A lower solubility recommends the use of desflurane more than isoflurane, halothane, and enflurane under low-flow conditions

Study Objective: To determine whether the lower solubility of desflurane, over that of isoflurane, enflurane, and halothane, favors its use in low-flow anesthesia. Design: Prospective clinical study. Setting: Technical University of Munich. Patients: 40 elderly (≥65 yrs), ASA physical status II and III surgical patients. Interventions: All patients were anesthetized and received delivered concentrations (F_D) of 4% desflurane, 1.5% isoflurane, 1.8% enflurane, or 0.9% halothane (n = 10 patients for each anesthetic) in a fresh gas inflow of 3 L/min (high-flow), until end-tidal target concentrations (F_A of 2% desflurane, 0.5% isoflurane, 0.6% enflurane, and 0.3 % halothane were obtained. After 30 minutes, the inflow was decreased to 1 L/min (low-flow), and the F_D and the inspired concentration (F_I) were adjusted to maintain the target concentration. Measurements and Main Results: The concentrations of the halogenated anesthetics, as well as nitrous oxide, oxygen (O₂), and carbon dioxide, were measured in delivered gas at the common gas outlet and at the endotracheal tube connector. Transcutaneous O₂ saturation, noninvasive blood pressure, and heart rate were also measured. During the first 30 minutes of high-flow administration, the target concentration was attained sooner with desflurane than with isoflurane, enflurane, or halothane (median levels: 4 min vs. 6 min, 8 min, or 10 min; p < 0.01). After the reduction of inflow to 1 L/min, F_D had to be materially increased to maintain F_I and F_A for the more soluble anesthetics, but not for desflurane. Conclusions: At low flows, F_D provides a reasonable surrogate of F_I and F_A for desflurane, but not for isoflurane, enflurane, or halothane. The rapid and predictable titrability of desflurane favors its safe use in low-flow technique.