studious mood objective: To determine the issue of the addition of heliox to standard medical care onward the course of acute asthma.

Design: Systematic review of randomized and nonrandomized prospective, controll trials of children and adults that compared heliox to placebo when used in conjunction with other standard acute treatments.

Main issue measures: Pulmonary function tests, hospital admissions, physiologic measures, side meanings and clinical outcomes.

Results: Seven trials were gooded for inclusion, with a total of 392 patients with acute asthma. Six studies involved adults, and the same study dealt solely with children. The main issue variable was spirometric measurements (peak expiratory grow or FE[V.sub.1]) in six trials. pair studies evaluated the effect of heliox upon airways resistance. No significant differences were demonstrated between heliox or oxygen/air assemblages (standardized mean difference [SMD], - 020; 95% confidence interval [CI], - 091 to 051; p = 06) However, the four studies that used heliox to deliver nebulized therapy showed a nonsignificant increase in pulmonary function (SMD - 021; 95% CI, - 043 to 001; p = 006) In sum of two units studies of the same subgroup heliox mixtures produc a significantly greater increase of heart rate than oxygen/air (weighted mean difference, 90; 95% CI, 127 to 168; p = 002) However, the four studies that used heliox to deliver nebulized therapy reported a nonsignificant difference in hospital admissions (odd ratio, 107; 95% CI, 046 to 248; p = 09) Overall, heliox appears to be safe and well tolerated.

Conclusions: The existing evidence does not provide support for the administration of helium-oxygen mixtures to turn of events department patients with moderate-to-severe acute asthma. However, these conclusions are based upon between-group comparisons and small studies, and these be deriveds should be interpreted with caution.

fundamental note words: acute asthma; emergency treatment; heliox; helium; oxygen; status asthmaticus

Abbreviations: CI = confidence interval; ed = emergency department; OR = additionals ratio; PEF = peak expiratory flow; SMD = standardized mean difference; WMD = weighted mean difference

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Helium and oxygen mixtures (heliox) have been used sporadically in respiratory medicine for decades. For example, as early as 1935 heliox was introduced to the medical community for treatment of upper and lower airway obstruction. (1) The interest in heliox for treatment of asthma became prominent in the 1980 when deaths from asthma began to rise. becoming to their low density with value to air (80% helium/20% oxygen mixture has a density approximately single third that of air), heliox mixtures have the potential to decrease airway resistance and therefore decrease the work of breathing in those situations associated with increased airway resistance. Thus, they may provide benefit to patients with obstructive lesions of the larynx, trachea, and airways. Additionally, research using heliox mixtures has demonstrated a greater percentage of lung particle retention and a large delivery of albuterol from the two metered-dose inhalers and nebulizers. (23) This advises that one of the beneficial tenors of heliox use in reactive airway diseases may include improved deposition of aerosolized bronchodilators. (45) Heliox has also been commended as a useful adjunct in the adult patient with chaste asthma, both during spontaneous ventilation as well as during mechanical ventilation. (6-9) Reports describing the use of heliox in children with asthma also provide conflicting eventuates with some failing (10) and others showing a benefit. (11) However, often of the evidence arises from either small trials or uncontroll studies. Fortunately, controll trials comparing the effectiveness of heliox to oxygen for [beta]-agonist therapy have newly been performed. (12,13)

abundant is unknown regarding the use of heliox in acute asthma. (14) First, without controll studies, the force of heliox is difficult to assess. other the duration of administration and optimal helium/oxygen mixture remain undetermined. Finally, the costliness of treatment is relatively high. Given the abovementioned controversies, the ne for a systematic review exists. However, to date no systematic reviews forward this topic have been published, and it is not surprising that heliox use is variable and institution specific. Despite the lapse of > 60 years since its use was first propos the part of heliox in treating patients with acute hard asthma is unclear. The objective of this systematic review was to determine the drift of the addition of heliox to standard medical care upon the course of acute asthma, as measured through pulmonary function and clinical completion points.

MATERIALS AND METHODS

Search Strategy for Identification of Studies

A search was carried abroad using five search strategies to identify potentially relevant trials. Firstly, we searched MEDLINE (1966 between the sides of 2002), EMBASE (1980 through 2002) and CINAHL (1982 from one side 2002) databases using the following medical subdue headings, full text, and keyword terms: Emerg * OR acute asthma OR status asthmaticus OR relentless asthma AND heliox OR helium AND oxygen Secondly an advanced search of the Cochrane Controll Trials Register was complet using the above-mentioned search strategy. Thirdly, intimations from included studies, reviews, and thesiss were searched for citations. Fourthly, authors of the studies were contacted to locate other unpublished or "in progress" studies that met the inclusion criteria. Finally, a hand searching of the 20 greatest in quantity productive respiratory care journals was completed

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