Extended out-of-hospital low-molecular-weight heparin prophylaxis against deep venous thrombosis in patients after elective hip arthroplasty: a systematic review

PURPOSE

Evidence-based medicine guidelines based on venographic end points recommend in-hospital prophylaxis with low-molecular-weight heparin (LMWH) in patients having elective hip surgery. Emerging data suggest that out-of-hospital use may offer additional protection; however, uncertainty remains about the risk-benefit ratio. To provide clinicians with a practical pathway for translating clinical research into practice, we systematically reviewed trials comparing extended out-of-hospital LMWH prophylaxis versus placebo.

DATA SOURCES

Studies were identified by 1) searching PubMed, MEDLINE, and the Cochrane Library Database for reports published from January 1976 to May 2001; 2) reviewing references from retrieved articles; 3) scanning abstracts from conference proceedings; and 4) contacting pharmaceutical companies and investigators of the original reports.

STUDY SELECTION

Randomized, controlled trials comparing extended out-of-hospital prophylaxis with LMWH versus placebo in patients having elective hip arthroplasty.

DATA EXTRACTION

Two reviewers extracted data independently. Reviewers evaluated study quality by using a validated four-item instrument.

DATA SYNTHESIS

Six of seven original articles met the defined inclusion criteria. The included studies were double-blind trials that used proper randomization procedures. Compared with placebo, extended out-of-hospital prophylaxis decreased the frequency of all episodes of deep venous thrombosis (placebo rate, 150 of 666 patients [22.5%]; relative risk, 0.41 [95% CI, 0.32 to 0.54; P < 0.001]), proximal venous thrombosis (placebo rate, 76 of 678 patients [11.2%]; relative risk, 0.31 [CI, 0.20 to 0.47; P < 0.001]), and symptomatic venous thromboembolism (placebo rate, 36 of 862 patients [4.2%]; relative risk, 0.36 [CI, 0.20 to 0.67; P = 0.001]). Major bleeding was rare, occurring in only one patient in the placebo group.

CONCLUSIONS

Extended LMWH prophylaxis showed consistent effectiveness and safety in the trials (regardless of study variations in clinical practice and length of hospital stay) for venographic deep venous thrombosis and symptomatic venous thromboembolism. The aggregate findings support the need for extended out-of-hospital prophylaxis in patients undergoing hip arthroplasty surgery.

Timing of initial administration of low-molecular-weight heparin prophylaxis against deep vein thrombosis in patients following elective hip arthroplasty: a systematic review

BACKGROUND

Perioperative and postoperative venous thrombosis are common in patients undergoing elective hip surgery. Prophylactic regimens include subcutaneous low-molecular-weight heparin 12 hours or more before or after surgery and oral anticoagulants. Recent clinical trials suggest that low-molecular-weight heparin initiated in closer proximity to surgery is more effective than the present clinical practice. We performed a systematic review of the literature to assess the efficacy and safety of low-molecular-weight heparin administered at different times in relation to surgery vs oral anticoagulant prophylaxis.

METHODS

Reviewers (A.F.M. and S.M.M.) identified studies by searching MEDLINE, reviewing references from retrieved articles, scanning abstracts from conference proceedings, and contacting investigators and pharmaceutical companies. Randomized trials comparing low-molecular-weight heparin administered at different times relative to surgery with oral anticoagulants in patients undergoing elective hip arthroplasty, evaluated using contrast phlebography, were selected. Two reviewers (A.F.M. and S.M.M.) extracted data independently.

RESULTS

The literature review identified 4 randomized trials meeting predefined inclusion criteria. The results indicate that low-molecular-weight heparin initiated in close proximity to surgery resulted in absolute risk reductions of 11% to 13% for deep vein thrombosis, corresponding to relative risk reductions of 43% to 55% compared with oral anticoagulants. Low-molecular-weight heparin initiated 12 hours before surgery or 12 to 24 hours postoperatively was not more effective than oral anticoagulants. Low-molecular-weight heparin initiated postoperatively in close proximity to surgery at half the usual dose was not associated with a clinically or statistically significant increase in major bleeding rates (P =.16).

CONCLUSIONS

The timing of initiating low-molecular-weight heparin significantly influences antithrombotic effectiveness. The practice of delayed initiation of low-molecular-weight heparin prophylaxis results in suboptimal antithrombotic effectiveness without a substantive safety advantage.

Low-molecular-weight heparin vs heparin in the treatment of patients with pulmonary embolism. American-Canadian Thrombosis Study Group

BACKGROUND

Pulmonary embolism (PE) occurs in 50% or more of patients with proximal deep-vein thrombosis. Low-molecular-weight heparin treatment is effective and safe in patients with deep vein thrombosis and may also be so in patients with PE. Recent rigorous clinical trials have established objective criteria for determining a high probability of PE by perfusion lung scanning.

OBJECTIVE

To compare low-molecular-weight heparin with intravenous heparin for the treatment of patients with objectively documented PE and underlying proximal deep vein thrombosis.

METHODS

In a multicenter, double-blind, randomized trial, we compared fixed-dose subcutaneous low-molecular-weight heparin (tinzaparin sodium) given once daily with dose-adjusted intravenous heparin given by continuous infusion using objective documentation of clinical outcomes. Pulmonary embolism at study entry was documented by the presence of high-probability lung scan findings.

RESULTS

Of 200 patients with high-probability lung scan findings at study entry, none of the 97 who received low-molecular-weight heparin had new episodes of venous thromboembolism compared with 7 (6.8%) of 103 patients who received intravenous heparin (95% confidence interval for the difference, 1.9%-11.7%; P = .01). Major bleeding associated with initial therapy occurred in 1 patient (1.0%) who was given low-molecular-weight heparin and in 2 patients (1.9%) given intravenous heparin (95% confidence interval for the difference, -2.4% to 4.3%).

CONCLUSIONS

Low-molecular-weight heparin administered once daily subcutaneously was no less effective and probably more effective than use of dose-adjusted intravenous unfractionated heparin for preventing recurrent venous thromboembolism in patients with PE and associated proximal deep vein thrombosis. Our findings extend the use of low-molecular-weight heparin without anticoagulant monitoring to patients with submassive PE.

Prevalence and incidence of carpal tunnel syndrome in a meat packing plant

OBJECTIVES

To determine prevalence and incidence of carpal tunnel syndrome (CTS) in a modern meat packing plant. The secondary objective was to explore the relation between ethnicity and CTS.

METHODS

Six hundred and sixty five workers were interviewed and examined to find the prevalence of CTS. Subsequently, 421 workers without CTS were followed up and examined at a median interval of 253 days; of those, 333 remained without CTS and were again examined at a median interval of 148 days.

RESULTS

The prevalence and incidence of CTS was 21% and 11/100 person-years, respectively. The incidence for Asian mixed, white, and other ethnicities was 12.0, 12.2, and 7.2 cases/100 person-years, respectively. The observed incidence for men and women was 9.7 and 18.4 cases/100 person-years, respectively. This difference was not quite significant (p = 0.068) with an estimated relative risk (women v men) of 1.9 (95% confidence interval (95% CI) 0.9 to 3.8). The interaction between sex and use of tools was significant (p = 0.04), however, although the relative risk for CTS in women who used tools was 4.2 the numbers were small and not significant. The relative risk for men who used tools was 0.64 and not significant. The percentage of incident cases with comorbid disease was only 6.3% (3/47).

CONCLUSIONS

The prevalence and incidence of CTS in this workforce were higher than in the general population. However, the prevalence of CTS in this modern, mechanised plant was not significantly different from that reported in older plants. No relation was found between ethnicity, age, body mass index, and CTS for either prevalence or incidence. Comorbid disease among the cases of CTS is significantly less than that found in other industry.

Preoperative vs postoperative initiation of low-molecular-weight heparin prophylaxis against venous thromboembolism in patients undergoing elective hip replacement

BACKGROUND

Although preoperative and postoperative initiation of prophylaxis for deep vein thrombosis (DVT) with low-molecular-weight heparin (LMWH) are effective, the relative effectiveness and safety of these approaches is unknown. In the absence of a published definitive level 1 trial addressing this question, a meta-analysis is appropriate.

OBJECTIVE

To report a meta-analysis comparing preoperative with postoperative initiation of prophylaxis of DVT in patients undergoing elective hip replacement.

METHODS

Relevant trials were identified, and potential biases in the meta-analysis were minimized by analyzing all rigorously performed randomized trials that met all of the following criteria for conduct of the trial: (1) double-blind design, (2) objective documentation of the frequencies of DVT by ascending contrast venography, (3) venography performed before or at the time of discharge from the hospital, (4) initiation of the same LMWH preoperatively or postoperatively in dosages shown to be effective, (5) compliance with the criteria for a level 1 trial, and (6) objective documentation of major and minor bleeding according to strict criteria.

RESULTS

Treatment with LMWH initiated preoperatively was associated with a DVT frequency of 10.0% compared with a frequency of 15.3% when the LMWH was initiated postoperatively (P = .02, Fisher exact test). Major bleeding was less frequent in patients receiving preoperatively initiated LMWH than in patients receiving postoperatively initiated LMWH (0.9%, vs. 3.5%; P = .01, Fisher exact test).

CONCLUSIONS

Our findings support the need for a randomized comparison of preoperative and postoperative initiation of pharmacological prophylaxis of DVT. Such a trial would resolve the divergent practices for DVT prophylaxis between Europe and the North American countries, the United States and Canada, and would affect the treatment for thousands of patients on both continents.

A clinical study of the relationship between silicone breast implants and connective tissue disease

OBJECTIVE

This study was a blinded, concurrent assessment of a historical cohort derived from a provincial registry (1978 to 1986) of breast implant recipients (cosmetic, not reconstructive) and controls (other cosmetic surgery) to test the hypothesis that connective tissue disease (CTD) is increased in breast implant recipients.

METHODS

Women who underwent breast implant or other cosmetic surgery during the interval from 1978 to 1986 were contacted confidentially by Alberta Health and asked to participate in the study. Those willing to participate completed an extensive questionnaire and supplied a blood sample, subsequent to which all surgical records were reviewed to confirm implant type(s) or cosmetic surgery(ies). All participants with any suggestion of rheumatic disease were assessed blindly by a rheumatologist for CTD.

RESULTS

One thousand five hundred seventy-six breast implant recipients were recruited, including 1112 who had received silicone gel-filled implants (> 13,500 person yrs exposure). Seven hundred twenty-six controls were recruited. Prevalence rates adjusted for sex and age for rheumatoid arthritis, systemic lupus erythematosus, scleroderma, and Sjögren's syndrome (the principal targeted conditions) were consistent with published reports for Caucasian women. While breast implant recipients self-reported significantly greater rates of symptoms than controls, post-surgical diagnoses of the principal targeted conditions did not indicate an increased incidence of typical or atypical CTD.

CONCLUSION

The results of the study do not support the hypothesis that silicone gel-filled implants induce or promote CTD.

Relation between the time to achieve the lower limit of the APTT therapeutic range and recurrent venous thromboembolism during heparin treatment for deep vein thrombosis

BACKGROUND

Randomized trials have demonstrated the importance of achieving adequate heparinization early in the course of therapy. Recently, some authors reported a pooled analysis of selected studies in the literature that suggested that there is no convincing evidence that the risk of recurrent venous thromboembolism is critically dependent on achieving a therapeutic activated partial thromboplastin time result at 24 to 48 hours.

METHODS

We provide the analyses of patient groups entered into our series of 3 consecutive double-blind randomized trials evaluating initial heparin therapy for proximal deep venous thrombosis.

RESULTS

Logistic regression analysis of the patient groups receiving the less intense initial intravenous heparin dose of 30,000 U/24 h demonstrated that subtherapy for 24 hours predicted the onset of venous thromboembolic events. Failure to achieve a therapeutic activated partial thromboplastin time by 24 hours was associated with a 23.3% frequency of venous thromboembolism vs 4% to 6% for those whose activated partial thromboplastin time exceeded the therapeutic threshold by 24 hours (P=.02). Time-to-event analysis shows the increased frequency of recurrent venous thromboembolic events during the period of study in patients who were subtherapeutic for 24 hours compared with those who were therapeutic (P=.001).

CONCLUSIONS

Our findings reaffirm the clinical importance of rapidly achieving therapeutic levels of heparin. Patients who failed to achieve the therapeutic threshold by 24 hours were at an increased risk of subsequent recurrent venous thromboembolism. These findings are independently supported by the results of a randomized trial comparing different intensities of initial heparin treatment by continuous infusion.

The importance of initial heparin treatment on long-term clinical outcomes of antithrombotic therapy. The emerging theme of delayed recurrence

BACKGROUND

Recent clinical trials of venous thromboembolism treatment suggest inadequate initial heparin therapy predisposes patients to late recurrence of thromboembolism. However, a recent review article was unable to demonstrate a relationship between initial heparin therapy and late recurrence.

OBJECTIVE

To evaluate the relationship between initial heparin treatment and long-term clinical outcome in 3 consecutive, randomized, double-blind trials that used similar study designs and patient populations and objective documentation of recurrent venous thromboembolism.

METHODS

The trials were performed sequentially and compared the use of continuous intravenous with subcutaneous heparin, continuous intravenous heparin for 10 or 5 days, and continuous intravenous heparin with once-daily subcutaneous low-molecular-weight heparin. All patients were followed up for 3 months to assess the a priori hypothesis that inadequate initial heparin therapy could lead to recurrent venous thromboembolism during long-term therapy with warfarin sodium.

RESULTS

The following were the observed rates of recurrent venous thromboembolism: continuous intravenous heparin, 3 (5.2%) of 58 patients vs subcutaneous heparin, 11 (19.3%) of 57 patients; continuous intravenous heparin for 10 days, 7 (7.0%) of 100 patients or for 5 days, 7 (7.1%) of 99 patients; and continuous intravenous heparin, 15 (6.9%) of 219 patients vs low-molecular-weight heparin, 6 (2.8%) of 213 patients. Pooled analysis of the patients treated with continuous intravenous heparin showed that of the total 32 patients with recurrent venous thromboembolism, in 6 patients thromboembolism occurred early (< 10 days) and 26 patients thromboembolism occurred late. Of these patients, the majority (20/32 [62.5%]) had therapeutic prothrombin time or international normalized ratio values before or at the time of the recurrent thromboembolic event.

CONCLUSION

Our findings demonstrate that the initial heparin treatment affects the long-term outcome. This conclusion applies when these data are analyzed for each individual study by treatment group, observed difference in outcome, and pooled analysis.

Disease-specific quality of life: the Gallstone Impact Checklist

OBJECTIVE

To develop a disease-specific quality-of-life scale for symptomatic cholelithiasis for use in clinical trials, and to evaluate its reliability, construct validity and responsiveness.

DESIGN

Questionnaire.

PARTICIPANTS

Health care professionals, patients with symptomatic cholelithiasis and their significant others.

INTERVENTIONS

A 114-item questionnaire was developed from open-ended questions completed by the participants. Questions dealt with physical symptoms, activities of daily living, job performance, leisure activities, emotional factors, marital and sexual relations, support networks and financial situation. The questionnaire was administered by an interviewer to 50 subjects booked for elective cholecystectomy: frequency-importance products were calculated for each of the 114 items. A final shortened scale (the Gallstone Impact Checklist [GIC]) contained 41 items and was completed by patients with symptomatic cholelithiasis on two occasions, 4 to 6 weeks apart.

RESULTS

The checklist requires 10 to 15 minutes to complete. Reliability of the questionnaire and its four subscales was assessed by Cronbach's alpha (overall questionnaire 0.88, pain 0.60, dyspepsia 0.73, emotional impact 0.78 and food and eating 0.84). Construct validity was established by comparison of questionnaire subscales with global ratings of physical and emotional health. Among subjects who reported a difference in their symptoms attributed to gallstones, there was a significant change in total GIC score and in each of the four subscales. Among patients who had undergone cholecystectomy, the absolute value of the effect size was 1.63.

CONCLUSIONS

The GIC has content validity and appears to be a reliable, responsive measure of within-person change for subjects with symptomatic cholelithiasis.

Intraoperative graft tensioning alters viscoelastic but not failure behaviours of rabbit medial collateral ligament autografts

The effects of three different degrees of intraoperative graft tensioning on measures of ex vivo laxity, viscoelastic behaviour, and structural and material failure of isolated healing medial collateral ligament autografts were investigated in a rabbit model. The grafts were orthotopically replaced at one of three different loads (too tight, anatomic, or too loose) and were mechanically evaluated after 0, 12, 24, and 48 weeks of healing. Laxity of the ligament was influenced by intraoperative graft tensioning at time zero. However, after 12 weeks of healing, values for laxity were indistinguishable among the experimental groups. Cyclic load relaxation, a measure of viscoelastic behaviour, was significantly influenced by intraoperative graft tensioning, and this effect persisted even after 48 weeks of healing. Grafts placed under excessive tension relaxed one-third less than grafts placed under abnormally low in situ tension. The relevance of these differences remains to be determined. Intraoperative tensioning had no significant influence on characteristics of structural or material failure of the graft during the first year of healing. These results suggest that, in this model, control of graft tension at the time of placement and fixation does not improve the failure characteristics of the medial collateral ligament. The structural strength of the grafts collectively improved to nearly normal values after 48 weeks; however, material recovery was less complete. Failure loads averaged 89% of control values, whereas failure stress averaged only 52% after 48 weeks of healing.

The low-probability lung scan. A need for change in nomenclature

BACKGROUND

The prognosis in patients with suspected pulmonary embolism who have a low-probability lung scan has been the focus of much clinical debate. This is particularly so in patients with underlying cardiac and pulmonary disease, because these disorders frequently cause low-probability lung scans in the absence of pulmonary embolism. Historically, the clinical response has been to exclude pulmonary embolism and withhold treatment on the basis of a low-probability lung scan, which has been regarded as synonymous with a good prognosis.

METHODS

A prospective cohort-analytic study to evaluate prognosis, using long-term follow-up, in patients with inadequate cardiorespiratory reserve who have presented with suspected pulmonary embolism (inadequate cardiorespiratory reserve, ie, pulmonary edema, right-ventricular failure, hypotension, syncope, acute tachyarrhythmia, abnormal spirometry [forced expiratory volume in 1 second, < 1.0, or vital capacity, < 1.5 L], or abnormal arterial blood gases [PO2, < 50 mm Hg, or PCO2, > 45 mm Hg]).

RESULTS

The outcomes of the 77 consecutive patients with low-probability lung scans, suspected pulmonary embolism, and inadequate cardiorespiratory reserve were compared with those in 711 consecutive patients with good cardiorespiratory reserve and nondiagnostic lung scans who were entered into the study over the same period of time. Six (7.8%) of the 77 patients died within days of entry with autopsy-proven pulmonary embolism compared with one (0.14%) of the 711 patients with nondiagnostic lung scans (P < .0001).

CONCLUSIONS

Our findings indicate that the term low-probability lung scan should be abandoned in reference to patients with inadequate cardiorespiratory reserve, because it is not synonymous with a good prognosis and is, indeed, misleading.

Freezing influences the healing of rabbit medial collateral ligament autografts

Connective tissue allografts are treated commonly with deep freezing to facilitate their storage in tissue banks and to reduce their immunogenicity. The influence of freezing on the healing of these grafts is unknown. The effect of an aggressive freezing protocol on ligament graft healing in a nonimmunogenic autograft model was investigated. The femoral-medial collateral ligament-tibial complex of the rabbit knee was transplanted orthotopically into the site from which it had just been harvested. The fresh group had their grafts rinsed in normal saline, and the frozen-thawed group had their grafts repetitively frozen-thawed in liquid nitrogen immediately before reimplantation. The healing of the ligament complexes were evaluated mechanically at intervals as long as 1 year after transplantation. Repeated freezing had little effect on the initial mechanical behavior of the graft complexes but was found to be detrimental to subsequent graft incorporation. The frozen-thawed grafts were weaker than the fresh grafts overall, and this effect persisted over time. The failure load and stress of the frozen-thawed grafts reached only 87% and 75% of that of the fresh grafts after 48 weeks. Because the initial mechanical effects of freezing were minimal, subsequent effects on graft healing must be attributed to factors other than gross structural injury. Despite showing almost no signs of damage to bone-ligament-bone grafts initially, freezing procedures may have important subsequent biologic consequences that may influence the clinical success of stored connective tissue grafts used in ligament reconstruction.

Influence of methodologic factors in a pooled analysis of 13 case-control studies of colorectal cancer and dietary fiber

We examined the study design features and data collection methods from 13 case-control studies of colorectal cancer and diet, which had been previously combined and analyzed, to determine whether they influenced the results obtained from a pooled analysis. We assessed the methods used in each study, estimated a quality score, and used random effects models to re-estimate the pooled odds ratio for the association between dietary fiber and colorectal cancer for these data. Key features of the methods used in each study and the quality score were examined in random effects models to determine whether the heterogeneity found between study-specific risk estimates could be explained by these variables. The odds ratio for dietary fiber and colorectal cancer was 0.46 (95% confidence interval = 0.34-0.64) for the 13 case-control studies as estimated with a random effects model. Two factors, whether the diet questionnaire had been validated before use in the case-control study and whether qualitative data on dietary habits and cooking methods had been incorporated into the nutrient estimation, explained some of the heterogeneity found between studies. Risk estimates for dietary fiber and colorectal cancer were closer to the null for the studies that had these two characteristics. Quality score did not explain any between-study heterogeneity. Random effects models, which included fixed effects covariates, explained some between-study heterogeneity in these data and would be useful for future pooled analyses.

An alternative method for determination of the carpal height ratio

Radiographs of the wrist often do not include the entire third metacarpal, so the standard method for measurement of the carpal height ratio (the carpal height divided by the length of the third metacarpal) cannot be used. In this study, the ratio of the carpal height relative to the length of the capitate was evaluated for its suitability as a reproducible alternative. The revised carpal height ratio (the carpal height divided by the capitate length) was evaluated for reproducibility and clinical utility in both in vitro and in vivo studies: it was determined from the radiographs of ten cadaveric wrists; those of 100 wrists (fifty pairs) of normal volunteers, made with controlled positioning; those of 100 wrists, drawn at random from radiographs that had been previously interpreted as showing normal findings; and those of fifty wrists of twenty-nine patients who had documented rheumatoid arthritis. The new ratio was found to be constant in the normal population, consistent bilaterally, decreased in patients who had carpal collapse, and reproducible.

Case-control study of prenatal ultrasonography exposure in children with delayed speech

OBJECTIVE

To determine whether there is an association between prenatal ultrasound exposure and delayed speech in children.

DESIGN

Case-control study.

SETTING

Network of community physicians affiliated with the Primary Care Research Unit, University of Calgary.

SUBJECTS

Thirty-four practitioners identified 72 children aged 24 to 100 months who had undergone a formal speech-language evaluation and were found to have delayed speech of unknown cause by a speech-language pathologist. For each case subject the practitioners found two control subjects matched for sex, date of birth, sibling birth order and associated health problems.

MAIN OUTCOME MEASURES

Rates of prenatal ultrasound exposure and delayed speech.

RESULTS

The children with delayed speech had a higher rate of ultrasound exposure than the control subjects. The findings suggest that a child with delayed speech is about twice as likely as a child without delayed speech to have been exposed to prenatal ultrasound waves (odds ratio 2.8, 95% confidence limit 1.5 to 5.3; p = 0.001).

CONCLUSION

An association between prenatal ultrasonography exposure and delayed speech was found. If there is no obvious clinical indication for diagnostic in-utero ultrasonography, physicians might be wise to caution their patients about the vulnerability of the fetus to noxious agents.

Detecting treatment effects in patients with rheumatoid arthritis: the advantage of longitudinal data

Assessment of therapy in patients with rheumatoid arthritis is important but difficult. We examined 4 different methods of analyzing pretreatment data and assessed the difference that each made in detecting a positive effect of intramuscular gold on the patient's overall disability. The methods were (1) calculating the arithmetic mean of prior data points, (2) taking the last data point pretreatment, (3) fitting a straight line to pretreatment points and (4) fitting the pretreatment points with a quadratic equation. After comparison with matched controls (not taking remittive agents) the most significant difference was found by fitting a straight line to pretreatment data. This technique demonstrated about one-third more of intramuscular gold's effectiveness than the usual technique of using the last data point pretreatment. We conclude that statistical power is improved by obtaining and analyzing longitudinal pretreatment data appropriately.