Covariates | Univariate model* | Multivariate model | ||||||
Coefficient (95% CI) | P value | R2 (%) | Coefficient (95% CI) | P value | R2 (%) | R2 (%) | ||
ECO2 (unconditional) | 2.90 (2.75 to 3.05) | |||||||
Ventilation characteristics |
Expired
tidal volume
(
V
TE
)
Per mL/kg increase Per standardised unit | 0.37 (0.33 to 0.42) 2.37 (2.10 to 2.65) | <0.001 | 19.3 | 0.32 (0.27 to 0.37) 2.02 (1.71 to 2.33) | <0.001 | 23.1† | 30.8 |
(
V
TE
)
2
Per 100 (mL/kg)2 increase Per standardised unit | −0.86 (−1.0 to 0.7) −1.29 (−1.53 to −1.06) | <0.001 | −0.78 (−0.9 to −0.6) −1.17 (−1.40 to −0.94) | <0.001 | ||||
Mask leak
Per 10% increase Per standardised unit | −0.30 (−0.33 to −0.27 −0.85 (−0.87 to −0.84) | <0.001 | 16.1 | −0.056 (−0.098 to −0.014) −0.16 (−0.29 to 0.42) | 0.009 | |||
Ventilation frequency
Per 10 bpm increase Per standardised unit | −0.17 (−0.23 to −0.11) −0.40 (−0.55 to −0.26) | <0.001 | 7.5 | −0.16 (−0.19 to −0.12) −0.37 (−0.45 to −0.28) | <0.001 | 16.1‡ | ||
Peak inflation pressure
(
PIP
)
Per 10 mbar increase Per standardised unit | 0.41 (0.16 to 0.67) 0.46 (0.18 to 075) | 0.001 | 1.1 | 0.24 (0.064 to 0.29) 0.27 (0.071 to 0.46) | 0.008 | −0.3 | ||
(
PIP)
2
Per 10 mbar2 increase Per standardised unit | −0.60 (−0.87 to −0.33) −0.61 (−0.88 to −0.33) | <0.001 | −0.47 (−0.64 to −0.29) −0.47 (−0.65 to −0.29) | <0.001 | ||||
Clinical factors |
Birth weight
Per kg increase Per standardised unit | 0.78 (0.51 to 1.04) 0.46 (0.30 to 0.62) | <0.001 | 4.4 | 0.81 (0.58 to 1.03) 0.48 (0.34 to 0.61) | <0.001 | 6.8 | 10.9 |
Initial
heart
rate
Per 10 bpm increase Per standardised unit | 0.081 (0.012 to 0.15) 0.17 (0.024 to 0.31) | 0.022 | 0.6 | 0.089 (0.034 to 0.14) 0.19 (0.070 to 0.30) | 0.002 | 1.3 | ||
5
min
Apgar score
Per one unit increase Per standardised unit | 0.054 (−0.021 to 0.13) 0.11 (−0.043 to 0.26) | 0.16 | 0.3 | 0.14 (0.068 to 0.22) 0.29 (0.14 to 0.44) | <0.001 | 2.9 | ||
Log2 of time in seconds Per unit increase Per standardised unit | 0.33 (0.28 to 0.38) 0.64 (0.54 to 0.73) | <0.001 | 2.0 | 0.15 (0.12 to 0.19) 0.29 (0.23 to 0.36) | <0.001 | 0.9 | 0.9 | |
Random-effects parameters | Var (_cons) 1.53 (1.31 to 1.77)§ Var (Residual) 1.53 (1.34 to 1.74) ICC 0.50 |
*Intercorrelation coefficient (ICC) varied between 0.47 and 0.56 for all covariates.
†VTE and mask leak were correlated (Spearman’s rho −0.65). Excluding VTE from the model, beta value for mask leak decreased from −0.056 (−0.098 to –0.014) to −0.28 (−0.31 to –0.24). R2 for VTE alone excluding mask leak from the model was 21.9%. R2 for mask leak excluding VTE was 17.1%.
‡Interaction term for VTE and frequency was significant with beta=−0.015 (−0.020 to −0.0091), p<0.001, the model is displayed without this term for interpretability. VTE and frequency were still significant in the model including the interaction term.
§R2 for the total model: 36.6%.