Man versus machine: comparison of naked-eye estimation and quantified capillary refill

Abstract

Background: Capillary refill (CR) time is traditionally assessed by 'naked-eye' inspection of the return to original colour of a tissue after blanching pressure. Few studies have addressed intra-observer reliability or used objective quantification techniques to assess time to original colour. This study compares naked-eye assessment with quantified CR (qCR) time using polarisation spectroscopy and examines intra-observer and interobserver agreements in using the naked eye.

Method: A film of 18 CR tests (shown in a random fixed order) performed in healthy adults was assessed by a convenience sample of 14 doctors, 15 nurses and 19 secretaries (Department of Emergency Medicine, Linköping University, September to November 2017), who were asked to estimate the time to return to colour and characterise it as 'fast', 'normal' or 'slow'. The qCR times and corresponding naked-eye time assessments were compared using the Kruskal-Wallis test. Three videos were shown twice without observers' knowledge to measure intra-observer repeatability. Intra-observer categorical assessments were compared using Cohen's Kappa analysis. Interobserver repeatability was measured and depicted with multiple-observer Bland-Altman plotting. Differences in naked-eye estimation between professions were analysed using ANOVA.

Results: Naked-eye assessed CR time and qCR time differ substantially, and agreement for the categorical assessments (naked-eye assessment vs qCR classification) was poor (Cohen's kappa 0.27). Bland-Altman intra-observer repeatability ranged from 6% to 60%. Interobserver agreement was low as shown by the Bland-Altman plotting with a 95% limit of agreement with the mean of ±1.98 s for doctors, ±1.6 s for nurses and ±1.75 s for secretaries. The difference in CR time estimation (in seconds) between professions was not significant.

Conclusions: Our study suggests that naked-eye-assessed CR time shows poor reproducibility, even by the same observers, and differs from an objective measure of CR time.

Keywords: acute care; clinical assessment; emergency department management; resuscitation; trauma.

Figure 1

Delineation of a capillary refill curve where baseline represents the redness of skin before application of pressure. T=0 is the moment of pressure release during CR test. tRtB1 and tPk are shown. Each dot represents an image in which the concentration of erythrocytes has been quantified. CR, capillary refill; tPk, time to peak; tRtB1, time to Return to Baseline1.

Figure 2

(A-C) Box plots of the naked-eye estimation of CR time in seconds, including the 5th to 95th percentile of the values. qCR time in tRtB1 (red circle) and tPk (green square) are shown for each video. The videos with the fastest tRtB1 values are plotted to the left and the slowest to the right on the x- axis. The number of each video indicates the order in which they were shown to the observers in the film. Videos 5 and 10, 6 and 13, and 3 and 15 (marked with arrows) are the videos that were shown twice. CR, capillary refill; qCR, quantified CR; tPk, time to peak; tRtB1, time to Return to Baseline1.

Figure 3

(A-C) Multiple observer Bland-Altman plots for interobserver variability of naked-eye-assessed CR time in seconds shown by profession, with each figure/form representing one observer. The 95% limits of agreement with the mean of all observers are shown as dotted lines. CR, capillary refill.