Negative-Pressure Ventilation: Better Oxygenation and Less Lung Injury

• Published in: American journal of respiratory and critical care medicine 2008-02, Vol.177 (4), p.412-418
• Main Authors: Grasso, Francesco, Engelberts, Doreen, Helm, Emma, Frndova, Helena, Jarvis, Steven, Talakoub, Omid, McKerlie, Colin, Babyn, Paul, Post, Martin, Kavanagh, Brian P
• Format: Article
• Language: English
• Subjects: Anesthesia. Intensive care medicine. Transfusions. Cell therapy and gene therapy; Animals; Biological and medical sciences; Disease Models, Animal; Emergency and intensive respiratory care; Female; Intensive care medicine; Lung Volume Measurements; Medical sciences; Oxygen Consumption - physiology; Perfusion - methods; Positive-Pressure Respiration - methods; Pulmonary Edema - physiopathology; Pulmonary Gas Exchange; Rabbits; Random Allocation; Respiration, Artificial - adverse effects; Respiration, Artificial - methods; Respiratory Distress Syndrome, Adult - etiology; Respiratory Distress Syndrome, Adult - prevention & control; Sensitivity and Specificity; Tidal Volume; Tomography, X-Ray Computed; Ventilators, Negative-Pressure
• ISSN: 1073-449X; 1535-4970
• DOI: 10.1164/rccm.200707-1004OC

Conventional positive-pressure ventilation delivers pressure to the airways; in contrast, negative pressure is delivered globally to the chest and abdomen. To test the hypothesis that ventilation with negative pressure results in better oxygenation and less injury than with positive pressure. 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 Fi(O(2)) was 1.0. 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 Pa(O(2)), a lower Pa-Pet(CO(2)) 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. 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.