Correlation Of CT Pulmonary Artery Obstruction Index With Blood Gas Values And Right Heart Function

OBJECTIVE.The purpose of our study was to investigate the relation between the pulmonary artery obstruction index assessed with helical CT and impairment in blood gases and right heart function in patients with acute pulmonary embolism. SUBJECTS AND METHODS.Helical CT pulmonary angiography was performed in 149 patients who were suspected of having acute pulmonary embolism and selected as being free of underlying cardiopulmonary disease.Findings consistent with acute pulmonary embolism were observed in 64 patients and without pulmonary embolism were observed in 25 patients.The severity was assessed by the pulmonary artery obstruction index,defined as[∑(n×d)/40]×100%,where n is the number of segmental arteries occluded and d is the degree of obstruction.1.The statistical difference of the arterial blood gas values and Pulmonary artery pressure,RV/LV between the two groups of patients(those with and those without pulmonary embolism)was evaluated using the Mann-Whitney U test.2.Spearman's rank correlation coefficients were used to assess the correlation between the index of arterial obstruction and PaO₂;PaCO₂;SaO₂;P_(A-a)O₂;PaO2_c;Pulmonary artery pressure;RV/LV.3.Blood gases and Pulmonary artery pressure,RV/LV were comparatively evaluated below and above different index values(from 30%to 70%) and different PaCO₂ values(30,35,and 40 mm Hg)as possible indexes of embolism severity using the same test.The level of significance was set at 99%(p=0.01). RESULTS.1.The values of PaO₂,PaCO₂ and SaO₂ were significantly lower(p= 0.000,p=0.000,and p= 0.007,respectively)and the values of P_A-a)O₂,Pulmonary artery pressure and RV/LV were significantly higher(p=0.000,respectively)in the pulmonary embolism group than in the no-pulmonary-embolism group.2.A significant correlation was observed between the obstruction index and PaO₂,PaCO₂, SaO₂,P_(A-a)O₂,PaO2_c,Pulmonary artery pressure and RV/LV(r=—0.451～—0.576,r=0.464～0.773,p=0.000).3.Using cutoff values for the pulmonary artery obstruction index of 30%,40%,50%,60%and 70%,,we observed that PaO₂, PaCO₂,P_(A-a)O₂,PaO_2c,RV/LV differed significantly between above and below the 30%,40%,50%,60%,and 70%cutoffs.SaO₂ differed significantly for the cutoff values of 30%,40%,60%,70%.The same was observed for Pulmonary artery pressure at 30%,40%,70%.4.Comparisons for PaCO₂ showed that a value of 35 mmHg significantly separates levels of the pulmonary artery obstruction index(p= 0.000).5.The pulmonary artery obstruction index 30%value showed a 87% sensitivity,80%specificity and 85.9%accuracy for indicating PaO₂ less than 80mmHg.CONCLUSION.The pulmonary artery obstruction index may be an effective method for the assessment of severity of impairment in respiratory function and right heart function in patients with acute pulmonary embolism.