Manipulation of the Radiosensitivity of Pig Epidermis by Changing the Concentration of Oxygen and Halothane in the Anaesthetic Gas Mixture

Summary

A gas mixture of halothane, oxygen and nitrous oxide has been used to anaesthetize pigs for irradiation. The effects of various concentrations of halothane and oxygen on the radiosensitivity of the epidermis were examined after irradiation with single doses of β-rays from strontium-90 plaques. The incidence of moist desquamation was used as an endpoint, and experiments were compared on the basis of the dose associated with a 50 per cent incidence of moist desquamation (ED₅₀ ± SE). For pigs inspiring an anaesthetic gas mixture of 2 per cent halothane, ∼ 70 per cent oxygen and ∼ 30 per cent nitrous oxide the ED₅₀ for moist desquamation was 27·32 ± 0·52 Gy. A similar ED₅₀ value of 27·39 ± 1·20 Gy was obtained when 4 per cent halothane was used in place of 2 per cent. When the pigs were breathing air (∼ 21 per cent oxygen) in place of oxygen and nitrous oxide the ED₅₀ values were increased significantly to 31·25 ± 0·94 Gy and 33·72 ± 1·08 Gy for 2, and 4 per cent halothane, respectively. This change in the radiosensitivity of the epidermis was represented by dose modification factors of ∼ 1·13 and ∼ 1·23 for 2 and 4 per cent halothane, respectively.

Irradiation with a high oxygen concentration in the inspired gas mixture did not result in any significant variation of the dose required to produce moist desquamation in 50 per cent of the fields irradiated for dorsal, lateral and ventral positioned skin fields on the flank. However, pigs breathing air and halothane during irradiation showed marked differences in the radiosensitivity of the various sites on the flank, with ED₅₀ values for moist desquamation of ∼ 37 Gy and 26–30 Gy for dorsal and ventral positioned fields, respectively. This marked difference in radiosensitivity suggests variations in the physiological compensation over the flank when pigs are breathing oxygen at low concentrations under anaesthesia.