Diffusion Limitation of Volatile Anesthetic Uptake: Reply

I am grateful to Grigoryan et al.¹  for their interest in this study²  and their comments. First, in an anesthetized, ventilated population, it is incorrect to simply assume that the respiratory quotient measured will be 0.8, the typical physiologic value determined by steady state metabolism in other situations. Patients are frequently in a state of mild to moderate hyperventilation, producing ongoing washout of the body’s substantial carbon dioxide stores in addition to metabolic carbon dioxide production in the first hour or more after induction. This has been previously shown by us in this population, and average respiratory quotient values in excess of 0.9 are entirely expected.³  Unlike our previous study comparing alveolar deadspace calculations for gases of different solubilities (where the findings would be little affected by the value assumed), a precise measurement of respiratory gas exchange was sought in the current study to achieve maximal...