Table 3

Cox regression for time to ECO2 >2% (n=321)*

Univariate modelMultivariate model†‡
Hazard Ratio (95% CI)P valueHazard Ratio (95% CI)P value
Expired tidal volume (VTE)
 Per 1 mL/kg increase
 Per standardised unit
1.18 (1.11 to 1.24)
1.33 (1.18 to 1.50)
<0.0011.22 (1.15 to 1.29)
3.75 (2.56 to 5.48)
<0.001
(VTE)2§
 Per unit increase
 Per standardised unit
0.99 (0.99 to 0.99)
1.16 (1.02 to 1.31)
<0.0010.99 (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)
<0.0011.32 (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)
0.0041.42 (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)
0.0041.08 (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)
0.0011.17 (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 ECO2 >2% in the first ventilation, 321 were included in the Cox regression, 23 never reached ECO2 >2%.

  • †Hazard Ratios were not proportional for VTE 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 VTE due to correlation with volume. Taking VTE 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.