title: Heliox vs air-oxygen mixtures for the treatment of patients with acute asthma: a systematic overview.
abstract: OBJECTIVE
  To evaluate, by systematic review, the efficacy of heliox on respiratory mechanics and outcomes in patients with acute asthma.
  
  
  METHODS
  The search strategy included searching electronic databases (MEDLINE, EMBASE, and The Cochrane Library) and the references of relevant articles. Study quality was assessed based on allocation concealment. Randomized controlled trials (RCTs) comparing heliox to an air-oxygen mixture (airO(2)) as an adjunct treatment in patients with acute asthmatic attacks were analyzed. For the qualitative portion of the analysis, all reports of the use of heliox in patients with acute asthma were included.
  
  
  RESULTS
  Four RCTs (n = 278) were found to have a common respiratory parameter (peak expiratory flow rate as a percentage of predicted) suitable for meta-analysis. Within the 92% confidence interval (CI), there was a small benefit with the use of heliox compared to airO(2) (weighted mean difference, + 3%; 95% CI, - 2 to + 8%). There was also a slight improvement in the dyspnea index (weighted mean difference, 0.60; 95% CI, 0.04 to 1.16) with the use of heliox over airO(2). Overall, five RCTs, one nonrandomized unblinded parallel trial, one retrospective case-matched control trial, three case series, and one case report had results in favor of heliox; one RCT and one case series showed no improvement with heliox; one RCT showed a possible detrimental effect with heliox; and 1 small RCT was inconclusive. Most investigators did not prevent entrainment of room air during heliox use or compensate for the lower nebulizing efficiency of heliox.
  
  
  CONCLUSIONS
  Based on surrogate markers, heliox may offer mild-to-moderate benefits in patients with acute asthma within the first hour of use, but its advantages become less apparent beyond 1 h, as most conventionally treated patients improve to similar levels, with or without it. The effect of heliox may be more pronounced in more severe cases. There are insufficient data on whether heliox can avert tracheal intubation, or change intensive care and hospital admission rates and duration, or mortality.
authors.affiliation: Department of Anaesthesia and Intensive Care, Faculty of Medicine, The Chinese University of Hong Kong, SAR. hoamh@cuhk.edu.hk
authors.forename: Anthony M-H
authors.initials: AM
authors.lastname: Ho
authors.forename: Anna
authors.initials: A
authors.lastname: Lee
authors.forename: Manoj K
authors.initials: MK
authors.lastname: Karmakar
authors.forename: Peter W
authors.initials: PW
authors.lastname: Dion
authors.forename: David C
authors.initials: DC
authors.lastname: Chung
authors.forename: LeeAnne H
authors.initials: LH
authors.lastname: Contardi
mesh_terms: D000208:Acute Disease; D001249:Asthma / Q000188:drug therapy*; D006371:Helium / Q000627:therapeutic use*; D006801:Humans; D010100:Oxygen / Q000627:therapeutic use*; D015656:Respiratory Mechanics; D012138:Respiratory Therapy / Q000379:methods*; D016896:Treatment Outcome
chemical_list: D006371:Helium; C038949:heliox; D010100:Oxygen