Table 2.

Data are presented as mean (sd). The first statistical change compared with 14 cm H₂O PEEP is indicated by *P<0.05 was considered significant. Tidal volume (VT), Airway dead space (VD_aw), Alveolar dead space (VD_alv), Alveolar dead space to alveolar tidal volume ratio (VD_alv/VT_alv), Normalized slope of phase III (Sn_III), Amount of expired CO₂ within one breath (VTCO₂,_br), Volume of phase III to tidal volume ratio (VIII/VT), Arterial minus end-tidal partial pressure of CO₂ (Pa-ETCO₂), Arterial partial pressure of O₂ $(P{\text{a}}_{{\mathrm{O}}_2})$, Arterial partial pressure of CO₂ $(P{\text{a}}_{\mathrm{C}{\mathrm{O}}_2})$, Fraction of inspired oxygen $(F{\mathrm{I}}_{{\mathrm{O}}_2})$

Dead space variables, blood gas analysis and compliance during the decremental PEEP trial
PEEP (cm H2O)	14	12	10	8	6	4	2	0
VT (ml)	472 (80)	476 (77)	474 (80)	473 (77)	472 (76)	471 (78)	474 (81)	473 (81)
VDaw (ml)	214 (40)	209 (42)	204 (39)	196 (40)*	188 (39)	182 (36)	174 (32)	167 (26)
VDalv (ml)	52 (37)	52 (34)	47 (31)	45 (33)	42 (33)*	35 (32)	39 (31)	35 (29)
VDBohr/VT	0.48 (0.06)	0.47 (0.07)	0.45 (0.07)*	0.43 (0.07)	0.40 (0.07)	0.38 (0.07)	0.35 (0.07)	0.33 (0.07)
VDEnghoff/VT	0.57 (0.07)	0.55 (0.08)	0.53 (0.08)*	0.52 (0.08)	0.49 (0.08)	0.47 (0.09)	0.46 (0.08)	0.44 (0.08)
VDalv/VTalv	0.19 (0.11)	0.18 (0.1)	0.17 (0.09)	0.15 (0.09)	0.14 (0.1)*	0.12 (0.1)	0.13 (0.09)	0.11 (0.09)
SnIII (mm Hg ml−1)	0.95 (1.19)	0.73 (0.64)	0.62 (0.31)	0.62 (0.43)	0.58 (0.33)	0.48 (0.25)*	0.47 (0.26)	0.50 (0.21)
VTCO2,br (ml)	12.5 (3.3)	13.3 (3.7)*	13.9 (3.7)	14.3 (3.6)	14.7 (3.7)	15.2 (3.7)	15.7 (3.8)	16.0 (3.9)
VIII/VT	0.42 (0.14)	0.39 (0.13)	0.41 (0.14)	0.43 (0.13)*	0.46 (0.13)	0.46 (0.13)	0.48 (0.12)	0.51 (0.11)
Pa-ETCO2 (mm Hg)	3.6 (2.8)	3.4 (2.5)	3.7 (2.6)	3.2 (2.5)	2.9 (2.7)	2.7 (2.4)	3.1 (2.4)	2.8 (2.5)*
$P{\text{a}}_{\mathrm{C}{\mathrm{O}}_2}$ (mm Hg)	43 (5)	43 (5)	44 (5)	43 (5)	42 (5)	42 (5)	42 (5)	41 (5)*
$P{\text{a}}_{{\mathrm{O}}_2}$ (mm Hg)	138 (35)	140 (32)	145 (25)	145 (24)	145 (23)	139 (21)	132 (24)	127 (23)*
$P{\text{a}}_{{\mathrm{O}}_2}/F{\mathrm{I}}_{{\mathrm{O}}_2}$ (mm Hg)	346 (87)	349 (80)	359 (71)	371 (71)	372 (68)	357 (65)	338 (72)	324 (70)*
Dynamic compliance (ml cm H2O−1)	34 (6)	36 (8)	35 (6)	35 (7)	35 (7)	34 (7)	33 (7)	31 (7)*