Oxygen tension in primary gynaecological tumours: the influence of carbon dioxide concentration

Background and purpose: To assess the effect of inhalation of various high oxygen content gases (HOCG) with different carbon dioxide concentrations on the tumour oxygen tension in patients with primary gynaecological malignancies. Materials and methods: Tumour oxygen tension was assessed on two protocols in those patients with locally advanced visible or palpable primary gynaecological malignancies. Patients were assessed initially while breathing room air (R/A). After 4 min of inhaling the first HOCG, a second assessment of the oxygen tension within the tumour was made. After a 10 min rest period while inhaling R/A, the second HOCG was administered for 4 min after which the third set of measurements were obtained. Protocol A involved assessing the tumour oxygen tension in 12 patients while breathing R/A, 100% oxygen (O-2) and 5% carbogen (95% O-2, 5% CO2) . For protocol B, tumour oxygen tension assessments of 13 patients while breathing R/A, 2.5% carbogen (97.5% O-2, 2.5% CO2), and 5% carbogen. Median pO(2) and percentage of values less than or equal to2.5 mmHg were assessed. Results: Regarding protocol A, the median of the median pO(2) values increased from 5 mmHg when breathing R/A to 47 mmHg for 100% O-2 and to 105 mmHg for 5% carbogen inhalation. The median of the percentage of values less than or equal to2.5 mmHg decreased: 17% for R/A vs. 16% for 100% O-2 (P = ns) vs. 0% for 5% carbogen (P = 0.015). In protocol B, the median of the median pO(2) values increased from 3 mmHg when breathing R/A to 73 mmHg when inhaling 2.5% carbogen and to 72 mmHg for 5% carbogen inhalation. The median of the percentage of values less than or equal to2.5 mmHg decreased with both carbogen mixtures compared with room air: 42% for R/A vs. 0% for 2.5% carbogen (P = 0.05) and 3% for 5% carbogen (P = 0.015). No statistically significant difference in this parameter was found between the two carbogen concentrations. Conclusion: Oxygen tension as measured with an Eppendorf pO(2) histograph, increased with inhalation of the oxygen and carbon dioxide gas mixtures tested. While 100% oxygen inhalation increased the median pO(2) compared with R/A a significantly greater increase in oxygen tension was seen with inhalation of either carbogen gas mixture. Pure oxygen inhalation did not decrease the percentage of values less than or equal to2.5 mmHg whereas inhalation of either 2.5 and 5% carbogen gas resulted in a significant decrease in this parameter. Both carbogen concentrations appear equal at increasing the oxygen tension in primary gynaecological tumours as measured with the Eppendorf pO(2) histograph. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.