Published ahead of print on December 13, 2007, doi:10.1164/rccm.200707-1004OC
© 2008 American Thoracic Society doi: 10.1164/rccm.200707-1004OC
Negative-Pressure VentilationBetter Oxygenation and Less Lung Injury1 Physiology and Experimental Medicine, and Departments of 2 Critical Care Medicine and 3 Anesthesia, Hospital for Sick Children, Toronto, Ontario, Canada; 4 Department of Anesthesia, University of Toronto, Toronto, Ontario, Canada; 5 Department of Radiology, Hospital for Sick Children, Toronto, Ontario, Canada; 6 Department of Radiology, University of Toronto, Toronto, Ontario, Canada; 7 Department of Electrical Engineering, Ryerson University, Toronto, Ontario, Canada; and Departments of 8 Laboratory Medicine and Pathobiology, 9 Physiology, and 10 Medicine, and the Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, Ontario, Canada Correspondence and requests for reprints should be addressed to Dr. Brian P. Kavanagh, M.B., Department of Critical Care Medicine, Hospital for Sick Children, 555 University Avenue, Toronto, ON, Canada M5G 1X8. 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 hours in pairs (positive or negative). Tidal volume was 12 ml · kg–1, normocapnia was maintained by adjusting respiratory rate, and FIO2 was 1.0. Measurements and Main Results: Lung injury was assessed with histologic scoring, perfusion using thermodilution (global perfusion), and injected intravascular microspheres (regional perfusion); and dynamic computed tomography was used to determine inflation patterns. 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 versus positive pressure. Dynamic computed tomography 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. Conclusions: 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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