To See or Not to See : A Study on Capillary Refill

Abstract

Background: Assessment of the critically ill is traditionally based on vital signs (blood pressure, pulse, respiratory rate, temperature and level of consciousness). Altered vital signs are, however, late indicators of deranged hemodynamics pointing to a need for additional, more sensitive markers of circulatory compromise. In the beginning of the 20 th century, the capillary refill (CR) time evolved as a possible, non-invasive adjunct to early prediction of outcome in the critically ill. The manoeuvre entails application of blanching pressure on the skin of e.g. the finger pulp or sternum for 5 seconds. After release of the pressure, the observer estimates time in seconds for the skin to return to original colour. This time is hypothesized to reflect the dynamics of the microcirculation and its possible connection with hemodynamics. In the 1980s the "normal capillary refill time" was set to < 2 seconds and later extended to 3 seconds, without a clear scientific foundation. Naked-eye estimations of CR time met increasing scepticism in the 1990s due to subjectivity and poor prognostic value for shock or death. Several basic traits, such as age and sex, as well as ambient temperature, were also shown to independently influence the CR time. Various methods have evolved with the capability to measure CR time quantitatively, one of which is Polarisation Spectroscopy Imaging (PSI). PSI measures the Red Blood Cell (RBC) concentration in tissue (e.g. the skin) and can be used to measure CR time. Objectives: The purpose of this study was to establish basic characteristics for quantitative Capillary Refill (qCR) time, identify possible influencing factors in healthy subjects and to investigate how this relates to current practice. We also sought to identify technical demands for transfer of the technique into clinical studies. In paper I we analysed the qCR time characteristics at 5 different skin sites (forehead, sternum, volar forearm, finger pulp and dorsum finger). The objective of paper II was to investigate the inter-and intra-observer variability of naked eye CR assessments of different professions, nurses, doctors and secretaries (representing laymen). In paper III we observed the effect of low ambient temperature on the qCR time in different skin sites. In paper IV, we transferred the equipment from a laboratory to a clinical setting in the Emergency Department (ED) for application in the potentially critically ill. In this study we evaluated the most important factors determining a reliable data collection and influencing the amount of data possible to analyse. Methods: qCR time was measured in a total of 38 volunteers and 10 patients in different skin sites (2-5 skin sites) at different ambient temperatures. An embodiment of PSI (TiVi 600 and 700, WheelsBridge AB, Linköping, Sweden) was used to determine the rapid temporal changes in RBC concentration in skin during the CR manoeuvre. Films using a range of the first measurements from paper I were shown for assessment to 48 observers working in the ED. Results: I...

emteqPRO—Fully Integrated Biometric Sensing Array for Non-Invasive Biomedical Research in Virtual Reality

“…The emteqPRO has a single PPG sensor centred on the forehead. Nailfold capillaroscopy of the forehead region has shown similar capillary density to the finger and forearm (Toll, 2020). A density of capillary coverage makes the forehead wellsuited as a placement location (Branson and Mannheimer, 2004) and can be used to detect changes to blood flow (Otsuka et al, 2017) and accurately measure heart rate features such as beats per minute (Gnacek et al, 2020) to reflect changes in arousal.…”