[The protective effects and mechanism of hypercapnia on acute lung injury]

To explore the protective effects of hypercapnia on acute lung injury (ALI) and the possible mechanisms.

Twenty-four healthy New Zealand white rabbits were involved in this study, and randomly divided to three groups, a control group, a therapeutic group, and a prophylactic group (n=8, each). Lipopolysaccharide (1 mg/kg) was injected intravenously to establish the ALI model. Blood gas analysis and artery pressure were monitored. IL-8 and TNF-alpha in the serum and bronchoalveolar lavage fluid (BALF), wet weight/dry weigh (W/D), index of quantitative assessment of histological lung injury (IQA), myeloperoxidase (MPO) and malondialdehyde (MDA) activity in the lung tissue were measured. Apoptosis index of neutrophils were determined.

(1) The mean artery pressure, heart rate, PaCO2, and PaO2/FiO2 changed in the ALI model of the therapeutic group and the prophylactic group [(79+/-6) mm Hg (1 mm Hg=0.133 kPa), (180+/-10)/min, (99+/-13) mm Hg, 250+/-26, (80+/-9) mm Hg, (181+/-12)/min, (95+/-11) mm Hg, 241+/-56, respectively]. In the control group, they were (66+/-10) mm Hg, (139+/-13)/min, (31+/-4) mm Hg, 182+/-35, respectively. The differences were significant compared with the control group (t=4.05, 26.32, 5.36, 28.15, 12.54, 11.07, 16.13, 12.36, P<0.05, 0.01). (2) The levels of W/D, MPO, and MDA in the therapeutic group and the prophylactic group were 1.98+/-0.28, 1.87+/-0.30, (6.1+/-1.6) U/g, (5.8+/-1.5) U/g, (20+/-5) mg/L, (19+/-4) mg/L; while in the control group, they were [2.43+/-0.26, (9.0+/-1.3) U/g, (36+/-8) mg/L] respectively. The difference was significant (t=11.07, 24.46, 2.35, 9.63, 12.34, 25.32, P<0.05, 0.01). (3) The levels of IL-8 and TNF-alpha in the serum and BALF and the apoptosis index in the three groups were (50+/-8) ng/ml, (103+/-49) ng/ml, (94+/-16) ng/ml, (44+/-9) ng/ml, (38+/-9)%, (56+/-5)%, (49+/-7) ng/ml, (96+/-50) ng/ml, (91+/-14) ng/ml, (39+/-6) ng/ml, (39+/-10)%, (55+/-10)%, (91+/-43) ng/ml, (177+/-60) ng/ml, (162+/-15) ng/ml, (67+/-7) ng/ml, (19+/-7)%, (43+/-7)%, respectively. The difference was significant among the three groups (t=7.12, 5.55, 7.30, 3.93, 13.08, 8.00, P<0.05, 0.01 respectively). (4) The apoptosis index of neutrophils was negatively correlated with the levels of IL-8 in the serum and BALF (r=-0.73, -0.72, -0.52, -0.64, -0.73, -0.56, all P<0.05), and the levels of TNF-alpha in the serum and BALF (r=-0.57, -0.78, -0.69, -0.75, -0.82, -0.84, all P<0.05).

Hypercapnia does not affect hemodynamics and has protective effects on ALI.