Cytokine screening
Of the 248 cardiac surgery patients for which samples were stored in the biobank, 129 had to be excluded due to surgery procedures different from CABG or AVR, or limited sample availability. In total 119 patients could be included for cytokine screening (Figure 1). Amongst those screened, 42 patients spent less than 48 hours on the ICU, representing the non-PICULOS group and 77 spent more than 48 hours on the ICU (PICULOS group). After randomly selecting 4 preoperative samples from the PICULOS group and another 4 control samples from the non-PICULOS group, we performed the cytokine screening with the Human XL Cytokine Array Kit.
We identified GDF-15 as a novel cytokine with higher preoperative expression in PICULOS patients after undergoing cardiac surgery. As depicted in figure 2, in the PICULOS group mean GDF-15 expression was more than twice as high as in non-PICULOS patients . Other cytokines also showed a higher expression in the PICULOS group, especially Chitinase-3-like-1, IGFPB-2, IL-18 Bpa and TIM-3, yet clearly less distinctive than GDF-15. Interestingly, Serpin-E1 and Vitamin D BP exhibited decreased expression. The other 98 cytokines were expressed at similar levels or not detectable. An example of both a PICULOS and non-PICUOS cytokine array with subsequent analysis is shown in figure 3
GDF-15 measurements
Patient characteristics
For further quantification of the preoperative GDF-15 levels, GDF-15 serum levels from 12 patients with PICULOS and 12 non-PICULOS patients were analyzed. The median age was 67 for the non-PICULOS group and 79 for the PICULOS group, which was a statistically significant difference (p= 0.032). Additionally, EuroSCORE II was raised significantly in the PICULOS group with 3.85 percent versus 1.34 for the non-PICULOS cohort (p= 0.006). All other preoperative baseline characteristics showed no differences between the groups and are shown in table 1.
Table 1. Baseline preoperative patient characteristics
|
non-PICULOS
n = 12
|
PICULOS
n = 12
|
p value
|
Age, years
|
67 (53 – 75)
|
79 (77 – 83)
|
0.032
|
BMI, kg/m2
|
27 (25 – 32)
|
26 (25 – 29)
|
0.630
|
Gender [male/female]
|
7/5
|
7/5
|
1.000
|
Cardiac disease, n
|
|
|
0.856
|
- CHD
|
5
|
4
|
|
- Valvular pathology
|
2
|
3
|
|
- Combined
|
5
|
5
|
|
Comorbidity, n
|
|
|
|
- respiratory
|
3
|
1
|
0.333
|
- neurological
|
1
|
0
|
1.000
|
- renal
|
0
|
2
|
0.478
|
- diabetes
|
3
|
5
|
0.667
|
- malignancy
|
0
|
3
|
0.217
|
Hemoglobin, g/dl
|
13.8 (12.9 – 15.1)
|
13.3 (11.9 – 14.4)
|
0.269
|
Leukocytes, /nl
|
7.0 (6.1 – 8.4)
|
7.4 (5.8 – 7.9)
|
0.884
|
CRP, mg/ml
|
1.5 (1.1 – 2.0)
|
3.8 (1.2 – 5.3)
|
0.113
|
Creatinine, mg/dl
|
0.99 (0.93 – 1.11)
|
1.04 (0.97 – 1.20)
|
0.200
|
GFR, ml/min/1.73m2
|
74 (58 – 87)
|
60 (55 – 71)
|
0.068
|
EuroSCORE II, percent
|
1.34 (0.81 – 2.93)
|
3.85 (2.21 – 6.21)
|
0.007
|
Data presented as median (IQR) or number (n)
BMI, body mass index; CHD, coronary heart disease; CRP, complement reactive protein; GFR, glomerular filtration rate.
Significance using Chi Squared Test, Mann Whitney U Test or where appropriate
The postoperative, during ICU stay, characteristics of the patients showed many significant differences which are described in table 2. All patients in the PICULOS group had a significantly higher risk stratification score in SAPS II, Apache II and SOFA. Also, the duration of mechanical ventilation was longer (8 vs. 200 hours, p= 0.000) as was the duration of vasopressor use (12 vs. 200 hours, p= 0.000). Severe sepsis was seen more frequently in the PICULOS group as was the need for dialysis and delirium. Interestingly, the duration of cardio-pulmonary bypass does not affect the duration of ICU stay within the groups compared.
Table 2. Postoperative, during ICU stay, patient characteristics
|
non-PICULOS
n = 12
|
PICULOS
n = 12
|
p value
|
CPB, minutes
|
106 (84 – 132)
|
125 (89 – 155)
|
0.453
|
SAPS II at ICU admission
|
47 (40 – 48)
|
53 (50 – 56)
|
0.001
|
APACHE II at ICU admission
|
20 (18 – 22)
|
24 (21 – 24)
|
0.036
|
SOFA at ICU admission
|
8 (7 – 9)
|
10 (8-10)
|
0.016
|
LOS ICU, hours
|
27 (18 – 45)
|
424 (264 – 664)
|
0.001
|
Mechanical Ventilation, hours
|
8 (6 – 12)
|
200 (24 – 447)
|
0.001
|
Vasopressors, hours
|
12 (7 – 21)
|
227 (81 – 439)
|
0.001
|
Severe sepsis , n
|
0
|
9
|
0.002
|
Delirium, n
|
0
|
7
|
0.046
|
Dialysis, hours
|
0
|
93 (82 – 183)
|
0.037
|
Death, n
|
0
|
2
|
0.478
|
Data presented as median (IQR) or number (n).
CABG, coronary artery bypass graft; CPB, cardiopulmonary bypass; LOS, length of stay;
Significance using Chi Squared Test or Mann Whitney U Test where appropriate.
GDF-15 and outcomes
Concentrations of GDF-15 were raised in preoperative blood samples of PICULOS versus non-PICULOS patients, showing a significant increase within the PICULOS group (median 713 versus 1041 pg/ml, p = 0.003, Figure 5).
The most commonly performed surgery was coronary artery bypass graft. Also, 9 patients underwent a combined operation, whereby both a coronary bypass and aortic valve replacement was performed. The median time of cardiopulmonary bypass was 106 minutes for non-PICULOS patients versus 125 minutes for PICULOS patients. Raised levels of preoperatively raised GDF-15 were not associated with prolonged cardiopulmonary bypass duration (Figure 6).
Patients with preoperatively raised GDF-15 levels spent longer time undergoing mechanical ventilation. Regarding further clinical outcomes, patients with raised levels of GDF-15 required longer vasopressor therapy and were subject to severe sepsis more frequently as could be depicted in figure 7. Rates of renal replacement therapy in the context with acute kidney failure were not increased with raised GDF-15 levels. Finally, rates of delirium were significantly associated with raised GDF-15 levels (median 718 versus 1491 pg/ml, p = 0.0006).
GDF-15 prediction
As described in methods, we performed a logistic regression analysis of GDF-15 for prediction of prolonged ICU stay and also for other values. Univariate analysis showed GDF-15 levels (Odds ratio 1.01, 95% Confidence Interval 1 – 1.02, p= 0.029) to be predictive for a prolonged ICU stay. Additionally, age, EuroSCORE II, SAPS II and SOFA scores were also prognostic for a prolonged ICU stay. However, when a multivariate analysis was performed no further predictive value was found (table 3).
In our population, preoperatively raised levels of GDF-15 were significantly better at predicting PICULOS than EuroSCORE II. ROC curve analysis of GDF-15 and PICULOS showed an AUC of 0.86 (95% Confidence Interval 0.71 – 0.99, p= 0.003) and a cut-off value of > 905.8 pg/ml (sensitivity 83.33%, specificity 83.33%). An analysis of EuroSCORE II and PICULOS revealed an AUC of 0.81 (95% Confidence Interval 0.65 – 0.99, p= 0.008) with a cut-off value of 2.82% mortality (sensitivity 75%, specificity 75%).
Table 3. Results of univariable and multivariable logistic regression analyses for identifying predictors of prolonged ICU stay.
|
Univariable logistic regression
|
Multivariable logistic regression
|
|
OR
|
95% CI
|
p
|
OR
|
95% CI
|
p
|
Age
|
1.17
|
1.02 – 1.34
|
0.025
|
1.132
|
0.91 – 1.47
|
0.260
|
Male
|
0.70
|
0.13 – 3.70
|
0.673
|
|
|
|
BMI
|
0.97
|
0.81 – 1.13
|
0.653
|
|
|
|
Diabetes
|
2.14
|
0.39 – 13.6
|
0.390
|
|
|
|
GDF 15
|
1.01
|
1.00 – 1.02
|
0.029
|
1.003
|
0.99 – 1.01
|
0.461
|
GFR
|
0.93
|
0.86 – 1.00
|
0.073
|
|
|
|
EuroSCORE II
|
1.80
|
1.12 – 3.59
|
0.043
|
1.149
|
0.48 – 2.79
|
0.738
|
CPB
|
1.01
|
0.99 – 1.03
|
0.370
|
|
|
|
SAPS II
|
1.50
|
1.06 – 2.13
|
0.022
|
1.140
|
0.71 – 1.94
|
0.562
|
Apache II
|
1.41
|
1.03 – 2.10
|
0.050
|
|
|
|
SOFA
|
2.21
|
1.02 – 4.80
|
0.045
|
1.590
|
0.52 – 8.04
|
0.463
|