Interrater agreement between expert and novice in measuring inferior vena cava diameter and collapsibility index

In critical care medicine, US views of the inferior vena cava (IVC) and its change with respiration are used to estimate the intravascular volume status of unwell patients and, in particular, to answer the question: 'Is this patient likely to be fluid responsive?' Most commonly in the literature, the subxiphisternal (SX) window in the longitudinal plane is utilised. To date, no study has specifically assessed interrater agreement in estimating IVC diameter between emergency medicine specialists (experts) and trainees (learners).

To determine the interrater agreement between an expert (senior emergency specialist with US qualifications) and learner (emergency medicine trainee) when measuring IVC diameter (IVCD) and IVC collapsibility index (IVCCI) in the SX longitudinal US window in healthy volunteers.

Healthy volunteers (ED staff) were scanned in the supine position using a sector (cardiac) probe of a portable US machine, in the SX longitudinal position. The maximum and minimum diameters of the IVC were measured in each of these positions and the IVCCI calculated. Results were analysed using Bland-Altman plots.

In the longitudinal SX window, the operators' measurements of maximum IVCD differed by an average of 1.9 mm (95% limits of agreement -9.4 mm to +5.5 mm) and their measurement of IVCCI differed by an average of 4% (95% limits of agreement -30% to 38%).

The wide 95% limits of agreement demonstrate a poor interrater agreement between the IVC US measurements obtained by expert and learner users in the assessment of fluid status. These ranges are greater than clinically acceptable.