Dead space estimates may not be independently associated with 28-day mortality in COVID-19 ARDS

Table 4 Predictive accuracy of lung-specific physiological variables

	Odds RATIO* (95% CI)	p value	AUC (95% CI)	Brier Score	NRI (95% CI)	p value	IDI (95% CI)	p value
Base model	–	–	0.751 (0.715 to 0.788)	0.167	–	–	–
At start of ventilation
+ Dead space fraction by HB	0.91 (0.74 to 1.11)	0.356	0.751 (0.715 to 0.788)	0.167	0.08 (− 0.07 to 0.23)	0.280	0.001 (− 0.000 to 0.003)	0.165
+ Dead space fraction direct	0.83 (0.67 to 1.02)	0.082	0.754 (0.718 to 0.790)	0.167	0.13 (− 0.02 to 0.28)	0.081	0.005 (− 0.000 to 0.009)	0.025
+ Ventilatory ratio	0.90 (0.71 to 1.14)	0.394	0.752 (0.716 to 0.788)	0.167	0.07 (− 0.08 to 0.22)	0.350	0.001 (− 0.000 to 0.004)	0.067
+ end-tidal-to-arterial PCO₂ ratio	0.93 (0.76 to 1.15)	0.521	0.739 (0.701 to 0.778)	0.168	− 0.13 (− 0.28 to 0.03)	0.106	− 0.009 (− 0.015 to − 0.003)	0.001
Day 01
+ Dead space fraction by HB	1.05 (0.86 to 1.29)	0.619	0.749 (0.712 to 0.786)	0.170	− 0.07 (− 0.22 to 0.08)	0.362	− 0.000 (− 0.003 to 0.004)	0.864
+ Dead space fraction direct	0.90 (0.74 to 1.11)	0.326	0.750 (0.713 to 0.787)	0.170	0.05 (− 0.10 to 0.20)	0.495	0.001 (− 0.003 to 0.006)	0.606
+ Ventilatory ratio	0.99 (0.78 to 1.25)	0.938	0.749 (0.712 to 0.786)	0.170	− 0.00 (− 0.15 to 0.15)	0.996	0.000 (− 0.003 to 0.003)	0.994
+ end-tidal-to-arterial PCO₂ ratio	0.87 (0.71 to 1.08)	0.206	0.743 (0.703 to 0.782)	0.170	− 0.09 (− 0.25 to 0.07)	0.257	− 0.006 (− 0.012 to − 0.000)	0.038

HB: Harris–Benedict; CI: confidence interval; AUC: area under the curve; NRI: net reclassification index; IDI: integrated discrimination index
*Represents the odds ratio for the lung-specific physiological variables in the multivariable model
All models are mixed-effect models with centers as random effect and considering a binomial distribution
All continuous variables were entered after standardization to improve convergence of the model, and odds ratio represent the increase in one standard deviation of the variable

ISSN: 1364-8535