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RESEARCH PRODUCT

Dynamics of tumor oxygenation and red blood cell flux in response to inspiratory hyperoxia combined with different levels of inspiratory hypercapnia.

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Abstract Background and purpose : Increasing arterial oxygen partial pressure (pO 2 ) by breathing hyperoxic gases is an effective means of improving tumor oxygenation, although the efficacy of adding CO 2 to the inspiratory gas has been discussed controversially. This study aimed at analyzing the impact of different inspiratory CO 2 fractions on the time course of oxygenation and perfusion changes in experimental tumors during and after inspiratory hyperoxia. Material and methods : Perfusion and oxygenation of rat DS-sarcomas were studied during spontaneous breathing of pure oxygen or hyperoxic gas mixtures containing different CO 2 fractions (1, 2.5 or 5%). Red blood cell (RBC) flux was assessed as a measure of tumor perfusion using the laser Doppler technique and temporal changes in mean tumor pO 2 were measured polarographically. Results : Mean tumor pO 2 increased 3.6-fold with pure oxygen, approx. 3.3-fold when 1 or 2.5% CO 2 was added and 2.7-fold during carbogen breathing. RBC flux also increased by 25–30% with all gases. With pure oxygen and with 1% CO 2 (+99% O 2 ), perfusion changes paralleled those of the mean arterial blood pressure whereas with higher CO 2 fractions, a decrease in resistance to flow was observed. The differences found with the various gas mixtures were more pronounced after the end of hyperoxia. With pure oxygen, perfusion immediately returned to pretreatment values whereas with higher CO 2 fractions perfusion remained elevated for at least 30 min. Conclusions : Higher inspiratory CO 2 fractions (2.5 or 5%) lead to a prolonged improvement of tumor perfusion after the end of inspiratory hyperoxia when compared with pure oxygen breathing. Since no principal differences in oxygenation and perfusion were seen between the gases containing 2.5 and 5% CO 2 , the former may be preferable for inspiratory hyperoxia.