Effect of hypercapnia on the clinical prognosis and severity of infection in patients with severe community-acquired pneumonia / 中华危重病急救医学

ABSTRACT

Objective:To investigate the effect of hypercapnia at admission on the clinical prognosis and the severity of infection in patients with severe community-acquired pneumonia (SCAP).Methods:The clinical data of 219 SCAP patients admitted to the department of emergency & critical care medicine of Guangdong Provincial People's Hospital from December 2017 to November 2019 were retrospectively analyzed. Based on the partial pressure of arterial carbon dioxide (PaCO 2) within 1 day after admission, the patients were divided into hypocapnia group [HO group, PaCO 2 < 35 mmHg (1 mmHg = 0.133 kPa)], normal carbonation group (NC group, PaCO 2 35-45 mmHg) and hypercapnia group (HC group, PaCO 2 > 45 mmHg). The clinical parameters of patients, such as gender, age, underlying diseases, white blood cell (WBC), procalcitonin (PCT), C-reactive protein (CRP), interleukin-6 (IL-6), pH value and lactate (Lac) within 1 day after admission were reviewed. The oxygenation index (PaO 2/FiO 2), pneumonia severity index (PSI) score and acute physiology and chronic health evaluation Ⅱ (APACHE Ⅱ) score were evaluated. The change tendencies of each index on day 1, day 3, and day 5 after admission were observed subsequently. Meanwhile, the rate of invasive mechanical ventilation (IMV), length of hospital stays and 28-day mortality among three groups were compared. Kaplan-Meier survival analysis was performed to assess the 28-day cumulative survival rate of patients with SCAP among three groups. Multivariate Logistic regression analysis was used to screen the risk factors of IMV and 28-day death in patients with SCAP. Results:Compared with the HO group ( n = 68) and NC group ( n = 72), the HC group ( n = 79) had higher proportion of preexisting comorbid chronic obstructive pulmonary disease (COPD) and PSI score, lower PCT, CRP, IL-6, and pH values. Compared with the HO group and NC group, there were smaller improvement trends on the levels of WBC, PCT, CRP, IL-6, PaO 2/FiO 2 and Lac at day 3 and day 5 as compared with day 1 in the HC group. On the 5th day after admission, the levels of WBC, PCT, CRP, IL-6, and Lac in the HC group were significantly higher than those in the HO group and NC group [WBC (×10 9/L) 18.33±1.44 vs. 10.89±2.37, 11.15±1.74; PCT (μg/L) 5.04±1.18 vs. 3.46±0.87, 3.58±0.83; CRP (mg/L) 78.43±7.17 vs. 54.24±4.97, 57.93±5.39; IL-6 (ng/L) 75.35±11.92 vs. 60.11±10.27, 57.88±12.34; Lac (mmol/L) 4.36±1.24 vs. 0.78±0.39, 0.86±0.64; all P < 0.01], and the lowest in PaO 2/FiO 2 was found in the HC group as compared with the HO and NC groups (mmHg 171.31±6.73 vs. 226.68±7.36, 225.93±6.92, both P < 0.01). Compared with the HO group and NC group, the HC group had highest proportion of IMV (29.1% vs. 22.1%, 22.2%, both P < 0.01) and 28-day mortality (26.6% vs. 13.2%, 13.9%, both P < 0.01). Even when the patients with COPD were excluded from the analysis, the differences persisted among the groups. Kaplan-Meier survival analysis suggested that HC group had a higher 28-day cumulative survival rate as compared with the HO and NC groups (Log-Rank test χ 12 = 4.976, P1 = 0.026; χ 22 = 4.629, P2 = 0.031). Multivariate Logistic regression analysis showed that IL-6, PSI score and hypercapnia within 1 day and PCT on the 5th day after admission were the independent risk factors of requiring IMV and 28-day death in patients with SCAP [odds ratio ( OR) were 0.325, 1.229, 1.396, 1.313, respectively, all P < 0.01]. Even when patients with COPD were excluded from the analysis, the above results had not been changed. Conclusion:Hypercapnia at admission was associated with higher proportion of IMV and 28-day mortality in patients with SCAP, which may be related to its early suppression of inflammation and then increment of infection.