Ultrasound measurement of inferior vena cava diameters by emergency department nurses

Sonographic measurement of the inferior vena cava (IVC) diameter is a potentially important noninvasive estimate of fluid status. We researched whether nurses without prior ultrasonography experience could accurately obtain vena cava diameter measurements on models and subjects in comparison with those obtained by an expert sonographer. The design was a prospective educational study using a pre- and posttest of knowledge and a comparison of imaging performance between a subject and an expert sonographer. The setting was an urban teaching medical center with emergency nurses and a convenience sample of volunteer patients selected from the emergency department (ED). Nurses completed a written survey and a pretest to document prior training and experience in ultrasonography and assess baseline knowledge. A structured training program (3.5 hr in length) was provided over three sessions. Training consisted of didactic presentations, practice on phantoms (manikin models designed to provide the sonographic image of the human body when scanned by a trainee) and classmates, and one volunteer patient in the ED. Each nurse then measured IVC diameters on three different volunteer patients in transverse and longitudinal orientations using frozen images. An expert sonographer, blinded to subject results, performed the same examination. Correlations were determined, and a posttraining written examination was completed and results compared with the pretest using a pair-wise t test. Fourteen nurses, with a mean of 8 yearsnursing experience (range= 2-18 years), participated. Nurse-expert R value correlation for the longitudinal orientation was 0.68 (95% confidence interval [CI] [0.35, 0.76]) and 0.59 (95% CI [0.47, 0.81]) for the transverse orientation. Posttest scores improved 8.2 percentage points (95% CI [4.0, 12.4]) from 83.3% to 91.5%. Following a brief training course, nurses with no prior sonography experience show moderately good correlation measuring the IVC diameter as compared with expert measurements, with better performance demonstrated in the longitudinal orientation.