ObjectiveBecause of high-altitude operations, cold exposure is common for helicopter emergency medical services. However, drug emulsions such as propofol and etomidate are prone to degradation and the formation of lipid droplets, possibly large enough to cause pulmonary embolism, when frozen. Amiodarone may be prone to crystallization, possibly causing phlebitis, when exposed to cold temperatures. The aim of this study was to microscopically identify physical changes in common emergency drugs under cold exposure. MethodsExposure time frames and temperature ranges were chosen according to real-world data collected on a rescue helicopter in Switzerland. Samples were stored in a laboratory freezer with a temperature range of −2.3°C (27.7°F) for 1 hour, 0.6°C to −3.6°C (33.1°F-25.5°F) for 12 hours, and −22°C (−7.6°F) for 1 hour and 12 hours. Analysis was performed under a light microscope. ResultsNo physical changes in the form of large lipid droplets or crystallization were found in the samples stored at −2.3°C (27.7°F). Lipid droplets were found in the propofol samples stored at 0.6°C to −3.4°C (33.1°F-25.5°F) and −22°C (−7.6°F) over 12 hours. ConclusionThere was no observation of physical changes under temperature conditions commonly found in helicopter emergency medical services. However, lipid droplets could be observed in the propofol samples with long exposure times or under deep frozen temperature conditions. These findings highlight the need to establish a safe threshold for cold exposure of medications in the prehospital environment.