[The comparison of IRV and PEEP on gas exchanges in RDS dogs]

The purpose of this study was to determine effects of inverse ratio ventilation (IRV) on gas exchanges and circulatory systems in 47 dogs in which bronchi were lavaged with 20 ml.kg-1 saline. The dogs were classified into 6 groups and were ventilated with IE ratio of 1:2 (control), 2:1 (2:1 IRV), 3:1 (3:1 IRV), 1:2 with 5 cmH2O PEEP (1:2 PEEP 5), 2:1 with 5 cmH2O PEEP (2:1 PEEP 5), and 3:1 with 5 cmH2O PEEP (3:1 PEEP 5), using Servo ventilator 900C. In all the groups, PaO2 decreased from about 140 mmHg to about 50 mmHg by bronchial lavage. In both 2:1 IRV and 3:1 IRV groups, PaO2 increased gradually during 8 hours. In the 3 PEEP groups, PaO2 increased markedly compared with the groups without PEEP after their ventilatory modes were used. In all the groups, PaCO2 increased after lavaging. Although PaCO2 did not change during 8 hours in control and 1:2 PEEP 5 groups, PaCO2 decreased slightly with 4 or 5 hours after RDS was induced in 3:1 IRV and 2:1 PEEP 5 groups. In 2:1 IRV and 3:1 PEEP 5 groups, PaCO2 decreased with time. Extravascular thermal volume index (ETVI) significantly decreased in IRV groups compared with control group. The peak airway pressure was much lower in IRV groups, when it was compared with the group whose IE ratio was 1:2. Although cardiac index decreased slightly in all groups, there was no significantly differences among them.