Hypocapnia and hypercapnia are predictors for ICU admission and mortality in hospitalized patients with community-acquired pneumonia

Objective: The purpose of our study was to examine in patients hospitalized with community-acquired pneumonia (CAP) the association between abnormal PaCO₂ and ICU admission and 30-day mortality. Methods: A retrospective cohort study was conducted at two tertiary teaching hospitals. Eligible subjects were admitted with a diagnosis of CAP. Arterial blood gas analyses were obtained with measurement of PaCO₂ on admission. Multivariate analyses were performed using 30-day mortality and ICU admission as the dependent measures. Results: Data were abstracted on 453 subjects with a documented arterial blood gas analysis. One hundred eighty-nine patients (41%) had normal PaCO₂ (35-45 mm Hg), 194 patients (42%) had a PaCO ₂ < 35 mm Hg (hypocapnic), and 70 patients (15%) had a PaCO ₂ > 45 mm Hg (hypercapnic). In the multivariate analysis, after adjusting for severity of illness, hypocapnic patients had greater 30-day mortality (OR = 2.84; 95% CI, 1.28-6.30) and a higher need for ICU admission (OR = 2.88; 95% CI, 1.68-4.95) compared with patients with normal PaCO₂. In addition, hypercapnic patients had a greater 30-day mortality (OR = 3.38; 95% CI, 1.38-8.30) and a higher need for ICU admission (OR = 5.35; 95% CI, 2.80-10.23). When patients with COPD were excluded from the analysis, the differences persisted between groups. Conclusion: In hospitalized patients with CAP, both hypocapnia and hypercapnia were associated with an increased need for ICU admission and higher 30-day mortality. These findings persisted after excluding patients with CAP and with COPD. Therefore, PaCO₂ should be considered for inclusion in future severity stratification criteria to appropriate identified patients who will require a higher level of care and are at risk for increased mortality.