Cold-induced stress responses during a self-rescue exercise from accidental immersion in ice water in military personnel

Yannick Beres^1*Raimund Lechner^1,2Andreas Koch³Elias August⁴Peter Radermacher^5,6Martin Kulla¹Enrico Staps⁷

• ¹Department of Anesthesiology, Intensive Care Medicine, Emergency Medicine and Pain Therapy, Bundeswehrkrankenhaus Ulm, Ulm, Germany
• ²Polizei Baden-Wurttemberg Landespolizeiprasidium, Stuttgart, Germany
• ³Schifffahrtmedizinisches Institut der Marine, Kronshagen, Germany
• ⁴Department of Anesthesiology, Intensive Care Medicine, Emergency Medicine and Pain Therapy, Bundeswehrkrankenhaus, Ulm, Germany
• ⁵Centre Hospitalier Universitaire d'Angers Service de Medecine Intensive-reanimation et Medecine Hyperbare, Angers, France
• ⁶Universitatsklinikum Ulm Klinik fur Anasthesiologie und Intensivmedizin, Ulm, Germany
• ⁷Mountain Infantry Brigade 23, Medical Service of the German Armed Forces, Bad Reichenhall, Sanitatsdienst der Bundeswehr, Munich, Germany

Introduction Cold-water immersion induces autonomic stress responses including sympathetic cold shock and parasympathetic diving and trigeminovagal reflexes, potentially leading to arrhythmias or bronchospasm. Another important complication of Cold-water immersion is hypothermia. This study evaluates physiological responses during ice-self-rescue training to assess safety and temperature monitoring accuracy. Methods We conducted a prospective observational cohort study of 80 healthy Mountain Infantry soldiers during a standardized ice-self-rescue training in Norway (air temperature -10°C). Participants underwent partial immersion (0.5°C water) resulting in transitory submersion (< 5 sec). They were equipped with with continuous 3-lead ECG (n=34) spirometry (n=26), and core temperature monitoring (ingestible telemetric capsule (n=23) versus bilateral tympanic thermometry with and without ear channel occlusion (n=34). Primary outcomes included cardiac rhythm changes, lung function parameters and temperature measurement agreement. Results ECG analysis revealed significant post-immersion tachycardia (median increase of 17 bpm, p=0.03) and increased RR-interval variability (+90 ms, p<0.01), without malignant arrhythmias. Spirometry showed no clinically significant changes in FVC or FEV₁ and peak expiratory flow. Tympanic readings underestimated core temperature post-immersion (median difference -2.8°C versus capsules, p<0.01), with ear canal occlusion did not improve accuracy (p=0.15). Conclusions Supervised cold-water immersion during military training exercise elicited expected autonomic stress responses without life-threatening complications in healthy soldiers. These findings suggest structured cold-water training can be safely conducted for fit individuals. Tympanic thermometry proved unreliable following immersion, even after ear channel occlusion. Ingestible capsule thermometry may be a more viable approach if invasive measurement is not possible.