Pneumonia Seen as Top Risk Factor for Postop VTE

By Mitchel L. Zoler

PHILADELPHIA -- Pneumonia was one of five new risk factors for postoperative venous thromboembolism that were identified in an analysis of more than 75,000 patients.

Other new risk factors for venous thromboembolism (VTE) were the need for a blood transfusion because of bleeding, renal insufficiency, urinary tract infection, and a low level of serum albumin, Dr. Chethan Gangireddy said at the Vascular Annual Meeting.

"These newly described risk factors can aid in further stratifying a patient's risk for postoperative VTE," said Dr. Gangireddy, a surgeon at the University of Michigan in Ann Arbor.

The analysis included data collected by the National Surgical Quality Improvement Program of the Department of Veterans Affairs system during 1996-2001. The database included all of the more than 118,000 patients who had surgery at any of 114 hospitals for one of the nine most common operations done at these hospitals. From this group, complete pre-, peri-, and postoperative data were available for 75,711 patients.

The overall incidence of venous thromboembolism was 0.7%, but the incidence varied significantly based on the type of surgery. Carotid endarterectomy carried the lowest risk for VTE, with a 0.14% postoperative risk. Total hip arthroplasty posed the biggest risk for VTE, with a 1.3% postoperative rate. The analysis also showed no significant change in the annual rate of VTE through the 6 years that were studied.

In a multivariate analysis that evaluated the independent risk added by many different clinical and demographic factors, pneumonia was found to be the strongest risk factor, boosting the risk of VTE 2.7-fold. Several other risk factors each boosted the risk for VTE by about twofold (see table), and three factors were found to reduce the VTE risk.

In an analysis of the two most common manifestations of VTE, the list of significant risk factors for causing deep vein thrombosis was found to be different from the list linked with pulmonary embolism.

The top risks for DVT were need for a transfusion due to bleeding (3.3-fold increased risk), pneumonia (2.5-fold increased risk), and urinary tract infection (1.7-fold increased risk). For pulmonary embolism the top risk factor was cardiac arrest (7.6-fold increased risk), followed by pneumonia (3.9-fold increased risk) and need for a transfusion (2.4-fold increased risk).

Another finding was that patients with VTE had a 2.4-fold increased risk of death compared with all other patients, Dr. Gangireddy said.

When asked to comment on this article, Dr. Frank Pomposelli, chief of vascular and endovascular surgery, Beth Israel Deaconess Medical Center, Boston, stated: "Identifying factors that put patients at risk for VTE is critical to prevent potentially lethal pulmonary embolism--one of the most devastating and usually unexpected complications of any surgical procedure. The identification of pneumonia as a significant risk factor for post operative VTE is on first pass, surprising. However on further reflection, probably makes sense. Most patients developing post operative pneumonia do so as a result of a myriad of other factors such as prolonged time on a ventilator, complex upper abdominal surgery, prolonged bed rest, etc.

"Many of these factors are also associated with an increased risk of VTE. In the current study it may be that perioperative pneumonia is a surrogate marker for the same risk factors causing VTE by identifying those seriously ill patients with the typical constellation of risk factors that we associate with VTE," he concluded.