Hemodynamic and gas exchange response to inhaled nitric oxide and prone positioning in acute respiratory distress syndrome patients

Objective: To analyze the single effect and the interaction of prone position and inhaled nitric oxide (iNO) on lung function and hemodynamic variables. Design: 2 x 2 factorial trial. Setting: Department of intensive care medicine at a university hospital. Patients: Fourteen patients on volume-controlled mechanical ventilation for acute respiratory distress syndrome (ARDS), Intervention: Four experimental conditions, each one characterized by the patient's position (supine or prone) with iNO or without iNO. Measurements and Results: Hemodynamic and gas exchange data were collected for each experimental condition. Pao(2) was increased both by positioning (p < .01) and iNO (p < .01); iNO caused also a reduction in venous admixture (p < .01), pulmonary artery pressure (p < .01), and pulmonary vascular resistance index (p < .05). We could not demonstrate any significant interaction between the two treatments. The average effect of prone positioning was the same both with and without iNO, whereas the average effect of iNO was the same in both the prone and the supine position. Conclusion: In the studied acute respiratory distress syndrome patients the average effects of iNO and positioning on oxygenation were additive and no interaction could be shown. A strategy including both treatments could warrant the best improvement in oxygenation, and should take into account the individual response to each treatment and the possible combination of the two.