title: Time required to achieve a stable cuff pressure by repeated aspiration of the cuff during anaesthesia with nitrous oxide.
abstract: OBJECTIVE
  When the endotracheal tube cuff is repeatedly aspirated to avoid excessive cuff pressure during nitrous oxide anaesthesia, a stable cuff pressure is eventually achieved. We assessed the time required to achieve a stable cuff pressure after repeated cuff deflation.
  
  
  METHODS
  During 67% nitrous oxide and oxygen anaesthesia, air-filled cuffs of a standard tracheal tube (Mallinckrodt Hi-Contour) were repeatedly deflated every 30 min for the first 3 or 4 h to inhibit excessive pressure (Groups Def-3 or Def-4, respectively, n = 10 for each); the cuff pressure was monitored for an additional 3 h. In some patients, the study was terminated at 1, 2, 3 and 4 h (n = 6 for each).
  
  
  RESULTS
  Cuff pressure in Group Def-3, but not in Group Def-4, > 22 mmHg after stopping cuff aspiration. Intracuff nitrous oxide concentrations increased during repeated cuff deflation and increased further in Group Def-3 during an additional 3 h (from 39.8 +/- 4.7% to 44.3 +/- 3.8%; P < 0.05), whereas intracuff nitrous oxide concentrations at 4 h were not different from those in Group Def-4 at the end of the study (43.7 +/- 4.5% versus 42.3 +/- 4.8%; P = 0.579).
  
  
  CONCLUSIONS
  When the air-filled cuff of the standard endotracheal tube is repeatedly deflated every 30 min for 4 h, but not for only 3 h, during nitrous oxide anaesthesia, a stable cuff pressure can be achieved without further deflation of the cuff. Our data also suggest that achieving an equilibrating nitrous oxide concentration in the cuff provides a subsequent stable cuff pressure.
authors.affiliation: National Defense Medical College, Department of Anaesthesiology, Tokorozawa, Saitama, Japan. karasawa@me.ndmc.ac.jp
authors.forename: F
authors.initials: F
authors.lastname: Karasawa
authors.forename: T
authors.initials: T
authors.lastname: Hamachi
authors.forename: I
authors.initials: I
authors.lastname: Takamatsu
authors.forename: T
authors.initials: T
authors.lastname: Oshima
mesh_terms: D000704:Analysis of Variance; D000769:Anesthesia, Inhalation / Q000295:instrumentation*; D018685:Anesthetics, Inhalation / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D007442:Intubation, Intratracheal / Q000295:instrumentation*; D008297:Male; D008875:Middle Aged; D009609:Nitrous Oxide / Q000627:therapeutic use*; D011312:Pressure; D013997:Time Factors
chemical_list: D018685:Anesthetics, Inhalation; D009609:Nitrous Oxide