Neuroscience
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Diffuse Reflectance Spectroscopy: Getting the Capillary Refill Test Under One's Thumb
Chapters
Summary December 2nd, 2017
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.
Transcript
The overall goal of this assessment is to quantify capillary refill time using reflectance spectroscopy in digital video to enable fast and objective detection of incipient circulatory change. Quantified objective assessment of capillary refill time using reflectance spectroscopy may provide an early warning to incipient circulatory change and facilitate triage and continuous monitoring of critically ill patients. The main advantage of this technique is that it, compared to naked eye assessment, offers a very exact and objective way to measure capillary refill time.
The implications of this technique extend toward early triage of trauma patients at an accident site or at the emergency or continuous supervision of critically ill patients. To begin, connect the camera and the computer using a USB cable, and set the camera to video mode. Then, turn on the camera and make sure that it connects to the computer.
Next, start the remote-controlled camera software. Also, remove any ambient light sources, and turn the computer screen away from the measurement area. To begin, bring in the test subject, and let them acclimate to the surroundings for at least 20 minutes in a supine position.
Then, click the Life View button and press Start. Switch between video mode and TV mode by clicking the radio buttons. Ensure that a live video stream of the subject's forehead is visible on the display of the camera and on the computer screen.
Next, adjust the camera to a height of approximately 15 centimeters directly above the subject's forehead, and make sure that the focus of the camera is set to autofocus. Ask the subject to keep their head still for the duration of the test and to refrain from talking. Then, inform the subject to place their head on a pillow and to keep it still for the duration of the test.
Ask them not to talk during the 20 seconds that the test will last. They may keep their eyes closed for the whole time if they find the light too bright. In the Life View window, find and click on HD Record to start a continuous recording for 20 seconds.
Do not move the camera during the duration of the test. At the end of the initial five seconds of baseline recording, apply a firm blanching pressure to the measurement area for five seconds using a plastic teaspoon for pressure equalization and temperature insulation. Then, release the pressure and quickly withdraw the plastic teaspoon from the measurement area.
Continue recording for another 10 seconds in order to capture the subsequent hyperemic response. At the end of the 20 seconds, stop the recording by clicking Stop in the Life View window. Once the recording has stopped, a window will open to save the video file.
Name the video and save it in mov format. Disconnect the camera from the computer once the video has downloaded to its designated folder on the computer. Start the analysis software by double-clicking on the desktop icon.
Once the software has started, on the main screen, select Movie Page. In the Movie Page window, click Load Movie. Wait for the software to upload and analyze the movie.
Once the upload and analysis of the movie is finished, click Save As Images and wait for the software to analyze the video and divide it into individual JPEG images. Then, find and select Crop Images Page in the main screen window. In the Crop Images Page menu, click First Photo and navigate to the folder that contains the JPEG photos from the video.
Select the first photo to be analyzed. The software will automatically select the following photos of that batch. Click the Edit menu and choose between circular or rectangular markers for the region of interest.
Then, in the Select Photos window, find the actual photo box and type in the name of the first photo in the batch, where the investigator's fingers fully retracted from the measurement area. To find this photo, look through the folder containing the individual photos from the video. Select a region of interest by clicking and holding the left mouse button, and draw a circle or rectangle in the photo window that is within the borders of the blanched area.
The selected region of interest is automatically applied to all photos of the batch. Next, click on the File menu and choose Save ROI to save the location of the selected region of interest for future reference. Then, click on the Curve Tracker and wait for the software to analyze the region of interest.
Once the Curve Tracker window opens, the change in red blood cell concentration for the selected region of interest over the duration of the test is displayed as a curve. Finally, click Export Data and save the raw data transcript for further analysis. Using this method, the capillary refilling response can be presented as the change in red blood cell concentration over time.
During the first five seconds of the test, the baseline values are collected. Then, pressure is applied to reach the blood zero point. Once the pressure is relieved, the blood begins to return to the area and will peak after a few seconds.
This representative graph is for a healthy male volunteer. A slower refill time would indicate poor skin perfusion, and can be indicative of adverse conditions. The use of reflectance spectroscopy videos gives more detailed data on changes in capillary refill time compared to naked eye assessment.
The presented method needs further development but clearly shows the potential of the technique in measuring capillary refill events.
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