Factors Affecting Hypoxic KHT Tumor Cells in Mice Breathing O₂, O₂+ CO₂, or Hyperbaric Oxygen with or without Anesthesia

The fraction of radiation-resistant hypoxic cells in KHT mouse tumor was reduced by a factor of 4 by allowing tumor-bearing animals to breathe 100% O2 or 95% O2 + 5% CO2 at 1 atmosphere instead of air. When tumor-bearing animals breathed hyperbaric oxygen, a similar reduction in the hypoxic fraction of tumor cells was obtained, provided that the animals were anesthetized with urethan. If they were not anesthetized (many patients undergoing hyperbaric radiotherapy are not) or given Nembutal, then the fraction of resistant hypoxic cells was greater than that of tumors in air-breathing animals.