Patient characteristics
Clinical features, collected from 174 patients before and during ECMO treatment were analyzed to identify potential biomarkers for the outcome. Among these 174 patients, 61were excluded (12 were < 18 years old, 12 received ECMO < 1 day, 23 without baseline height or weight data, 14 with insufficient clinical information). In the end, 113 patients were included in the final analysis.
The patient’s characteristics are shown in Table 1 and Supplementary Table S1. Among these patients, we found that a total of 36 patients (31.9%) died during the hospital stay. The patients’ characteristics include age, hospital stay, multiple organ failure, and bleeding complications were significant differences in the surviving group from the dead group (all p < 0.05). However, there were no significant differences between the two groups in other variables.
Table 1
Population characteristics
|
ALL
|
dead
|
alive
|
p-value
|
|
N = 113
|
N = 36
|
N = 77
|
|
age
|
46 [32;55]
|
51 [41;60]
|
44 [30;54]
|
0.025
|
sex
|
|
|
|
0.073
|
man
|
73 (64.6%)
|
28 (77.8%)
|
45 (58.4%)
|
|
feman
|
40 (35.4%)
|
8 (22.2%)
|
32 (41.6%)
|
|
BMI
|
23.1 [21.3;26.0]
|
23.4 [21.8;26.2]
|
23.0 [20.8;25.6]
|
0.430
|
ECMO duration (d)
|
7.00 [4.00;13.0]
|
9.50 [3.00;17.0]
|
7.00 [4.00;12.0]
|
0.387
|
ECMO model
|
|
|
|
0.876
|
V-A
|
53 (46.9%)
|
16 (44.4%)
|
37 (48.1%)
|
|
V-V
|
60 (53.1%)
|
20 (55.6%)
|
40 (51.9%)
|
|
hospital stay(d)
|
23.0 [13.0;39.0]
|
16.0 [6.75;25.2]
|
28.0 [16.0;42.0]
|
0.003
|
Coronary heart disease
|
|
|
|
0.072
|
no
|
103 (91.2%)
|
30 (83.3%)
|
73 (94.8%)
|
|
yes
|
10 (8.85%)
|
6 (16.7%)
|
4 (5.19%)
|
|
Multiple organ failure
|
|
|
|
0.049
|
no
|
84 (74.3%)
|
22 (61.1%)
|
62 (80.5%)
|
|
yes
|
29 (25.7%)
|
14 (38.9%)
|
15 (19.5%)
|
|
Bleeding complications
|
|
|
|
0.006
|
no
|
75 (66.4%)
|
17 (47.2%)
|
58 (75.3%)
|
|
yes
|
38 (33.6%)
|
19 (52.8%)
|
19 (24.7%)
|
|
Values are median (interquartile range) or n (%). Abbreviations BMI: Body mass index (kg/m²) ; ECMO : extracorporeal membrane oxygenation ; VV:veno-venous; VA:veno-arterial. |
Laboratory parameters
The laboratory parameters are shown in Table 2 and Supplementary Table S2. Comparison of biological parameters of patients receiving ECMO treatment between the two groups, we found that the TBIL, DBIL, and PT in the dead group was much higher than in the surviving group (all p < 0.05). However, the PLT counts were significantly decreased in the dead group when compared to the survival group (p = 0.003). However, there was no remarked difference between the two groups in RBC, HB, WBC, APTT, FIB, TT, and so on.
Table 2
Laboratory parameters during ECMO treatment.
|
ALL
|
dead
|
alive
|
p-value
|
|
N = 113
|
N = 36
|
N = 77
|
|
Red blood cell 1012/L
|
3.08 [2.89;3.48]
|
3.09 [2.89;3.48]
|
3.08 [2.89;3.46]
|
0.841
|
Hemoglobin g/L
|
92.3 [85.9;101]
|
91.2 [85.8;102]
|
92.4 [85.9;101]
|
0.808
|
White blood cell 109/L
|
12.9 (5.17)
|
13.1 (6.00)
|
12.8 (4.78)
|
0.824
|
Platelet counts 109/L
|
86.8 [65.5;126]
|
74.6 [53.8;96.3]
|
91.6 [69.7;128]
|
0.003
|
Total bilirubin umol/L
|
31.1 [20.3;66.8]
|
50.2 [27.0;97.3]
|
25.9 [17.7;55.2]
|
0.006
|
Direct bilirubin umol/L
|
18.7 [10.1;52.6]
|
26.5 [14.8;68.7]
|
16.4 [8.80;39.9]
|
0.012
|
Prothrombin time (s)
|
15.8 [14.0;19.0]
|
16.6 [14.9;19.9]
|
15.5 [13.6;18.5]
|
0.043
|
INR
|
1.42 [1.25;1.72]
|
1.46 [1.33;1.81]
|
1.41 [1.18;1.70]
|
0.075
|
APTT (s)
|
54.5 [46.3;65.8]
|
57.0 [49.2;74.4]
|
54.2 [45.2;64.8]
|
0.079
|
Fibrinogen g/L
|
2.51 [1.92;3.78]
|
2.47 [1.92;3.80]
|
2.51 [1.94;3.77]
|
0.988
|
Thrombin time (s)
|
30.2 [20.5;53.6]
|
28.7 [21.9;45.4]
|
33.4 [20.5;54.0]
|
0.460
|
INR: International normalized ratio; APTT: Activated partial thromboplastin time |
Blood product utilization
Blood product utilization of patients receiving ECMO treatment was shown in Table 3. The median FFP (mL/kg/d) transfusion was higher in the dead patients (4.44; IQR = 1.67–8.41) when compared to survival patients (2.15; IQR = 0.75–4.62) (p = 0.012). However, no significant statistical difference was found in the utilization of other blood products including RBC, PLT, and cryoprecipitate between the two groups. The proportion of FFP and PLT transfusion in the dead group was higher than in the survival group. Furthermore, compared with cryoprecipitate and PLT transfusion, the proportion of FFP and RBC transfusion is the highest in all ECMO patients (Fig. 1).
Table 3
Blood product utilization during ECMO
|
[ALL]
|
dead
|
alive
|
p.value
|
|
N = 113
|
N = 36
|
N = 77
|
|
RBC utilization (mL/kg/d)
|
4.08 [1.78;6.81]
|
4.24 [2.03;9.83]
|
3.85 [1.78;6.24]
|
0.363
|
FFP utilization (mL/kg/d)
|
3.01 [1.06;5.55]
|
4.44 [1.67;8.41]
|
2.15 [0.75;4.62]
|
0.012
|
PLT utilization(U)
|
1.00 [0.00;3.00]
|
2.00 [0.00;6.25]
|
1.00 [0.00;3.00]
|
0.074
|
Cryoprecipitate(U)
|
0.00 [0.00;0.00]
|
0.00 [0.00;0.00]
|
0.00 [0.00;0.00]
|
0.648
|
Abbreviations RBC = red blood cell, FFP = fresh frozen plasma, PLT = platelet. |
Independent predictors for mortality
Although there are differences in the part of clinical indicators between the survival group and the death group of ECMO patients, it is still unknown which indicators were associated with the risk of death. Here, we analyzed all clinical indicators including patient characteristics, laboratory parameters, and blood transfusion index by univariate logistic regression analysis and found that 13 clinical indicators were significantly correlated with patients’ death (supplementary Table S3). Next, we further evaluated these 13 clinical variables by selecting features with coefficients in the LASSO binomial regression model (Fig. 2) and finally identified 11 variables including age, CHD, multiple organ failure, bleeding complications, anemia, FFP transfusion, PLT transfusion, DBIL, LDH, APTT, and ECMO duration could as an independent predictor for patients’ death in this model.
Feature importance confirmation
Because 11 certain variables were confirmed significantly correlated with the patients’ death, we chose to focus on the variable importance interpretation of these 11 indicators by different Machine Learning algorithms such as Random Forest and XGBoost. We found 6 confirmed importance variables including ECMO duration time, PLT transfusion, age, FFP transfusion, CHD, and bleeding complications in the Random Forest model (Fig. 3). Furthermore, we found that the most important variables in the XGBoost model are consistent with the Random Forest model, with ECMO duration, age, and FFP transfusion being ranked in the top three (Fig. 4).
Shapley values explanation the prediction of mortality
From Random Forest and XGBoost model, we found that ECMO duration time, age, and FFP transfusion contribute more to the model than other variables. However, we do not know how each variable affects the probability of mortality. To overcome this issue, we further employed the Shapley values, one technique from game theory, to provide consistent interpretations on both local and global levels. We also found that ECMO duration, age, and FFP transfusion are the most important for patient mortality (Fig. 5A). Moreover, the positive or negative relationship between each variable and patient mortality prediction in Shapley values. High leves of age, FFP and ECMO_duration in the mode were assignated positive Shapley values are more likely to predict patients’ mortality (Fig. 5B).
In addition, to investigate the interaction between the explanatory variables and the patient's corresponding outcome, we performed the non-linear interaction analysis of age, FFP and ECMO_duration. From the interaction between the FFP value and its patients corresponding Shapley value, we found the proportion of patients’ mortality was increasd when FFP over 2.5, and these patients were assigned positive Shapley values (Fig. 6A). we also found the same result that patients are more likely to died when older than 48 years (Fig. 6B). However, we found ECMO duration time over 15 days or lower than 1.5 days more likely dead in ECMO patients (Supplementary Fig. S1).
Next, we divide age, FFP, and ECMO duration time into different categories to understand the interaction between the distribution of characteristics and patient outcome. The results indicated that the patients who spent more time on ECMO treatment and with older ages, and the overdose of FFP transfusion more likely died in the duration of ECMO treatment (Fig. 7).
Determinants of FFP transfusion
Based on the results described in the previous sections, we found FFP transfusion was an important variable on ECMO treatment-related death. So, we further investigate which variables affect the FFP transfusion duration ECMO treatment. Firstly, we analyzed the correlation of laboratory indicators by using Spearman's method, and the result found that 10 variables such as RBC transfusion, PT, INR, APTT, PLT, AST, ALT, CREA, UA, and LDH were correlated with FFP transfusion (R2 > 0.3, pvalue < 0.5, Fig. 8). Secondly, we further divided FFP transfusion into high transfusion group and low transfusion group by the optimal threshold of 2.5 mL/kg/d, and investigate the difference between the two groups. The results showed that 13 clinical variables included patients’ status, severe pneumonia, anemia, RBC transfusion, PLT count, CREA, UA, AST, LDH, ALT, PT, INR, and APTT were significantly different between the two groups (Supplementary Table S4).
Next, we performed a stepwise multiple linear regression analysis to explore the influencing factors of FFP transfusion. Before analysis, we performed a multicollinearity index elimination by the method of Variance Inflation Factor (VIF) in these 13 variables to reduce the collinear interference between variables. According to the standard of VIF less than 10, we finally selected 8 indicators including severe pneumonia, PLT, CREA, UA, ALT, PT, INR and APTT for further analysis. The associations were identified by building multiple linear regression models with stepwise backward variable selection. The results showed that PLT counts, UA and APTT remained the significant factor for predicting FFP transfusion (Fig. 9), especially PLT and APTT (Supplementary Fig. S2).