The role of hypercapnia among hospitalised patients with chronic obstructive pulmonary disease exacerbations

<bold>Background:</bold> Excluding if related to respiratory acidosis (RA), little is known concerning the single role of hypercapnia (Hy) in short- and intermediate-term outcomes of patients with chronic obstructive pulmonary disease exacerbations (ECOPD). <bold>Objective:</bold> To evaluate the association between Hy at admission and outcomes of hospitalised ECOPD patients. <bold>Methods:</bold> In our retrospective analysis, we considered 407 hospitalised ECOPD patients divided into three groups: without RA and Hy (Group 1, N=176), without RA and with Hy (PaCO2 > 45 mmHg, Group 2, N=126), and with RA (pH<7.35) and with Hy (Group 3, N=105). Data about general characteristics, clinical, laboratory, microbiological and outcomes (in-hospital mortality until 3 years) were collected. <bold>Results:</bold> Although patients in Group 3 have more severe functional and clinical characteristics, the mortality rate at 1 year (primary outcome) was similar in Groups 2 and 3 (24% and 25%, respectively), higher if compared with Group 1 (14%). Similar mortality trends were shown from 6 months to 3 years. By a ROC-curve, a threshold value of a PaCO2 ≥ 55 mmHg was associated with the 1-year mortality (Gehan-Breslow-Wilcoxon test p<0.001). In a multivariate Cox regression analysis and compared to patients without RA and without Hy (PaCO2 < 55 mmHg), the hypercapnia with a value of PaCO2 ≥ 55 mmHg, also without RA, was associated with a higher mortality risk at 1 year (HR 2.87; 95% CI 1.60 to 5.14; p<0.001). <bold>Conclusion:</bold> In hospitalised ECOPD patients, hypercapnia itself, albeit compensated, is associated with a worse prognosis in an intermediate-term follow-up. Some considerations should be made on the need to ventilate these patients regardless of RA.