Table 3. Mediation analysis.
| Adjusted Absolute Difference (95% CI)a | p value | |
|---|---|---|
| Univariable Mediation Modelb | ||
| Body height as mediator | ||
| Total effect of sex | -27.6 (-29.7 to -26.0) | < 0.001 |
| Average causal mediation effect of body height | -27.7 (-29.7 to -26.0) | < 0.001 |
| Average direct effect of female sex | 0.1 (-2.5 to 3.0) | 0.940 |
| Body weight as mediator | ||
| Total effect of sex | -27.6 (-29.7 to -26.0) | < 0.001 |
| Average causal mediation effect of body weight | 1.0 (0.4 to 2.0) | < 0.001 |
| Average direct effect of female sex | -28.6 (-30.7 to -26.0) | < 0.001 |
| Default VT as mediator | ||
| Total effect of sex | -27.7 (-29.8 to -26.0) | < 0.001 |
| Average causal mediation effect of titrated VT | 0.0 (-0.0 to 0.0) | 0.150 |
| Average direct effect of female sex | -27.7 (-29.9 to -26.0) | < 0.001 |
| Body height, weight and titrated VT as mediators* | ||
| Total effect of sex | -28.0 (-32.2 to -23.9) | < 0.001 |
| Average causal mediation effect of height | -30.7 (-34.2 to -27.2) | < 0.001 |
| Average causal mediation effect of weight | 3.3 (2.7 to 4.0) | < 0.001 |
| Average causal mediation effect of titrated VT | 0.0 (-0.1 to 0.1) | 0.818 |
| Average direct effect of female sex | -0.7 (-3.8 to 2.5) | 0.671 |
| Multivariable Mediation Modelc | ||
| Body height as mediator** | ||
| Total effect of sex | -28.4 (-30.7 to -26.0) | < 0.001 |
| Average causal mediation effect of body height | -28.4 (-30.4 to -26.0) | < 0.001 |
| Average direct effect of female sex | -0.0 (-2.8 to 3.0) | 0.960 |
| Body weight as mediator*** | ||
| Total effect of sex | -0.3 (-3.1 to 3.0) | 0.820 |
| Average causal mediation effect of body weight | -0.3 (-0.8 to 0.0) | 0.310 |
| Average direct effect of female sex | -0.0 (-2.8 to 3.0) | 0.970 |
| Default VT as mediator**** | ||
| Total effect of sex | 0.1 (-2.6 to 3.0) | 0.939 |
| Average causal mediation effect of titrated VT | 0.2 (0.0 to 0.0) | 0.021 |
| Average direct effect of female sex | -0.0 (-2.8 to 3.0) | 0.968 |
| Body height, weight and titrated VT as mediators* | ||
| Total effect of sex | -27.0 (-31.3 to -22.7) | < 0.001 |
| Average causal mediation effect of body height | -30.1 (-33.5 to -26.6) | < 0.001 |
| Average causal mediation effect of body weight | 3.6 (2.9 to 4.4) | < 0.001 |
| Average causal mediation effect of titrated VT | 0.1 (-0.1 to 0.2) | 0.459 |
| Average direct effect of female sex | -0.7 (-3.9 to 2.5) | 0.679 |
a All estimated generated after 10,000 simulations if not otherwise indicated.
b Mixed–effect mediation model with Quasi–Bayesian confidence intervals, with hospitals and year as random effects and dataset as fixed effect.
c Mixed–effect mediation model with Quasi–Bayesian confidence intervals, with hospitals and year as random effects and dataset as fixed effect and adjusted for: age, OASIS, SOFA, type of admission, pH and PaCO2.
* Confidence intervals estimated from robust clustered standard errors.
** Further adjusted by weight and titrated tidal volume.
*** Further adjusted by height and titrated tidal volume.
**** Further adjusted by weight and height.