2.6 | Experimental protocol
After starting the above-mentioned intratracheal treatments, the PEEP of the ventilator setting was turned up to 5 cm H2O. A total of 4 h was used for observation for each experiment. During the study period, sodium bicarbonate (1–2 meq/kg/dose) was given to the animals displaying metabolic acidosis (pH < 7.20) with a base excess lower than -8 meq/L. Epinephrine (0.01 mg/kg, one bolus injection) was given to the animals displaying bradycardia (heart rate < 100 beats/min) every 3–5 min if necessary. The arterial blood samples (0.2 mL) were obtained hourly for blood gas analysis (Chiron, Ciba Corning Diagnostics Corporation, MA, USA) at 0 and 30 min and then hourly until the end of experiment.