Results
Demographic and clinical characteristics of the patients
The main demographic and clinical characteristics of the 88 patients with a median age of 70.7(62.3-78.3) years are presented in Table 1. The median age of the patients in the \(\leq\)7 days, 8–14 days, and >14 days categories was 74.1 (65.6–80.3), 69.3(60.6–75.3), and 68.3(58.8–74) years, respectively. Most patients were male. All patients developed fever (37.3±1.0 ℃). Nevertheless, the heart and respiratory rates of the patients of the three groups significantly varied; the heart rates were 103±23.8, 91.7±17.3, and 91.7±12.6 (P =0.03), while the respiratory rates were 27.72±8.0, 27.4±7.3, and 23.4±6.2 (P =0.04) for the patients of the \(\leq\)7 days, 8–14 days, and >14 days categories, respectively. The mean arterial pressure (MAP) and pulse oxygen saturation (SpO2) of the patients of the three categories were similar. At the time of admission, patients of the 8–14days and >14days categories showed higher Glasgow Coma Scale scores (13.1±2.6 and 14.3±1.9, respectively) than those of the ≤7 days category (11.0±2.9, P <0.01).
The most frequently recorded underlying medical co-morbidities included hypertension (43.2%), followed by diabetes (23.9%), cardiovascular disease (20.5%), chronic lung diseases (13.6%), cerebrovascular disease (3.4%), chronic kidney disease (2.3%), chronic liver disease (1.1%), and malignancy (1.1%). The proportions of co-morbidities and smoking histories of the patients of the three groups were similar. However, acute kidney failure occurred more frequently in the patients of the ≤ 7 days category (45.2%) than in the patients of the 8–14 days and >14 days categories (21.2% and 4.2%, respectively;P <0.01). Among the 88 critically ill patients whose mortality data were reported, 17 survived and 71 died at the end of the study, indicating different rates of mortality for different categories: 31deaths in the \(\leq\)7 dayscategory, 33 deaths in the 8–14days category, and 7 deaths in the >14 days category. In other words, mortality rates of the patients with three different survival times differed as follows: 57.9% in 8–14 days, 35.2% in \(\leq\)7 days, and 29.2% in >14 days (P =0.01). Figures 1 and 2 show the survival curves of the 88 patients and time distributions of their mortality rates.
Laboratory indices
Laboratory findings provided substantial information on the severity of the disease. White blood cell (WBC) counts (×109/L) were elevated in most patients (11.7±5.5), while the lymphocyte percentages were much lower than the normal value in all patients (4.1±0.78). Particularly, the lymphocyte percentage in the patients of the ≤7 days category was 5.3±4.8, which was significantly lower than that in the patients of the >14days category (9.1±6.4,P =0.03). Red blood cell (RBC) and platelet counts did not differ much from the normal values and among the patients of the three categories. Blood biochemical indices, including alanine aminotransferase (ALT), aspartate aminotransferase (ast), serum creatinine, sodium, potassium, and creatine kinase (CK), also showed no significant deviations from the normal values. In addition, blood urea nitrogen (BUN) and lactate dehydrogenase (LDH) levels in the patients of the >14 days category (8.7±4.4 and 434.4±136.1, respectively) were significantly lower than those in the patients of the ≤7 days (16.4±10.5and 703.4±459.2, respectively) and 8–14 days (15.5±9.9 and 637.8±331.3, respectively) categories (P =0.02). Lower levels of CK-MB were found in the patients of the >14days category, compared to that in the patients of the ≤7 days category (P< 0.01).
Coagulation function was seriously affected in all patients, showing prothrombin time of 18.7±16.5 s. Patients of the >14days category showed shorter prothrombin times(15.1±1.9) and lower D-dimer levels (4.6±6.2) than those of the ≤7 days (19.2±8.9 and 11.6±8.5, respectively) and 8–14 days (20.9±24.9 and 11.2±9.3, respectively) categories (P< 0.01). Likewise, patients of the >14 days category showed lower C-reactive protein (CRP) (93.9±54.7) and procalcitonin (PCT) (0.4±0.6) levels (P =0.02 and P< 0.01, respectively). Levels of serum cytokines, such as IL-6, IL-10, and TNF-α, were obviously elevated in all patients, but did not differ among the patients of the three categories. The partial pressure of oxygen (PaO2)/fraction of inspirational oxygen (FiO2) index was dramatically decreased in all patients, but did not differ among the patients of the three categories. Baseline laboratory parameters of the patients are shown in Table 2. Constant changes in the routine blood tests are shown in Figure 3. Constant changes in the laboratory parameters and inflammatory biomarkers are shown in Figures 4 and 5, respectively.
Complications that could be attributed to mortality
Although the patients received aggressive treatment in the ICU, 71 of the 88 patients died within 28 days. Multiple organ dysfunction syndromes (MODS) were prevalent in these patients. Considering one major cause of mortality, we found that 35 deaths (49.3%) were attributed to respiratory causes, 23(32.4%) to cardiovascular causes, 7(9.9%) to shock, 5(7%) to kidney injury, and 1(1.4%) due disseminated intravascular coagulation (DIC), indicating that respiratory failure was the most predominant complication. Figure 6 shows the main causes of mortality.