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Blood refill time: Clinical bedside monitoring of peripheral blood perfusion using pulse oximetry sensor and mechanical compression

Open AccessPublished:April 05, 2018DOI:https://doi.org/10.1016/j.ajem.2018.04.006
      Letter to the Editor:
      Shock states can be detected rapidly by measuring the capillary refill time (CRT) or other measures of blood refill time (BRT) at the peripheral body parts of patients [
      • Pickard A.
      • Karlen W.
      • Ansermino J.M.
      Capillary refill time: is it still a useful clinical sign?.
      ,
      • Lima A.
      • Bakker J.
      Noninvasive monitoring of peripheral perfusion.
      ]. CRT is defined as the time required for a distal capillary bed (e.g., fingertip) to regain its color after receiving enough compression to cause blanching [
      • Pickard A.
      • Karlen W.
      • Ansermino J.M.
      Capillary refill time: is it still a useful clinical sign?.
      ,
      • Schriger D.L.
      • Baraff L.
      Defining normal capillary refill: variation with age, sex, and temperature.
      ]. CRT measured at the bedside is promulgated as an acceptable method to identify circulatory shock in critically ill patients [
      • Pickard A.
      • Karlen W.
      • Ansermino J.M.
      Capillary refill time: is it still a useful clinical sign?.
      ,
      • Lima A.
      • Bakker J.
      Noninvasive monitoring of peripheral perfusion.
      ]. However, since the measurement of CRT involves visual inspection of fingertip color, it is subject to inter-observer variability [
      • Alsma J.
      • van Saase J.L.C.M.
      • Nanayakkara P.W.B.
      • et al.
      The power of flash mob research: conducting a nationwide observational clinical study on capillary refill time in a single day.
      ,
      • Espinoza E.D.
      • Welsh S.
      • Dubin A.
      Lack of agreement between different observers and methods in the measurement of capillary refill time in healthy volunteers: an observational study.
      ] and may be unreliable [
      • Pickard A.
      • Karlen W.
      • Ansermino J.M.
      Capillary refill time: is it still a useful clinical sign?.
      ].
      The optical technology of infrared spectroscopy has been used to noninvasively measure the concentration of hemoglobin and oxygen saturation [
      • Severinghaus J.W.
      • Honda Y.
      History of blood gas analysis. VII. Pulse oximetry.
      ]. This technology is used in pulse oximetry and it can trace blood in tissues and be used to monitor BRT at the fingertips [
      • Lima A.
      • Bakker J.
      Noninvasive monitoring of peripheral perfusion.
      ,
      • Morimura N.
      • Takahashi K.
      • Doi T.
      • et al.
      A pilot study of quantitative capillary refill time to identify high blood lactate levels in critically ill patients.
      ]. Since blood is a major component affecting skin color (oxyhemoglobin is visually perceived as red and deoxyhemoglobin as blue), this technology can provide an alternative measure of skin color change that does not rely on visual inspection. Driven by the motivation to develop objective and reliable measures of peripheral blood perfusion, we applied a new method of analysis that uses the pulse oximetry waveform. In addition, we created a mechanical compression device that applies firm pressure to the fingertip. The combination of these two components allows for a precise, consistent, and objective measure of BRT.
      The purpose of this report is to show how the technology works in vivo. The peripheral perfusion of a healthy volunteer subject was altered by cooling down the fingertip temperature, which was observed by our device. We measured BRT and fingertip temperature before and after changing the conditions wherein the subject's hand was at room temperature and then immersed in cold water. This report provides clinicians a fine perspective of how blood flows when they perform CRT measurements in clinical settings.
      The study was approved by University of Pennsylvania. All procedures were performed in a climate controlled environment at an ambient temperature of 20–22 °C. We measured BRT under two different conditions: hands at room temperature (ROOM TEMPERATURE) and immersed in cold water (COLD, 15 ± 2 °C). The hand was immersed in a cold water bath for 5 min and then BRT was measured inside a temperature controlled box. A thermocouple sensor was attached to the fingertip as an adjunction to the BRT sensor.
      We defined BRT as the time required for a fingertip to recover its blood volume after release from compression. The device consists of two components (Fig. 1): a measuring device and a fingertip compression device. A pulse oximeter (OLV-3100, Nihon Kohden Corporation, Tokyo, Japan) was used as the measuring device to capture pulse oximetry waveforms. We used one wavelength (infrared light: 940 nm) to trace the change in hemoglobin concentration that reflects the recovery of blood flow to the fingertip.
      Fig. 1
      Fig. 1The investigation device is composed of two devices, which are modified pulse oximeter (measuring device) and compression device. A pulse oximetry sensor is attached to the measuring device and the compression device controls a bladder cuff inside a finger-cap.
      The fingertip compression device is composed of an air pump and a finger-cap with a polyurethane soft bladder. The air pump supplies air to the bladder when measuring BRT. The device controls the pressure of the inflated bladder at approximately 400 mm Hg. The duration of the bladder inflation is 5 s. The device deflates the bladder pressure 5 s after inflation. The thermocouple sensor was attached to the side of the fingertip in order to avoid interference with either the transmission light from the pulse oximetry sensor or the fingernail compression with the polyurethane bladder (Fig. 2).
      Fig. 2
      Fig. 2The inflation and deflation of a polyurethane soft bladder cuff are controlled by the compression device.
      Light intensity was recorded by the measuring device and the data were analyzed thereafter. The light intensity transmitted through the fingertip increases during compression as blood, which is the major absorber of the light, is squeezed out of the fingertip. The compression phase is followed by the release phase during which the light intensity returns to the original level (Fig. 3). The measuring device captures the changes in the transmitted light intensity and records the waveforms. The curve describing the recovery phase of the intensity waveform (intensity returning to its original levels) is modeled as an exponential decay using the least squares method. The time to achieve 90% return of the intensity was reported as BRT.
      Fig. 3
      Fig. 3The measuring device captures the changes in the transmitted light intensity and records the waveforms. The time to achieve 90% return of the intensity was reported as BRT. BRT was measured at two different temperature conditions of a healthy subject.
      Fig. 3A shows the light intensity curve from the fingertip at room temperature, where Fig. 3B shows the altered intensity curve at lowered fingertip temperature. BRT was 1.6 s with a fingertip temperature of 29.3 °C at room temperature. Our device successfully detected prolonged BRT after the fingertip temperature was cooled down to 22.8 °C and BRT at this condition was 5.8 s.
      Prolonged BRT induced by low fingertip temperature was observed well by our device. This technology provides clinicians a fine perspective of how blood flows through the fingertip following release from firm compression. Clinical implications of the technology include both continuous monitoring and spot check measurement. For example in ICU or operation room, the device can be used to measure BRT repeatedly. The trend in repeated measurements may provide patient's information about the alteration of peripheral blood perfusion over time. For spot check measurements, the device can be used for detecting the alteration of peripheral blood perfusion in both acute and chronic conditions. It can be used in pre-hospital or emergency department for triaging patients. It can be also used for diagnosing peripheral artery disease. This technology provides an objective measure of peripheral perfusion and may provide more reliable results than a subjective visual assessment.

      Conflict of interest and sources of funding

      Research reported in this publication was supported by the research grant of Nihon Kohden Corporation .
      JK and MJC have no known conflicts of interest associated with this study and there has been no significant financial support for this work that could have influenced its outcome. Kota S., HH, KH, NK, and SW are employees of Nihon Kohden Corporation and Nihon Kohden Innovation Center, INC. There are no products in market to declare. This does not alter the authors' adherence to all the journal's policies on sharing data and materials. Koichiro S., JWL, and LBB have a patent right of metabolic measurements in critically ill patients. Koichiro S. has a grant/research support from Nihon Kohden Corp. JWL has a grant/research support from Zoll Medical Corp., Philips Healthcare, Nihon Kohden Corp., and the NIH, and owns intellectual property in resuscitation devices. LBB has a grant/research support from Philips Healthcare, the NIH, Nihon Kohden Corp., BeneChill Inc., Zoll Medical Corp, and Medtronic Foundation, patents in the areas of hypothermia induction and perfusion therapies, and inventor's equity within Helar Tech LLC.

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