Patient characteristics
During the study period (January 2019 to September 2019), 497 pediatric patients were consecutively included. Due to incomplete NLR data, only 424 infants (219 male and 205 female) were included in the final analysis. The number of patients with poor outcomes was 68/424 (16.0%). Comparisons of the patient-related variables and surgery-related variables between patients with and without poor outcomes are presented in Table 1. Differences were apparent in the following variables: age, gender, previous cardiac surgery, cyanotic heart disease, height, weight, complex procedure (RACHS score ≥ 3), CPB duration, clamping time, lower body circulatory arrest, lowest nasopharyngeal temperature, and maximum lactate during surgery.
Table 1
The characteristics of patients with poor outcomes and non-poor outcomes.
Variable
|
Poor outcomes
n=68
|
Non-poor outcomes
n=356
|
p-value
|
Patient-related variables
|
|
|
|
Age (months)
|
5.66 ± 3.24
|
6.95 ± 2.70
|
0.001a
|
Female
|
23 (33.8%)
|
182 (51.1%)
|
0.009b
|
Previous cardiac surgery
|
5 (7.4%)
|
3 (0.8%)
|
0.004b
|
Birth weight (kg)
|
3.13 ± 0.62
|
3.17 ± 0.62
|
0.77a
|
Pulmonary arterial hypertension
|
33 (48.5%)
|
164 (46.1%)
|
0.709b
|
Cyanotic heart disease
|
30 (44.1%)
|
109 (30.6%)
|
0.03b
|
Height (cm)
|
62.76 ± 7.19
|
66.06 ± 6.11
|
<0.001a
|
Weight (kg)
|
6.19 ± 1.73
|
6.93 ± 1.49
|
<0.001a
|
Preoperative hemoglobin (g/L)
|
122.0 ± 26.63
|
114.42 ± 16.09
|
0.083a
|
Preoperative LVEF (%)
|
64.72 ± 10.04
|
67.35 ± 5.74
|
0.133a
|
Surgery-related variables
|
|
|
|
Complex procedure (RACHS score ≥ 3)
|
33(48.5%)
|
113 (31.7%)
|
0.008b
|
CPB duration (min)
|
119.46 ± 58.34
|
85.07 ± 34.62
|
<0.001a
|
Clamping time (min)
|
73.15 ± 39.0
|
55.81 ± 28.71
|
<0.001a
|
Repeated CPB
|
4 (5.9%)
|
9 (2.5%)
|
0.135b
|
Lower body circulatory arrest
|
5 (7.4%)
|
6 (1.7%)
|
0.019b
|
lowest nasopharyngeal temperature (℃)
|
29.47 ± 2.46
|
30.89 ± 3.0
|
<0.001a
|
Lowest hematocrit during CPB (%)
|
23.88 ± 3.33
|
23.77 ± 2.85
|
0.74a
|
Maximum lactate during surgery (mmol/L)
|
2.22 ± 1.22
|
1.69 ± 0.76
|
0.013a
|
LVEF, left ventricular ejection fraction; RACHS, Risk Adjustment for Congenital Heart Surgery; CPB: cardiopulmonary bypass; a Mann-Whitney U test; b χ2 test
Perioperative NLR and clinical outcomes
NLR variation among different days between infants with poor outcomes and non-poor outcomes is illustrated in Figure 1. A definite trend is evident that perioperative NLR increased from baseline due to the operation and CPB. NLR in patients without poor outcomes increased to a peak one day after the surgery and then decreased gradually. However, postoperative NLR in patients with poor outcomes maintained at a high level within 3 days after the surgery and still higher until Day6.
Baseline, Day0, Day2, Day3, and Day6 NLR showed statistical significance between the two groups. Repeated measurement analysis of variance showed that NLR was different in two groups, including both single NLR (F = 330.529,p < 0.001), an interaction term between NLR and poor outcomes (F = 19.416,p < 0.001). To explore the predictive value of NLR on different days, ROC curve analysis with NLR and poor outcomes was applied, results are shown in Table 2. According to AUC and p-value, Baseline, Day2, Day3, and Day6 NLR have a predictive diagnostic effect, with cutoff values of 0.37, 5.24 2.05, and 1.38 respectively, and Day3 NLR (AUC = 0.763, 95%CI 0.700-0.826) showed the best prognostic significance (Table 2).
Table 2
ROC comparison of NLR on different days for predicting poor outcomes
Variable
|
p value
|
AUC
|
95%CI
|
Cut-off Value
|
Baseline NLR
|
0.018
|
0.591
|
0.516-0.666
|
0.37
|
Day0 NLR
|
0.098
|
0.563
|
0.491-0.636
|
-
|
Day1 NLR
|
0.717
|
0.514
|
0.436-0.592
|
-
|
Day2 NLR
|
<0.001
|
0.719
|
0.658-0.781
|
5.24
|
Day3 NLR
|
<0.001
|
0.763
|
0.700-0.826
|
2.05
|
Day6 NLR
|
<0.001
|
0.748
|
0.679-0.817
|
1.38
|
ROC, receiver operating characteristic; NLR, neutrophil-lymphocyte ratio
Since Day3 NLR showed a larger AUC than other days, we choose it as postoperative NLR in the following analysis. As presented in Table 3, preoperative NLR was significantly correlated with mechanical ventilation time (p = 0.002) and ICU length of stay (p = 0.023) but had no obvious correlation with hospital length of stay (p = 0.081). Postoperative NLR was closely related to mechanical ventilation time (p <0.001), length of ICU (p <0.001) and hospital stay (p <0.001).
Table 3
Correlation between perioperative NLR and clinical outcomes.
Variable
|
Preoperative NLR
|
Postoperative NLR
|
Coefficient
|
p-value
|
Coefficient
|
p value
|
MV time
|
0.148
|
0.002
|
0.554
|
<0.001
|
ICU LOS
|
0.110
|
0.023
|
0.469
|
<0.001
|
Hospital LOS
|
0.081
|
0.094
|
0.421
|
<0.001
|
NLR, neutrophil-lymphocyte ratio; MV, mechanical ventilation; ICU, intensive care unit; LOS, length of stay
The Predictive Effect of NLR on Poor Outcomes
According to postoperative NLR cutoff thresholds (2.05), 424 infants were grouped to evaluate the relationship between postoperative NLR and poor outcomes. 54/195 (27.7%) of elevated postoperative NLR (≥2.05) patients experienced at least one of the poor outcomes compared to only 6.1% (14/229) without elevated postoperative NLR (p < 0.001). Infants in the elevated NLR group had a higher incidence of comorbidity: postoperative re-intubation (9.2% vs 1.3%, p <0.001), re-operation (7.7% vs 1.7%, p = 0.003), need for peritoneal dialysis (3.6% vs 0%, p = 0.004), pulmonary infection (25.1% vs 8.1%, p < 0.001), prolonged ICU stay (20.5% vs 3.5%, p < 0.001), and prolonged mechanical ventilation time (20.5% vs 3.9%, p < 0.001). However, differences in death (1.5% vs 0.9%, p = 0.665), incision infection (0% vs 0.9%, p = 0.502) and requirement of ECMO (1.0% vs 0%, p = 0.211) were not significant between the two groups. Median mechanical ventilation time, length of ICU and hospital stay were 26 hours, 5 days and 17days in elevated NLR patients, respectively, but only 9 hours, 3 days, and 12 days in non-elevated NLR patients (p < 0.001). Results are shown in Table 4.
Table 4
Comparison of poor outcomes between the elevated postoperative NLR and non-elevated postoperative NLR patients
|
NLR<2.05
(n = 229)
|
NLR≥2.05
(n = 195)
|
p Value
|
Poor outcomes
|
14(6.1%)
|
54(27.7%)
|
<0.001
|
Re-intubation
|
3(1.3%)
|
18(9.2%)
|
<0.001
|
Death
|
2(0.9%)
|
3(1.5%)
|
0.665
|
Re-operation
|
4(1.7%)
|
15(7.7%)
|
0.003
|
ECMO
|
0
|
2(1.0%)
|
0.211
|
Peritoneal dialysis
|
0
|
7(3.6%)
|
0.004
|
Incision infection
|
2(0.9%)
|
0
|
0.502
|
Pulmonary infection
|
19(8.3%)
|
49(25.1%)
|
<0.001
|
Prolonged MV time
|
9(3.9%)
|
40(20.5%)
|
<0.001
|
Prolonged ICU LOS
|
8(3.5%)
|
40(20.5%)
|
<0.001
|
MV time
|
9(6, 19)
|
26(18, 86)
|
<0.001
|
ICU LOS
|
3(1,4)
|
5(3,8)
|
<0.001
|
Hospital LOS
|
12(10, 16)
|
17(13, 24)
|
<0.001
|
NLR, neutrophil-lymphocyte ratio; ECMO, extracorporeal membrane oxygenation; MV, mechanical ventilation; ICU, intensive care unit; LOS, length of stay. |
As presented in Table 5, the multivariable logistic regression model showed that postoperative NLR (OR 1.298, 95%CI 1.153-1.461, p <0.001) predicted a composite of poor outcomes, after adjusting for basic clinical predictions (age, gender, weight, RACHS score, and CPB duration). When NLR was analyzed as a categorical variable, elevated postoperative NLR (≥2.05) (OR 3.722, 95%CI 1.895-7.309, p <0.001) was also an independent risk factor for poor outcomes. However, preoperative NLR showed no prognostic significance for poor outcomes (p = 0.097).
Table 5
Multivariate logistic regression of poor outcomes
Variable
|
Wald
|
p-value
|
OR
|
95%CI
|
NLR Model 1
|
|
|
|
|
Gender
|
5.185
|
0.023
|
2.062
|
1.106-3.844
|
Weight
|
9.964
|
0.002
|
0.716
|
0.581-0.881
|
CPB duration
|
13.025
|
<0.001
|
1.016
|
1.006-1.021
|
Postoperative NLR
|
18.620
|
<0.001
|
1.298
|
1.153-1.461
|
NLR Model 2
|
|
|
|
|
Gender
|
8.662
|
0.003
|
2,488
|
1.356-4.565
|
Weight
|
11.378
|
0.001
|
0.708
|
0.580-0.865
|
CPB duration
|
13.816
|
<0.001
|
1.012
|
1.006-1.019
|
Elevated postoperative NLR
|
14.561
|
<0.001
|
3.722
|
1.895-7.309
|
NLR Model 3
|
|
|
|
|
Gender
|
4.353
|
0.037
|
1.861
|
1.038-3.334
|
Age
|
9.960
|
0.002
|
0.849
|
0.767-0.940
|
CPB duration
|
27.261
|
<0.001
|
1.017
|
1.011-1.023
|
Preoperative NLR
|
2.759
|
0.097
|
1.739
|
0.905-3.341
|
NLR, neutrophil-lymphocyte ratio; CPB: cardiopulmonary bypass;
The basic model included age, gender, weight, RACHS score, and CPB duration demonstrated good predictive power (AUC 0.759, 95%CI 0.693-0.826), with better discrimination in the NLR Model 1 (AUC 0.813, 95%CI 0.754-0.872) and NLR Model 2 (AUC 0.797, 95%CI 0.739-0.855) containing postoperative NLR as a categorical variable. Results are shown in Table 6. The NLR Model 1 and NLR Model 2 demonstrated improvement on the basic model as measured by the absolute difference in AUC, respectively (ΔAUC = 0.0538, p = 0.0043) and (ΔAUC = 0.0378, p = 0.0436). The NLR Model 1 had the best predictive performance among the three models (sensitivity 82.35%, specificity 71.63%). ROC comparison between the NLR model and basic model is illustrated in Figure 2
Table 6
ROC comparison of different models for predicting poor outcomes
Variables
|
AUC (95%CI)
|
Sensitivity
|
Specificity
|
Youden index
|
p-value
|
Basic Model
|
0.759 (0.693-0.826)
|
79.41
|
65.17
|
0.4458
|
<0.001
|
NLR Model 1
|
0.813 (0.754-0.872)
|
82.35
|
71.63
|
0.5398
|
<0.001
|
NLR Model 2
|
0.797 (0.739-0.855)
|
75.00
|
73.60
|
0.4860
|
<0.001
|
ROC, receiver operating characteristic; NLR, neutrophil-lymphocyte ratio