carbogen

Carbogen, also called Meduna's Mixture after its inventor Ladislas J. Meduna, is a life-supporting mixture of carbon dioxide and oxygen gas. Meduna's original formula was 30 O2 and 70% oxygen, but carbogen can refer to any mixture of these two gases, from 1.5% to 50% CO2.
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An inhalant of oxygen and carbon dioxide that increases the sensitivity of tumor cells to the effects of radiation therapy.