1-1-12 one-step wash-in scheme for desflurane-nitrous oxide low-flow anesthesia: rapid and predictable induction

The effect of different flow levels and concentrations of sevoflurane during the wash-in phase on volatile agent consumption: a randomized controlled trial

PURPOSE

The standard procedure for low-flow anesthesia usually incorporates a high fresh gas flow (FGF) of 4-6 L/minute during the wash-in phase. However, the administration of a high FGF (4-6 L/min) increases the inhaled anesthetic agent consumption. This study was designed to compare the sevoflurane consumption at 2 rates of flow and vaporizer concentration during the wash-in period.

METHODS

Patients were randomly enrolled into high FGF (HFGF) (n = 30) and low FGF (LFGF) (n = 30) groups. During the wash-in, the HFGF group received 4 L/minute FGF with a sevoflurane vaporizer setting of 2.5%, and the LFGF group received 1 L/minute FGF with a vaporizer setting of 8%. Once the wash-in was complete, anesthesia maintenance was performed with 0.5 L/min FGF with a vaporizer setting of 2.5-4.5% in both groups. The patient demographic data, bispectral index values, hemodynamic variables, wash-in time, sevoflurane consumption during the wash-in phase, and total sevoflurane consumption were analyzed.

RESULTS

The median sevoflurane consumption in the wash-in phase was 8.2 mL (7.1-9.3) in the HFGF group and 2.7 mL (2.2-3.1) in the LFGF group (p = 0.001). The mean total sevoflurane consumption was 17.41 ± 3.58 mL in the patients who received HFGF and 14.93 ± 3.57 mL in the LFGF group (p = 0.001). The mean wash-in completion time was 12.49 ± 2.79 min in the HFGF group and 3.35 ± 0.67 min in the LFGF group (p = 0.001).

CONCLUSIONS

The anesthetic agent consumption during the wash-in phase was approximately 3 times lower with the administration of sevoflurane at 1 L/minute FGF than the use of 4 L/minute FGF.

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 N₂O and Air. The objective of our study was to identify time for achieving each level of alveolar concentration of sevoflurane (F_AS) 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 F_AS and inspired concentration of sevoflurane (F_IS) are similar, running parallel between the groups. The F_AS/F_IS 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 F_AS 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 F_AS 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 F_AS 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.

A randomised prospective comparison of equilibration point and changing gas composition during low-flow anaesthesia with sevoflurane vs desflurane

Background and Aims:

Safety and economy are the main concerns while using low- flow anaesthesia with newer inhalational agents. The main objective of this study was to use and compare 'equilibration time' of sevoflurane and desflurane after change-over from high-to-low flow anaesthesia.

Methods:

This prospective study included consenting adult patients between 18–70 years undergoing elective surgery under general anaesthesia. Patients were randomised initially to receive high-flow anaesthesia with 1.3 MAC of either desflurane or sevoflurane with nitrous oxide. After equilibration point, low-flow anaesthesia was initiated. Heart rate, non-invasive blood pressure, pulse oximeter, 5 electrode ECG and gas monitoring was done. Statistical analysis was done with the help of Med CalC version 12.5.0.0 (student version) and IBM SPSS Version 20.0.

Results:

Mean equilibration time in sevoflurane group was higher (4.59 ± 0.77 minutes) than desflurane group (3.78 ± 0.56 minutes, P < 0.001). Inspired concentrations of both inhalational agents varied from their vaporiser settings over 2 hours, more so with sevoflurane than desflurane. Inspired oxygen concentration (FiO2) remained above 30% during anaesthesia in both groups with stable haemodynamics.

Conclusion:

Change-over from high-to-low flow anaesthesia is faster in desflurane. With fresh gas flow (FGF) of 1 L with 50% oxygen and dial concentration of 1–1.5% of sevoflurane and 3.8–4.4% of desflurane, the risk of hypoxia is minimal. The disparity between the set and delivered concentrations is more (20%) in sevoflurane than desflurane (12%).

Advantages of 1-1-12 Wash in Scheme during Induction with Low Flow Anesthesia with and without Nitrous Oxide

Introduction

In the past, many wash-in schemes have been used with initially high fresh gas flow (FGF) to achieve the necessary alveolar concentration of inhalational agent in 10-15 min. This study was designed to show whether 1-1-12 wash-in scheme proposes an earlier achievement of induction or is there any requirement of high FGF phase to know the time taken for induction with and without nitrous oxide (N₂O).

Aims

The aim of the study was to find out the time required for the alveolar concentration of desflurane to be from 1% to 6% with and without N₂O.

Design

It was a potential randomized study which was conducted on sixty patients admitted for elective surgery.

Materials and Methods

Two groups of thirty patients each were made and randomly assigned. Group N received desflurane with N₂O plus oxygen and Group A received desflurane with air plus oxygen.

Statistical Analysis

The observations were noted and evaluated accordingly. Analysis was done using unpaired t-test.

Results

Hemodynamic parameters were almost similar in both the groups. In Group N, gradual F_AD (Alveolar Desflurane concentration, i.e., end-tidal desflurane) from 1% to 6% was achieved at 0.5, 1, 1.5, 2, 3, and 4 min. In Group A, the same was achieved at 0.6, 1, 1.5, 2, 3, and 4 min (P > 0.05). No significant difference was found between the recuperation time and score in both the groups. Rather complications were more in Group N and statistically significant for nausea and vomiting.

Conclusion

Time taken to attain F_AD from 1% to 6% was 4 min in both the groups. It is concluded that the recitation of 1-1-12 wash-in scheme is autonomous on the use of N₂O and high FGF phase.

1-1-12 one-step wash-in scheme for desflurane low flow anesthesia: performance without nitrous oxide

Background

We reported a 1-1-12 wash-in scheme for desflurane-nitrous oxide (N₂O) low flow anesthesia that is simple, rapid, and predictable. There remain some situations where N₂O should be avoided, which limits the generalizability of this wash-in scheme. The objective of our study was to determine the performance of this scheme in contexts where N₂O is not used.

Methods

We recruited 106 patients scheduled for elective surgery under general anesthesia. After induction and intubation, wash-in was started with a fresh gas flow of air:O₂ 1:1 L/min and a vaporizer concentration of desflurane of 12%. Controlled ventilation was then adjusted to maintain P_ACO₂ at 30–35 mmHg.

Results

The alveolar concentration of desflurane (F_AD) rose rapidly from 0% to 6% in 4 minutes in the same pattern as observed in our previous study in which N₂O was used. An F_AD of 7% was achieved in 6 minutes. An F_AD of 1% to 7% occurred at 0.6, 1, 1.5, 2, 3, 4, and 6 minutes. The rise in heart rate during wash-in was statistically significant, although not clinically so. There was a slight but statistically significant decrease in blood pressure, but this had no clinical significance.

Conclusion

Performance of the 1-1-12 wash-in scheme is independent of the use of N₂O. Respective F_ADs of 1%, 2%, 3%, 4%, 5%, 6%, and 7% can be expected at 0.6, 1, 1.5, 2, 3, 4, and 6 minutes.