Aspirin May Be Best to Prevent

By Laurie Bouck
Medscape Medical News

Laurie Bouck

March 7, 2008 (San Francisco) — Aspirin may be the most effective choice to prevent pulmonary embolism (PE) and venous thromboembolism (VTE) in patients undergoing orthopaedic surgery, according to a new study examining a potential role for aspirin in these patients.

Aspirin is not currently recommended by the American College of Chest Physicians to help prevent deep vein thrombosis (DVT) after surgery. The American Academy of Orthopaedic Surgeons (AAOS), however, has developed separate guidelines to prevent PE and VTE that are more clinically relevant to orthopaedic surgeons. The AAOS guidelines recommend aspirin to prevent PE and VTE in patients with a low risk of DVT or a higher risk of bleeding.

A 2003 to 2005 retrospective study of 93,840 total knee arthroscopy (TKA) patients at 307 hospitals nationwide looked at aspirin's effect on VTE. The study was presented here at the AAOS 75th Annual Meeting by lead investigator Kevin J. Bozic, MD, MBA, associate professor in residence at the Department of Orthopaedic Surgery and Philip R. Lee Institute for Health Policy Studies, University of California, San Francisco.

Many aspects of TKA have changed in recent years, lowering the risk of VTE, Dr. Bozic said during his presentation, and as a result, "The risk-benefit balance of aspirin has shifted." He adds in a press release that "patients undergoing knee surgery today are more likely to be younger and healthier than when the current treatment guidelines were developed."

In his study, Dr. Bozic analyzed administrative data for primary TKA patients and measured VTE, bleeding events, surgical site infections, and mortality. A total of 4719 patients (5%) received aspirin as a chemoprophylactic. Patients who received aspirin had a lower VTE risk score than the patients who received warfarin (51,923 patients [55%]) or injectable VTEP (37,198 patients [40%]). On average, patients who received aspirin recovered more quickly than other patients, with a shorter hospital stay and more discharges directly home. Adjusted bleeding and mortality risks were similar among all 3 groups, but aspirin patients were less likely to develop VTE than warfarin patients.

In his presentation, Dr. Bozic said that the patients who received aspirin had a much lower use of sequential compression devices than high-risk patients. He pointed out that even aspirin patients should receive sequential compression as needed. "Aspirin alone is not indicated, even in low-risk patients," he said.

"There have been trials comparing aspirin to other venous thromboembolic prophylactic agents," Dr. Bozic told Medscape Orthopaedics. "Those were done in an era where knee replacement surgery was practiced very differently than it is today, in terms of the care protocols and in terms of the patient demographics. What our study shows, in a very large population of patients, is that aspirin as it is being used in clinical practice today, in a certain subset of patients under very specific care pathways, is as effective and as safe as other chemoprophylactic agents."

After the presentation, Dr. Bozic was asked whether he looked at nonsteroidal anti-inflammatory drug (NSAID) use among the patients. He said that he did not look at NSAID use because he thought that it probably did not vary across the 3 groups of patients.

Dr. Bozic told Medscape Orthopaedics that randomized controlled trials are now needed to better understand which patients and care pathways are appropriate for aspirin therapy.

Session moderator Michael A. Kelly, MD, chair of Orthopaedics at Hackensack University Medical Center, New Jersey, found Dr. Bozic's study "very reasonable." Dr. Kelly said that VTE is "an interesting topic because these issues are very critical to the orthopaedists who practice now." Dr. Kelly said that he uses aspirin and sequential compression devices to help prevent VTE in the low-risk, unilateral TKA patients at his hospital, a therapy that he found "quite efficacious for preventing catastrophic problems related to DVT."

Dr. Bozic and coauthors received research grants from the Orthopaedic Research and Education Foundation, the California Healthcare Foundation, and a patient safety research and training grant from the Agency for Healthcare Research and Quality.

American Academy of Orthopaedic Surgeons 75th Annual Meeting: Abstract. Presented March 5, 2008.