title: The effect of heat and moisture exchanger and gas flow on humidity and temperature in a circle anaesthetic system.
abstract: OBJECTIVE
  The aim of the study was to measure the humidity and temperature of the inspired gas in a circle absorber system at fresh gas flows of 11/min and 31/min and assess the need of a heat and moisture exchanger (HME).
  
  
  METHODS
  This prospective randomised controlled study received the Hospital Ethics Committee approval and informed consent. Forty adult ASA 1 and 11 patients were randomised into four groups to receive with or without HME fresh gas flow of 1L/min or 3L/min. Temperature and the relative humidity readings were taken at the start and every 10 minutes for the first hour of anaesthesia.
  
  
  RESULTS
  There was a significantly higher relative humidity, absolute humidity and temperatures of the inspired gases at fresh gas flow of 1L/min and 3L/min with a HME compared to 3L/min without HME. Patients receiving fresh gas flows of lL/min had higher relative and absolute humidity than patients with fresh gas flows of 3L/min. However, the addition of the HME improved the absolute and relative humidity of the inspired gas in patients receiving fresh gas flow of 3l/min to a comparable level. However, the addition of a HME to a fresh gas flow of 1L/min did not significantly improve the humidity of the inspired gas.
  
  
  CONCLUSIONS
  This suggests that the inherent humidifying property of the circle system at low fresh gas flow of 1L/min was sufficient in short surgeries lasting less than one hour and that the addition of a HME may not be necessary.
authors.affiliation: Department of Anaesthesia and Surgical Intensive Care, Singapore General Hospital, Outram Road, Singapore 169608. rumini@singnet.com.sg
authors.forename: R
authors.initials: R
authors.lastname: Poopalalingam
authors.forename: M H
authors.initials: MH
authors.lastname: Goh
authors.forename: Y W
authors.initials: YW
authors.lastname: Chan
mesh_terms: D000328:Adult; D000368:Aged; D000769:Anesthesia, Inhalation / Q000379:methods*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage; D006358:Hot Temperature; D006801:Humans; D006813:Humidity; D008875:Middle Aged; D009609:Nitrous Oxide / Q000008:administration & dosage; D011446:Prospective Studies; D012121:Respiration, Artificial / Q000379:methods; D013696:Temperature; D013997:Time Factors
chemical_list: D018685:Anesthetics, Inhalation; D009609:Nitrous Oxide