Design and validation of capillary refill time measuring device

Abstract

Capillary refill time (CRT) is a simple, non-invasive bedside test used to assess peripheral perfusion. In critical care, particularly in conditions like septic shock, early and effective resuscitation is essential for reducing mortality. While traditional hemodynamic monitoring techniques, such as central venous oxygen saturation and lactate clearance, provide valuable insights, they often require invasive procedures, limiting their accessibility in resource-constrained settings. Recent clinical studies, including the ANDROMEDA-SHOCK trial, have highlighted the potential of CRT as an alternative resuscitation target, showing that CRT-guided resuscitation may lead to lower mortality rates compared to lactate-guided strategies. However, traditional CRT assessment is subjective and prone to variability between clinicians, as it is typically performed manually through visual inspection and timing.
This thesis presents the development and validation of a novel CRT measuring device designed to measure CRT automatically. The system integrates an optical sensor, LEDs, and a signal processing algorithm to measure the reflected and transmitted light through the finger and calculate the time it takes for blood to return to the capillaries after pressure is applied. Five different light wavelengths were tested (reflected red (620 nm), green (520 nm), blue (465 nm) and transmitted red (620 nm), and infrared light (940 nm)) to determine the optimal wavelength for CRT measurement. An air bladder surrounding the finger ensures consistent and controlled pressure application, standardizing the occlusion and release process.

To validate the system’s accuracy and determine which light wavelength is better for CRT measurements, experimental tests were conducted on 12 healthy volunteers. The experiments involved immersing the subject's hand in cold water to induce vasoconstriction and inflating a blood pressure cuff around the arm to temporarily stop blood flow, simulating peripheral perfusion failure. The results showed that all tested wavelengths were able to detect the peripheral perfusion changes, with findings suggesting that transmitted red (620 nm) and infrared (940 nm) light provide the most reliable measurements. Further research is needed, but this automated device has the potential to improve the objectivity and reliability of CRT measurements and contribute to its standardization.