Anesthesia is a potent determinant of ultra-high dose rate sparing in the murine total abdominal irradiation model

These findings identify anesthetic-dependent oxygenation as a reproducible confounder in pre-clinical FLASH studies: elevated pO2 under ISO negates abdominal sparing, whereas K/X preserves it across two clinically relevant doses. Rigorous control and reporting of factors that alter tissue oxygenation are therefore essential when designing experiments and, ultimately, translating FLASH radiotherapy.