End-tidal to arterial PCO2 ratio: a bedside meter of the overall gas exchanger performance

Intensive Care Medicine Experimental

Table 4 Gas exchange across P_ETCO₂/PaCO₂ ratio quartiles

P_ETCO₂/PaCO₂ quartiles	I	II	III	IV	p value
Ranges	[0.416,0.709]	[0.709,0.796]	[0.796,0.886]	[0.886,1.16]
Number of patients	N = 52	N = 51	N = 48	N = 49
PaO_2, mmHg	62.6 [55.0; 73.6]	71.0 [63.5; 81.2]	75.0 [65.8; 89.7]	71.8 [65.0; 83.0]	0.001
PaCO_2, mmHg	48.1 [43.3; 53.8]	46.0 [41.1; 52.4]	44.7 [40.4; 50.1]	39.9 [36.5; 43.2]	< 0.001
PaO₂/FiO₂	103 [76.7; 131]	117 [102; 158]	164 [139; 203]	171 [143; 207]	< 0.001
Arterial pH	7.36 (0.07)	7.37 (0.07)	7.38 (0.08)	7.40 (0.07)	0.009
SaO₂	90.8 [87.5; 94.0]	92.4 [90.5; 95.3]	94.1 [92.0; 96.2]	94.7 [92.7; 96.8]	< 0.001
Venous pH	7.34 (0.07)	7.35 (0.06)	7.36 (0.07)	7.37 (0.05)	0.141
PvO_2, mmHg	42.1 [39.8; 45.6]	42.0 [39.2; 44.1]	40.8 [37.2; 49.0]	42.9 [40.0; 47.7]	0.667
PvCO_2, mmHg	50.2 [46.9; 56.9]	52.0 [46.8; 55.3]	49.8 [45.0; 56.5]	45.8 [41.0; 47.3]	< 0.001
SvO₂	73.5 [70.1; 76.5]	74.3 [71.4; 77.7]	76.4 [70.0; 80.6]	77.7 [72.6; 81.0]	0.073
v-a difference	2.31 [1.30; 2.83]	2.46 [1.92; 2.83]	2.65 [2.00; 3.26]	2.10 [1.56; 2.53]	0.036
Q_s/Q_t	0.54 [0.40; 0.66]	0.42 [0.36; 0.48]	0.35 [0.27; 0.43]	0.39 [0.30; 0.46]	< 0.001
V_d/V_t	0.74 [0.67; 0.80]	0.63 [0.60; 0.68]	0.56 [0.51; 0.61]	0.47 [0.44; 0.55]	< 0.001

Variables are expressed in medians and IQR or means ± SD according to distribution. P for Mann–Whitney test or one-way Anova. Q_s/Q_t: shunt fraction; V_d/V_t: dead space fraction