Objective methods for achieving an early prediction of the effectiveness of regional block anesthesia using thermography and hyper-spectral imaging

An objective method to measure the effectiveness of regional anesthesia can reduce time and unintended pain inflicted to the patient. A prospective observational study was performed on 22 patients during a local anesthesia before undergoing hand surgery. Two non-invasive techniques thermal and oxygenation imaging were applied to observe the region affected by the peripheral block and the results were compared to the standard cold sensation test. The supraclavicular block was placed under ultrasound guidance around the brachial plexus by injecting 20 cc Ropivacaine. The sedation causes a relaxation of the muscles around the blood vessels resulting in dilatation and hence an increase of blood perfusion, skin temperature and skin oxygenation in the lower arm and hand. Temperatures were acquired with an IR thermal camera (FLIR ThermoCam SC640). The data were recorded and analyzed with the ThermaCam (TM) Researcher and Matlab software. Narrow band spectral images were acquired at selected wavelengths with a CCD camera either combined with a Liquid Crystal Tunable Filter (420-730 nm) or a tunable hyper-wavelength LED light source (450-880nm). Concentration changes of oxygenated and deoxygenated hemoglobin in the dermis of the skin were calculated using the modified Lambert Beer equation. Both imaging methods showed distinct oxygenation and temperature differences at the surface of the skin of the hand with a good correlation to the anesthetized areas. A temperature response was visible within 5 minutes compared to the standard of 30 minutes. Both non-contact methods show to be more objective and can have an earlier prediction for the effectiveness of the anesthetic block.