Learning to apply the pocket ultrasound device on the critically ill: comparing six 'quick-look' signs for quality and prognostic values during initial use by novices

Biais and colleagues [1] have shown that echocardiographers can adequately perform a three-view cardiac examination in the emergency setting using a pocket ultrasound device (PUD). We have similarly noted that an evidence-based 'quick-look', cardiac limited ultrasound examination has diagnostic and prognostic value [2], can affect medical decision-making [3], and can be successfully taught to internal medicine residents [4]. As few data describe the learning curve of ultrasound imaging with PUDs, we observed the initial quality and prognostic value of six 'quick-look' signs obtained by residents learning to use the PUD. Internal medicine residents in an ultrasound training program [4] recorded a brief, previously described [2] cardiac limited ultrasound examination designed to detect six 'quick-look' signs of left ventricular systolic dysfunction, left atrial enlargement, ultrasound lung comet (ULC) tail artifact representing interstitial lung edema, elevated central venous pressure, pleural effusion, and right ventricular enlargement on a convenience-sample of intensive care unit (ICU) patients with respiratory failure, shock, or severe cardiac disease, using a PUD (Vscan, GE Healthcare, Wauwatosa, WI, USA). An expert echocardiographer reviewed the resident-acquired images and assigned a quality score: 0 (no image), 1 (only motion detected; off-axis), 2 ('suboptimal', poor delineation of structures), 3 ('adequate' for diagnosis of particular sign), or 4 ('optimal', good delineation of all structures). Only technically adequate quality views (score >2) were entered into a multivariate logistic regression combining the six signs, clinical presentation and inpatient mortality (SPSS version 12.0). A P-value <0.05 was considered statistically significant. The Scripps Institutional Review Board approved the study. Twenty-one residents recorded 749 views on 107 critically ill patients (mean 5.1 patients/resident): mean patient age of 65.2 ± 16.8 years, inpatient mortality of 25.2%, and mean quality score of 2.1 ± 1.4. Presentation, mortality and overall percentage adequate quality views were: respiratory failure (n = 55, 32.7%, 48.0%), shock (n = 16, 25.0%, 51.6%) and cardiac disease (n = 36, 13.9%, 51.7%). ULC had the most adequate quality images and is the only sign that had statistically significant prognostic value in the residents’ and cardiologist’s interpretations (Table 1). Table 1 Mortality odds ratios for 'quick-look' signs determined by residents’ and cardiologist’s interpretations of adequate quality images Galen cautioned against extrapolating Biais and colleagues’ data for non-expert users [5]. As few studies address the learning curve of quick-look ultrasound imaging tasks, this study suggests that novice users learning to use the PUD readily learn to image ULC, which was prognostic in this ICU population. In light of a substantial number of initially difficult psternal long-axis and subcostal views, the PUD’s most simple and immediate use may be in the rapid detection of life-threatening pulmonary edema.