SINGLE WHOLE-LEG COMPRESSION ULTRASOUND FOR EXCLUSION OF DEEP VEIN THROMBOSIS IN SYMPTOMATIC AMBULATORY PATIENTS: A PROSPECTIVE OBSERVATIONAL COHORT STUDY
Authors: Horner D , Hogg K , Body R , Mackway-Jones K 
Published: September 2013

Objectives & BackgroundInternational guidance has recently recommended serial proximal compression ultrasound (CUS) as first line imaging for suspected deep vein thrombosis (DVT). Limitations with this strategy include attrition, lack of a clear diagnosis, and increased costs associated with serial resource use / clinical review. Single whole-leg CUS is a routine alternative diagnostic strategy that can reduce repeat attendance and identify alternative pathology. We sought to assess the performance characteristics of an established emergency department ambulatory protocol incorporating whole-leg CUS by non-physicians for exclusion of DVT.MethodsA prospective observational cohort study, conducted between July 2011 and April 2012. Consecutive, ambulatory, adult patients with suspected DVT and negative or inconclusive whole-leg CUS had anticoagulation initially withheld and were followed up after three months. The primary outcome was a predefined clinically relevant adverse event rate: a subsequent diagnosis of symptomatic venous thromboembolism (VTE) or VTE related death during three month follow up. Secondary outcomes included alternative diagnoses, technical failure rate and characteristics associated with failure.Results212 patients agreed to participate and were followed for three months. One patient was subsequently diagnosed with an isolated distal DVT. The adverse event rate was thus 1/212, 0.47% (95% confidence interval 0.08 to 2.62%). 150/212 patients were provided with a clear documented alternative diagnosis. CUS directly contributed to or confirmed the alternate diagnosis in 55/150 patients. Technical imaging failure occurred in 11.3% of suspected cases (95% CI 7.7 to 16.3). Several potential predictors of an inconclusive result were identified on multivariate analysis, including obesity, active infection, immobilisation and active cancer.ConclusionPatients who have anticoagulation withheld following a negative or inconclusive whole leg CUS for suspected DVT have a low rate of adverse events at 3 months. Including the calf in ultrasound examination aided and clarified diagnosis in approximately one third of patients. Technical failure remains an issue: several factors were significantly associated with inconclusive results in our cohort and may warrant an alternative diagnostic approachAbstract 008 Table 1Measuring ED crowdingMeasureOperational DefinitionAbility of ambulances to offload patients.An ED is crowded when the 90th percentile time between ambulance arrival and offload is greater than 15 minutesPatients who leave without being seen or treated (LWBS)An ED is crowded when the number of patients who LWBS is greater than or equal to 5%.Time until TriageAn ED is crowded when there is a delay greater than 5 minutes from patient arrival to begin their initial triage.ED occupancy rate.An ED is crowded when the occupancy rate is greater than 100%.Patients' total length of stay in the EDAn ED is crowded when the 90th percentile patient's, total length of stay is greater than 4 hours.Time until a physician first sees the patientAn ED is crowded when an emergent (1 or 2) patient waits longer than 30 minutes to be seen by a physicianED boarding timeAn ED is crowded when less than 90% of patients have left the ED 2 hour after the admission decision.Number of patients boarding in the ED.Boarders are defined as admitted patients waiting to be placed in an inpatient bed. An ED is crowded when there is greater than 10% occupancy of boarders in the EDED; Emergency DepartmentAbstract 008 Table 2Performance of the ICMED against clinician perception of crowdingSensitivity (95% CI)Specificity (95% CI)Ambulance Offload55.9 (45.3–66.5)90.0 (83.6–96.4)Nurse Triage70.6 (60.8–80.3)76.0 (66.9–85.1)Occupancy55.9 (45.3–66.5)78.0 (69.1–86.9)Total stay55.9 (45.3–66.5)100.0 (88.8–100)ED Boarding Time55.9 (45.3–66.5)100.0 (88.8–100)Time to see a Physician32.4 (22.4–42.4)84.0 (76.2–91.8)Patients Boarding85.3 (77.7–92.9)70.0 (60.2–79.8)One Violation100.0 (89.7–100)38.0 (27.6–48.4)Two Violations100.0 (89.7–100)60.0 (49.5–70.5)Three Violations91.2 (85.1–97.2)100.0 (92.9–100)Four Violations50.0 (39.3–60.7)100.0 (88.8–100)Five Violations26.5 (17.0–35.9)100.0 (88.8–100)Six Violations23.5 (14.5–32.6)100.0 (88.8–100)Seven Violations8.8 (2.8–14.9)100.0 (88.8–100)