Liquid lung ventilation reduces neutrophil sequestration in a neonatal swine model of cardiopulmonary bypass

Objective: Liquid lung ventilation has been demonstrated to improve cardior espiratory function after cardiopulmonary bypass. We hypothesized that liqu id lung ventilation (LLV) would decrease the pulmonary inflammatory respons e after cardiopulmonary by-pass (CPB). Design: Prospective, randomized, experimental, controlled, nonblinded study . Setting: Animal research laboratory at a university setting. Subjects: A total of 24 neonatal piglets. Interventions: After intubation with a cuffed endotracheal tube, swine were conventionally ventilated. After surgical cannulation, each piglet was pla ced on conventional nonpulsatile CPB and cooled to 18 degreesC (64.4 degree sF). Subsequently, the animals were exposed to 90 mins of low-flow CPB (35 ml/kg/min). Animals were rewarmed to 37 degreesC (98.6 degreesF), removed f rom CPB, and ventilated for 90 min. Ten animals received conventional gas v entilation only (control), seven received initiation of LLV before CPB (pre vention), and seven received initiation of LLV during the rewarming phase o f CPB (treatment), After the animals were killed, the lungs were removed en bloc, The left lobe was dissected and formalin-fixed at 20 cm H2O overnigh t, followed by paraffin embedding, Sections were taken from the paraffin-em bedded lungs, Neutrophil accumulation and lung injury were assessed by hist ochemical staining with leukocyte esterase and morphometrics, respectively. One hundred microscopic images were digitized from each tissue sample for lung morphometrics, and neutrophil counts were obtained from every fifth im age. Measurements and Main Results:Lung tissue sections showed a significantly l ower number of neutrophils per alveolar area in the prevention and treatmen t groups than in the control group (control 681 +/- 65, prevention 380 +/- 49, treatment 412 +/- 101 neutrophils per alveolar area [cells/mm(2)]; p < .05 for both prevention and treatment compared with control). There were no differences in lung injury as assessed with morphometrics or hemodynamic m easurements between any of the three groups, Conclusions: The data suggest that LLV reduces the CPB-induced neutrophil s equestration in the pulmonary parenchyma independent of its effects on the circulatory physiology or evidence of early lung injury.