Univariate model | Multivariate model†‡ | |||

Hazard Ratio (95% CI) | P value | Hazard Ratio (95% CI) | P value | |

Expired tidal volume (V_{TE}) | ||||

Per 1 mL/kg increase Per standardised unit | 1.18 (1.11 to 1.24) 1.33 (1.18 to 1.50) | <0.001 | 1.22 (1.15 to 1.29) 3.75 (2.56 to 5.48) | <0.001 |

(V_{TE})^{2}§ | ||||

Per unit increase Per standardised unit | 0.99 (0.99 to 0.99) 1.16 (1.02 to 1.31) | <0.001 | 0.99 (0.99 to 1.0) 0.34 (0.22 to 0.52) | <0.001 |

Peak inflation pressure | ||||

Per 10 mbar increase Per standardised unit | 1.24 (1.15 to 1.35) 1.28 (1.17 to 1.40) | <0.001 | 1.32 (1.21 to 1.43) 1.36 (1.24 to 1.50) | <0.001 |

Birth weight | ||||

Per kg increase Per standardised unit | 1.32 (1.09 to 1.59) 1.18 (1.05 to 1.32) | 0.004 | 1.42 (1.17 to 1.72) 1.23 (1.10 to 1.38) | 0.001 |

Initial heart rate | ||||

Per 10 bpm increase Per standardised unit | 1.08 (1.02 to 1.14) 1.18 (1.05 to 1.32) | 0.004 | 1.08 (1.02 to 1.14) 1.17 (1.05 to 1.30) | 0.006 |

Apgar at 5 min | ||||

Per unit increase Per standardised unit | 1.10 (1.04 to 1.16) 1.23 (1.09 to 1.38) | 0.001 | 1.17 (1.11 to 1.24) 1.42 (1.25 to 1.61) | <0.001 |

*Among n=434 included newborns, 113 were censured before analysis due to ECO

_{2}>2% in the first ventilation, 321 were included in the Cox regression, 23 never reached ECO_{2}>2%.†Hazard Ratios were not proportional for V

_{TE}alone, including a quadratic term gave acceptable fit in the multivariate model.‡Mask leak was significant (p<0.001) in univariate model, but not in multivariate model (p=0.26) including V

_{TE}due to correlation with volume. Taking V_{TE}out of the model, mask leak was significant with p<0.001, Hazard Ratio 0.89 (0.86 to 0.93) per 10% increase.§Ventilation frequency was not significant with p=0.63 in the univariate and p=0.18 in the multivariate Cox model and was omitted from the final models.