1-1-12 One-Step Wash-In Scheme for Desflurane-Nitrous Oxide Low-Flow Anesthesia: Rapid and Predictable Induction

Background. We propose a 1-1-12 wash-in scheme for desflurane-nitrous oxide (N(2)O) low-flow anesthesia. The objective of our study was to determine the time to achieve alveolar concentration of desflurane (F(A)D) at 1, 2, 3, 4, 5, and 6%. Methods. We enrolled 106 patients scheduled for elective surgery under general anesthesia. After induction and intubation, wash-in was started with a fresh gas flow (FGF) of N(2)O : O(2) 1 : 1 L min(−1) and vaporizer concentration of desflurane (FD) of 12%. Ventilation was controlled to maintain P(A)CO(2) at 30–35 mmHg. Results. The F(A)D rose rapidly from 0 to 4% in 2 min in a linear manner in 0.5 min increments. An F(A)D of 6% was achieved in 4 min in a linear fashion from F(A)D of 4% but in 1 min increments. An F(A)D of 1 to 6% occurred at 0.6, 1, 1.5, 2, 3, and 4 min. Heart rate during wash-in showed a statistically, albeit not clinically, significant pattern of increase. By contrast, blood pressure slightly decreased during this period. Conclusions. We developed a 1-1-12 wash-in scheme using a FGF of N(2)O : O(2) 1 : 1 L min(−1) and FD of 12% for desflurane-nitrous oxide low-flow anesthesia. A respective F(A)D of 1, 2, 3, 4, 5, and 6% can be expected at 0.6, 1, 1.5, 2, 3, and 4 min.