title: The ideal oxygen/nitrous oxide fresh gas flow sequence with the Anesthesia Delivery Unit machine.
abstract: 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 > or =50% with an Anesthesia Delivery Unit anesthesia machine.
  
  
  METHODS
  Prospective, randomized clinical study.
  
  
  METHODS
  Large teaching hospital in Belgium.
  
  
  METHODS
  53 ASA physical status I and II patients requiring general endotracheal anesthesia and controlled mechanical ventilation.
  
  
  METHODS
  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 > or =50% and ensures an adequate bellows volume during the ensuing low-flow period.
authors.affiliation: Department of Anesthesiology, Intensive Care and Pain Therapy, Onze Lieve Vrouw Hospital, 9300 Aalst, Belgium. jcnwahendrickx@yahoo.com
authors.forename: Jan F A
authors.initials: JF
authors.lastname: Hendrickx
authors.forename: Sara
authors.initials: S
authors.lastname: Cardinael
authors.forename: Rik
authors.initials: R
authors.lastname: Carette
authors.forename: Hendrikus J M
authors.initials: HJ
authors.lastname: Lemmens
authors.forename: Andre M
authors.initials: AM
authors.lastname: De Wolf
mesh_terms: D000328:Adult; D000776:Anesthesiology / Q000295:instrumentation*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009609:Nitrous Oxide / Q000008:administration & dosage*; D010100:Oxygen / Q000008:administration & dosage*; D011446:Prospective Studies
chemical_list: D018685:Anesthetics, Inhalation; D009609:Nitrous Oxide; D010100:Oxygen