The influence of acute hypercapnia on the quantity and oxidative metabolism of bronchoalveolar lavage-derived leukocytes in the mechanically ventilated rabbit.

Background: Permissive hypercapnia exerts a protective influence in tissue injury, possibly by attenuating free radical activity. Increased CO2 concentrations may decrease the production of phagocyte reactive oxygen intermediates (ROI). In this study, we used bronchoalveolar lavage (BAL) to determine whether isooxic permissive hypercapnia due to hypoventilation would influence neutrophil recruitment into alveolar spaces and ROI production of BAL phagocytes, as measured by luminol dependent chemiluminescence.

Material/methods: 27 Chinchilla rabbits randomized into three groups: control group (C; n=7), normocapnia (NC; n=10), and hypercapnia (HC; n=10) were anaesthetized with pentobarbitone and intubated. Bronchoalveolar lavage was obtained either after intubation (controls) or after mechanical ventilation lasting 240 minutes under normocapnia or permissive hypercapnia conditions. BAL cells were counted and luminol-dependent chemiluminescence estimations were performed.

Results: The BAL neutrophil count was significantly higher in the hypercapnia group than in normocapnia animals. The chemiluminescence of opsonized zymosan-stimulated cells was significantly higher in the normocapnia group than in the controls; the differences between the HC and NC animals, and between the HC and control animals, did not reach statistical significance.

Conclusions: In the mechanically ventilated rabbit under pentobarbitone anaesthesia, acute isooxic hypercapnia due to hypoventilation increases neutrophil BAL count, without direct impact on mixed BAL-cell chemiluminescence; moreover, conventional ventilation increases the chemiluminescence of opsonized zymosan-stimulated BAL cells