399

Abstract

Introduction: iNO challenge in patients with PAH and normal pulmonary capillary wedge pressure is one method to test vasoreactivty and determine possible therapeutic options. A positive test is defined as a decrease in mean PA pressure by >10 mmHG to a level less than 40mmHG with preserved cardiac output(CO). Fick and Thermodilution(TD) methods of calculating CO are commonly used to determine change in CO. Hypothesis: We propose that there are discrepancies between the Fick CO vs TD CO following iNO challenge. Methods: Retrospective chart review of 131 patients who underwent right heart catherization over in a 1 year period in a teaching institution. A Pearson correlation was used to determine strength of correlation between pre iNO CO by Fick(PreFickCO), pre iNO CO by TD(PreTDCO), post iNO CO by Fick(PostFickCO) and post iNO CO by TD(PostTDCO). PA oxygen saturation pre and post iNO was also evaluated. They were then compared with T-test. Results: Of the 131 patients, 45 (34%) had iNO challenge at 40ppm with 100% oxygen. Twenty one (16%) had both TD and Fick calculated before and after the iNO. Pre and postFickCO had a significantly weaker correlation(r=0.47,p=0.03) when compared to Pre and Post TD CO(r= 0.9 (P<0.001). PreFickCO and PreTDCO had a relatively stronger correlation(r=0.5, p=0.01) than PostFickCO and PostTDCO(r=0.37, p=0.09). PA Saturations were significantly higher post iNO with an average of 80% vs 69% pre iNO. The Post Fick CO differed from the Post TD CO by an average of 2 L/min(p<0.001). Conclusions: In patients with PAH, the CO is important in prognosis and to determine whether the patients have a positive vasodilation challenge or not. The CO determination by both TD and Fick correlate pre-iNO but not post iNO. The weak correlation of the PostFickCO can be explained by the administration of 100% O2 with the iNO and the fact that iNO increases ventilation-perfusion matching. TD CO has a much stronger correlation pre and post iNO, as its method of calculation is not dependent on the arterial or PA saturations. Therefore, for iNO vasoreactivty testing in patients with pulmonary hypertension, TD CO should be used rather than Fick CO as it has a much stronger correlation before and after the iNO.