Comparison of Compression Ultrasound vs Ascending Contrast Venography for Proximal DVT in Medical-Surgical ICU Patients.

Background: Ascending contrast venography is the reference standard for diagnosing DVT. Observational studies suggest that compression ultrasound has 97% sensitivity and 94% specificity for proximal DVT in symptomatic patients. However, in asymptomatic patients, such as those in the medical-surgical ICU, the test properties of ultrasound may be substantially worse. Surveys, observational studies and professional documents show that many intensivists, Research Ethics Boards, and the American College of Radiology have rejected the routine use of venography in the ICU setting.

Objective: To compare the results of positive lower limb compression ultrasound with ascending contrast venography in medical-surgical ICU patients.

Design: One year longitudinal cohort study.

Setting: 15 bed medical-surgical closed ICU in Hamilton, Canada.

Methods: We enrolled consecutive patients age >18y with an expected ICU admission >72h. Exclusion criteria were trauma, orthopedic surgery, cardiac surgery, pregnancy or palliative care. Patients underwent bedside lower limb compression ultrasonography by a certified ultrasonographer on ICU admission, twice weekly, and upon clinical suspicion of VTE. Patients with a positive or nondiagnostic ultrasound underwent bilateral lower extremity ascending contrast venography, unless they had pre-specified contraindications: serum creatinine >150 umol/L, pre-existing insulin-requiring diabetes, known or suspected contrast allergy, or contraindications to transport to the Radiology Department. The study radiologist and thrombosis consultant independently interpreted the venograms in duplicate; disagreements were resolved by a third adjudicator.

Results: Of 261 patients, lower limb DVT was identified by compression ultrasound in 32 patients (7, 2.7% on ICU admission and 25, 9.6% during the ICU stay). Using the a priori venogram eligibility criteria, 8 of 32 patients (25.0%) with DVT by screening ultrasound were suitable for venography; 7 of the 8 venograms (87.5%) were positive.

Conclusions: Venogram eligibility criteria (e.g., low oxygen requirements, hemodynamic stability, and low risk for contrast nephropahthy) designed to safely confirm or refute positive or nondiagnostic screening ultrasound findings resulted in only selected, less seriously ill ICU patients undergoing venography. Concerns about the risk: benefit ratio of research interventions not used in current practice means that in multicenter trials, serial compression ultrasound will be the only safe and feasible method of screening for proximal DVT in the medical-surgical critically ill population.