We hypothesized that animals treated with nasal continuous positive airway pressure following surfactant administration (NCPAP+S) would have decreased inflammatory markers and pathologic lung injury compared with those treated with synchronized intermittent mandatory ventilation following surfactant administration (SIMV+S) or NCPAP without surfactant administration (NCPAP-S).
Methods We compared NCPAP+S, SIMV+S, and NCPAP-S in spontaneously breathing piglets with saline lavage induced lung injury (PaO2 of 80-100 torr in FIO2 1.0). Animals were randomized to NCPAP (n=7), SIMV+S (n=8), or to NCPAP+S (n=10) and were treated for 4 hours. Settings were PIP 20, PEEP 5, rate 20, VT 8ml/kg. NCPAP was initiated at 5cmH2O. Oxygen was adjusted to maintain PaO2 of 80-100 torr. Physiologic parameters and arterial blood gases were continuously monitored and recorded hourly. Bronchoalveolar lavage (BAL) samples were collected for neutrophil count and H2O2 after 4 hours treatment. Animals were euthanized and lungs were fixed for histopathologic scoring and morphometric analysis. Physiologic data were analyzed using ANOVA for repeated measures. Neutrophil count and H2O2 were analyzed using ANOVA.
Results No physiologic differences were noted between groups. BAL fluid from NCPAP-S piglets contained significantly more neutrophils than those from the SIMV+S group (p≤0.05) with a similar trend in the CPAP+S group (p≤0.17). BAL cells from the SIMV+S and NCPAP+S groups contained significantly less H2O2 than cells from the NCPAP-S group (p≤0.01 and 0.03 respectively). Morphometric analysis showed more total open alveolar airspace in the dorsal regions in the NCPAP+S group compared to the NCPAP-S group (p≤0.01) with a similar trend in the SIMV+S vs NCPAP-S groups (p≤0.09). Conversely, ventral regions showed more total open alveolar airspace in the NCPAP-S group compared to NCPAP+S or SIMV+S (p≤0.05 and 0.01 respectively).
Conclusion Animals treated with surfactant prior to initiation of respiratory support had less evidence of acute lung injury after treatment for 4 hours. Morphometric data suggest surfactant administration results in regionally dependent lung expansion.