1-1-8 one-step sevoflurane wash-in scheme for low-flow anesthesia: simple, rapid, and predictable induction

Abstract

Abstract Background Sevoflurane is suitable for low-flow anesthesia (LFA). LFA needs a wash-in phase. The reported sevoflurane wash-in schemes lack simplicity, target coverage, and applicability. We proposed a one-step 1-1-8 wash-in scheme for sevoflurane LFA to be used with both N2O and Air. The objective of our study was to identify time for achieving each level of alveolar concentration of sevoflurane (FAS) from 1 to 3.5% in both contexts. Methods We recruited 199 adults requiring general anesthesia with endotracheal intubation and controlled ventilation—102 in group N2O and 97 in group Air. After induction and intubation, a wash-in was started using a fresh gas flow of O2:N2O or O2:Air at 1:1 L·min− 1 plus sevoflurane 8%. The ventilation was controlled to maintain end-tidal CO2 of 30–35 mmHg. Results The rising patterns of FAS and inspired concentration of sevoflurane (FIS) are similar, running parallel between the groups. The FAS/FIS ratio increased from 0.46 to 0.72 within 260 s in group N2O and from 0.42 to 0.69 within 286 s in group Air. The respective time to achieve an FAS of 1, 1.5, 2, 2.5, 3, and 3.5% was 1, 1.5, 2, 3, 3.5, and 4.5 min in group N2O and 1, 1.5, 2, 3, 4, and 5 min in group Air. The heart rate and blood pressure of both groups significantly increased initially then gradually decreased as FAS increased. Conclusions The 1-1-8 wash-in scheme for sevoflurane LFA has many advantages, including simplicity, coverage, swiftness, safety, economy, and that it can be used with both N2O and Air. A respective FAS of 1, 1.5, 2, 2.5, 3, and 3.5% when used with N2O and Air can be expected at 1, 1.5, 2, 3, 3.5, and 4.5 min and 1, 1.5, 2, 3, 4, and 5 min. Trial registration This study was retrospectively registered with ClinicalTrials.gov (NCT03510013) on June 8, 2018.