Diffuse Reflectance Spectroscopy: Getting the Capillary Refill Test Under One's Thumb

Summary

This protocol describes how the use of diffuse polarization spectroscopy can improve the clinical usefulness of the capillary refill test. We suggest a more detailed analysis of the course of the capillary refill in healthy volunteers using diffuse reflectance spectroscopy videos and new informatic endpoints.

Abstract

The capillary refill test was introduced in 1947 to help estimate circulatory status in critically ill patients. Guidelines commonly state that refill should occur within 2 s after releasing 5 s of firm pressure (e.g., by the physician's finger) in the normal healthy supine patient. A slower refill time indicates poor skin perfusion, which can be caused by conditions including sepsis, blood loss, hypoperfusion, and hypothermia. Since its introduction, the clinical usefulness of the test has been debated. Advocates point out its feasibility and simplicity and claim that it can indicate changes in vascular status earlier than changes in vital signs such as heart rate. Critics, on the other hand, stress that the lack of standardization in how the test is performed and the highly subjective nature of the naked eye assessment, as well as the test's susceptibility to ambient factors, markedly lowers the clinical value. The aim of the present work is to describe in detail the course of the refill event and to suggest potentially more objective and exact endpoint values for the capillary refill test using diffuse polarization spectroscopy.

Introduction

Assessment and triage of the critically ill patient centers on the classical vital signs blood pressure (BP), heart rate (HR), respiratory rate (RR), oxygen saturation, and body temperature¹. Changes in these parameters appear relatively late in the course of circulatory deterioration. For instance, in hemorrhage, a decrease in BP will not occur until blood loss becomes moderate to severe², and HR increase can also be an insensitive and unspecific marker³.

The capillary refill test (CR test) may offer an earlier indication of incipient circulatory collapse, as the refil....

Protocol

The study described here followed the local ethic guidelines and was approved by the regional ethical review board in Linköping (permit number 2015/99-31).

1. Informed Consent and Screening

1. Obtain informed consent from the subject.
2. Screen according to inclusion/exclusion criteria.
   NOTE: Inclusion criteria were: (i) Healthy adult >18 years of age, (ii) Able to understand written and oral information, and (iii) Provides oral and written consent. Exclusion criteria were: (i) Unable or unwilling to provide informed consent, (ii) Ongoing skin conditions, (iii) Cardiovascular disease, (iv) Medication tha....

Results

Filming the course of the capillary refilling generates vast amounts of data not possible to obtain by naked eye assessment. We suggest here new endpoints to further improve the usability of the CR test as an early indicator of deterioration in circulatory status. We call these endpoints: "Baseline," "Blood Zero" (or "BZ"), "Time to Return to Baseline 1" (or "tRtB1"), "Time to Peak" or "Tpk." The "Baseline" value is derived by calculating a mean value of all the values obtained during the.......

Discussion

In order to get the best results with the system, variability caused by environmental factors must be controlled. All ambient light must be turned off. The camera must be positioned in vertical alignment with the measurement area. In order to ensure a constant measurement area, subjects should not move or talk during measurement. For the same reason, the camera is preferably mounted on a stand to avoid movement and to maintain a constant distance to the measurement area. Test subjects should avoid caffeine

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
TiVi701 Camera	WheelsBridge AB	TiVi701 Camera, version 1.5.1	Software
TiVi700	WheelsBridge AB	TiVi700 Analysis, version 1.2.9	Software
Canon EOS 700D	Canon U.S.A., inc.	Canon EOS 700D	Digital SLR Camera
Camera stand	Manfrotto	681B	Modified camera stand to hold the digital camera in position
Camera stand	Disa Denmark	9020B	Modified camera stand to hold the digital camera in position