IntroductionTrauma is a leading cause of death throughout the world, with hemorrhage being responsible for more than 35% of pre-hospital trauma deaths and more than 40% of deaths within the first 24 hours after injury. Despite first aid having a demonstrable effect on mortality from trauma, relatively little research has compared the best methods for bleeding control in the prehospital first aid setting. The most common first-line therapy for external bleeding control in the pre-hospital first aid setting is direct manual compression (DMC). However, a prior study demonstrated that the primary cause of failure in a simulated model of life-threatening bleeding was the inability to maintain adequate direct pressure for three minutes. In this study, we evaluated the effect of fatigue on DMC for the duration of a typical urban emergency medical services (EMS) response time.MethodsWe conducted a prospective observational trial of 33 participants, 18 years of age or older to measure the pressure generated on a model of life-threatening bleeding over an eight-minute period using a “CPR posture” for applying pressure. The primary analyses were longitudinal two-level multilevel models (MLM) with repeated measures of outcome (i.e., CPR posture pressure) nesting within participants. The demographic factors of gender, age, and weight were included as moderators in the analyses and each was analyzed independently.ResultsThe participants’ average age was 31 (SD = 11) and the average weight was 161 pounds (SD = 31). The sample consisted of 18 female participants (54.5%) and 15 male participants (45.5%). Applied DMC pressure declined over time, more sharply initially from the beginning to approximately 250 seconds, at which point the decrease in pressure was gradual. Of the demographic factors, gender was associated with a difference in cardiopulmonary resuscitation (CPR) posture pressure over time.ConclusionRescuers should be aware that fatigue may occur and may affect the quality of direct manual compression for control of life-threatening bleeding. Further research is needed to define the external pressures needed to control life-threatening bleeding and the extent that rescuer fatigue affects this pressure.