Hypercapnia at Hospital Admission as a Predictor of Mortality

INTRODUCTION: Hypercapnia is an indicator of ventilatory exhaustion. There is some disagreement regarding whether hypercapnia is also a predictor of mortality. In this prospective study, we aimed to investigate whether hypercapnia can predict in-hospital and 1-year mortality rates in patients with dyspnea or pulmonary diseases. PATIENTS AND METHODS: All patients with dyspnea or pulmonary diseases underwent routine blood gas analysis at hospital admission. During the 12-month enrollment period, 2710 patients were enrolled, and 588 patients with hypercapnia at admission were identified. Of the 1626 normocapnic patients, 62 were randomly selected as controls. In-hospital and 1-year mortality rates were determined. RESULTS: There were significant increases in mortality rate between acute hypercapnic patients and both chronic hypercapnic patients and normocapnic controls. Their in-hospital mortality rates were 17%, 6.7% and 3.2%, respectively. Their 1-year mortality rates were 32%, 20.2% and 14.5%, respectively. The 1-year mortality rates of hypercapnic patients with different underlying diseases were 24.6% (chronic obstructive pulmonary disease), 28.4% (congestive heart disease), 1.6% (obstructive sleep apnea syndrome/obesity hypoventilation syndrome), 50.9% (pneumonia), 0% (suppressed central respiratory drive, primarily due to opiate abuse) and 22.8% (other conditions). DISCUSSION: The 1-year mortality rate of patients with acute hypercapnia at hospital admission was 32%, with significant differences compared to chronic hypercapnic patients (20.2%) and normocapnic patients (14.5%). There was a wide range of 1-year mortality rates between the hypercapnic patients with different underlying diseases.