Fig. 4

Effect of vitamin C on the duration of ventilation by the duration of ventilation in the control group. The horizontal dashed line indicates the null effect. The diagonal line shows the meta-regression line for the eight trials, with P = 10⁻⁷ for the test that the slope is not null. Vitamin C was administered orally (open circles) or intravenously (filled circles). The regression line follows the formula ln(RoM) = 0.150–0.263 × log₁₀(length of ventilation). For example, for a ventilation time of 100 h (log₁₀[100] = 2), the formula gives ln(RoM) = − 0.377, and predicts a vitamin C effect of RoM = 0.69, i.e., a 31% shorter ventilation time. The Sadeghpour trial [19] is not included in the statistical model, since the dropout rate was high; however, it is overlaid here for information. For calculations, see Additional file 2. RoM ratio of means [22]