Relationships between early acute pain scores, autonomic nervous system function, and injury severity in wounded soldiers

Background: Acute pain after injury affects the comfort and function of the wounded soldier and the physiology of multiple body systems. In the civilian population, pain alters the function of the autonomic nervous system, causing increased heart rate and blood pressure. However, there are no data regarding the impact of combat-related pain on physiologic responses. This study is a retrospective analysis that examined the relationship of pain and physiologic parameters in injured soldiers. Methods: After Institutional Review Board approval, the Joint Trauma Theater Registry (JTTR) was queried to identify soldiers who had pain scores recorded in the Emergency Department (ED) in theater. Subject data collected from the JTTR included the following: pain score, Injury Severity Score (ISS), blood pressure, heart rate, and respiratory rate. Results: We identified 2,646 soldiers with pain scores recorded in the ED. The pain score was not related to most physiologic parameters measured in the ED. Pain intensity had no correlation with blood pressure or heart rate. However, there were relationships between the pain score and respiratory rate, with patients reporting a pain score of 10 having a slightly higher respiratory rate. Increasing pain scores were also associated with increased ISS (p < 0.001). Conclusions: In contrast to data from civilian patients, early pain scores were not related to heart rate or blood pressure. A pain score of 10 corresponded to an increased respiratory rate. Despite little relationship between pain and injury severity in the civilian population, the increasing ISS was proportional to the pain scale in wounded soldiers.