Published ahead of print on December 13, 2007, doi:10.1164/rccm.200707-1004OC Am. J. Respir. Crit. Care Med., Volume 177, Number 4, February 2008, 412-418 A more recent version of this article appeared on February 15, 2008
Submitted on July 9, 2007 Negative-Pressure Ventilation: Better Oxygenation and Less Lung InjuryFrancesco Grasso1,1 Physiology and Experimental Medicine, Hospital for Sick Children, Toronto, Ontario, Canada; Department of Critical Care Medicine, Hospital for Sick Children, Toronto, Ontario, Canada; Department of Anesthesia, Hospital for Sick Children, Toronto, Ontario, Canada, 2 Department of Anesthesia, University of Toronto, Toronto, Ontario, Canada, 3 Department of Radiology, Hospital for Sick Children, Toronto, Ontario, Canada; Department of Radiology, University of Toronto, Toronto, Ontario, Canada, 4 Physiology and Experimental Medicine, Hospital for Sick Children, Toronto, Ontario, Canada; Department of Critical Care Medicine, Hospital for Sick Children, Toronto, Ontario, Canada, 5 Department of Critical Care Medicine, Hospital for Sick Children, Toronto, Ontario, Canada, 6 Department of Electrical Engineering, Ryerson University, Toronto, Ontario, Canada, 7 Physiology and Experimental Medicine, Hospital for Sick Children, Toronto, Ontario, Canada; Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada, 8 Physiology and Experimental Medicine, Hospital for Sick Children, Toronto, Ontario, Canada; Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada; Department of Physiology, University of Toronto, Toronto, Ontario, Canada * To whom correspondence should be addressed. E-mail: brian.kavanagh{at}sickkids.ca.
Rationale: Conventional positive pressure ventilation delivers pressure to the airways; in contrast negative pressure is delivered globally to the chest and abdomen. Objectives: To test the hypothesis that ventilation with negative pressure results in better oxygenation and less injury than with positive pressure. Methods: Anesthetized, surfactant depleted rabbits were ventilated for 2.5 h in pairs (positive or negative). Tidal volume was 12 mL/kg, normocapnia maintained by adjusting respiratory rate, and FiO2 was 1.0. Measurements: Lung injury was assessed with histologic scoring, perfusion using thermodilution (global perfusion) and injected intravascular microspheres (regional perfusion), and dynamic CT was used to determine inflation patterns. Main Results: Negative pressure was associated with a higher PaO2, a lower Pa-PETCO2 gradient (despite identical minute ventilation), and less lung injury. Lung perfusion (global and regional) was similar with positive and negative pressure. Positive end-expiratory pressure applied to the airway was more efficiently transmitted to the pleural space than comparable levels of negative end-expiratory pressure applied to the chest wall; however, the oxygenation associated with any level of end-expiratory lung volume was greater when achieved by negative vs. positive pressure. Dynamic CT suggested that lung distension achieved with negative pressure is characterized by greater proportions of normally aerated lung (with less atelectasis) during inspiration and at end-expiration. Conclusion: Negative pressure ventilation results in superior oxygenation that is unrelated to lung perfusion and may be explained by more effective inflation of lung volume during both inspiration and expiration. Key words: lung injury, mechanical ventilation, oxygenation
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