General characteristics
Initially 536 patients were enrolled in this study. Following the flow chart with strict inclusion and exclusion criteria, 428 patients were finally analyzed in this study (Figure 1). Of which 310 were medical patients, and 118 were surgical patients. Overall, ICU mortality was 24.5% (105 of 428 patients), with 41.0% (43 of 105) deaths occurring during the first 7 days after admission, and 59% (62 of 105) deaths occurring between 7 and 28 days after admission. Table 1 shows the general characteristics of the total enrolled critical ill patients.
Neutrophil count ratio abnormality did not differentiate between survival and mortality groups. Body temperature did not present to have such discriminant potency either. However, the WBC count in 7-day mortality group was much higher than other groups. Surgery patients population in 7-day mortality group presented to be the lowest among all groups, as shown in Table 1, indicating a surgical background may refer a better outcome in critical patients.

Microorganisms profile
Of total analyzed patients, 290 were with evidences of infection, either bacteria (total 300 isolates, with 275 gram-negative and 26 gram-positive isolates), fungi (69 isolates), virus (3 isolates), anaerobe (1 isolate) or tuberculosis (1 isolate). Among all patients, 93 cases (survival: 77 cases, 28-day mortality: 14 cases, 7-day mortality: 6 cases) were with mixed infection with multiple microorganisms, and 148 cases (survival: 116 cases , 28-day mortality: 14 cases, 7-day mortality: 18 cases) were not infected. According to infection sites the patients were with pneumonia (208 cases), bacteremia (19 cases), peritonitis (23 cases), intra-cranial infection (15 cases), and other infections (15 cases). The specific microorganism profile for each group was displayed in table 2.
Table 2. Microorganisms isolated from the patients in the study cohort
|
Survival
n=323
|
28-day mortality
n = 62
|
7-day mortality
n = 43
|
Gram-Negative isolates (n, %)
|
216 (66.9%)
|
39 (62.9%)
|
20 (46.5%)*
|
Acinetobacter baumannii
|
75 (23.2%)
|
19 (30.6%)
|
13 (30.2%)
|
Klebsiella spp.
|
44 (13.6%)
|
14 (22.6%)
|
3 (7.0%)
|
Pseudomonas spp.
|
43 (13.3%)
|
5 (8.1%)
|
2 (4.7%)
|
Enterobacter spp.
|
21 (6.5%)
|
1 (1.6%)
|
1 (2.3%)
|
S. maltophilia
|
14 (4.3%)
|
0 (0)
|
1 (2.3%)
|
Other
|
19 (5.9%)
|
0 (0)
|
0 (0)
|
Gram-positive isolates (n, %)
|
13 (4.0%)
|
9 (14.5%)**
|
4 (9.3%)
|
S.Aureus
|
6 (1.9%)
|
6 (9.7%)**
|
1 (2.3%)
|
MRSA
|
2 (0.6%)
|
1 (1.6%)
|
1 (2.3%)
|
Streptococcus spp.
|
2 (0.6%)
|
0 (0)
|
1 (2.3%)
|
Enterococcus spp.
|
2 (0.6%)
|
1 (1.6%)
|
1 (2.3%)
|
Other
|
1 (0.3%)
|
1 (1.6%)
|
0 (0)
|
Fungi isolates (n, %)
|
52 (16.1%)
|
10 (16.1%)
|
7 (16.3%)
|
Candida albicans
|
35 (10.8%)
|
8 (12.9%)
|
2 (4.7%)
|
Candida glabrada
|
9 (2.8%)
|
1 (1.6%)
|
1 (2.3%)
|
Candida tropicalis
|
5 (1.5%)
|
1 (1.6%)
|
1 (2.3%)
|
Other
|
3 (0.9%)
|
0 (0)
|
3 (%)*
|
Virus isolates (n, %)
|
2 (0.6%)
|
1 (1.6%)
|
0 (0)
|
Anaerobes isolates (n, %)
|
1 (0.3%)
|
0 (0)
|
0 (0)
|
Tuberculosis isolates (n, %)
|
0 (0)
|
0 (0)
|
1 (2.3%)
|
Data were expressed as number (percentage of current group) of isolates, not number of patients. *p < 0.05, **p < 0.01 vs survival group. Spp., species; S. maltophilia, stenotrophomonas maltophilia; S. aureus, staphylococcus aureus; MRSA, methicillin-resistant staphylococcus aureus.
Co-morbid conditions
The incidence of cardiovascular co-morbid conditions on admission to the ICU was higher in patients of both 28- and 7-day mortality groups than in survival group, indicating that cardiovascular disease background might be a major risk factor for negative outcomes. On the other hand the incidence of malignancies was much lower in mortality groups than that of survival group. Apart from this, the surgery operation incidence in survival group was much higher than that of 7-day mortality group, as described in Table 1. The general co-morbid disease profile was presented for overall population in Table 3.
Table 3 Coexisting disease of the study population stratified by survival and mortality
28-day mortality
n = 62
|
Survival
n = 323
|
28-day mortality
n = 62
|
7-day mortality
n = 43
|
Diabetes mellitus
|
3 (0.9%)
|
0 (0)
|
0 (0)
|
Cardiovascular disease
|
18 (5.6%)
|
4 (6.5%)
|
10 (23.3%)***
|
Hypertension
|
4 (1.2%)
|
0 (0)
|
0 (0)
|
Malignancies
|
29 (9.0%)
|
1 (1.6%)**
|
4 (9.3%)
|
COPD
|
8 (2.5%)
|
4 (6.5%)
|
1 (2.3%)
|
Liver cirrhosis
|
0 (0)
|
0 (0)
|
0 (0)
|
Renal failure
|
6 (1.9%)
|
4 (6.5%)
|
2 (4.7%)
|
Data were expressed as number (percentage of current group), ** p < 0.01, *** p < 0.001 vs survival group. COPD, chronic obstructive pulmonary disease.
Diagnostic character of APACHE II and biomarkers
APACHE II is a severity-of-disease classification system, one of several ICU scoring systems. It is applied within 24 hours of admission of a patient to an ICU. Higher APACHE II score negatively correlates with survival rate. In our study, we applied APACHE II to be the comparable reference for the analyzed biomarkers.
NLCR, APACHE II score and other biomarker levels of survival, 28- and 7-day mortality groups were presented in Figure 2. Considering the total cohort of 428 critical patients, the APACHE II score at admission in mortality groups were much higher than that of survivors . Both CRP and PCT levels of mortality groups were significantly elevated than those of survival groups (Table 1, Figure 2). Regarding to LAC, only 28-day mortality group levels were higher than that of survivals, but not 7-day mortality group levels, probably because of relatively large deviation and small count of group population. Of note, NLCR did not differentiate among survivals and non-survival patients (Table 1, Figure 2).
Discriminant performance of APACHE II and biomarkers
The discriminant ability of NLCR, CRP, PCT, LAC and APACHE II score to predict 28- and 7-day mortality was presented in Figure 2. With group comparison, we found that PCT, CRP and APACHE II score were all discriminant between survival and mortality groups. While NLCR presented to be not discriminant between groups. Among all biomarkers, both PCT and CRP showed greater differential potency than others, as their p value at comparison of the survival and mortality groups presented to be most significant. On the other hand, LAC showed less differential potency among all groups (Figure 2).
According to area under ROC curves analysis, the AUROCs of NLCR were 0.580 and 0.575 for 28- and 7-day mortality group respectively. And the P values were 0.045 and 0.111, which did not make NLCR a powerful discriminator to predict mortality. On the other hand, not only APACHE II score, but also CRP and PCT had much higher levels of AUROCs than NLCR, which also made NLCR a relatively weak predictor of mortality (Figure 3).
For discrimination of 28-day mortality, APACHE II score presented highest AUROC than all the biomarkers, while PCT and CRP presented to be less potent biomarkers. LAC had relatively higher levels of AUROC, which made it a good indicator to predict 28-day mortality. For prediction of 7-day mortality, LAC had the lowest value of prediction, meanwhile, APACHE II score remained the highest value of predicting 7-day mortality. Compared to PCT and CRP, NLCR was determined a very weak biomarker to predict both short and long term mortality according to AUROC levels (data shown in Figure 3).
In regard to survive analysis, all the biomarkers selected in this study presented good potential to predict outcomes of critical patients. We calculated the cutoff values for each biomarker and graphed the survival curves according to its values higher or lower than cutoffs. The results showed both PCT and CRP had higher differential ability, with p values lower than 0.001, better sensitivity and specificity than other markers such as NLCR and LAC. Compared to PCT and CRP, NLCR had presented relatively weak potential to indicate prognosis of critical patients (Figure 4).