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

Table 3 Lung-specific physiological variables in the first four days of ventilation according to 28-day mortality

	All Patients (n = 927)	Non-Survivors (n = 266)	Survivors (n = 661)	p value*
Dead space fraction by HB
At start of ventilation	0.58 ± 0.11	0.60 ± 0.11	0.58 ± 0.11	< 0.001
Day 01	0.62 ± 0.10	0.64 ± 0.09	0.61 ± 0.11	< 0.001
Day 02	0.64 ± 0.10	0.67 ± 0.09	0.63 ± 0.10	< 0.001
Day 03	0.67 ± 0.09	0.69 ± 0.08	0.65 ± 0.10	< 0.001
p value (interaction survival × day)		0.005
Dead space fraction direct
At start of ventilation	2.22 ± 0.55	2.28 ± 0.61	2.19 ± 0.52	0.022
Day 01	2.35 ± 0.54	2.40 ± 0.55	2.33 ± 0.54	0.036
Day 02	2.48 ± 0.58	2.60 ± 0.63	2.44 ± 0.54	< 0.001
Day 03	2.62 ± 0.65	2.77 ± 0.71	2.56 ± 0.61	< 0.001
p value (interaction survival × day)		< 0.001
Ventilatory ratio
At start of ventilation	1.72 ± 0.60	1.77 ± 0.56	1.70 ± 0.62	0.114
Day 01	1.85 ± 0.64	1.88 ± 0.53	1.84 ± 0.68	0.142
Day 02	1.99 ± 0.66	2.09 ± 0.60	1.95 ± 0.68	< 0.001
Day 03	2.12 ± 0.70	2.26 ± 0.68	2.06 ± 0.70	< 0.001
p value (interaction survival × day)		< 0.001
end-tidal-to-arterial PCO₂ ratio
At start of ventilation	0.85 ± 0.18	0.81 ± 0.18	0.87 ± 0.18	< 0.001
Day 01	0.84 ± 0.14	0.81 ± 0.14	0.85 ± 0.13	< 0.001
Day 02	0.82 ± 0.14	0.78 ± 0.15	0.83 ± 0.14	< 0.001
Day 03	0.80 ± 0.15	0.77 ± 0.15	0.81 ± 0.14	< 0.001
p value (interaction survival × day)		0.455

Data are median (quartile 25%—quartile 75%)
HB: Harris–Benedict
*Calculated using pairwise contrasts in a mixed-effect generalized linear model considering a Gaussian distribution and with day, group and an interaction day × group as fixed effect, and with patients and center as random effect. A binomial distribution was used for binary variables and a Gaussian distribution for continuous

ISSN: 1364-8535