Chest
Laboratory and Animal InvestigationsEffects of Positive End-Expiratory Pressure and Body Position on Pulmonary Blood Flow Redistribution in Mechanically Ventilated Normal Pigs
Section snippets
Animal Preparation and Experimental Protocol
The study was approved by the University of Lyon Animal Research Committee. The investigation was performed in seven healthy pigs (mean [± SD] weight, 26.1 ± 1.1 kg) of both genders, who were premedicated with an IM injection of xylazine (20 mg), ketamine (70 mg), and droperidol (5 mg). Anesthesia was induced with 100 mg IV propofol followed by a continuous infusion of 350 mg/h. Analgesia was performed with repeated injections of fentanyl (100 μg) every 30 min. A continuous IV infusion of
Hemodynamics and Gas Exchange
Mean pulmonary artery pressures and pulmonary wedge pressures were significantly higher in PP-PEEP than in PP-ZEEP (Table 1). Cardiac output was, on average, significantly lower in PP-PEEP than in SP-PEEP. Arterial oxygenation was significantly higher in the PP than in the SP at both ZEEP and PEEP.
PBF Heterogeneity
The complete extraction of microspheres by the pulmonary circulation was achieved in our study since no radioactivity was found in the kidney or the heart. The number of microspheres was large,
Discussion
In this study, we found the following in mechanically ventilated normal pigs: (1) the magnitude of redistribution of PBF toward the anterior and peripheral regions in the PP-ZEEP condition was significantly increased in the PP-PEEP condition; (2) the PEEP-induced shift of PBF to the posterior in the SP was reversed by the PP; and (3) compared with the SP, the PP resulted in a more homogeneous distribution of PBF.
Conclusion
In normal mechanically ventilated pigs, the PP reduced anterior-to-posterior difference through PBF redistribution along the vertical axis. In addition, the PP induced a shift in perfusion toward the superior and peripheral regions. Both effects were more marked at PEEP.
Acknowledgment
The authors thank Véronique Berthier for her help with the preparation of the animals.
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