eCO levels before and after steroid treatment. The WMD of eCO levels before and after steroid treatment is 1.98 ppm (95%CI: 0.53 to 3.43) using the random effects model. Test for heterogeneity I
2 = 94%. SD: standard deviation; IV: inverse variance; CI: confidence interval; WMD: weighted mean difference; eCO: exhaled carbon monoxide.