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

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 N(2)O and Air. The objective of our study was to identify time for achieving each level of alveolar concentration of sevoflurane (F(A)S) 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 N(2)O and 97 in group Air. After induction and intubation, a wash-in was started using a fresh gas flow of O(2):N(2)O or O(2):Air at 1:1 L·min(− 1) plus sevoflurane 8%. The ventilation was controlled to maintain end-tidal CO(2) of 30–35 mmHg. RESULTS: The rising patterns of F(A)S and inspired concentration of sevoflurane (F(I)S) are similar, running parallel between the groups. The F(A)S/F(I)S ratio increased from 0.46 to 0.72 within 260 s in group N(2)O and from 0.42 to 0.69 within 286 s in group Air. The respective time to achieve an F(A)S 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 N(2)O 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 F(A)S 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 N(2)O and Air. A respective F(A)S of 1, 1.5, 2, 2.5, 3, and 3.5% when used with N(2)O 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.