Venoarterial PCO2-to-arteriovenous oxygen content difference ratio is a poor surrogate for anaerobic metabolism in hemodilution: an experimental study

• Published in: Annals of intensive care 2017-06, Vol.7 (1), p.1-65, Article 65
• Main Authors: Dubin, Arnaldo, Ferrara, Gonzalo, Kanoore Edul, Vanina Siham, Martins, Enrique, Canales, Héctor Saúl, Canullán, Carlos, Murias, Gastón, Pozo, Mario Omar, Estenssoro, Elisa
• Format: Article
• Language: English
• Subjects: Anaerobic metabolism; Anesthesiology; Carbon dioxide; Critical Care Medicine; Emergency Medicine; Hemodilution; Hemorrhage; Intensive; Intensive care; Medicine; Medicine & Public Health; Metabolism; Oxygen; Respiratory quotient
• ISSN: 2110-5820; 2110-5820
• DOI: 10.1186/s13613-017-0288-z

Background The identification of anaerobic metabolism in critically ill patients is a challenging task. Observational studies have suggested that the ratio of venoarterial PCO 2 (P v–a CO 2 ) to arteriovenous oxygen content difference (C a–v O 2 ) might be a good surrogate for respiratory quotient (RQ). Yet P v–a CO 2 /C a–v O 2 might be increased by other factors, regardless of anaerobic metabolism. At present, comparisons between P v–a CO 2 /C a–v O 2 and RQ have not been performed. We sought to compare these variables during stepwise hemorrhage and hemodilution. Since anemia predictably produces augmented P v–a CO 2 and decreased C a–v O 2 , our hypothesis was that P v–a CO 2 /C a–v O 2 might be an inadequate surrogate for RQ. Methods This is a subanalysis of a previously published study. In anesthetized and mechanically ventilated sheep ( n  = 16), we compared the effects of progressive hemodilution and hemorrhage by means of expired gases analysis. Results There were comparable reductions in oxygen consumption and increases in RQ in the last step of hemodilution and hemorrhage. The increase in P v–a CO 2 /C a–v O 2 was higher in hemodilution than in hemorrhage (1.9 ± 0.2 to 10.0 ± 0.9 vs. 1.7 ± 0.2 to 2.5 ± 0.1, P