Gas exchange parameters in radiotherapy patients during breathing of 2%, 3.5% and 5% carbogen gas mixtures

The gas mixture carbogen may be breathed by patients to enhance the oxygena tion level and therefore the radiosensitivity of tumours. However, owing to the high CO2 content, its inhalation is associated with patient intoleranc e. Our aim was to determine a suitable carbon dioxide and oxygen gas mixtur e with similar enhancement of arterial oxygenation to 5% carbogen and with improved patient tolerance. 14 patients entered the study; of those 14, 8 w ere able to tolerate 2%, 3.5% and 5% carbogen mixtures as well as a control gas for sufficient time to allow successful arterial blood gas sampling. G as exchange parameters were measured using a carbon dioxide monitor and a b lood gas analyser. Arterial carbon dioxide tension ranged from 2.9 kPa to 6 .82 kPa whilst breathing the carbogen mixtures, and arterial oxygen tension increased at least three-fold from basal values. There were no significant changes in the respiratory rate, heart rate and blood pH. The results sugg est that 2% CO2 in O-2 enhances arterial oxygen levels to a similar extent as 3.5% and 5% CO2 and that it is well tolerated.