Mortality and Healthcare Use of Patients with Compensated Hypercapnia.

Abstract

Rationale: Acute hypercapnic respiratory failure has been shown to be associated with worse outcomes for various disease states, but less is known about patients with compensated hypercapnic respiratory failure. Although these patients have a normal pH, it remains unknown whether chronically elevated carbon dioxide partial pressure (Pco2), irrespective of etiology, puts patients at risk of adverse events. Objectives: To understand the burden of and clinical factors associated with morbidity and mortality in patients with compensated hypercapnic respiratory failure. Methods: We performed a query of the electronic medical record to identify patients hospitalized at the University of Michigan from January 1 to December 31, 2018, who had compensated hypercapnia, by using a Pco2 ⩾ 50 mm Hg and a pH of 7.35-7.45 on arterial blood gas . We obtained demographic and clinical data from the electronic medical record. Survival probabilities for Pco2 subgroups (50.0-54.9, 55.0-64.9, and ⩾65.0 mm Hg) were determined by using the Kaplan-Meier product limit estimator. Cox proportional hazard models were constructed to test the association between Pco2 and all-cause mortality. Results: We identified 491 patients with compensated hypercapnia. The mean age was 60.5 ± 16.2 years. Patients were 57.4% male and 86.2% white. The mean pH and Pco2 were 7.38 ± 0.03 and 58.8 ± 9.7 mm Hg, respectively. There was a total of 1,030 hospitalizations, with 44.4% of patients having two or more admissions. The median numbers of cumulative hospital and intensive care unit days were 21.0 (interquartile range [IQR], 11.0-38.0) and 7.0 (IQR, 3.0-14.0) days, respectively. Two hundred seventeen patients (44.2%) died over a median of 592 days. In univariate analysis, every 5-mm Hg increase in Pco2 was associated with a higher risk of all-cause death (hazard ratio, 1.09; 95% confidence interval [CI]: 1.03-1.16; P = 0.004). This association was maintained after adjusting for the age, sex, body mass index (BMI), and Charlson comorbidity index (hazard ratio of 1.09 for every 5-mm Hg increase in Pco2; 95% CI: 1.02-1.16; P = 0.009). There was a statistically significant interaction between the Pco2 and the BMI in relation to mortality (P = 0.01 for the interaction term). Conclusions: Patients with compensated hypercapnic respiratory failure have high mortality and healthcare use, with higher Pco2 being associated with worse survival. Hypercapnic patients with obesity have a higher risk of death with increases in Pco2.