Effect of obesity on FD/FA and FI/FA ratios for isoflurane and desflurane. FD/FA will always be higher than FI/FA. Obesity modestly affects FD/FA and FI/FA for isoflurane but not desflurane. From Lemmens HJ, et al., “Obesity Modestly Affects Inhaled Anesthetic Kinetics in Humans,” Anesthesia & Analgesia, 2008; 107: 1864–70, with permission from Wolters Kluwer Health.