin PROTECT better than heparin? 
Critical Care  2011;15(6):315.
Expanded abstract
Citation
The PROTECT Investigators for the Canadian Critical Care Trials Group and the Australian and New Zealand Intensive Care Society Clinical Trials Group: Dalteparin versus Unfractionated Heparin in Critically Ill Patients. N Engl J Med 2011, 364:1305-1314.
Background
It is unclear whether there is a clinically significant advantage to prophylactic low-molecular-weight heparin (LMWH) versus unfractionated heparin (UFH) in mixed medical/surgical critically ill adult patients.
Methods
Objective: To compare once daily dalteparin with twice daily unfractionated heparin for primary prophylaxis of proximal deep venous thrombosis in critically ill adults.
Design: A superiority randomized double-blinded controlled trial from 2006 to 2010 in both medical and surgical ICUs. (ClinicalTrials.gov registration number: NCT00182143)
Setting: Multi-center, international medical and surgical intensive care units (ICUs)
Subjects: Critically ill adults expected to remain in the ICU for at least 3 days.
Intervention: Patients were randomized to either twice daily UFH or daily dalteparin for the duration of ICU admission.
Outcomes: The primary endpoint was proximal leg deep venous thrombosis (DVT), at least three days after randomization, detected on twice weekly screening ultrasound. Secondary endpoints were: any DVT, pulmonary embolism (PE), venous thromboembolism (VTE), death, heparin-induced thrombocytopenia (HIT), major bleeding, and composite death/VTE.
Results
Three thousand seven hundred and forty-six subjects were included in the intention-to-treat analysis. Proximal leg DVT occurred in 96 of 1873 (5.1%) patients randomized to dalteparin versus 109 of 1873 (5.8%) patients randomized to UFH (hazard ratio in the dalteparin group, 0.92; 95% confidence interval [CI], 0.68 to 1.23; P = 0.57). The incidence of PE was 1.3% in the dalteparin group compared to 2.3% in the UFH group (hazard ratio, 0.51; 95% CI, 0.30 to 0.88; P = 0.01). There was no mortality difference and no difference in major bleeding between the two study arms. There was a statistically significant decrease in incidence of HIT in the dalteparin group in the per-protocol analysis, but not in the intention-to-treat analysis.
Limitations
Comparing the incidence of PE was a secondary endpoint and the study was not appropriately powered for this conclusion.
Conclusions
Among critically ill adult patients, dalteparin was not superior to UFH at preventing proximal lower extremity DVTs. There is a suggestion that dalteparin might be superior to UFH at preventing pulmonary embolism but a larger trial is necessary to confirm this result.
doi:10.1186/cc10581
PMCID: PMC3388642  PMID: 22152126
3.  Safety and efficacy of low-molecular-weight heparins in prophylaxis of deep vein thrombosis in postoperative/ICU patients: A comparative study 
Background:
Venous thromboembolism (VTE), although a very common problem in everyday clinical practice, remains asymptomatic in most cases. Clinical diagnosis helps identify those who are going to have thromboembolic episode. A combination of clinical scoring systems like Wells’ score and D-dimer assay provide a useful diagnostic tool. Trauma (surgical or accidental) and critically ill patients are found to have greatest risk. Enoxaparin and dalteparin are amongst the most common low-molecular-weight heparins (LMWHs) used for deep venous thrombosis (DVT) prophylaxis in such patients.
Aim:
The present study is designed to compare their role in preventing DVT in postoperative or critically ill patients and to determine their relative safety profiles.
Materials and Methods:
The study included 36 critically ill adult patients. All the patients were allocated into three groups of 12 patients each. Group I patients received no prophylaxis, group II received inj. enoxaparin s/c 0.6-0.8 mg/kg twice daily, and group III received inj. dalteparin s/c 125-250 units/kg once daily. Routine investigations and coagulation profile were recorded on admission to intensive care unit (ICU) and at every third day thereafter. Patients were daily assessed for pretest probability of DVT using Wells’ scoring, and D-dimer test was done on the 7th day. Occurrence of any bleeding (visible or occult) was noted, and incidence of DVT was determined in each group using positive results of D-dimer test and the clinical assessment with Wells’ score.
Results:
A significant difference in Wells’ score (P < 0.05) was found between groups I and III on day 5 and day 7. A lower, but insignificant difference in the incidence of DVT was found between the study and control groups. No significant difference in major bleeding or other side effects was found. Better hemodynamic status and arterial blood gases in the study groups may indirectly refer to absence of asymptomatic DVT or silent pulmonary embolism in this group.
Conclusion:
The present study suggests that LMWHs, namely, enoxaparin and dalteparin, provide effective means of preventing DVT in high-risk, critically ill or postoperative patients, without causing any significant increase in the risk of bleeding or other side effects. Dalteparin appears to be unaffected by low creatinine clearance as explained by its clearance by a non-saturable mechanism. Still, a more extensive study with larger population is needed to make the outcomes worthwhile.
doi:10.4103/0976-9668.107290
PMCID: PMC3633277  PMID: 23633862
D-dimer; deep vein thrombosis; low-molecular-weight heparin; venous thromboembolism
4.  Pulmonary embolism in intensive care unit: Predictive factors, clinical manifestations and outcome 
Annals of Thoracic Medicine  2010;5(2):97-103.
OBJECTIVE:
To determine predictive factors, clinical and demographics characteristics of patients with pulmonary embolism (PE) in ICU, and to identify factors associated with poor outcome in the hospital and in the ICU.
METHODS:
During a four-year prospective study, a medical committee of six ICU physicians prospectively examined all available data for each patient in order to classify patients according to the level of clinical suspicion of pulmonary thromboembolism. During the study periods, all patients admitted to our ICU were classified into four groups. The first group includes all patients with confirmed PE; the second group includes some patients without clinical manifestations of PE; the third group includes patients with suspected and not confirmed PE and the fourth group includes all patients with only deep vein thromboses (DVTs) without suspicion of PE. The diagnosis of PE was confirmed either by a high-probability ventilation/perfusion (V/Q) scan or by a spiral computed tomography (CT) scan showing one or more filling defects in the pulmonary artery or in its branches. The diagnosis was also confirmed by echocardiography when a thrombus in the pulmonary artery was observed.
RESULTS:
During the study periods, 4408 patients were admitted in our ICU. The diagnosis of PE was confirmed in 87 patients (1.9%). The mean delay of development of PE was 7.8 ± 9.5 days. On the day of PE diagnosis, clinical examination showed that 50 patients (57.5%) were hypotensive, 63 (72.4%) have SIRS, 15 (17.2%) have clinical manifestations of DVT and 71 (81.6%) have respiratory distress requiring mechanical ventilation. In our study, intravenous unfractionated heparin was used in 81 cases (93.1%) and low molecular weight heparins were used in 4 cases (4.6%). The mean ICU stay was 20.2 ± 25.3 days and the mean hospital stay was 25.5 ± 25 days. The mortality rate in ICU was 47.1% and the in-hospital mortality rate was 52.9%. Multivariate analysis showed that factors associated with a poor prognosis in ICU are the use of norepinephrine and epinephrine. Furthermore, factors associated with in-hospital poor outcome in multivariate analysis were a number of organ failure associated with PE ≥ 3.
Moreover, comparison between patients with and without pe showed that predictive factors of pe are: acute medical illness, the presence of meningeal hemorrhage, the presence of spine fracture, hypoxemia with PaO2/FiO2 ratio <300 and the absence of pharmacological prevention of venous thromboembolism.
CONCLUSION:
Despite the high frequency of DVT in critically ill patients, symptomatic PE remains not frequently observed, because systematic screening is not performed. Pulmonary embolism is associated with a high ICU and in-hospital mortality rate. Predictive factors of PE are acute medical illness, the presence of meningeal hemorrhage, the presence of spine fracture, hypoxemia with PaO2/FiO2 < 300 and the absence of pharmacological prevention of venous thromboembolism.
doi:10.4103/1817-1737.62473
PMCID: PMC2883205  PMID: 20582175
ICU; predictive factors; prophylactic anticoagulation; pulmonary embolism
5.  Post-traumatic pulmonary embolism in the intensive care unit 
Annals of Thoracic Medicine  2011;6(4):199-206.
OBJECTIVE:
To determine the predictive factors, clinical manifestations, and the outcome of patients with post-traumatic pulmonary embolism (PE) admitted in the intensive care unit (ICU).
METHODS:
During a four-year prospective study, a medical committee of six ICU physicians prospectively examined all available data for each trauma patient in order to classify patients according to the level of clinical suspicion of pulmonary thromboembolism. During the study period, all trauma patients admitted to our ICU were classified into two groups. The first group included all patients with confirmed PE; the second group included patients without clinical manifestations of PE. The diagnosis of PE was confirmed either by a high-probability ventilation/perfusion (V/Q) scan or by a spiral computed tomography (CT) scan showing one or more filling defects in the pulmonary artery or its branches.
RESULTS:
During the study period, 1067 trauma patients were admitted in our ICU. The diagnosis of PE was confirmed in 34 patients (3.2%). The mean delay of development of PE was 11.3 ± 9.3 days. Eight patients (24%) developed this complication within five days of ICU admission. On the day of PE diagnosis, the clinical examination showed that 13 patients (38.2%) were hypotensive, 23 (67.7%) had systemic inflammatory response syndrome (SIRS), three (8.8%) had clinical manifestations of deep venous thrombosis (DVT), and 32 (94%) had respiratory distress requiring mechanical ventilation. In our study, intravenous unfractionated heparin was used in 32 cases (94%) and low molecular weight heparin was used in two cases (4%). The mean ICU stay was 31.6 ± 35.7 days and the mean hospital stay was 32.7 ± 35.3 days. The mortality rate in the ICU was 38.2% and the in-hospital mortality rate was 41%. The multivariate analysis showed that factors associated with poor prognosis in the ICU were the presence of circulatory failure (Shock) (Odds ratio (OR) = 9.96) and thrombocytopenia (OR = 32.5).Moreover, comparison between patients with and without PE showed that the predictive factors of PE were: Age > 40 years, a SAPS II score > 25, hypoxemia with PaO2/FiO2 < 200 mmHg, the presence of spine fracture, and the presence of meningeal hemorrhage.
CONCLUSION:
Despite the high frequency of DVT in post-traumatic critically ill patients, symptomatic PE remains, although not frequently observed, because systematic screening is not performed. Factors associated with poor prognosis in the ICU are the presence of circulatory failure (shock) and thrombocytopenia. Predictive factors of PE are: Age > 40 years, a SAPS II score > 25, hypoxemia with PaO2/FiO2 < 200, the presence of a spine fracture, and the presence of meningeal hemorrhage. Prevention is highly warranted.
doi:10.4103/1817-1737.84773
PMCID: PMC3183636  PMID: 21977064
Anticoagulation; ICU; predictive factors; pulmonary embolism; trauma patients
6.  Dalteparin Vs Low-Dose Unfractionated Heparin for Prophylaxis Against Clinically Evident Venous Thromboembolism in Acute Traumatic Spinal Cord Injury: A Retrospective Cohort Study 
Background:
When venous thromboembolism (VTE) includes deep-vein thrombosis (DVT) and pulmonary embolism (PE), patients with acute traumatic spinal cord injury (SCI) have the highest incidence of VTE among all hospitalized groups, with PE the third most common cause of death. Although low–molecular-weight heparin (LMWH) outperforms low-dose unfractionated heparin (LDUH) in other patient populations, the evidence in SCI remains less robust.
Objective:
To determine whether the efficacy for LMWH shown in previous SCI surveillance studies (eg, routine Doppler ultrasound) would translate into real-world effectiveness in which only clinically evident VTE is investigated (ie, after symptoms or signs present).
Methods:
A retrospective cohort study was conducted of 90 patients receiving LMWH dalteparin (5,000 U daily) or LDUH (5,000 U twice daily) for VTE prophylaxis after acute traumatic SCI. The incidence of radiographically confirmed VTE was primarily analyzed, and secondary outcomes included complications of bleeding and heparin-induced thrombocytopenia.
Results:
There was no statistically significant association (p = 0.7054) between the incidence of VTE (7.78% overall) and the type of prophylaxis received (LDUH 3/47 vs dalteparin 4/43). There was no significant differences in complications, location of VTE, and incidence of fatal PE. Paraplegia (as opposed to tetraplegia) was the only risk factor identified for VTE.
Conclusions:
There continues to be an absence of definitive evidence for dalteparin (or other LMWH) over LDUH as the choice for VTE prophylaxis in patients with SCI. Novel approaches to VTE prophylaxis are urgently required for this population, whose risk of fatal PE has not decreased over the last 25 years.
PMCID: PMC2582433  PMID: 18959355
Dalteparin; Heparin, low–molecular-weight; Pulmonary embolism; Rehabilitation; Spinal cord injuries; Venous thrombosis; Tetraplegia; Paraplegia
7.  Venous thromboembolism prophylaxis for hospitalized medical patients, current status and strategies to improve 
Annals of Thoracic Medicine  2010;5(4):195-200.
Venous thromboembolism (VTE), comprising life-threatening pulmonary embolism (PE) and its precursor deep-vein thrombosis (DVT), is commonly encountered problem. Although most patients survive DVT, they often develop serious and costly long-term complications. Both unfractionated heparin and low molecular weight heparins significantly reduce the incidence of VTE and its associated complications. Despite the evidence demonstrating significant benefit of VTE prophylaxis in acutely ill medical patients, several registries have shown significant underutilization. This underutilization indicates the need for educational and audit programs in order to increase the number of medical patients receiving appropriate prophylaxis. Many health advocacy groups and policy makers are paying more attention to VTE prophylaxis; the National Quality Forum and the Joint Commission recently endorsed strict VTE risk assessment evaluation for each patient upon admission and regularly thereafter. In the article, all major studies addressing this issue in medical patients have been reviewed from the PubMed. The current status of VTE prophylaxis in hospitalized medical patients is addressed and some improvement strategies are discussed.
doi:10.4103/1817-1737.69104
PMCID: PMC2954373  PMID: 20981179
Deep vein thrombosis; heparin; low molecular weight heparin; pulmonary embolism; thromboprophylaxis
8.  Venous thromboembolism deserves your attention 
Critical Care  2001;5(6):277-279.
The survey of how Canadian intensive care units (ICUs) prevent and diagnose venous thromboembolism (VTE) presented in this issue of Critical Care illustrates considerable variability. Lack of optimal patient care reflects how VTE is rated in ICUs. The discussion should no longer focus on the incidence of thrombosis, but rather on its prevention. Unfractionated heparin remains the most commonly used agent to prevent VTE, despite the recognized efficacy and safety of low-molecular-weight heparins (LMWHs) in the ICU setting. In addition, too few ICU directors consider the use of mechanical prophylactic measures, such as graded elastic stockings and venous foot pump. The present situation calls for large randomized controlled trials in either medical or surgical ICU patients, and for new education programmes in order to modify the care of ICU patients with regard to VTE.
doi:10.1186/cc1046
PMCID: PMC137365  PMID: 11737903
compression; intensive care unit; low-molecular-weight heparin; thromboembolism
9.  Current and Former Smoking and Risk for Venous Thromboembolism: A Systematic Review and Meta-Analysis 
PLoS Medicine  2013;10(9):e1001515.
In a meta-analysis of 32 observational studies involving 3,966,184 participants and 35,151 events, Suhua Wu and colleagues found that current, ever, and former smoking was associated with risk of venous thromboembolism.
Please see later in the article for the Editors' Summary
Background
Smoking is a well-established risk factor for atherosclerotic disease, but its role as an independent risk factor for venous thromboembolism (VTE) remains controversial. We conducted a meta-analysis to summarize all published prospective studies and case-control studies to update the risk for VTE in smokers and determine whether a dose–response relationship exists.
Methods and Findings
We performed a literature search using MEDLINE (source PubMed, January 1, 1966 to June 15, 2013) and EMBASE (January 1, 1980 to June 15, 2013) with no restrictions. Pooled effect estimates were obtained by using random-effects meta-analysis. Thirty-two observational studies involving 3,966,184 participants and 35,151 VTE events were identified. Compared with never smokers, the overall combined relative risks (RRs) for developing VTE were 1.17 (95% CI 1.09–1.25) for ever smokers, 1.23 (95% CI 1.14–1.33) for current smokers, and 1.10 (95% CI 1.03–1.17) for former smokers, respectively. The risk increased by 10.2% (95% CI 8.6%–11.8%) for every additional ten cigarettes per day smoked or by 6.1% (95% CI 3.8%–8.5%) for every additional ten pack-years. Analysis of 13 studies adjusted for body mass index (BMI) yielded a relatively higher RR (1.30; 95% CI 1.24–1.37) for current smokers. The population attributable fractions of VTE were 8.7% (95% CI 4.8%–12.3%) for ever smoking, 5.8% (95% CI 3.6%–8.2%) for current smoking, and 2.7% (95% CI 0.8%–4.5%) for former smoking. Smoking was associated with an absolute risk increase of 24.3 (95% CI 15.4–26.7) cases per 100,000 person-years.
Conclusions
Cigarette smoking is associated with a slightly increased risk for VTE. BMI appears to be a confounding factor in the risk estimates. The relationship between VTE and smoking has clinical relevance with respect to individual screening, risk factor modification, and the primary and secondary prevention of VTE.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Blood normally flows throughout the human body, supplying its organs and tissues with oxygen and nutrients. But, when an injury occurs, proteins called clotting factors make the blood gel (coagulate) at the injury site. The resultant clot (thrombus) plugs the wound and prevents blood loss. Occasionally, a thrombus forms inside an uninjured blood vessel and partly or completely blocks the blood flow. Clot formation inside one of the veins deep within the body, usually in a leg, is called deep vein thrombosis (DVT) and can cause pain, swelling, and redness in the affected limb. DVT can be treated with drugs that stop the blood clot from getting larger (anticoagulants) but, if left untreated, part of the clot can break off and travel to the lungs, where it can cause a life-threatening pulmonary embolism. DVT and pulmonary embolism are collectively known as venous thromboembolism (VTE). Risk factors for VTE include having an inherited blood clotting disorder, oral contraceptive use, prolonged inactivity (for example, during a long-haul plane flight), and having surgery. VTEs are present in about a third of all people who die in hospital and, in non-bedridden populations, about 10% of people die within 28 days of a first VTE event.
Why Was This Study Done?
Some but not all studies have reported that smoking is also a risk factor for VTE. A clear demonstration of a significant association (a relationship unlikely to have occurred by chance) between smoking and VTE might help to reduce the burden of VTE because smoking can potentially be reduced by encouraging individuals to quit smoking and through taxation policies and other measures designed to reduce tobacco consumption. In this systematic review and meta-analysis, the researchers examine the link between smoking and the risk of VTE in the general population and investigate whether heavy smokers have a higher risk of VTE than light smokers. A systematic review uses predefined criteria to identify all the research on a given topic; meta-analysis is a statistical method for combining the results of several studies.
What Did the Researchers Do and Find?
The researchers identified 32 observational studies (investigations that record a population's baseline characteristics and subsequent disease development) that provided data on smoking and VTE. Together, the studies involved nearly 4 million participants and recorded 35,151 VTE events. Compared with never smokers, ever smokers (current and former smokers combined) had a relative risk (RR) of developing VTE of 1.17. That is, ever smokers were 17% more likely to develop VTE than never smokers. For current smokers and former smokers, RRs were 1.23 and 1.10, respectively. Analysis of only studies that adjusted for body mass index (a measure of body fat and a known risk factor for conditions that affect the heart and circulation) yielded a slightly higher RR (1.30) for current smokers compared with never smokers. For ever smokers, the population attributable fraction (the proportional reduction in VTE that would accrue in the population if no one smoked) was 8.7%. Notably, the risk of VTE increased by 10.2% for every additional ten cigarettes smoked per day and by 6.1% for every additional ten pack-years. Thus, an individual who smoked one pack of cigarettes per day for 40 years had a 26.7% higher risk of developing VTE than someone who had never smoked. Finally, smoking was associated with an absolute risk increase of 24.3 cases of VTE per 100,000 person-years.
What Do These Findings Mean?
These findings indicate that cigarette smoking is associated with a statistically significant, slightly increased risk for VTE among the general population and reveal a dose-relationship between smoking and VTE risk. They cannot prove that smoking causes VTE—people who smoke may share other unknown characteristics (confounding factors) that are actually responsible for their increased risk of VTE. Indeed, these findings identify body mass index as a potential confounding factor that might affect the accuracy of estimates of the association between smoking and VTE risk. Although the risk of VTE associated with smoking is smaller than the risk associated with some well-established VTE risk factors, smoking is more common (globally, there are 1.1 billion smokers) and may act synergistically with some of these risk factors. Thus, smoking behavior should be considered when screening individuals for VTE and in the prevention of first and subsequent VTE events.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001515.
The US National Heart Lung and Blood Institute provides information on deep vein thrombosis (including an animation about how DVT causes pulmonary embolism), and information on pulmonary embolism
The UK National Health Service Choices website has information on deep vein thrombosis, including personal stories, and on pulmonary embolism; SmokeFree is a website provided by the UK National Health Service that offers advice on quitting smoking
The non-profit organization US National Blood Clot Alliance provides detailed information about deep vein thrombosis and pulmonary embolism for patients and professionals and includes a selection of personal stories about these conditions
The World Health Organization provides information about the dangers of tobacco (in several languages)
Smokefree.gov, from the US National Cancer Institute, offers online tools and resources to help people quit smoking
MedlinePlus has links to further information about deep vein thrombosis, pulmonary embolism, and the dangers of smoking (in English and Spanish)
doi:10.1371/journal.pmed.1001515
PMCID: PMC3775725  PMID: 24068896
10.  Outcomes of thromboprophylaxis with enoxaparin vs. unfractionated heparin in medical inpatients 
Thrombosis Journal  2006;4:17.
Background
Clinical trials have shown low-molecular weight heparin (LMWH) to be at least as safe and efficacious as unfractionated heparin (UFH) for preventing venous thromboembolism (VTE) in acutely-ill medical inpatients.
Objective
To compare clinical and economic outcomes among acutely-ill medical inpatients receiving the LMWH enoxaparin versus UFH prophylaxis in clinical practice.
Methods
Using a large, multi-hospital, US database, we identified persons aged ≥40 years hospitalized for ≥6 days for an acute medical condition (including circulatory disorders, respiratory disorders, infectious diseases, or neoplasms) from Q4 1999 to Q1 2002. From these patients, those who received thromboprophylaxis with either enoxaparin or UFH were identified. Surgical patients and those requiring or ineligible for anticoagulation were excluded. We compared the incidence of deep-vein thrombosis (DVT), pulmonary embolism (PE), and all VTE (i.e., DVT and/or PE). Secondary outcomes were occurrence of side-effects, length of hospital stay and total costs. RESULTS: 479 patients received enoxaparin prophylaxis and 2,837 received UFH. The incidence of VTE was 1.7% with enoxaparin prophylaxis versus 6.3% with UFH (RR = 0.26; p < 0.001). Occurrence of side effects, length of stay (10.00 days with enoxaparin vs. 10.26 days with UFH; p = 0.348) and total costs ($18,777 vs. $17,602; p = 0.463) were similar in the 2 groups.
Conclusion
We observed a 74% lower risk of VTE among patients receiving enoxaparin prophylaxis versus UFH prophylaxis. There was no significant difference in side effects or economic outcomes. These results provide evidence that the LMWH enoxaparin is more effective than UFH in reducing the risk of VTE in current clinical practice.
doi:10.1186/1477-9560-4-17
PMCID: PMC1624807  PMID: 17005045
11.  Economic evaluation of the prophylaxis for thromboembolism in critical care trial (E-PROTECT): study protocol for a randomized controlled trial 
Trials  2014;15:502.
Background
Venous thromboembolism (VTE) is a common complication of critical illness with important clinical consequences. The Prophylaxis for ThromboEmbolism in Critical Care Trial (PROTECT) is a multicenter, blinded, randomized controlled trial comparing the effectiveness of the two most common pharmocoprevention strategies, unfractionated heparin (UFH) and low molecular weight heparin (LMWH) dalteparin, in medical-surgical patients in the intensive care unit (ICU). E-PROTECT is a prospective and concurrent economic evaluation of the PROTECT trial.
Methods/Design
The primary objective of E-PROTECT is to identify and quantify the total (direct and indirect, variable and fixed) costs associated with the management of critically ill patients participating in the PROTECT trial, and, to combine costs and outcome results to determine the incremental cost-effectiveness of LMWH versus UFH, from the acute healthcare system perspective, over a data-rich time horizon of ICU admission and hospital admission. We derive baseline characteristics and probabilities of in-ICU and in-hospital events from all enrolled patients. Total costs are derived from centers, proportional to the numbers of patients enrolled in each country. Direct costs include medication, physician and other personnel costs, diagnostic radiology and laboratory testing, operative and non-operative procedures, costs associated with bleeding, transfusions and treatment-related complications. Indirect costs include ICU and hospital ward overhead costs. Outcomes are the ratio of incremental costs per incremental effects of LMWH versus UFH during hospitalization; incremental cost to prevent a thrombosis at any site (primary outcome); incremental cost to prevent a pulmonary embolism, deep vein thrombosis, major bleeding event or episode of heparin-induced thrombocytopenia (secondary outcomes) and incremental cost per life-year gained (tertiary outcome). Pre-specified subgroups and sensitivity analyses will be performed and confidence intervals for the estimates of incremental cost-effectiveness will be obtained using bootstrapping.
Discussion
This economic evaluation employs a prospective costing methodology concurrent with a randomized controlled blinded clinical trial, with a pre-specified analytic plan, outcome measures, subgroup and sensitivity analyses. This economic evaluation has received only peer-reviewed funding and funders will not play a role in the generation, analysis or decision to submit the manuscripts for publication.
Trial registration
Clinicaltrials.gov Identifier: NCT00182143. Date of registration: 10 September 2005.
Electronic supplementary material
The online version of this article (doi:10.1186/1745-6215-15-502) contains supplementary material, which is available to authorized users.
doi:10.1186/1745-6215-15-502
PMCID: PMC4413997  PMID: 25528663
Economic; Cost-effectiveness; Venous; Thromboembolism; PROTECT; Unfractionated; Heparin; Low molecular weight; Intensive; Critical
12.  Comparing Clinical Predictors of Deep Venous Thrombosis vs. Pulmonary Embolus After Severe Injury: A New Paradigm for Post-Traumatic Venous Thromboembolism? 
Background
The traditional paradigm is that deep venous thrombosis (DVT) and pulmonary embolus (PE) are different temporal phases of a single disease process, most often labeled as the composite endpoint venous thromboembolism (VTE). However, we theorize that after severe blunt injury, DVT and PE may represent independent thrombotic entities rather than different stages of a single pathophysiologic process and therefore exhibit different clinical risk factor profiles.
Methods
We examined a large, multi-center prospective cohort of severely injured blunt trauma patients to compare clinical risk factors for DVT and PE, including indicators of injury severity, shock, resuscitation parameters, comorbidities and VTE prophylaxis. Independent risk factors for each outcome were determined by cross-validated logistic regression modeling using advanced exhaustive model search procedures.
Results
The study cohort consisted of 1,822 severely injured blunt trauma patients (median ISS = 33, median base deficit = −9.5). Incidence of DVT and PE were 5.1% and 3.9% respectively. Only 9 of 73 (5.7%) patients with a PE were also diagnosed with DVT. Independent risk factors associated with DVT include prophylaxis initiation within 48 hours (OR 0.57, 95% CI 0.36–0.90) and thoracic AIS ≥ 3 (OR 1.82, 95% CI 1.12–2.95), while independent risk factors for PE were serum lactate >5 (OR 2.33, 95% CI 1.43–3.79) and male gender (OR 2.12, 95% CI 1.17–3.84). Both DVT and PE exhibited differing risk factor profiles from the classic composite endpoint of VTE.
Conclusion
Deep venous thrombosis and pulmonary embolus exhibit differing risk factor profiles following severe injury. Clinical risk factors for diagnosis of DVT after severe blunt trauma include the inability to initiate prompt pharmacologic prophylaxis and severe thoracic injury, which may represent overall injury burden. In contrast, risk factors for PE are male gender and physiologic evidence of severe shock. We hypothesize that post-injury DVT and PE may represent a broad spectrum of pathologic thrombotic processes as opposed to the current conventional wisdom of peripheral thrombosis and subsequent embolus.
Level of Evidence
Prognostic study, Level III
doi:10.1097/TA.0b013e31828cc9a0
PMCID: PMC3716365  PMID: 23609272
Venous thromboembolism; Deep venous thrombosis; Pulmonary embolus; Trauma; Injury
13.  Risk of Venous Thromboembolism in Patients with Cancer: A Systematic Review and Meta-Analysis 
PLoS Medicine  2012;9(7):e1001275.
Venous thromboembolism in patients with cancer is common, but precise incidence rates in different cancers are not known, making it difficult to target prevention strategies. This study summarizes the existing literature to determine the risk of venous thromboembolism in high- and average-risk groups of patients with different cancers.
Background
People with cancer are known to be at increased risk of venous thromboembolism (VTE), and this risk is believed to vary according to cancer type, stage of disease, and treatment modality. Our purpose was to summarise the existing literature to determine precisely and accurately the absolute risk of VTE in cancer patients, stratified by malignancy site and background risk of VTE.
Methods and Findings
We searched the Medline and Embase databases from 1 January 1966 to 14 July 2011 to identify cohort studies comprising people diagnosed with one of eight specified cancer types or where participants were judged to be representative of all people with cancer. For each included study, the number of patients who developed clinically apparent VTE, and the total person-years of follow-up were extracted. Incidence rates of VTE were pooled across studies using the generic inverse variance method. In total, data from 38 individual studies were included. Among average-risk patients, the overall risk of VTE was estimated to be 13 per 1,000 person-years (95% CI, 7 to 23), with the highest risk among patients with cancers of the pancreas, brain, and lung. Among patients judged to be at high risk (due to metastatic disease or receipt of high-risk treatments), the risk of VTE was 68 per 1,000 person-years (95% CI, 48 to 96), with the highest risk among patients with brain cancer (200 per 1,000 person-years; 95% CI, 162 to 247). Our results need to be considered in light of high levels of heterogeneity, which exist due to differences in study population, outcome definition, and average duration of follow-up between studies.
Conclusions
VTE occurs in greater than 1% of cancer patients each year, but this varies widely by cancer type and time since diagnosis. The absolute VTE risks obtained from this review can aid in clinical decision-making about which people with cancer should receive anticoagulant prophylaxis and at what times.
Please see later in the article for the Editors' Summary.
Editors' Summary
Background
A venous thrombosis is the medical term for a blood clot that forms in a vein, often completely blocking the vessel. The most common type is a deep vein thrombosis of the lower leg, which apart from causing pain and immobility, can break off (embolize), flow through the blood stream back to the heart, get caught in one of the blood vessels supplying the lungs, and cause a life-threatening pulmonary embolism. The term venous thromboembolism (VTE) refers to both a deep venous thrombosis and a pulmonary embolism and is a common cause of death, responsible for at least 300,000 deaths a year in the United States alone. There are many risk factors for developing a VTE, including age, immobility, certain medications, and some conditions, such as cancer: an estimated 20% of deaths from VTE occur among patients with cancer, and importantly, cancer patients with VTE have a much higher risk of death than those who do not have a VTE. The increased risk of developing a VTE is due to the treatments and surgery involved in the management of cancer, in addition to the risks associated with the condition itself.
Why Was This Study Done?
Previous studies have suggested that certain types of cancer, such as brain and pancreatic cancer, are associated with an increased risk of developing a VTE, but to date, clinical guidelines recommend preventative treatment of VTE only for cancer patients during hospital admissions for medical treatment and surgery, not for those patients receiving outpatient care. In this study, the researchers systematically reviewed the available published evidence to quantify the risks of developing a VTE in patients with cancer according to the type of cancer, and to determine whether certain patient groups are at particularly high risk of developing a VTE.
What Did the Researchers Do and Find?
The researchers used a comprehensive keyword search of two medical literature databases to identify relevant studies published between 1966 and 2011. Then they examined these studies according to certain criteria, such as the type of study and the type of cancer: the researchers were specifically looking for cohort studies of adult patients with one of eight cancer types—breast, lung, colorectal, prostate, brain, bone, pancreatic, and hematologic (including all leukemias, lymphomas, and multiple myeloma). The selected studies also had to include follow-up of more than 30 days and VTE outcomes. Then the researchers categorized selected studies according to the risk of developing a VTE—the researchers judged high-risk patients to be those with metastatic disease or receiving certain types of high-risk treatments, and judged average-risk patients to be representative of all patients with a cancer diagnosis. The researchers then pooled all the data from these studies and did a separate statistical analysis for high and average risk and for each cancer type.
Using these methods, the researchers identified 7,274 potentially relevant articles, of which 46 reports from 38 individual cohorts met the criteria to be included in their review. Of the 38 cohorts, the researchers categorized 31 as high risk and seven as average risk. In the pooled analysis the researchers found that among average-risk patients, the overall risk of VTE was 13 per 1,000 person-years, with the highest risk among patients with cancers of the pancreas, brain, and lung. Among patients judged to be at high risk, the researchers found that the risk of VTE was 68 per 1,000 person-years, with the highest risk among patients with brain cancer (200 per 1,000 person-years).
What Do These Findings Mean?
These findings suggest that the annual incidence rate of VTE in patients with cancer is between 0.5% and 20%, depending on the cancer type, background risk, and time since diagnosis. Cancers of the brain and pancreas have the highest risk of VTE for both high- and average-risk patient groups. Based on these more accurate data on the risks of VTE in different groups of cancer patients, future updates of clinical guidelines can now include more information about categories of risk to help guide clinicians when they make decisions about which patients should receive preventative treatment for VTE and when they should receive such treatment.
Additional Information
Please access these websites via the online version of this summary at http://dx.doi.org/10. 1371/journal.pmed.1001275.
Wikipedia gives more information about VTE (note that Wikipedia is a free online encyclopedia that anyone can edit)
Information about VTE for patients and health professionals is available from the American Cancer Society, the US National Cancer Institute, and the UK-based thrombosis charity Lifeblood
doi:10.1371/journal.pmed.1001275
PMCID: PMC3409130  PMID: 22859911
14.  High incidence of silent venous thromboembolism before treatment in ovarian cancer 
British Journal of Cancer  2007;97(8):1053-1057.
Venous thromboembolism (VTE) such as deep-vein thrombosis (DVT) and pulmonary thromboembolism (PTE) often occurs after surgery and rarely occurs even before surgery in patients with ovarian cancer. It is well known that levels of plasma D-dimer (DD) before treatment in most ovarian cancer patients are increased. This study therefore examined whether increased levels of DD are associated with presence of VTE before treatment of ovarian cancer. Between November 2004 and March 2007, DD levels prior to initial treatment were measured in 72 consecutive patients with presumed epithelial ovarian cancer (final diagnosis: epithelial ovarian cancer, n=60; and epithelial ovarian borderline malignancy, n=12). Venous ultrasound imaging (VUI) of the lower extremity was conducted for all patients except for two patients in whom DVT was detected by pelvic computed tomography (CT). When DVT was found, pulmonary scintigraphy was subsequently performed to ascertain presence of PTE. D-dimer levels were above the cut-off value (0.5 μg ml−1) in 65 of 72 patients (90.2%). Venous ultrasound imaging or CT revealed DVT in 18 of 72 patients (25.0%) and pulmonary scintigraphy found PTE in 8 patients (11.1%). All patients with VTE were asymptomatic when VTE was found. D-dimer levels were associated with incidence of VTE (0–1.4 μg ml−1; 0 of 26 (0%), 1.5–7.4 μg ml−1; 9 of 30 (30%) and ⩾7.5 μg ml−1; 9 of 16 (56.3%), P for trend=0.0003). However, even if 1.5 μg ml−1 was used as a cut-off value, this had low specificity and positive predictive value (47.2, 38.3%), though it had high sensitivity and negative predictive value (100, 100%). Therefore, ovarian cancer patients with DD level ⩾1.5 μg ml−1 should be examined using VUI to detect silent DVT. Patients with VTE underwent preventive managements including anticoagulant therapy before initial treatment, chemotherapy or surgery, and after surgery. There was no clinical onset of postoperative VTE in all 72 patients. Measurement of DD levels and subsequent ultrasonography revealed that silent or subclinical VTE frequently occurs before surgery in ovarian cancer. The usefulness of preoperative assessment of VTE needs further confirmation in randomised controlled trials.
doi:10.1038/sj.bjc.6603989
PMCID: PMC2360447  PMID: 17895896
ovarian cancer; deep-vein thrombosis; pulmonary thromboembolism; plasma D-dimer; clear cell adenocarcinoma
15.  MORTALITY-ADJUSTED DURATION OF MECHANICAL VENTILATION IN CRITICALLY ILL CHILDREN WITH SYMPTOMATIC CENTRAL VENOUS LINE-RELATED DEEP VENOUS THROMBOSIS 
Critical care medicine  2011;39(5):1151-1156.
Objective
To determine the association between symptomatic central venous line (CVL) related deep venous thrombosis (DVT) and a mortality-adjusted measure of duration of mechanical ventilation (MV) in critically ill children with CVL.
Design
Retrospective matched cohort study.
Setting
11 pediatric ICUs across the United States.
Patients
Twenty-nine index critically ill children with CVL-related DVT from a previous prospective observational study on symptomatic venous thromboembolism (VTE) were compared to 116 control children with CVL without VTE. Each index patient was matched to 4 control patients based on age group, disease category, severity of illness score and number of days in the ICU prior to CVL insertion.
Interventions
None.
Measurements and Main Results
Index patients were appropriately matched to control patients, with similar characteristics between the 2 groups. Index patients had fewer ventilator free days (VFD i.e. days alive and breathing unassisted within 28 days after CVL insertion) compared to matched control patients (16.8±11.5 days versus 22.3±4.9 days, P=.040). Index patients also had less ICU free days (ICUFD i.e. days alive and discharged from the ICU within 28 days after CVL insertion) (9.8±9.9 days versus 17.9±5.7 days, P<.001). Durations of MV (17.6±40.6 days versus 5.2±5.5 days, P=.236) and ICU stay (38.1±61.7 days versus 11.9±10.9 days, P=.011) were longer in index patients. The mortality rate was statistically similar between the 2 groups.
Conclusions
The presence of symptomatic CVL-related DVT is associated with worse outcomes, particularly fewer VFD, in critically ill children. The causal relationship that DVT leads to impairment in lung function and delays weaning from MV and discharge from the ICU needs to be proven prospectively. VFD is a possible alternative outcome measure for future DVT studies.
doi:10.1097/CCM.0b013e31820eb8a1
PMCID: PMC3101274  PMID: 21336130
Venous thromboembolism; mortality; intensive care unit; catheter; pediatrics; outcome; critical care
16.  Deep Vein Thrombosis Prophylaxis in Trauma Patients 
Thrombosis  2011;2011:505373.
Deep vein thrombosis (DVT) and pulmonary embolism (PE) are known collectively as venous thromboembolism (VTE). Venous thromboembolic events are common and potentially life-threatening complications following trauma with an incidence of 5 to 63%. DVT prophylaxis is essential in the management of trauma patients. Currently, the optimal VTE prophylaxis strategy for trauma patients is unknown. Traditionally, pelvic and lower extremity fractures, head injury, and prolonged immobilization have been considered risk factors for VTE; however it is unclear which combination of risk factors defines a high-risk group. Modalities available for trauma patient thromboprophylaxis are classified into pharmacologic anticoagulation, mechanical prophylaxis, and inferior vena cava (IVC) filters. The available pharmacologic agents include low-dose heparin (LDH), low molecular weight heparin (LMWH), and factor Xa inhibitors. Mechanical prophylaxis methods include graduated compression stockings (GCSs), pneumatic compression devices (PCDs), and A-V foot pumps. IVCs are traditionally used in high risk patients in whom pharmacological prophylaxis is contraindicated. Both EAST and ACCP guidelines recommend primary use of LMWHs in trauma patients; however there are still controversies regarding the definitive VTE prophylaxis in trauma patients. Large randomized prospective clinical studies would be required to provide level I evidence to define the optimal VTE prophylaxis in trauma patients.
doi:10.1155/2011/505373
PMCID: PMC3195354  PMID: 22084663
17.  Air Travel and Venous Thromboembolism: A Systematic Review 
Context
Despite multiple attempts to document and quantify the danger of venous thromboembolism (VTE) following prolonged travel, there is still uncertainty about the magnitude of risk and what can be done to lower it.
Objectives
To review the methodologic strength of the literature, estimate the risk of travel-related VTE, evaluate the efficacy of preventive treatments, and develop evidence-based recommendations for practice.
Data Sources
Studies identified from MEDLINE from 1966 through December 2005, supplemented by a review of the Cochrane Central Registry of Controlled Trials, the Database of Abstracts of Reviews of Effects, and relevant bibliographies.
Study Selection
We included all clinical studies that either reported primary data concerning travel as a risk factor for VTE or tested preventive measures for travel-related VTE.
Data Extraction and Analysis
Two reviewers reviewed each study independently to assess inclusion criteria, classify research design, and rate methodologic features. The effect of methodologic differences, VTE risk, and travel duration on VTE rate was evaluated using a logistic regression model.
Data Synthesis
Twenty-four published reports, totaling 25 studies, met inclusion criteria (6 case-control studies, 10 cohort studies, and 9 randomized controlled trials). Method of screening for VTE [screening ultrasound compared to usual clinical care, odds ratio (OR) 390], outcome measure [all VTE compared to pulmonary embolism (PE) only, OR 21], duration of travel (<6 hours compared to 6–8 hours, OR 0.011), and clinical risk (“higher” risk travelers compared to “lower,” OR 3.6) were significantly related to VTE rate. Clinical VTE after prolonged travel is rare [27 PE per million flights diagnosed through usual clinical care, 0.05% symptomatic deep venous thrombosis (DVT) diagnosed through screening ultrasounds], but asymptomatic thrombi of uncertain clinical significance are more common. Graduated compression stockings prevented travel-related VTE (P < 0.05 in 4 of 6 studies), aspirin did not, and low-molecular-weight heparin (LMWH) showed a trend toward efficacy in one study.
Conclusions
All travelers, regardless of VTE risk, should avoid dehydration and frequently exercise leg muscles. Travelers on a flight of less than 6 hours and those with no known risk factors for VTE, regardless of the duration of the flight, do not need DVT prophylaxis. Travelers with 1 or more risk factors for VTE should consider graduated compression stockings and/or LMWH for flights longer than 6 hours.
doi:10.1007/s11606-006-0016-0
PMCID: PMC1824715  PMID: 17351849
venous thromboembolism; deep venous thrombosis; pulmonary embolism; air travel; transportation; systematic review
18.  Air Travel and Venous Thromboembolism: A Systematic Review 
Context
Despite multiple attempts to document and quantify the danger of venous thromboembolism (VTE) following prolonged travel, there is still uncertainty about the magnitude of risk and what can be done to lower it.
Objectives
To review the methodologic strength of the literature, estimate the risk of travel-related VTE, evaluate the efficacy of preventive treatments, and develop evidence-based recommendations for practice.
Data Sources
Studies identified from MEDLINE from 1966 through December 2005, supplemented by a review of the Cochrane Central Registry of Controlled Trials, the Database of Abstracts of Reviews of Effects, and relevant bibliographies.
Study Selection
We included all clinical studies that either reported primary data concerning travel as a risk factor for VTE or tested preventive measures for travel-related VTE.
Data Extraction and Analysis
Two reviewers reviewed each study independently to assess inclusion criteria, classify research design, and rate methodologic features. The effect of methodologic differences, VTE risk, and travel duration on VTE rate was evaluated using a logistic regression model.
Data Synthesis
Twenty-four published reports, totaling 25 studies, met inclusion criteria (6 case-control studies, 10 cohort studies, and 9 randomized controlled trials). Method of screening for VTE [screening ultrasound compared to usual clinical care, odds ratio (OR) 390], outcome measure [all VTE compared to pulmonary embolism (PE) only, OR 21], duration of travel (<6 hours compared to 6–8 hours, OR 0.011), and clinical risk (“higher” risk travelers compared to “lower,” OR 3.6) were significantly related to VTE rate. Clinical VTE after prolonged travel is rare [27 PE per million flights diagnosed through usual clinical care, 0.05% symptomatic deep venous thrombosis (DVT) diagnosed through screening ultrasounds], but asymptomatic thrombi of uncertain clinical significance are more common. Graduated compression stockings prevented travel-related VTE (P < 0.05 in 4 of 6 studies), aspirin did not, and low-molecular-weight heparin (LMWH) showed a trend toward efficacy in one study.
Conclusions
All travelers, regardless of VTE risk, should avoid dehydration and frequently exercise leg muscles. Travelers on a flight of less than 6 hours and those with no known risk factors for VTE, regardless of the duration of the flight, do not need DVT prophylaxis. Travelers with 1 or more risk factors for VTE should consider graduated compression stockings and/or LMWH for flights longer than 6 hours.
doi:10.1007/s11606-006-0016-0
PMCID: PMC1824715  PMID: 17351849
venous thromboembolism; deep venous thrombosis; pulmonary embolism; air travel; transportation; systematic review
19.  Venous Thromboembolism in Critically Ill Cirrhotic Patients: Practices of Prophylaxis and Incidence 
Thrombosis  2013;2013:807526.
Objectives. We compared venous thromboembolism (VTE) prophylaxis practices and incidence in critically ill cirrhotic versus noncirrhotic patients and evaluated cirrhosis as a VTE risk factor. Methods. A cohort of 798 critically ill patients followed for the development of clinically detected VTE were categorized according to the diagnosis of cirrhosis. VTE prophylaxis practices and incidence were compared. Results. Seventy-five (9.4%) patients had cirrhosis with significantly higher INR (2.2 ± 0.9 versus 1.3 ± 0.6, P < 0.0001), lower platelet counts (115,000 ± 90,000 versus 258,000 ± 155,000/μL, P < 0.0001), and higher creatinine compared to noncirrhotic patients. Among cirrhotics, 31 patients received only mechanical prophylaxis, 24 received pharmacologic prophylaxis, and 20 did not have any prophylaxis. Cirrhotic patients were less likely to receive pharmacologic prophylaxis (odds ratio, 0.08; 95% confidence interval (CI), 0.04–0.14). VTE occurred in only two (2.7%) cirrhotic patients compared to 7.6% in noncirrhotic patients (P = 0.11). The incidence rate was 2.2 events per 1000 patient-ICU days for cirrhotic patients and 3.6 events per 1000 patient-ICU days for noncirrhotics (incidence rate ratio, 0.61; 95% CI, 0.15–2.52). On multivariate Cox regression analysis, cirrhosis was not associated with VTE risk (hazard ratio, 0.40; 95% CI, 0.10–1.67). Conclusions. In critically ill cirrhotic patients, VTE incidence did not statistically differ from that in noncirrhotic patients.
doi:10.1155/2013/807526
PMCID: PMC3872442  PMID: 24386564
20.  Venous thromboembolism after total joint arthroplasty: results from a Japanese multicenter cohort study 
Arthritis Research & Therapy  2014;16(4):R154.
Introduction
Real-world evidence of the effectiveness of pharmacological thromboprophylaxis for venous thromboembolism (VTE) is limited. Our objective was to assess the effectiveness and safety of thromboprophylactic regimens in Japanese patients undergoing joint replacement in a real-world setting.
Method
Overall, 1,294 patients (1,073 females and 221 males) who underwent total knee arthroplasty (TKA) and 868 patients (740 females and 128 males) who underwent total hip arthroplasty (THA) in 34 Japanese national hospital organization (NHO) hospitals were enrolled. The primary efficacy outcome was the incidence of deep vein thrombosis (DVT) detected by mandatory bilateral ultrasonography up to post-operative day (POD) 10 and pulmonary embolism (PE) up to POD28. The main safety outcomes were bleeding (major or minor) and death from any cause up to POD28.
Results
Patients undergoing TKA (n = 1,294) received fondaparinux (n = 360), enoxaparin (n = 223), unfractionated heparin (n = 72), anti-platelet agents (n = 45), or no medication (n = 594). Patients undergoing THA (n = 868) received fondaparinux (n = 261), enoxaparin (n = 148), unfractionated heparin (n = 32), anti-platelet agents (n = 44), or no medication (n = 383). The incidence rates of sonographically diagnosed DVTs up to POD10 were 24.3% in patients undergoing TKA and 12.6% in patients undergoing THA, and the incidence rates of major bleeding up to POD28 were 1.2% and 2.3%, respectively. Neither fatal bleeding nor fatal pulmonary embolism occurred. Significant risk factors for postoperative VTE identified by multivariate analysis included gender (female) in both TKA and THA groups and use of a foot pump in the TKA group. Only prophylaxis with fondaparinux reduced the occurrence of VTE significantly in both groups. Propensity score matching analysis (fondaparinux versus enoxaparin) showed that the incidence of DVT was lower (relative risk 0.70, 95% confidence interval (CI) 0.58 to 0.85, P = 0.002 in TKA and relative risk 0.73, 95% CI 0.53 to 0.99, P = 0.134 in THA) but that the incidence of major bleeding was higher in the fondaparinux than in the enoxaparin group (3.4% versus 0.5%, P = 0.062 in TKA and 4.9% versus 0%, P = 0.022 in THA).
Conclusions
These findings indicate that prophylaxis with fondaparinux, not enoxaparin, reduces the risk of DVT but increases bleeding tendency in patients undergoing TKA and THA.
Trial registration
University Hospital Medical Information Network Clinical Trials Registry: UMIN000001366. Registered 11 September 2008.
doi:10.1186/ar4616
PMCID: PMC4223565  PMID: 25047862
21.  IgG-class anti-PF4/heparin antibodies and symptomatic DVT in orthopedic surgery patients receiving different anti-thromboembolic prophylaxis therapeutics 
Background
Heparin-induced thrombocytopenia (HIT) is a thromboembolic complication that can occur with unfractionated heparin (UFH) or low molecular weight heparin (LMWH). Our objective was to determine and compare the incidence of IgG-class HIT antibodies in patients undergoing total hip arthroplasty (THA) or total knee arthroplasty (TKA) with different antithrombotic prophylaxis therapies and their contributions to the occurrence of venous thromboembolism (VTE).
Methods
A prospective observational study was performed for 374 Japanese patients undergoing THA or TKA to determine the incidence of VTE. IgG-class anti-PF4/heparin antibodies were measured using IgG-specific EIA before and after the operation.
Results
In the clinical outcome, the incidence of symptomatic deep vein thrombosis (DVT) was 15.0% (56/374, TKA; 35, THA; 21) and pulmonary emboli (PE) were not observed. The total seroconversion incidence of IgG-class PF4/heparin antibodies was 19.8% (74/374). The seroconversion incidence of IgG-class PF4/heparin antibodies was higher in patients receiving UFH (32.7%) compared to those receiving LMWH (9.5%) or fondaparinux (14.8%). Furthermore, the seroconversion incidence was significantly higher in patients undergoing TKA compared to those undergoing THA. Based on multivariate analysis, seroconversion of the IgG-class PF4/heparin antibodies was independent a risk factor for symptomatic DVT.
Conclusion
Our findings show that the seroconversion of IgG-class anti-PF4/heparin antibodies differed with various anti-thrombotic prophylaxis therapeutics and was associated with the risk of DVT in a subset of patients undergoing total joint arthroplasty (TKA and THA).
doi:10.1186/1471-2474-12-22
PMCID: PMC3224260  PMID: 21261941
22.  Is routine thromboprophylaxis justified among Indian patients sustaining major orthopedic trauma? A systematic review 
Indian Journal of Orthopaedics  2011;45(3):197-207.
Venous thromboembolism (VTE) is one of the most common preventable cause of morbidity and mortality after trauma. Though most of the western countries have their guidelines for thromboprophylaxis in these patients, India still does not have these. The increasing detection of VTE among Indian population, lack of awareness, underestimation of the risk, and fear of bleeding complications after chemical prophylaxis have made deep vein thrombosis (DVT) a serious problem, hence a standard guideline for thromboprophylaxis after trauma is essential. The present review article discusses the incidence of DVT and role of thromboprophylaxis in Indian patients who have sustained major orthopedic trauma. A thorough search of ‘PubMed’ and ‘Google Scholar’ revealed 10 studies regarding venous thromboembolism in Indian patients after major orthopedic trauma surgery (hip or proximal femur fracture and spine injury). Most of these studies have evaluated venous thromboembolism in patients of arthroplasty and trauma. The incidence, risk factors, diagnosis and management of VTE in the subgroup of trauma patients (1049 patients) were separately evaluated after segregating them from the arthroplasty patients. Except two studies, which were based on spinal injury, all other studies recommended screening/ thromboprophylaxis in posttraumatic conditions in the Indian population. Color Doppler was used as common diagnostic or screening tool in most of the studies (eight studies, 722 patients). The incidence of VTE among thromboprophylaxis-receiving group was found to be 8% (10/125), whereas it was much higher (14.49%, 40/276) in patients not receiving any form of prophylaxis. Indian patients have definite risk of venous thromboembolism after major orthopedic trauma (except spinal injury), and thromboprophylaxis either by chemical or mechanical methods seems to be justified in them.
doi:10.4103/0019-5413.80037
PMCID: PMC3087220  PMID: 21559098
Thromboprophylaxis; trauma; venous thromboembolism
23.  Venous thromboembolism and bleeding in critically ill patients with severe renal insufficiency receiving dalteparin thromboprophylaxis: prevalence, incidence and risk factors 
Critical Care  2008;12(2):R32.
Background
Critically ill patients with renal insufficiency are predisposed to both deep vein thrombosis (DVT) and bleeding. The objective of the present study was to evaluate the prevalence, incidence and predictors of DVT and the incidence of bleeding in intensive care unit (ICU) patients with estimated creatinine clearance <30 ml/min.
Methods
In a multicenter, open-label, prospective cohort study of critically ill patients with severe acute or chronic renal insufficiency or dialysis receiving subcutaneous dalteparin 5,000 IU once daily, we estimated the prevalence of proximal DVT by screening compression venous ultrasound of the lower limbs within 48 hours of ICU admission. DVT incidence was assessed on twice-weekly ultrasound testing. We estimated the incidence of major and minor bleeding by daily clinical assessments. We used Cox proportional hazards regression to identify independent predictors of both DVT and major bleeding.
Results
Of 156 patients with a mean (standard deviation) creatinine clearance of 18.9 (6.5) ml/min, 18 had DVT or pulmonary embolism within 48 hours of ICU admission, died or were discharged before ultrasound testing – leaving 138 evaluable patients who received at least one dose of dalteparin. The median duration of dalteparin administration was 7 days (interquartile range, 4 to 12 days). DVT developed in seven patients (5.1%; 95% confidence interval, 2.5 to 10.1). The only independent risk factor for DVT was an elevated baseline Acute Physiology and Chronic Health Evaluation II score (hazard ratio for 10-point increase, 2.25; 95% confidence interval, 1.03 to 4.91). Major bleeding developed in 10 patients (7.2%; 95% confidence interval, 4.0 to 12.8), all with trough anti-activated factor X levels ≤ 0.18 IU/ml. Independent risk factors for major bleeding were aspirin use (hazard ratio, 6.30; 95% confidence interval, 1.35 to 29.4) and a high International Normalized Ratio (hazard ratio for 0.5-unit increase, 1.68; 95% confidence interval, 1.07 to 2.66).
Conclusion
In ICU patients with renal insufficiency, the incidence of DVT and major bleeding are considerable but appear related to patient comorbidities rather than to an inadequate or excessive anticoagulant from thromboprophylaxis with dalteparin.
Clinical Trial Registration
Number NCT00138099.
doi:10.1186/cc6810
PMCID: PMC2447552  PMID: 18315876
24.  Evaluation of the Management of Acute Venous Thromboembolism and Its Outcomes 
Pharmacy and Therapeutics  2008;33(2):107-117.
Background:
There is often a divergence between standardized practice guidelines and actual practice. Such deviations can result in adverse outcomes. In addition, studies that identify independent risk factors associated with bleeding or recurrent venous thromboembolism (VTE) are often limited.
Objective:
We sought to evaluate the appropriateness of VTE management at our Veterans Affairs facility in Fargo and to identify independent patient characteristics or treatments that were associated with recurrence of VTE or major bleeding.
Methods:
We performed a retrospective chart review of patients admitted for deep vein thrombosis (DVT) and/or pulmonary embolism (PE).
Results:
Of the patients who were given enoxaparin, 96% received an appropriate dose; however, of the patients receiving unfractionated heparin, only 54.7% received an appropriate initial dose. The International Normalized Ratio (INR) was below 1.9 in 19.3% of patients when heparin was stopped, unknown in 12.7%, and 1.9 or higher in 68%. Thirty-two patients (21.3%) continued to take warfarin for three months or less, and 13 of these patients (41%) were treated for an idiopathic VTE. Forty-eight patients (57%) being treated for VTE for the first time continued with warfarin for more than six months. Twenty-one patients (14%) were started on 10 mg of warfarin daily; 40% received heparin for less than five days. The only significant difference between the bleeding and non-bleeding groups was an INR above 3 at the time of the bleeding episode (P < 0.0001).
Conclusion:
We learned that the management of VTE at our institution diverged from standardized practice guidelines. Larger randomized, prospective studies are needed to identify independent risk factors for major bleeding or recurrence of VTE and their correlation with patient outcomes.
PMCID: PMC2730069  PMID: 19749995
25.  Venous thromboembolism prophylaxis in hospitalized elderly patients: Time to consider a ‘MUST’ strategy 
Venous thromboembolism (VTE) is the commonest cause of preventable death in hospitalized patients. Elderly patients have higher risk of VTE because of the high prevalence of predisposing co-morbidities and acute illnesses. Clinical diagnosis of VTE in the elderly patient is particularly difficult and, as such, adequate VTE prophylaxis is of pivotal importance in reducing the mortality and morbidities of VTE. Omission of VTE prophylaxis is, however, very common despite continuous education. A simple way to overcome this problem is to implement universal VTE prophylaxis for all hospitalized elderly patients instead of selective prophylaxis for some patients only according to individual's risk of VTE. Although pharmacological VTE prophylaxis is effective for most patients, a high prevalence of renal impairment and drug interactions in the hospitalized elderly patients suggests that a multimodality approach may be more appropriate. Mechanical VTE prophylaxis, including calf and thigh compression devices and/or an inferior vena cava filter, are often underutilized in hospitalized elderly patients who are at high-risk of bleeding and VTE. Because pneumatic compression devices and thigh length stockings are virtually risk free, mechanical VTE prophylaxis may allow early or immediate implementation of VTE prophylaxis for all hospitalized elderly patients, regardless of their bleeding and VTE risk. Although the cost-effectiveness of this Multimodality Universal STat (‘MUST’) VTE prophylaxis approach for hospitalized elderly patients remains uncertain, this strategy appears to offer some advantages over the traditional ‘selective and single-modal’ VTE prophylaxis approach, which often becomes ‘hit or miss’ or not implemented promptly in many hospitalized elderly patients. A large clustered randomized controlled trial is, however, needed to assess whether early, multimodality, universal VTE prophylaxis can improve important clinical outcomes of hospitalized elderly patients.
doi:10.3724/SP.J.1263.2011.00114
PMCID: PMC3390075  PMID: 22783295
age; bundle of care; deep vein thrombosis; prevention; pulmonary embolism

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