2.1 In this study, a total of 261 patients were enrolled with a mean age of 69.5, and the total mortality rate was 47.5%. The blood lactate levels of patients showed no significnat differences between the Survival Group and Death Group [5.8 (4.6~7.6) vs. 5.9 (4.9~8.4), p=0.767].However, after 6-hour treatment, the blood lactate levels of patients in the Survival Group were significantly lower than that of patients in the Death Group [4.10 (2.6~5.4) vs. 5.65 (4.6~7.8), p< 0.001]. The 6-hour lactate clearence rate of Survival Group was higher than that of the Death Group [(36.4%(-86.00~86.52) vs. 4.0%(-177.7~53.6), p<0.001]. In addition, compared with patients of Death Group, the patients of Survival Group had less volume of fluid input and lower APACHE II scores (all P <0.001). The results were shown in Table 1.
Table 1 Comparison between 28 days of survival and death
Variables
|
Whether or not the 28 day was alive
|
Statistics
|
P
|
Yes (n=137)
|
No (n=124)
|
Age (years old)
|
67.28±18.39
|
72.05±14.85
|
t=2.312
|
0.022
|
Sexual (male)
|
86 (62.77%)
|
75 (60.48%)
|
χ2=0.144
|
0.704
|
Rehydration (ml)
|
1949.77±132.11
|
2048.50±66.74
|
F=55.873
|
<0.001
|
APACHE IIscores
|
13.75±2.86
|
16.01±2.34
|
F=47.981
|
<0.001
|
LAC1{M(Min, Max)}
|
5.80 (4.00-15.00)
|
5.75 (4.00-15.00)
|
Z=0.296
|
0.767
|
LAC2{M(Min, Max)}
|
4.10 (0.90-8.10)
|
5.65 (1.90-15.00)
|
Z=8.061
|
<0.001
|
clearance {M(Min, Max)}
|
36.48% (-86.00%-86.52%)
|
4.07% (-177.78%-53.66%)
|
Z=8.366
|
<0.001
|
2.2 The results of single Logistic regression were shown in Table 2. These results suggested that age (OR=1.02, 95%CI: 1.00-1.03,P=0.025), LAC2 (OR=0.92, 95%CI:0.83-1.02) (OR=1.87,95%CI:1.56- 2.24,P<0.001)and lactate clearance rate (OR=13.30, 95%CI:5.59-31.61)(OR=0.028, 95%CI:0.01–0.08,P<0.001)were significantly correlated with mortality. However, LAC1 showed no significant correlation (OR=0.92, 95%CI: 0.83- 1.02)(OR=1.03,95%CI:0.93- 1.14,P=0.544)with mortality rate. These two variables age and LAC2 were further incorporated into multivariate regression analysis. Results showed that age (OR=1.020, 95%CI:1-1.03, P=0.032) and lactate clearance rate (OR=0.028, 95%CI:0.01-0.07, P<0.001) were significantly correlated with 28-day mortality (Table 2).
Table 2 Logistic regression analysis of 28 days of death
Factors
|
Crude OR (95%CI)
|
P
|
Adjusted OR (95%CI)
|
P
|
age
|
1.017(1.002-1.033)
|
0.025
|
1.020(1.002-1.039)
|
0.032
|
clearance
|
0.028(0.010-0.080)
|
<0.001
|
0.028(0.010-0.079)
|
<0.001
|
APACHE II
|
1.21(1.11-1.32)
|
<0.001
|
1.22(1.13-1.33)
|
<0.001
|
sexual
|
1.101(0.668-1.814)
|
0.704
|
|
|
LAC1
|
1.032(0.931-1.141)
|
0.544
|
|
|
LAC2
|
1.876(1.567-2.247)
|
<0.001
|
|
|
2.3 ROC curve analysis: The ROC curve was conducted to determine the optimal cut off value of lactate clearance rate for 28-day survival. The AUC value was 0.800 (95%CI:0.747-0.853, P<0.001), and the cut off value was 18.93%, with asensitivity of 0.759 and specificity of 0.718. The ROC curve was shown in figure 1.
2.4 Subgroup analysis accorrding to age stratification (age>65 years old or not)
2.4.1 >65 years old: A total of 175 patients were observed with an average age of 78.99±7.70. Among them, 110 cases were male (62.86%), and 65 were female (37.14%). The mean value of lactic acid clearance rate was 19.32% (-177.78%-86.52%), 84 patients achieved 28-day survival, and the mortality rate was about 52.00%. The AUC value was 0.778 (95%CI:0.711-0.845, P<0.001), with a cut-off value of 18.25%, sensitivity of 0.750, and specificity of 0.681. The mean value of lactate clearance rate for survivors was 35.17% (-45.00~86.52), and the mean value of lactate clearance rate fordead patients was 4.44% (-177.78~53.66). The ROC curve results were shown in Figure 2 and comparion of lactate clearance rates and cut-off values between patients with age stratificationwas presented in Table 3.
2.4.2 ≤65 years old: A total of 86 patients were observed with an average age of 50.34±14.11. Among them, 51 cases were male (59.30%), and 35 were female (40.70%). The mean value of lactic acid clearance rate was 25.14% (-87.50%-86.09%), 53 patients achieved 28-day survival, and the mortality rate was about 38.37%. The AUC value was 0.845 (95%CI:0.762-0.927, P<0.001), with a cut-off value of 29.16%, sensitivity of 0.698, and specificity of 0.909.The average lactic acid clearance rate of the patients with survival rate was 37.21% (-85.00~86.09), and the average lactic acid clearance rate of the dead patients was 3.70% (-87.50~41.89).
The ROC curve was shown in Figure 3, and comparion of lactate clearance rates and cut-off values between patients with age stratificationwas presented in Table 3.
2.5 Subgroup analysis accorrding to different age groups (age>80 years old or not)
2.5.1 >80 years old: A total of 77 patients were observed. Thirty four patietns achieved 28-day survival, and the mortality rate was about 55.84%. The AUC value was 0.751 (95%CI: 0.642-0.859, P<0.001), with cut-off value of 18.25%, sensitivity of 0.735, and specificity of 0.651.The average lactic acid clearance rate of the patients with survival was 30.36% (-45.00~86.52), and the average lactic acid clearance rate of the dead patients was 2.27% (-177.78~51.85). The ROC curve was shown in Figure 4, and comparion of lactate clearance rates and cut-off values between patients with age stratificationwas presented in Table 3.
2.5.2 ≤80 years old: A total of 184 patients were observed. One hundred and three patients achieved 28-day survival, and the mortality rate was about 44.02%. The AUC value was 0.818 (95%CI: 0.758-0.879,P<0.001), with a cut-off value of 29.36%, sensitivity of 0.660, and specificity of 0.882. The average lactic acid clearance rate of the patients with survival was 37.21% (-85.00~86.09), and the average lactic acid clearance rate of the dead patients was 3.70% (-87.50~41.89). The ROC curve was shown in Figure 5, and comparion of lactate clearance rates and cut-off values between patients with age stratificationwas presented in Table 3.
2.6 Comparisons of APACHE II score and volume of fluid input between Survival Group and Death Group with age stratification. The APACHE II score showed significant differences between Survival Group and Death Group in patients >65 years old (P=0.004), and similar results were observed in patients >80 years old(P≤0.001). The 6h volume of fluid input also showed significant differences between Survival Group and Death Group at each age stratification (all P≤0.0001). The 6-hour lactate clearance rates were also compared between Survival Group and Death Group: patients≤65 years (37.21 vs.3.70), patients>65 years old (35.17 vs.4.44); patients≤80 years (37.21, vs.4.55); patients >80 years (30.36 vs. 2.27). The results were shown in Table 3.
Table 3 Comparions of lactate clearance rates and cut off values between patients with different age stratifications.
Age
|
Group
|
Nmuber
|
APACHE II score
|
6h volume of fluid input
|
ml/kg
|
Mean 6-hour clearance rate(%)
{M(Min, Max)}
|
Cut of point
(%)
|
≤65 years old
|
Survival Group
|
53
|
15.06±3.01
|
2118.43±301.25
|
28.23±46.56
|
37.21(-85.00, 86.09)
|
29.16
|
Death Group
|
33
|
15.00±2.53
|
2199.67±291.47
|
29.12±46.56
|
3.70(-87.50, 41.89)
|
>65 years old
|
Survival Group
|
84
|
15.40±3.02
|
2134.12±314.84
|
27.81±47.99
|
35.17(-45.00, 86.52)
|
18.25
|
Death Group
|
91
|
14.80±3.17
|
2117.31±327.07
|
28.49±41.45
|
4.44(-177.78, 53.66)
|
≤80 years old
|
Survival Group
|
103
|
13.71±2.70
|
2231.34±327.19
|
28.87±44.10
|
37.21(-85.00, 86.09)
|
29.36
|
Death Group
|
81
|
14.36±3.08
|
2277.22±356.33
|
29.38±43.84
|
4.55(-109.30, 53.66)
|
>80 years old
|
Survival Group
|
34
|
14.66±2.89
|
2189.48±335.74
|
28.87±44.10
|
30.36(-45.00, 86.52)
|
18.25
|
Death Group
|
43
|
16.02±2.78
|
2318.22±370.65
|
29.38±43.84
|
2.27(-177.78, 51.85)
|
2.7 Comparison of lactate clearance rate in survival patients with different age stratifications: According to the stratification of age, the lactate clearance rate of 65-years-old patients showed no signficant difference in survival patients (37.21vs. 35.17, p=0.5413).Similar results were observed in patients of 80 years (37.21vs.30.36, p=0.3338). The results were shown in Table 4.
Table 4 Comparison of lactate clearance rate in survival patients with different age stratifications
Group
|
Lactate clearance rate {M(Min, Max)}
|
P
|
≤65 years old
|
37.21 (-85.00, 86.09)
|
0.5413
|
>65 years old
|
35.17 (-45.00, 86.52)
|
|
≤80 years old
|
37.21 (-85.00, 86.09)
|
0.3338
|
>80 years old
|
30.36 (-45.00, 86.52)
|
|