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Biomedical subjects

J Hirsh

Publications and source records attributed to J Hirsh.

At least 145 records · Page 8Linked to original sources
PubMed1995

Starting prophylaxis for venous thromboembolism postoperatively.

A large proportion of hospitalized patients who are at high risk for venous thromboembolism (VTE) do not receive prophylaxis. Reluctance to use VTE prophylaxis in surgical patients may be due to fear of perioperative bleeding when anticoagulants are given preoperatively. We preformed a literature review to determine (1) whether prophylaxis for VTE is effective when it is started postoperatively and (2) the relative efficacy of preoperatively and postoperatively initiated prophylaxis. Studies were included in the review (1) if they were randomized trials with "blind" assessment of appropriate VTE outcomes, and (2) if prophylaxis was started postoperatively. Randomized, controlled trials establish that pharmacologic and nonpharmacologic methods of prophylaxis that are effective when started preoperatively are also effective when they are started postoperatively, with relative risks for VTE of 0.16 to 0.49. Low rates of VTE in noncontrolled randomized trials that included postoperatively initiated prophylactic regimens support this finding. The relative efficacy of preoperatively and postoperatively initiated VTE prophylaxis could not be determined definitively, as direct comparisons of the same regimens have not been performed. Indirect comparisons suggest that any loss of efficacy resulting from deferring VTE prophylaxis until after surgery is unlikely to be marked. Randomized trials are required to resolve this question. This comparison may be of greatest clinical importance when twice-daily, low-molecular-weight heparin is used to prevent VTE after major orthopedic surgery.

Clinical Trials as Topic↗
PubMed1995

Thrombosis.

Explore the source record for details and available documents.

Arteriosclerosis↗
PubMed1995

Optimal intensity and monitoring warfarin.

The risk of bleeding with warfarin can be markedly reduced without affecting efficacy by using a low-intensity therapeutic range. The reliability of warfarin monitoring has also improved with the development of the international normalized ratio (INR) to standardize prothrombin time despite use of nonuniform thromboplastins by different laboratories. There are 2 recommended therapeutic ranges of intensity for warfarin: the less intense corresponds to INR 2.0-3.0, the more intense, to INR 2.5-3.5. Dosage response to warfarin is influenced by concomitant medication, dietary vitamin K, hepatic dysfunction, and hypermetabolic states. For rapid anticoagulant effect, the initial dosage is 10 mg/day (plus heparin). For nonemergent treatment, the initial dosage is 4-5 mg/day, which achieves a steady-state anticoagulant effect in 5-7 days; this is also the anticipated maintenance dosage. Prothrombin time (PT) monitoring is performed daily until the therapeutic range is achieved, then progressively less often, depending on stability of PT results. Bleeding while on warfarin (INR > 3.0) may respond to reduced dosage; for severe bleeding, vitamin K reverses warfarin effects in 6-12 hours. Bleeding on low-intensity warfarin (INR < 3.0) suggests an underlying pathologic condition. Warfarin is contraindicated in pregnancy because of its teratogenicity but may be used by nursing mothers, as it does not pass into breast milk.

Dose-Response Relationship, Drug↗
PubMed1995

Accuracy of ultrasound for the diagnosis of deep venous thrombosis in asymptomatic patients after orthopedic surgery. A meta-analysis.

OBJECTIVE: To evaluate, by meta-analysis, the accuracy of ultrasound screening for deep venous thrombosis in patients after orthopedic surgery. DATA SOURCES: The MEDLINE database from January 1982 to October 1993. Bibliographies of retrieved articles and recent journal publications were searched independently and using Current Contents. STUDY SELECTION: All articles evaluating the use of venous ultrasound imaging (B-mode, duplex, and color Doppler) compared with standard contrast venography for detecting deep venous thrombosis. We excluded abstracts, early reports of studies later reported in full, and studies in which venography was not done in all patients. Seventeen of 30 identified studies were eligible. DATA EXTRACTION: Eligible articles were reviewed for the presence of three key criteria necessary for evaluating the accuracy of the diagnostic tests: 1) previously established objective criteria for venography and ultrasound, 2) independent blinded comparisons of venography and ultrasound, and 3) prospective evaluations of consecutive patients. Studies including all three key criteria were defined as level 1 (minimized bias) studies; otherwise, they were defined as level 2 studies. DATA SYNTHESIS: In level 1 studies, ultrasonography had a sensitivity of 62% (95 of 153; 95% CI, 54% to 70%), a specificity of 97% (CI, 96% to 98%), and a positive predictive value of 66% (95 of 144; CI, 58% to 74%) for detecting proximal thrombi. For level 2 studies, the sensitivity was 95% (CI, 87% to 99%), the specificity was 100% (CI, 99% to 100%), and the positive predictive value was 100% (CI, 94% to 100%). Differences between level 1 and level 2 studies appeared to be related to bias in study design. CONCLUSIONS: Venous ultrasound imaging has only moderate sensitivity and a moderate positive predictive value when used to screen for deep venous thrombosis in patients after orthopedic surgery; thus, ultrasound imaging may have limitations as a screening test.

Aged↗
PubMed1995

INR reporting in Canadian medical laboratories. Thrombosis Interest Group of Canada.

A written survey of all licensed medical laboratories in Canada performing coagulation testing was performed to investigate the level of knowledge and overall usage of the INR system for reporting prothrombin time results in medical laboratories. There was an overall response rate of 857 of 1,228 laboratories surveyed. Fifty-seven percent of responding laboratories utilized some format of INR reporting. The ISI of the individual thromboplastin utilized was known by 89% of laboratories. The ISI of the thromboplastin utilized was known to be specific for the particular reagent/instrument combination in 44% of cases. Fifty-five percent of client physicians preferred PT results to be reported in seconds while 42% desired an INR format. The situation in Canada is similar to the United States in that further education regarding the INR system for PT reporting is required by both medical laboratories and physicians.

Administration, Oral↗
PubMed1995

The value of plasma calibrants in correcting coagulometer effects on international normalized ratios. An international multicenter study.

A study of lyophilized plasma calibrants in correcting for coagulometer effects on International Normalized Ratios (INR) has been conducted in an international survey. Prothrombin times were performed with the calibrants on 2 "common" thromboplastins and in-house thromboplastins in 3 brands of coagulometer at 37 centers. The International Sensitivity Indices (ISI) of 95 local systems with the calibrants were derived. The "true" INR of 10 test plasmas from warfarin-treated patients were established centrally using thromboplastin International Reference Preparations (IRP). International Normalized Ratios of these plasmas for each center were calculated using both the manufacturers' stated and the local ISI. The mean deviation of the 95 systems from the "true" INR of the warfarin plasmas was +14.4% with the manufacturers' ISI, but reduced to +1.04% with the local ISI. Local ISI determination with the calibrants avoids many of the difficulties of conventional thromboplastin calibrations. Plasmas from patients on warfarin and parallel manual PT with thromboplastin IRP are not required.

Blood Coagulation Tests↗
PubMed1995

A comparison of lyophilized artificially depleted plasmas and lyophilized plasmas from patients receiving warfarin in correcting for coagulometer effects on international normalized ratios.

The comparative value of lyophilized artificially depleted plasmas and plasmas from warfarin-treated patients in local (thromboplastin/coagulometer) system International Sensitivity Indices (ISI) determination has been studied at 39 centers in an international collaborative study. At each center, both types of plasmas were tested with two common thromboplastins (low ISI RecombiPlasTin and high ISI OBT), and in-house reagents using three brands of coagulometers. In 95 local systems, they was agreement. With both thromboplastins, coagulometers lowered the ISI from the manual or stated ISI with all systems. Differences between the two types of lyophilized plasmas with the two common thromboplastins were not of clinical importance. Artificially depleted plasmas are easier to obtain in sufficient volumes than plasma from warfarin-treated patients, and more easily provide the wide range of INR values required for reliable local ISI calibration. The agreement between the two types of lyophilized calibrant is reassuring.

Blood Coagulation Tests↗
PubMed1995

Advances in antithrombotic drug therapy for coronary artery disease.

Compounds which inhibit the coagulation cascade and antagonize platelet function are fundamental to the successful treatment of acute coronary syndromes. In a high proportion of patients with acute myocardial infarction, unstable angina, or sudden cardiac death, the acute ischaemic event is precipitated by intracoronary thrombus. Occlusive or non-occlusive thrombi have been found in the majority of cases, either in vivo or at autopsy. Aspirin and unfractionated heparin have been the cornerstones of antithrombotic therapy in such patients for the past decade, but while their benefits have been convincingly demonstrated, there are significant pharmacokinetic, pharmacodynamic, and clinical limitations. These limitations have provided the impetus for the development of newer antithrombotic agents with several theoretical advantages over aspirin and heparin. This paper has four aims. First it reviews the pathogenesis of intracoronary thrombi in acute coronary artery syndromes. Second, it outlines the limitations of current antithrombotic therapies. Third, it explores the potential advantages of new antithrombin and antiplatelet compounds, which may be understood and classified by their mechanism of action (Table 1); how the theoretical advantages may translate into clinical practice will be examined. Fourth, the initial clinical experience with these new agents will be reviewed briefly.

Animals↗
PubMed1995

Effect of nifedipine on the renal functional reserve in cyclosporine-treated renal-transplant recipients.

Cyclosporine decreases renal perfusion and impairs the renal hemodynamic response to a protein load. High-dose nifedipine has been shown to elevate renal plasma flow (RPF). We measured the renal functional reserve of 6 cyclosporine-treated renal-transplant recipients following intravenous administration of an amino acid solution, before and 2 weeks after therapy with high-dose nifedipine (up to 120 mg/day). Pretreatment renal functional reserve was nil Following administration of nifedipine, RPF increased by 22% (p < 0.01), filtration fraction decreased by 14% (p < 0.005) and renal vascular resistance declined by 39% (p < 0.005). Renal functional reserve remained unchanged. High-dose nifedipine increases renal perfusion but does not restore renal functional reserve in cyclosporine-treated renal-transplant recipients.

Adult↗
PubMed1995

Very low-dose warfarin prophylaxis to prevent thromboembolism in women with metastatic breast cancer receiving chemotherapy: an economic evaluation.

PURPOSE: A recent double-blind, randomized trial demonstrated that very low-dose warfarin (VLDW) reduced the incidence of venous thromboembolism (VTE) without increasing the rate of bleeding in women with metastatic breast cancer receiving chemotherapy. We have evaluated the economic impact on the health care system of using VLDW in such patients. METHODS: The records of patients entered onto the trial and a simultaneous, fully allocated, costing model for a tertiary care hospital in Hamilton, Canada were used to determine the difference in costs associated with the care of patients with and without VLDW. RESULTS: The cost of providing VLDW was $ 21,854 (Canadian dollars) per 100 patients. This therapy led to a reduction in costs of $ 24,297 per 100 patients, thus saving the health care system $ 2,443 per 100 patients. In the sensitivity analysis, VLDW prophylaxis still did not increase health care costs unless the cost of VLDW was greatly increased, the cost of treating thromboembolic episodes was markedly reduced, or the incidence of either VTE or bleeding with VLDW was increased above the rates observed in the trial. CONCLUSION: We conclude that for women receiving chemotherapy for metastatic breast cancer, the benefits of VLDW can be realized without increased health care costs.

Breast Neoplasms↗