Objective: To evaluate the effects of a double-lumen, two-stage endotracheal tube an gas exchanges (ventilatory efficiency) during conventional mechanical ventilation, using a ventilator in rabbits. Design: Prospective, randomized, crossover laboratory animal trial. Setting: Research laboratory in the Beijing Children's Hospital. Subjects: Five adult New Zealand rabbits, weighing 3.2 to 3.7 kg. Interventions: A new type of endotracheal tube - the double-lumen two-stage endotracheal tube - was designed and tested for ventilation efficiency in rabbits with normal and injured lungs. The new tube (size 3.0 mm) was made out of two Porter endotracheal tubes (size 3.0 mm) by adhering two vertical cross-sections at the distal end of the two tubes. The new tube and a conventional endotracheal tube of the same size (inner diameter 3.0 mm) were randomly used in pressure control ventilation. Each trial was maintained for 30 mins. Measurements and Main Results: Effects from the two endotracheal tubes on pulmonary mechanics, hemodynamics, and gas exchange were observed. We measured peak inspiratory pressure, positive end-expiratory pressure (PEEP), intrinsic PEEP, mean airway pressure, acid arterial blood and mixed expired gas variables (Pao(2), Paco(2), pH, and mixed expired gas Pco(2)). The new endotracheal tube acutely increased CO2 elimination in all animals with normal and injured lungs. Paco(2) decreased from 46 +/- 4 to 36 +/- 5 torr(6.1 +/- 0.5 to 4.8 +/- 0.7 kPa; p<.01) in normal lungs and from 48 +/- 5 to 36 +/- 5 (6.4 +/- 0.7 to 4.8 +/- 0.7 kPa; p<.01). Meanwhile, tidal volume fraction decreased from 0.48 +/- 0.07 to 0.35 +/- 0.05 (p<.01) and from 0.56 +/- 0.07 to 0.40 +/- 0.07 (p<.01) in normal and injured lungs, respectively. Intrinsic PEEP of the new tube slightly increased, but there were no significant differences in comparison with the conventional tube. Conclusion: Compared with the conventional endotracheal tube, the new double-lumen, two-stage endotracheal tube reduced Pace, by decreasing anatomical deadspace in rabbits with normal and injured lungs under pressure control ventilation, thus enhancing ventilatory efficiency and reducing ventilator-induced injury.