In a patient going into shock, blood is redistributed from the periphery to the central circulation, making an assessment of skin perfusion useful in a prehospital setting. Capillary refill time (CRT) is the time required for a pressure blanched skin site to reperfuse. Currently, CRT is tested by manually applying pressure for 5s to the skin and observing the time before reperfusion. Guidelines state that CRT should be 2-3s in a healthy patient. Shortcomings in this procedure include lack of standardization of pressure, subjective assessment of the time for reperfusion, and not accounting for the patient’s skin temperature.

To develop a standardized objective procedure for testing CRT in the prehospital setting.

The study protocol was approved by the Ethics Committee at Linköping University (M200-07, 2015-99-31). An electro-pneumatic device exerting constant force (9N) over 5s was developed. CRT was measured using the Tissue Viability Imager (Wheelsbridge AB, Sweden) which relies on polarization spectroscopy. To simulate hypothermic conditions, healthy volunteers were subjected to low ambient temperature (8°C). Blood loss was simulated using a custom-built lower body negative pressure (LBNP) chamber. In both scenarios, the CRT test was carried out on three test sites (finger pulp, forehead, and sternum).

CRT on the finger pulp and sternum was shown to be increased following the hypothermic conditions, but not on the forehead. Skin temperature on the three sites followed the same pattern, with the forehead being virtually unchanged. Tests performed during LBNP revealed an apparent effect on CRT following the simulated blood loss, with prolonged CRT for all sites tested.

A successful methodology for objective assessment of CRT was developed, which was validated on healthy volunteers following hypothermia or simulated blood loss. Ongoing work will investigate a combination of hypothermia and blood loss to more accurately simulate the prehospital setting.