Decreased lung injury after surfactant in piglets treated with continuous positive airway pressure or synchronized intermittent mandatory ventilation.

BACKGROUND: Treatment with surfactant (S) decreases lung injury in paralyzed, mechanically ventilated animals. The use of nasal continuous positive airway pressure (CPAP) as an alternative to mechanical ventilation may further improve acute pulmonary outcomes. OBJECTIVES: To evaluate the effect of surfactant (+S, -S) and synchronized intermittent mandatory ventilation (SIMV) on lung morphology and inflammatory markers in 24 spontaneously breathing piglets treated with CPAP or SIMV after saline lavage-induced lung injury. METHODS: After induction of lung injury, animals were randomized to CPAP-S, CPAP+S or SIMV+S and treated for 4 h. Physiologic parameters were continuously monitored. After treatment, animals were euthanized and lungs fixed. Bronchoalveolar lavage (BAL) samples were collected for neutrophil count and H(2)O(2). RESULTS: No physiologic differences were noted. BAL fluid from CPAP-S animals contained more neutrophils and more neutrophil H(2)O(2) than fluid from the SIMV+S or CPAP+S groups (p < 0.05 or greater). Pathologic injury scores were higher in dependent lung regions from CPAP groups (p < 0.05). Injury pattern scores showed greater dependent alveolar inflammation in all (p < 0.02), with more dependent atelectasis in the CPAP groups (p < 0.01). Morphometrics showed less total open alveolar air space in nondependent regions of the SIMV+S group compared to CPAP groups (p < 0.001). Dependent regions showed less total open alveolar air space compared to nondependent regions in the CPAP groups (p < 0.001). CONCLUSIONS: Animals treated with surfactant prior to CPAP or SIMV had less acute lung injury. SIMV+S animals had less open air space in nondependent regions. This suggests, during early ventilatory support, surfactant administration may modulate pulmonary inflammation. CPAP alone without surfactant may not provide optimal pulmonary protection. The addition of mechanical breaths may alter and add to injury.

Standardized lung recruitment during high frequency and conventional ventilation: similar pathophysiologic and inflammatory responses in an animal model of respiratory distress syndrome.

OBJECTIVE: To evaluate standardized lung recruitment strategy during both high frequency oscillation (HFO) and volume-targeted conventional ventilation (CV+V) in spontaneously breathing piglets with surfactant washout on pathophysiologic and inflammatory responses. DESIGN: Prospective animal study. SETTING: Research laboratory. SUBJECTS: Twenty-four newborn piglets. INTERVENTIONS: We compared pressure support and synchronized intermittent mandatory ventilation, both with targeted tidal volumes, (PSV+V, SIMV+V) to HFO. Animals underwent saline lavage to produce lung injury, received artificial surfactant and were randomized to one of the three treatment groups (each n=8). After injury and surfactant replacement, lung volumes were recruited in all groups using a standard protocol. Ventilation continued for 6 h. MEASUREMENTS AND MAIN RESULTS: Arterial and central venous pressures, heart rates, blood pressure and arterial blood gases were continuously monitored. At baseline, post lung injury and 6 h we collected serum and bronchoalveolar lavage samples for proinflammatory cytokines: IL 6, IL 8 and TNF-alpha, and performed static pressure-volume (P/V) curves. Lungs were fixed for morphometrics and histopathologic analysis. No physiologic differences were found. Analysis of P/V curves showed higher opening pressures after lung injury in the HFO group compared to the SIMV+V group ( p<0.05); no differences persisted after treatment. We saw no differences in change in proinflammatory cytokine levels. Histopathology and morphometrics were similar. Mean airway pressure (P(aw)) was highest in the HFO group compared to SIMV+V ( p<0.002). CONCLUSIONS: Using a standardized lung recruitment strategy in spontaneously breathing animals, CV+V produced equivalent pathophysiologic outcomes without an increase in proinflammatory cytokines when compared to HFO.

Surfactant and partial liquid ventilation via conventional and high-frequency techniques in an animal model of respiratory distress syndrome.

OBJECTIVE: To compare the physiologic and pathologic effects of conventional ventilation (CV) and high-frequency ventilation (HFV) during partial liquid ventilation (PLV) with perflubron after surfactant treatment with the results of HFV plus surfactant in an animal lung-injury model created by saline lavage. We also studied the dose effects of perflubron during HFV. DESIGN: Randomized experimental study. SETTING: Research animal laboratory. SUBJECTS: A total of 32 newborn piglets. INTERVENTIONS: After lung injury was induced, the animals were randomized to one of four groups: a) CV + surfactant + perflubron to functional residual capacity (FRC); b) HFV + surfactant + perflubron to FRC; c) HFV + surfactant + 10 mL/kg perflubron; and d) HFV + surfactant. All then received intratracheal surfactant. After 30 mins, perflubron was administered to the PLV groups. The animals underwent ventilation for 20 hrs. MEASUREMENTS AND MAIN RESULTS: Arterial blood gases and hemodynamic variables were continuously monitored. Pulmonary histologic and morphometric analyses were performed after death or euthanasia at 20 hrs. All animals had sustained improvements in arterial/alveolar oxygen ratios, and no differences were observed among groups. All HFV groups required higher mean airway pressures to maintain oxygenation (p <.05). Hemodynamics did not differ among groups. Pathologic analysis demonstrated decreased lung injury in both cranial-dorsal (nondependent) and caudal-ventral (dependent) lobes of all animals treated with PLV when compared with those treated with HFV + surfactant (p <.05). CONCLUSIONS: After surfactant treatment, physiologic support over 20 hrs was similar during HFV with or without perflubron and CV with perflubron. All PLV modalities improved lung pathologic factors uniformly to a greater degree than did HFV + surfactant. A lower treatment volume of perflubron during HFV produced physiologic and pathologic results similar to those produced by perflubron with respect to FRC during either CV or HFV.