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Introduction The effectiveness of out-of-hospital bleeding controlling interventions in combat operations or civilian immediate response rely in part on the operator’s ability to complete the intervention. Combat casualty care during cold weather operations (CWO) were recently discussed during the Summit on Combat Casualty Care Research in Cold Weather Operations (SoCCCR) in 2024 as a particular challenge. In field care settings during CWO, cold exposure can negatively impact the care 1 as well as hand dexterity and strength2 of the operators. Mental stressors, such as cold exposure, may further affect the operator’s mental status and performance.3 We recently conducted a study aimed at investigating how tourniquet application ability, and the operators stress profile, are affected by cold exposure, reported in full in4 and summarized here.Methods 29 medial laypeople completed tourniquet application on the leg of a rescue manikin in one baseline and three conditions with hand skin temperature lowered to 16°C, 12°C, and 8°C respectively. Their hands were cooled by immersing hands and lower arms into approximately 0°C water. Tourniquet application performance was measured using an eight-step procedural checklist, time until bleeding control and total application time. Stress was measured with the Short Stress State Questionnaire 5 with a pre/post design enveloping all four conditions.Results The results show that the performance is significantly affected by the cold exposure at 8°C hand skin temperature. Specifically, the time to bleeding control (Baseline: M 65.5 s, SD 17.0 s; 8 °C: M 76.9 s, SD 19.6 s, t(28) = 3.77, p < .01, r = 0.38) and total application time (Baseline: M 77.1 s, SD 18.0 s; 8 °C: M 89.6 s, SD 21.3 s, t(28) = 3.92, p < .01, r = 0.39) differed significantly. The procedural checklist score showed no effect of cold exposure (F(3, 84) = 2.21, p = .09).The stress profile of tourniquet application with cold exposure showed a significant increase in Task Engagement (Normalized change score 0.87, 95% CI [0.55, 1.19]), significant decrease in Worry (Normalized change score -1.01, 95% CI [-1.35, -0.67]), and no change in Distress (Normalized change score -0.02, 95% CI [-0.45, 0.41]).Conclusions Tourniquet application with cold exposed hands is unaffected until 8°C hand skin temperature at which point the time of application increases significantly. The operators may also experience an increased narrowing in attention due to the cold stressor, with increased Task Engagement. The results suggest further research on operator cold hand mitigation strategies is warranted to improve casualty care in cold weather operations.References Hindle EM, Henning JD. Critical care at extremes of temperature: effects on patients, staff and equipment. BMJ Military Health. 2014 Dec 1;160(4):279–85.Havenith G, Heus R, Daanen HA. The hand in the cold, performance and risk. Arctic medical research. 1995 Jan 1;54:37–47.Friberg M, Jonson CO, Jaeger V, Prytz E. The effects of stress on tourniquet application and CPR performance in layperson and professional civilian populations. Human Factors. 2023 May;65(3):495–507.Brodin W, Friberg M, Jonson CO, Prytz E. The effect of cold hands on immediate responder’s tourniquet application ability: a within-group trial. Human Factors in Healthcare. 2023 Jun 1;3:100038.Helton WS. Validation of a short stress state questionnaire. InProceedings of the human factors and ergonomics society annual meeting 2004 Sep (Vol. 48, No. 11, pp. 1238–1242). Sage CA: Los Angeles, CA: Sage Publications.Statement of Conflicts of Interest and Approval by Sponsoring Authority The authors have no conflicts of interest to report.This work was funded by the Swedish Civil Contingencies Agency under Grant 2018–12395-8 and publishing is approved through the grant contract.