The ideal oxygen/nitrous oxide fresh gas flow sequence with the Anesthesia Delivery Unit machine

Jan F.A. Hendrickx*, Sara Cardinael, Rik Carette, Hendrikus J.M. Lemmens, Andre M. De Wolf

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

7 Scopus citations

Abstract

Study Objective: To determine whether early reduction of oxygen and nitrous oxide fresh gas flow from 6 L/min to 0.7 L/min could be accomplished while maintaining end-expired nitrous oxide concentration ≥50% with an Anesthesia Delivery Unit anesthesia machine. Study Design: Prospective, randomized clinical study. Setting: Large teaching hospital in Belgium. Patients: 53 ASA physical status I and II patients requiring general endotracheal anesthesia and controlled mechanical ventilation. Interventions: Patients were randomly assigned to one of 4 groups depending on the duration of high oxygen/nitrous oxide fresh gas flow (two and 4 L/min, respectively) before lowering total fresh gas flow to 0.7 L/min (0.3 and 0.4 L/min oxygen and nitrous oxide, respectively): one, two, three, or 5 minutes (1-minute group, 2-minute group, 3-minute group, and 5-minute group), with n = 10, 12, 13, and 8, respectively. The course of the end-expired nitrous oxide concentration and bellows volume deficit at end-expiration was compared among the 4 groups during the first 30 minutes. Results: At the end of the high-flow period the end-expired nitrous oxide concentration was 35.6 ± 6.2%, 48.4 ± 4.8%, 53.7 ± 8.7%, and 57.3 ± 1.6% in the 4 groups, respectively. Thereafter, the end-expired nitrous oxide concentration decreased to a nadir of 36.1 ± 4.5%, 45.4 ± 3.8%, 50.9 ± 6.1%, and 55.4 ± 2.8% after three, 4, 6, and 8 minutes after flows were lowered in the 1- to 5-minute groups, respectively. A decrease in bellows volume was observed in most patients, but was most pronounced in the 2-minute group. The bellows volume deficit gradually faded within 15 to 20 minutes in all 4 groups. Conclusions: A 3-minute high-flow period (oxygen and nitrous oxide fresh gas flow of 2 and 4 L/min, respectively) suffices to attain and maintain end-expired nitrous oxide concentration ≥50% and ensures an adequate bellows volume during the ensuing low-flow period.

Original languageEnglish (US)
Pages (from-to)274-279
Number of pages6
JournalJournal of Clinical Anesthesia
Volume19
Issue number4
DOIs
StatePublished - Jun 1 2007

Keywords

  • Anesthesia techniques
  • Circle system
  • Low-flow anesthesia
  • Nitrous oxide
  • oxygen

ASJC Scopus subject areas

  • Anesthesiology and Pain Medicine

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