title: Oxygen concentrators performance with nitrous oxide at 50:50 volume.
abstract: OBJECTIVE
  Few investigations have addressed the safety of oxygen from concentrators for use in anesthesia in association with nitrous oxide. This study evaluated the percent of oxygen from a concentrator in association with nitrous oxide in a semi-closed rebreathing circuit.
  
  
  METHODS
  Adult patients undergoing low risk surgery were randomly allocated into two groups, receiving a fresh gas flow of oxygen from concentrators (O293) or of oxygen from concentrators and nitrous oxide (O293N2O). The fraction of inspired oxygen and the percentage of oxygen from fresh gas flow were measured every 10 min. The ratio of FiO2/oxygen concentration delivered was compared at various time intervals and between the groups.
  
  
  RESULTS
  Thirty patients were studied in each group. There was no difference in oxygen from concentrators over time for both groups, but there was a significant improvement in the FiO2 (p<0.001) for O293 group while a significant decline (p<0.001) for O293N2O. The FiO2/oxygen ratio varied in both groups, reaching a plateau in the O293 group. Pulse oximetry did not fall below 98.5% in either group.
  
  
  CONCLUSIONS
  The FiO2 in the mixture of O293 and nitrous oxide fell during the observation period although oxygen saturation was higher than 98.5% throughout the study. Concentrators can be considered a stable source of oxygen for use during short anesthetic procedures, either pure or in association with nitrous oxide at 50:50 volume.
authors.affiliation: Hospital Geral de Bonsucesso do Ministério da Saúde, Rio de Janeiro, RJ, Brazil.
authors.forename: Jorge Ronaldo
authors.initials: JR
authors.lastname: Moll
authors.affiliation: Departament of Surgery, Faculdade de Medicina, Universidade de São Paulo, São Paulo, SP, Brazil. Electronic address: joaquimev@usp.br.
authors.forename: Joaquim Edson
authors.initials: JE
authors.lastname: Vieira
authors.affiliation: Faculdade de Ciências Médicas da Santa Casa de São Paulo, São Paulo, SP, Brazil.
authors.forename: Judymara Lauzi
authors.initials: JL
authors.lastname: Gozzani
authors.affiliation: Faculdade de Ciências Médicas da Santa Casa de São Paulo, São Paulo, SP, Brazil.
authors.forename: Lígia Andrade Silva Telles
authors.initials: LA
authors.lastname: Mathias
mesh_terms: D000328:Adult; D000758:Anesthesia / Q000379:methods; D000764:Anesthesia, Closed-Circuit / Q000295:instrumentation / Q000379:methods; D000776:Anesthesiology / Q000295:instrumentation / Q000379:methods; D018685:Anesthetics, Inhalation / Q000008:administration & dosage*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009609:Nitrous Oxide / Q000008:administration & dosage*; D010092:Oximetry; D010100:Oxygen / Q000008:administration & dosage* / Q000378:metabolism; D010102:Oxygen Inhalation Therapy / Q000379:methods*; D013997:Time Factors; D055815:Young Adult
chemical_list: D018685:Anesthetics, Inhalation; D009609:Nitrous Oxide; D010100:Oxygen
keywords: Anesthesia; Developing countries; Equipment and supplies; Inhalation; Nitrous oxide; Oxygen inhalation therapy