How Big a Problem is DVT in the ICU?

Abstract & Commentary

By Uday B. Nanavaty, MD, Pulmonary and Critical Care Medicine, Rockville, MD, is Associate Editor for Critical Care Alert

Dr. Nanavaty reports no financial relationships related to this field of study.

Synopsis: In this prospective study, despite the use of currently recommended prophylactic measures, nearly 10% of patients developed deep venous thrombosis during their ICU stay.

Source: Cook D, et al. Deep venous thrombosis in medical-surgical critically ill patients: prevalence, incidence, and risk factors. Crit Care Med. 2005;33:1565-1571.

In this prospective study, cook and associates looked at prevalence and incidence of deep vein thrombosis (DVT) as diagnosed by compression ultrasonography in ICU patients. Although the DVT prophylaxis was universal, the incidence of DVT was nearly 10%. Further studies are needed to define the group at highest risk of DVT and to assess the risk benefit ratio of aggressive preventive strategies.

Cook et al performed a prospective cohort study to determine the prevalence and incidence of proximal lower extremity DVT in critically ill patients admitted to a university-affiliated medical-surgical ICU. Patients who were older than 18 years and who were expected to have longer than 72 hours of ICU stay were enrolled. Patients with admitting diagnoses of trauma, orthopedic surgery, or pregnancy, or in whom life support was withdrawn, were excluded. To measure the prevalence of DVT, compression ultrasonography was performed in both lower extremities within 48 hours of admission in all patients. To measure the incidence of DVT, compression ultrasonography was performed twice weekly and upon clinical suspicion for DVT. The screening continued until development of DVT, ICU death, or ICU discharge.

Over one year, 817 patients were admitted to Cook et al’s ICU and 261 were enrolled in the study. These patients were relatively sick (average APACHE II score, 25.5); the majority were mechanically ventilated (88.9%), and they experienced relatively high ICU and hospital mortality rates (27.2% and 39.5%, respectively). Of the 261 patients, 10 had active bleeding and did not receive any anticoagulant prophylaxis. Of the remaining 251 patients, 18 did not receive any anticoagulant prophylaxis due to a variety of contraindications; 205 patients (81.7%) received unfractionated heparin (UFH) via the subcutaneous route for DVT prophylaxis. An additional 17 patients needed UFH intravenously for therapeutic anticoagulation. Ten patients received low molecular weight heparin in therapeutic doses for acute coronary syndromes, and one patient was on therapeutic warfarin.

The prevalence of occlusive DVT at the time of admission (within the first 48 hours) was 2.7 % (7 patients out of 261). In only 3 of these 7 patients was DVT clinically suspected based on a structured clinical examination. During their ICU stay (median, 10 days), 25 patients developed DVT, for an incidence of 9.6%, in spite of near universal thromboprophylaxis. Only 3 out of these 25 DVTs were clinically suspected. Out of all the 32 DVTs identified, only 3 were related to a catheter. In 3 patients with DVT, pulmonary embolism was diagnosed.

In univariate analyses, a personal or family history of venous thrombosis, thrombophilia, chronic hemodialysis, femoral central venous catheter, surgical operation, platelet transfusion, and vasopressor administration were identified as risk factors for lower limb DVT. In multivariate analysis, a personal or family history of DVT (hazard ratio [HR], 4.0), end-stage renal disease (HR, 3.7), platelet transfusion (HR, 3.2) and vasopressor administration (HR, 2.8) were found to be independent risk factors for development of DVT.

Patients with DVT in general had longer ICU stays (median, 17.5 days compared to 9 days in patients without DVT); they required longer mechanical ventilation (median, 9 days vs 6 days), and had longer overall hospital stays (median, 51 days vs 23 days). There was no statistically significant difference in ICU mortality (25% vs 27.3%) or hospital mortality (53% vs 37.4%) among patients with or without DVT.

Commentary

Venous thrombosis and pulmonary embolism are dreaded complications often thought to go unrecognized in the ICU. Almost all patients admitted to critical care units are believed to be at risk of venous thromboembolism (VTE), and hence guidelines have been established to increase the awareness of a VTE problem in the ICU as well to reduce the morbidity and mortality from VTE. Different units have differing policies to prevent VTE. When its use is not contraindicated, unfractionated heparin in a dose of 5000 Units 2 or 3 times a day is the standard of care. Low molecular weight heparin has been used as effective prophylaxis against VTE in orthopedic surgery patients. In the neurosurgical literature, especially in patients with intracranial hemorrhage, as well as in other patients with life threatening hemorrhage, compression stockings and or sequential pneumatic compression devices have been shown to be effective at reducing the incidence of DVT.

This particular study has several important highlights. At least in this study, in more than 200 patients where UFH was used, no episode of heparin-induced thrombocytopenia was reported. Also, although it is not clear from the paper, I believe the dose of UFH was twice a day as opposed to 3 times a day. Thrice daily dosing of UFH may further reduce the incidence of DVT. In addition, although 3 episodes of pulmonary embolism were reported, no fatality due to VTE occurred in this study. It is possible that since DVT was diagnosed even when not suspected, and could have resulted in the decision to therapeutically anticoagulate the patients, hence subsequent episodes of pulmonary embolisms may have gone undetected. This study is reaffirms the old saying, "an ounce of prevention is worth a pound of cure," as far as VTE is concerned.