Chest
Volume 123, Issue 3, March 2003, Pages 882-890
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Reviews
Heliox vs Air-Oxygen Mixtures for the Treatment of Patients With Acute Asthmaa: A Systematic Overview

https://doi.org/10.1378/chest.123.3.882Get rights and content

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 (airO2) 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 airO2 (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 airO2. 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.

Conclusion

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.

Section snippets

Physical Principles

Gas flow in the upper respiratory tract is largely laminar and follows the Hagen-Poiseuille law, which states that fluid flow rate () through a straight tube is related inversely to gas viscosity (μ) and the length (L) of the tube, and is proportional to the pressure gradient (ΔP) and the fourth power of the radius (r): = ΔPπr4/8 μL.1 Helium offers no advantage in laminar flow since gas density (ρ) does not appear in the above-mentioned equation, and gas viscosities are similar among

Search Strategy

MEDLINE (1966 to June 2002), EMBASE (1989 to June 2002), and the Cochrane Controlled Trials Registry were searched for relevant articles. Medical subject headings and text words used in the searches included asthma, helium, and heliox in English. Further articles were identified from the reference lists of relevant articles. Non-English language articles were not included, as they have not been found to add substantially to the body of evidence in reviews.20 During article selection, reviewers

Study Selection

Our search yielded 24 articles, of which 15 articles met the inclusion criteria.456789101112131415161718 There were minor discrepancies between the selections of articles by the authors, and they were resolved easily by consensus. The articles are presented in descending order in Table 1according to the strength of the level of evidence. There were eight RCTs,4567891011 one nonrandomized prospective controlled trial,12 one retrospective case-match controlled trial,13 four before-after case

Discussion

This article reviews the published literature on the use of heliox in patients with acute asthma. The studies included varied widely in design, types of patients recruited, and outcomes collected. Meta-analysis was used only in some of the RCTs,6789 based on the common outcomes of PEFR%, Spo2, and DI. For the majority, significant clinical and statistical heterogeneity (as tested by χ2) prevented pooling of outcomes. These meta-analyses demonstrated an advantage with the use of heliox when

Conclusion

Heliox improves certain respiratory (surrogate) parameters in some asthmatic patients during an attack, but not in others. Heliox may offer 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. Since there is insufficient data, future studies should focus on whether heliox can

Acknowledgment

We thank LTC E. R. Carter, MD, of the Madigan Army Medical Center, Tacoma, WA, for providing us with the raw data from his trial6 and for his helpful comments, and J. S. Rose, MD, of the University of California Davis Medical Center, Sacramento, CA, for providing us with the preprint of his article.4 We also thank the reviewers and Dr. J. P. Kress of the University of Chicago for their insightful comments.

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Support of this work was entirely from institutional/departmental resources.

This work was presented in part at the 11th European Congress of Anaesthesiology. June 5–7, 2001; Florence, Italy.

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