Correlation between pulmonary gas exchange and basal and nitroglycerin (GTN)-induced exhaled nitric oxide (eNO) in patients undergoing cardiac surgery

Abstract

The relationship between eNO and events in the alveolar-capillary unit in acute lung injury remains to be established. Since endogenous eNO largely originates from the airway epithelium, but nitroglycerin (GTN)-induced eNO is due to microvascular/alveolar metabolism, we have proposed to use basal and GTN-induced eNO as metabolic markers of the airway--and microvascular/alveolar function, respectively. The current work investigates the relationship between basal and GTN-induced eNO and oxygenation parameters (PaO(2)/FiO(2) ratio) in patients undergoing cardiac surgery utilising cardiopulmonary bypass (CPB). Breath by breath eNO measurements were made in 10 patients before, and 1 and 3 h after CPB either under basal conditions or following intravenous administration of GTN (1, 2 and 3 microg/kg). Basal eNO remained unchanged, whereas GTN-induced eNO was reduced following CPB. Also, there was a transient reduction in PaO(2)/FiO(2) ratio 1 h after CPB (32+/-4 vs. 44+/-3 kPa). A negative correlation was found between oxygenation and basal eNO by Pearson's correlation test and linear regression analysis suggesting that decreased oxygenation was associated with increased basal eNO. In contrast, a decrease in GTN-induced eNO positively correlated with reduced oxygenation index (R=0.533, p=0.002). These data suggest that differential relationships exist between basal and nitrovasodilator-induced eNO and oxygenation indices during subclinical lung injury in patients following CPB and that GTN-induced eNO evolution may reflect better microvascular events and injury.