Thromboprophylaxis: Questions and Controversies

BY SHARON WORCESTER

ORLANDO -- Meta-analyses favor the administration of subcutaneous heparin every 8 hours to avert venous thromboembolism in general surgery patients, Dr. William Geerts said at the annual meeting of the American Society of Hematology.

In one meta-analysis, for example, a 5,000-U dose of heparin given every 8 hours was associated with a 66% reduction in risk for deep vein thrombosis, compared with a 52% reduction with dosing every 12 hours, said Dr. Geerts of the University of Toronto.

The risks and benefits of 8-hour vs. 12-hour dosing of subcutaneous heparin for prophylaxis have not been studied in a controlled, prospective fashion.

BECAUSE OF THE COST AND EFFORT INVOLVED, 'I'M OPPOSED TO THE USE OF MECHANICAL PROPHYLAXIS, EXCEPT WHEN THERE IS NO ALTERNATIVE.'

Based on the available evidence, moderate-risk medical patients and general or gynecologic surgical patients with benign disease can be given subcutaneous heparin at 5,000 U either every 8 hours or every 12 hours; in higher-risk patients, such as general surgical or gynecologic surgical patients with cancer, those undergoing bariatric surgery, and those with multiple risk factors, dosing at 5,000 U every 8 hours is recommended, he said.

Heparin dosing is just one of the controversial aspects of thromboprophylaxis that Dr. Geerts addressed. Others are listed below:

PIThe use of mechanical prophylaxis. Although sequential compression devices, graduated compression stockings, and venous foot pumps don't cause bleeding, such methods haven't been as well studied as pharmacologic methods of prophylaxis, so there is less certainty about their efficacy. Existing studies suggest that with proper compliance, mechanical prophylaxis methods can benefit some patients; however, compliance in routine clinical practice tends to be low. Furthermore, providing mechanical prophylaxis and ensuring proper use is costly and requires a great deal of effort, Dr. Geerts noted. "I'm opposed to the use of mechanical prophylaxis, except when there is no alternative," he said.

Combining mechanical and anticoagulant prophylaxis is generally not recommended except in very high-risk patients, such as cancer surgery patients with a history of deep vein thrombosis. In patients with a high bleeding risk, such as those with a major head injury or those undergoing neurosurgery, starting thromboprophylaxis with a mechanical device and then switching to an anticoagulant method of prophylaxis when the bleeding risk decreases is a sensible approach. When mechanical and anticoagulant prophylaxis methods are combined, there is a "very real possibility" that both methods will be used suboptimally, he said.

• Contraindications to anticoagulant prophylaxis. Although thromboprophylaxis is indicated for most hospitalized patients, there are some contraindications: active bleeding or a known major bleeding disorder in the patient, platelet count below 50x109/L, intracranial bleeding in the previous few days, and heparin-induced thrombocytopenia (contraindication for heparin or low-molecular-weight heparin [LMWH] only).
• The need for preoperative anticoagulant thromboprophylaxis. Despite long-held beliefs to the contrary, there is evidence that preoperative anticoagulant thromboprophylaxis is not necessary as long as postoperative prophylaxis includes an efficacious drug given at an appropriate dose, at the right time, and for an adequate duration.
• The compatibility of anticoagulant thromboprophylaxis and epidural analgesia. Regional anesthesia/analgesia and anticoagulant prophylaxis can be used at the same time, but common sense should be used in regard to patient selection, timing of anticoagulant administration, and catheter insertion and removal. Spinal/epidural anesthesia and low-molecular-weight heparin should not be combined in patients with bleeding disorders, for example. No preoperative anticoagulant treatment should be given, and the first dose can be provided the day after surgery as usual. The epidural catheter should be removed just prior to a scheduled dose of low-molecular-weight heparin, with the next dose given at least 2 hours after catheter removal.
• The appropriate duration of prophylaxis. Data are lacking on the appropriate duration of prophylaxis. For most patients, prophylaxis should continue until hospital discharge. With major orthopedic surgery, for which there are considerable data regarding optimal thromboprophylaxis duration, treatment should be provided for at least 10 days and up to 6 weeks.
• The relevance of considering heparin-induced thrombocytopenia (HIT) when selecting anticoagulant prophylaxis. In one meta-analysis, HIT was shown to be 40 times more common with low-dose heparin (LDH) than with low-molecular-weight heparin (2.4% vs. 0.6% incidence) in more than 1,700 patients per treatment group, but the HIT risk in the particular patient group and the relative costs of low-dose heparin vs. a HIT-safe alternative should be considered. Low-molecular-weight heparin is preferred for major orthopedic surgery, because it is more efficacious than low-dose heparin. In cardiac surgery, it remains reasonable to consider low-molecular-weight heparin, because HIT is relatively common in this patient group. If the cost difference between low-dose heparin and low-molecular-weight heparin is small, then low-molecular-weight heparin is preferred.
• The use of inferior vena cava (IVC) filters as prophylaxis. There is absolutely no evidence that prophylactic IVC filters are needed by any patient group. In fact, the major complication rates associated with IVC filters (which are generally low) are at least as high as the estimated risk of pulmonary embolism, Dr. Geerts noted.

Furthermore, filters do not reduce deep vein thrombosis risk; in fact, they might increase the risk. They don't eliminate the need for anticoagulants, and they are extremely costly, he said.

The bottom line when it comes to thromboprophylaxis? Keep it simple, Dr. Geerts said (see box).

Thromboprophylaxis prevents most symptomatic and fatal thromboembolic events when used sensibly, but it is not possible to prevent every symptomatic venous thromboembolism or fatal pulmonary embolism. Several strategies, however, have been shown to improve adherence with evidence-based prophylaxis: having written policies about prophylaxis in place, putting compliance in the hands of nurses and pharmacists, providing preprinted physician orders, and using computer reminders and physician order entry, he said.