Desflurane usage during anesthesia with and without N 2 O using FLOW-i Automatic Gas Control with three different wash-in speeds

Robrecht De Medts*, Rik Carette, Andre M. De Wolf, Jan F.A. Hendrickx

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


AGC ® (Automatic Gas Control) is the FLOW-i’s automated low flow tool (Maquet, Solna, Sweden) that target controls the inspired O 2 (F I O 2 ) and end-expired desflurane concentration (F A des) while (by design) exponentially decreasing fresh gas flow (FGF) during wash-in to a maintenance default FGF of 300 mL min −1 . It also offers a choice of wash-in speeds for the inhaled agents. We examined AGC performance and hypothesized that the use of lower wash-in speeds and N 2 O both reduce desflurane usage (Vdes). After obtaining IRB approval and patient consent, 78 ASA I-II patients undergoing abdominal surgery were randomly assigned to 1 of 6 groups (n = 13 each), depending on carrier gas (O 2 /air or O 2 /N 2 O) and wash-in speed (AGC speed 2, 4, or 6) of desflurane, resulting in groups air/2, air/4, air/6, N 2 O/2, N 2 O/4, and N 2 O/6. The target for F I O 2 was set at 35%, while the F A des target was selected so that the AGC displayed 1.3 MAC (corrected for the additive affect of N 2 O if used). AGC was activated upon starting mechanical ventilation. Varvel’s criteria were used to describe performance of achieving the targets. Patient demographics, end-expired N 2 O concentration, MAC, FGF, and Vdes were compared using ANOVA. Data are presented as mean ± standard deviation, except for Varvel’s criteria (median ± quartiles). Patient demographics did not differ among the groups. Median performance error was −2–0% for F I O 2 and −3–1% for F A des; median absolute performance error was 1–2% for F I O 2 and 0–3% for F A des. MAC increased faster in N 2 O groups, but total MAC decreased 0.1–0.25 MAC below that in the O 2 /air groups after 60 min. The effect of wash-in speed on Vdes faded over time. N 2 O decreased Vdes by 62%. AGC performance for O 2 and desflurane targeting is excellent. After 1 h, the wash-in speeds tested are unlikely to affect desflurane usage. N 2 O usage decreases Vdes proportionally with its reduction in F A tdes.

Original languageEnglish (US)
Pages (from-to)763-769
Number of pages7
JournalJournal of Clinical Monitoring and Computing
Issue number4
StatePublished - Aug 1 2018


  • Anesthesia machine
  • Automated low flow
  • Closed loop
  • Equipment
  • Target control

ASJC Scopus subject areas

  • Health Informatics
  • Critical Care and Intensive Care Medicine
  • Anesthesiology and Pain Medicine


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