Resistance index of frostbite as a predictor of cold injury in arctic operations

Introduction: Cold-induced vasodilation (CIVD) is mentioned as a mechanism that may prevent the occurrence of local cold injuries. The magnitude of the CIVD reaction differs considerably between subjects and there were some indications that those subjects with a fast CIVD reaction with high amplitude had a reduced risk for cold injuries. The purpose of this investigation was to determine the magnitude of the finger CIVD reaction in subjects prior to operation in cold areas and to relate these scores to the occurrence of cold injuries. Methods: In order to evaluate the magnitude of the CIVD response, 206 subjects immersed their left middle finger in ice water for 30 min. The Resistance Index for Frostbite (RIF) according to Yoshimura was determined on the basis of the finger skin temperature response. This index ranges from 3 (high risk) to 9 (low risk) depending on the response time and response magnitude. Later, most of the screened subjects deployed as part of a group of 1080 marines for winter operations in Norway. Results: The Caucasian subjects in this study had higher RIF scores than the non-Caucasians (7.0 ± 1.6 vs. 6.1 ± 2.1). The mean RIF was relatively high as compared with a reference group of Japanese male soldiers (6.9 ± 1.7 vs. 5.7 ± 1.7). Unexpectedly, smokers had a higher RIF score than non-smokers did. The RIF score was inversely related to pain during the test. There were 54 marines who suffered cold injuries during training in Norway. Of those, 11 were in the measured group of 206 marines. These subjects had a RIF of 5.2 ± 1.6, as compared with 7.0 ± 1.6 for the remaining subjects, which was significantly different. Conclusions: The RIF shows considerable differences between subjects. The RIF, determined in a simple lab test, may be related to the risk for cold injuries during operations in the field.