A computer model for the accurate quantification of blood gas exchange components was used to assess the impact of respiratory quotient (RQ) on venoarterial CO2 tension and pH differences over a large group of patient measurements. The combined use of measured and computer-generated data has shown that, for any given increase in blood CO2 concentration (i.e., when the arterial blood becomes venous), the associated increase in CO2 tension and decrease in pH are inversely related to the RQ, and that this relationship is mediated by the Haldane effect. These results are useful for a through understanding of blood gas and metabolic interactions in normal and abnormal states, and for improving the interpretation of changes in venoarterial CO2 tension gradient in clinical monitoring.