REDUCTION IN ADVERSE-EFFECTS OF MECHANICAL VENTILATION IN RABBITS WITH ACUTE RESPIRATORY-FAILURE BY TREATMENT WITH EXTRACORPOREAL CO2 REMOVAL AND A LARGE FLUID VOLUME OF DILUTED SURFACTANT

The long-term outcome of infants with severe respiratory distress synd rome can be improved by optimizing surfactant therapy and minimizing t he risk for pulmonary barovolutrauma and oxygen toxicity. The authors hypothesized that this may be achieved with low frequency ventilation and extracorporeal CO2 removal (LFV-ECCO2R), in combination with intra tracheal instillation of a large fluid volume with diluted surfactant. Lung lavaged rabbits were initially ventilated with continuous positi ve pressure ventilation. The rabbits were randomized to treatment with LFV-ECCO2R and surfactant (experimental group), or surfactant only (c ontrol group). In the experimental group, the rabbits were treated wit h a large volume (16 ml/kg) of diluted surfactant (6.25 mg/ml) at a do se of 100 mg/kg body weight. After surfactant therapy, the FiO(2) 100% was gradually decreased. During 4 hours, the extracorporeal bloodflow was adjusted to maintain the PaCO2 between 4.0-6.0 kPa. Thereafter, t he rabbits were allowed to breathe spontaneously with 2.5 cm H2O conti nuous positive airway pressure ventilation (CPAP) and 40% oxygen. In t he control group, the rabbits received the same surfactant therapy. Du ring the study period, the rabbits remained ventilated with an inspira tory oxygen concentration (FiO(2)) of 100% for 4 hours. The ventilator flow was adjusted to maintain the PaCO2 between 4.0 and 6.0 kPa. Ther eafter, positive-end expiratory pressure was decreased to 2.5 cm H2O a nd FiO(2) was gradually decreased to 40%. In the experimental group, F iO(2) was decreased to 40% in a stepwise fashion whereby the PaO2 coul d be maintained easily within the normal range. Extracorporeal flow ra tes during perfusion ranged from 20-35 ml/kg/min and were sufficient t o keep the PaCO2 and pH within normal limits. After 4 hours, the rabbi ts could breathe spontaneously with CPAP and 40% oxygen, while normal blood gas values were maintained. All rabbits survived the experiment. In the control group, all rabbits experienced severe hypoxemia, despi te FiO(2) of 100% oxygen and, during the course of weaning, all rabbit s died because of hypoxia. In conclusion, the present study demonstrat ed that barovolutrauma due to mechanical ventilation, and oxygen toxic ity due to high FiO(2), can be minimized in an animal model of acute r espiratory failure by the combination of LFV-ECCO2R and surfactant the rapy.