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

Abstract

The gas mixture carbogen may be breathed by patients to enhance the oxygenation level and therefore the radiosensitivity of tumours. However, owing to the high CO2 content, its inhalation is associated with patient intolerance. Our aim was to determine a suitable carbon dioxide and oxygen gas mixture with similar enhancement of arterial oxygenation to 5% carbogen and with improved patient tolerance. 14 patients entered the study; of those 14, 8 were 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. Gas exchange parameters were measured using a carbon dioxide monitor and a blood 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 suggest that 2% CO2 in O2 enhances arterial oxygen levels to a similar extent as 3.5% and 5% CO2 and that it is well tolerated.

Cerebrovascular Reactivity Mapping: An Evolving Standard for Clinical Functional Imaging

“…White matterpenetrating arteries have resistances typically Ͼ3-4 times higher than those of penetrating arteries in the cortex. [26][27][28] In view of the added complexity rendered by the total of these issues, accurate assessment of the state of CVR deficits requires measurement of the entire vasodilatory portion of the sigmoidal curve (resting partial pressure of carbon dioxide level to 15-20 mm Hg above the resting level). This would require precision control of CO 2 , preferably holding arterial O 2 constant while mapping CVR for all increments of CO 2 from resting values to marked hypercapnia.…”

“…29 Furthermore, administration of exogenous CO 2 can stimulate ventilation depending on the CO 2 chemoreflex sensitivity of the individual so that partial pressure of CO 2 may not change at all or may even decrease. 28 Therefore, if quantitative CVR is required, simple mask application of CO 2 stimuli is unsuitable. The ability to precisely control arterial blood gasses including CO 2 and O 2 independent of the respiratory rate and tidal volume is desirable for several reasons.…”

Effect of Hypoxia and Hyperoxia on Cerebral Blood Flow, Blood Oxygenation, and Oxidative Metabolism

“…The subjects were instructed to maintain a uniform breathing pattern throughout the experiment. However, due to O 2 effects on chemoreceptors in the brain (Dean et al, 2004), hyperventilation is known to occur during a hyperoxia challenge, which results in a reduced EtCO 2 as documented by a number of studies in the literature (Baddeley et al, 2000;Dean et al, 2004;Guyton and Hall, 2005). To minimize CO 2 changes during the hyperoxia challenge, we added a small amount of CO 2 to the hyperoxic air (1% and 2% CO 2 to FiO 2 50% and 98%, respectively).…”

Detecting gas‐induced vasomotor changes via blood oxygenation level‐dependent contrast in healthy breast parenchyma and breast carcinoma

“…Physiological effects of carbogen when breathed for longer periods include a sensation of air hunger and an increased respiratory drive, associated with symptoms of breathlessness and anxiety in some subjects. The original rationale for using 5% carbogen was empirical, but experimental evidence has shown lower CO 2 concentrations to be much better tolerated by patients, with no compensatory increase in tidal volume or respiratory rate, while still achieving maximum tissue oxygenation 24, 28. However, no adverse side effects were reported in this study with the 2‐minute block design experiment, with no corresponding increase in cardiac or respiratory rate during carbogen breathing.…”