Effect of inhaled nitric oxide on pulmonary function after sepsis in a swine model

Background. Inhaled nitric oxide (NO) has been shown to improve sepsis induced pulmonary dysfunction. This study evaluated the mechanism by which inhaled NO improves pulmonary function in a porcine sepsis model. Methods. After an infusion of Escherichia coli lipopolysaccharide (LPS, 200 μg/kg), animals were resuscitated with saline solution (1 ml/kg/min) and observed for 3 hours while mechanically ventilated, (fraction of inspired oxygen, 0.6; tidal volume, 12 ml/kg; positive end-expiratory pressure, 5 cm H₂O). Group 1 (LPS, n = 6) received no additional treatment. Group 2 (NO, n = 6) received inhaled NO (40 ppm) for the last 2 hours. Group 3 (control, n = 5) received only saline solution without LPS. Cardiopulmonary variables and blood gases were measured serially. Multiple inert gas elimination technique was performed at 3 hours. Wet to dry lung weight ratio was measured after necropsy. Results. Lipopolysaccharide resulted in pulmonary arterial hypertension, pulmonary edema, and hypoxemia. Multiple inert gas elimination technique analysis indicated a significant increase in blood flow to true shunt and high ventilation perfusion distribution (V(A)/Q) areas with an increased dispersion of V(A)/Q distribution. All of these changes were significantly attenuated by NO. Conclusions. Inhaled NO significantly improved LPS induced V(A)/Q mismatching by decreasing both true shunt and high V(A)/Q areas, by decreasing pulmonary edema, and by redistributing blood flow from true shunt to ventilated areas.