We identified 742 unique citations, six of which met our inclusion criteria ( Figure 1 outlines the reasons for exclusion). Most reports excluded enrolled neonates or were retrospective or uncontrolled in design. Chance corrected agreement was excellent (kappa = 0.91, 95% confidence interval = 0.73-1.1). Table 1 presents a complete description of our quality assessment. Only one trial did not report allocation concealment [20] . Although effective blinding of surfactant is challenging, two trials reported blinding of the PICU team [12, 20] . The two Flow diagram of included trials Flow diagram of included trials. RCTs, randomized controlled trials. groups were generally well matched in terms of baseline characteristics in most trials. The most significant imbalance was the numerically higher number of immunosuppressed patients in the placebo group. These patients had higher mortality (56%) than the immunocompetent group (13%). The authors attempted to adjust for this imbalance with logistic regression, which suggested that the treatment effect seemed to be relatively consistent between the two groups [12] . Only one trial reported a priori criteria for rescue therapy [13] . Table 2 describes the included trials. Three trials enrolled exclusively infants with RSV-induced respiratory failure [20, 21] or with severe bronchiolitis [22] . The remaining three trials enrolled a heterogeneous group of patients with ARDS or ALI [12, 23, 24] . While the individual treatment protocols varied, all trials used comparable doses (50-100 mg/kg phospholipids) of natural or modified natural surfactants and each patient typically received one or two doses. A variety of interventions were used in the control groups: no intervention, air placebo or similar sedation and ventilation manoeuvres without a placebo. Although one study [20] used a modified natural surfactant, all the products used contained surfactant proteins B and C. All studies administered surfactant early in the course of respiratory failure; most patients were treated within 12-48 hours of requiring mechanical ventilation.