Background: Given the time, expense, and radiation exposure associated with computed tomography (CT), ultrasonography (US) is considered an alternative imaging study that could expedite patient care in patients with suspected obstructive uropathy. However, there is a paucity of literature regarding bedside US for obstructive uropathy in the emergency department (ED), and it is unknown how much experience is required for competency in such exams.
Objectives: The objective was to assess the learning curve for the detection of obstructive uropathy of resident physicians training in ED bedside US (EUS) during a dedicated EUS elective.
Methods: This was a prospective cohort study of residents participating in an EUS elective. Patients presenting with acute abdominal or flank pain suggestive of an obstructive uropathy were enrolled and underwent EUS prior to noncontrast CT. Physicians who had previously performed at least 10 EUS exams for obstructive uropathy recorded results on a standardized data sheet, which was subsequently compared to the results of noncontrast CT read by board-certified radiologists blinded to the results of the EUS. In addition to an unadjusted chi-square test for trend, a multivariable logistic regression analysis, adjusting for stone size and operator, was performed. Finally, generalized estimating equations were used to describe test characteristics while accounting for potential clustering between exams by operator.
Results: Twenty-three resident physicians participated and enrolled a convenience sample of 393 patients. A total of 157 patients (40%) were diagnosed with an obstructing ureterolith, and three (1%) were diagnosed with nonobstructing ureterolithiasis. An unadjusted chi-square test for trend demonstrated a statistically significant increase in both sensitivity (χ(2) = 11.4, p = 0.02) and specificity (χ(2) = 6.4, p = 0.04) for each level of increase in number of exams. On multivariable regression analysis, when adjusting for size of stone and operator, for every five additional exams after the first 10 EUS exams, the odds ratio for a true positive for obstruction increased by 1.7 (95% confidence interval [CI] = 1.2 to 2.5, p = 0.003). After accounting for clustering of exams by operator, overall EUS sensitivity and specificity for obstructive uropathy were 82% (95% CI = 77% to 87%) and 88% (95% CI = 85% to 92%). Stratifying by number of exams, the sensitivity was 72% (95% CI = 62% to 80%) for the 11th through 20th exams, 90% (95% CI = 83% to 96%) for the 21st through 30th exams, and 95% (95% CI = 91% to 99%) for the 31st through 43rd exams. Likewise, specificity was 82% (95% CI = 75% to 89%) for the 11th through 20th exams, 90% (95% CI = 85% to 95%) for the 21st through 30th exams, and 92% (95% CI = 86% to 98%) for the 31st through 50th exams.
Conclusions: Physicians training in EUS may be able to accurately assess for obstructive uropathy after 30 exams.
2010 by the Society for Academic Emergency Medicine.