Almitrine, a peripheral chemoreceptor agonist, was given intravenously in a dose of 0.5 mg/kg/h for 2 h in a randomized double-blind manner with placebo, to 11 patients with severe chronic air-flow obstruction and hypoxemia (SaO2 less than 90%). There was no significant placebo effect. Maximal respiratory effect occurred at the end of the almitrine infusion with an increase in ventilation from 8.2 + 0.9 to 11.6 + 1.5 L/min (mean +/- SEM), and improvements in SaO2 from 83 +/- 3 to 90 +/- 2%, in PaO2 from 48 +/- 2 to 55 +/- 3 mmHg, and in PaCO2 from 54 + 3 to 47 +/- 4 mmHg. Venous admixture was reduced from 38 +/- 4% to 22 +/- 3%. In 4 patients, blood gas values substantially improved, but there was no change in total ventilation for ventilatory pattern. This study of acute effects showed that almitrine improved arterial PO2 and PCO2 in patients with chronic air-flow obstruction both by increasing ventilation and by improving ventilation-perfusion relationships.

Unless cardiac output is reduced, alveolar ventilation can be monitored without arterial blood gas analysis by estimating arterial carbon dioxide tension (PaO2) from rebreathing measurement of mixed venous carbon dioxide tension (PvCO2) (PaCO2 = 0.8 PvCO2). If cardiac output is reduced, the PvCO2 - PaCO2 difference increases, reflecting the increased venoarterial carbon dioxide (CO2) content difference (Fick principle). A reduction in cardiac output can thus be quantified without catheterization of the central circulation by measuring both PaCO2 and PvCO2. The significance of such a reduction in cardiac output for oxygen (O2) delivery to tissues is determined by calculation of mixed venous O2 saturation (SvO2), using the inter-relationship of CO2 production to O2 consumption. With normal arterial oxygenation (SaO2) and hemoglobin concentration, PaCO2 less than 0.8 PvCO2 - 12 implies a reduction in cardiac output such that SvO2 is less than 33 per cent, which indicates inadequate O2 delivery to tissues. Ear oximetry and rebreathing measurement of PvCO2 are simple, noninvasive, bedside techniques.