Laser speckle contrast analysis for quantifying the Allen test: A feasibility study

Background and Objective The radial artery has become a routinely used conduit for coronary artery bypass graft surgery (CABG). Prior to surgery the Allen test is performed to test the patency of the ulnar artery. A positive Allen test, reperfusion >5 seconds, suggests an insufficient perfusion of the hand by the ulnar artery. In this study we investigated if laser speckle contrast analysis (LASCA) provides an objective determination of the reperfusion time. Materials and Methods When the hand is illuminated with coherent laser light, the backscattered light will result in an interference pattern consisting of bright and dark areas called speckles. This speckle pattern will change due to movement of red blood cells. LASCA uses these changes to visualize the perfusion during the Allen test. Reperfusion is measured on the palmar side of the hand. The reperfusion time is defined as the time from onset of reperfusion to maximum perfusion calculated by a polynomial curve fit. The reperfusion time of the hand of patients undergoing CABG (n = 30) is measured using LASCA and is compared to the conventional Allen test performed by the nurse practitioner. Results LASCA measurements showed a negative Allen test of both hands of 16 patients. Fourteen had a borderline reperfusion time of 5–6 seconds and/or a positive Allen test of one or both hands. No statistical significant difference was observed for the LASCA Allen test compared to the conventional Allen test, P = 0.549 for the left hand and P = 0.223 for the right hand. Conclusion LASCA is able to visualize perfusion of the hand and measure a quick, moderate, slow reperfusion response or no reperfusion. It is technically feasible to determine the reperfusion time of the hand. LASCA can be a useful and objective tool to assess ulnar collateral blood supply to the hand prior to harvesting of the radial artery as a bypass graft