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

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.

Keywords: Air; Low flow anesthesia; Nitrous oxide; Sevoflurane; Wash-in.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1

Trajectories of FAS vs. time to achieve each FAS during wash-in of group N2O. FAS, alveolar concentration of sevoflurane

Fig. 2

Trajectories of FAS vs. time to achieve each FAS during wash-in of group Air. FAS, alveolar concentration of sevoflurane

Fig. 3

Rising pattern of FAS and FIS of group N2O and group Air. FAS, alveolar concentration of sevoflurane; FIS, inspired concentration of sevoflurane

Fig. 4

Rising pattern of FAS/FIS ratio of group N2O and group Air. FAS, alveolar concentration of sevoflurane; FIS, inspired concentration of sevoflurane

Fig. 5

Pattern of changes in heart rate and blood pressure of group N2O and group Air at each FAS. p < 0.001 for all values. FAS, alveolar concentration of sevoflurane; BPs, systolic blood pressure; BPd, diastolic blood pressure; HR, heart rate