MATERIALS AND METHODS

Twenty-one mongrel dogs weighing 15-25 kg were anesthetized with pentobarbital sodium (15 mg/kg) and paralyzed with pancuronium bromide (2 mg iv). The dogs were intubated and ventilated with room air at a tidal volume of 15 ml/kg and rate of approximately 12 breaths/min, which was adjusted to achieve an arterial CO2 tension (PhOJ of 30-40 Torr. The animals were placed supine, and catheters were positioned in the femoral artery and pulmonary artery via the femoral vein. The pulmonary arterial catheter was 7 Fr and thermistor tipped (Instrumentation Laboratory). Approximately 15 ml. kg-‘. he1 of Ringers lactate was infused continuously during the 4-h period of the experiment through the central venous port of the pulmonary arterial catheter.