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Heliox for nonintubated acute asthma patients.

BACKGROUND
Helium and oxygen mixtures (heliox), have been used sporadically in respiratory medicine for decades. Their use in acute respiratory emergencies such as asthma has been the subject of considerable debate. Despite the lapse of more than 60 years since it was first proposed, the role of heliox in treating patients with acute severe asthma remains unclear.


OBJECTIVES
To determine the effect of the addition of heliox to standard medical care on the course of acute asthma, as measured by pulmonary function testing and clinical endpoints.


SEARCH STRATEGY
Randomised controlled trials were identified from the Cochrane Airways Review Group Asthma Register which is a compilation of systematic searches of CINAHL, EMBASE, MEDLINE, and CENTRAL and hand searching of the 20 most productive respiratory care journals. In addition, primary authors and experts were contacted to identify eligible studies. References from included studies, known reviews and texts were also searched.


SELECTION CRITERIA
Studies were selected for inclusion in the review if they met the following inclusion criteria: 1) randomised, single or double blind, controlled trials; 2) children or adults with a clinical diagnosis of acute asthma seen in emergency departments or equivalent acute care settings; and 3) compared treatment with inhaled heliox to placebo (oxygen or air). Two reviewers independently assessed the studies for inclusion and quality assessment; disagreement was resolved by a third reviewer and consensus.


DATA COLLECTION AND ANALYSIS
Data from all included trials were combined using the Review Manager (Version 4.1) using random effects weighted mean (WMD) and standardised mean differences (SMD), with 95% confidence intervals (95% CI). Homogeneity of effect sizes were tested with the Dersimonian and Laird method with p<0.1 as the cut point for significance. Sensitivity analyses were performed on age (adults vs. children), different helium-oxygen mixtures (80/20, vs. 70/30 or 60/40), methodological quality (Jadad score >2 vs. <3) and method of heliox use (studies designed to washout air in the lungs and replace it with heliox versus studies that used heliox to deliver nebulized therapy).


MAIN RESULTS
This review has been updated in 2002 to include two new trials. A total of six randomised controlled trials were selected for inclusion with a total of 369 acute asthma patients. Five studies involved adults and one study dealt solely with children. Two were assessed as high quality (Jadad score >3). The main outcome variable was spirometric measurements (PEF % predicted, PEF L/min, FEV1 % of predicted, FEV1L). Heliox use did not improve pulmonary functions compared to standard care (SMD = 0.13; 95% CI: -0.09 to 0.34). All pulmonary function tests were recorded during heliox administration (15 to 60 min). The test of homogeneity was not significant (p=0.25). There were no significant differences between groups when adults vs. children, high vs. low quality, and high vs. low heliox dose studies were compared.


REVIEWER'S CONCLUSIONS
The existing evidence does not provide support for the administration of helium-oxygen mixtures to ED patients with moderate to severe acute asthma. At this time, heliox treatment does not have a role to play in the initial treatment of patients with acute asthma. Since these conclusions are based upon between-group comparisons and small studies, they should be interpreted with caution. Additional research in this setting is needed.