Table 2

Author, date and countryPatient groupStudy type (level of evidence)OutcomesKey resultsStudy weaknesses
Rodrigo G et al, 2004 Six RCTs including 369 patients with acute asthma (five studies involving adults, one study dealing only with children)Meta-analysisSpirometric measurements (PEF l/min, PEF % predicted, FEV1 L, FEV1 % predicted)Use of heliox did not improve pulmonary function compared with standard care (SMD = 0.13; 95% CI: −0.09 to 0.34)Surrogate end points