Risk factors
R 4.2.1 language was used to perform logistic univariate analysis on 25 related factors, such as general data and preoperative laboratory test results of patients. The results showed that 15 of the 25 related factors were statistically significant, namely, age, urea nitrogen, pulse, haemoglobin, red blood cells, haematocrit, fibrinogen, total protein, albumin, prothrombin time, alanine aminotransferase, aspartate aminotransferase, total bilirubin, direct bilirubin, and blood glucose (Table 2). These 15 statistically significant indicators were included in the multivariate logistic regression. The results showed that age, blood glucose, direct bilirubin, alanine aminotransferase, serum albumin, prothrombin time, and haemoglobin were independent influencing factors for planned ICU transfer after hip arthroplasty in elderly patients (Table 3). We show this independent influencing factor in the form of a forest chart (Fig. 2).
Table 2
univariate logstic analysis of planned ICU transfer after elderly hip arthroplasty
Variable
|
B
|
SE
|
OR
|
CI
|
Z
|
P
|
CCI
|
0.097
|
0.076
|
1.10
|
0.95–1.28
|
1.283
|
0.200
|
Age
|
0.077
|
0.014
|
1.08
|
1.05–1.11
|
5.639
|
< 0.001
|
Gender
|
-0.277
|
0.232
|
0.76
|
0.48–1.2
|
-1.19
|
0.234
|
GLU
|
0.081
|
0.041
|
1.08
|
1-1.18
|
1.981
|
0.048
|
SCR
|
0.001
|
0.001
|
1.00
|
1–1
|
1.622
|
0.105
|
BUN
|
0.052
|
0.024
|
1.05
|
1.01–1.1
|
2.151
|
0.031
|
DBIL
|
0.206
|
0.045
|
1.23
|
1.13–1.34
|
4.539
|
< 0.001
|
TBIL
|
0.048
|
0.016
|
1.05
|
1.02–1.08
|
3.091
|
0.002
|
ALT
|
0.028
|
0.01
|
1.03
|
1.01–1.05
|
2.695
|
0.007
|
AST
|
0.032
|
0.01
|
1.03
|
1.01–1.05
|
3.125
|
0.002
|
ALB
|
-0.154
|
0.026
|
0.86
|
0.81–0.9
|
-5.916
|
< 0.001
|
TP
|
-0.075
|
0.018
|
0.93
|
0.9–0.96
|
-4.112
|
0.016
|
K+
|
-0.072
|
0.209
|
0.93
|
0.62–1.4
|
-0.344
|
0.731
|
FIB
|
0.213
|
0.081
|
1.24
|
1.06–1.45
|
2.635
|
0.008
|
APTT
|
-0.006
|
0.019
|
0.99
|
0.96–1.03
|
-0.291
|
0.771
|
TT
|
-0.034
|
0.051
|
0.97
|
0.87–1.07
|
-0.676
|
0.499
|
INR
|
-0.023
|
0.042
|
0.98
|
0.9–1.06
|
-0.532
|
0.595
|
PT
|
0.178
|
0.074
|
1.19
|
1.03–1.38
|
2.399
|
< 0.001
|
PLT
|
-0.001
|
0.001
|
1.00
|
1–1
|
-1.083
|
0.279
|
HCT
|
-0.106
|
0.021
|
0.90
|
0.86–0.94
|
-5.062
|
< 0.001
|
RED
|
-0.786
|
0.163
|
0.46
|
0.33–0.63
|
-4.818
|
< 0.001
|
Pulse
|
0.026
|
0.011
|
1.03
|
1-1.05
|
2.461
|
0.014
|
HP
|
-0.031
|
0.006
|
0.97
|
0.96–0.98
|
-5.059
|
< 0.001
|
Anesthesia
|
0.221
|
0.231
|
1.25
|
0.79–1.96
|
0.955
|
0.339
|
Blood.pressure
|
-0.017
|
0.229
|
0.98
|
0.63–1.54
|
-0.072
|
0.943
|
ICU Intensive care unit, CCI Charlson comorbidity index, GLU Blood glucose,SCR Serum creatinine, BUN Usea nitrogen,DBIL Direct bilirubin, TBIL Total bilirubin, ALT Glutamic-pyruvic transaminase, AST Glutamic-oxalacetic transaminase, ALB Albumin,TP Total protein, FIB Fibrinogen, APTT Activated partial thromboplastin timepartial thromboplastin time, TT Thrombin time, INR International normalized ratio, PT Prothrombin time, PLT Platelet, HCT Hematocrit, RED Red blood cell, HP Hemoglobin.
GLU Blood glucose, DBIL Direct bilirubin,ALT Glutamic-pyruvic transaminase, ALB Albumin, PT Prothrombin time, HP Hemoglobin.
Table 3
multivariate Logistic regression of planned transfer to ICU after elderly hip arthroplasty
Variable
|
B
|
SE
|
OR
|
CI
|
Z
|
P
|
Age
|
0.061
|
0.016
|
1.06
|
1.031–1.098
|
3.827
|
< 0.001
|
GLU
|
0.063
|
0.044
|
1.07
|
0.982–1.167
|
1.450
|
0.147
|
DBIL
|
0.114
|
0.048
|
1.12
|
1.023–1.236
|
2.367
|
0.018
|
ALT
|
0.033
|
0.012
|
1.03
|
1.011–1.061
|
2.675
|
0.007
|
ALB
|
-0.075
|
0.029
|
0.93
|
0.874–0.982
|
-2.541
|
0.011
|
PT
|
0.115
|
0.063
|
1.12
|
0.995–1.287
|
1.818
|
0.069
|
HP
|
-0.015
|
0.007
|
0.98
|
0.97–0.999
|
-2.056
|
0.040
|
GLU Blood glucose,DBIL Direct bilirubin,ALT Glutamic-pyruvic transaminase, ALB Albumin,PT Prothrombin time, HP Hemoglobin.
Prediction Model Construction
The risk factors in multivariate logistic regression were analysed by R language and screened by the backwards LR method to establish a visual prediction model, namely, a nomogram. A nomogram is able to personalize a prediction so that it can identify and assess the risk of each patient [ 5 ]. (Fig. 3). A nomogram converts the regression equation into a visual graph that is easy to understand, which makes the results of the prediction model more readable and facilitates patient risk assessment. In Fig. 3, the indicator on the left represents the independent variable, with each variable representing the axis corresponding to the line chart and indicating the score for the variable. The total score of each variable plus the total score of the corresponding total score table corresponds to the diagnostic possibility of planned transfer to the ICU after hip arthroplasty.
Evaluation And Verification Of The Model
Discrimination
The predicted probability of planned transfer to the ICU after hip arthroplasty in elderly individuals was expressed by P-m. According to the prediction probability P-m and the actual postoperative planned transfer to the ICU in the model set, the ROC curve of the P-m value was drawn, and the AUC was used to evaluate the discrimination of the prediction model. AUC is usually used to quantify a logical model [ 6 ]. The closer the AUC is to the value of 1, the better the discrimination of the model, and in clinical practice, when 0.7 < AUC < 0.9, the model has better discrimination [ 7 ]. The ROC curve of this model had an AUC of 0.793, the diagnostic threshold was 0.396, the sensitivity was 0.779, the specificity was 0.686, and the 95% CI (0.718–0.874) indicated that this model had good discrimination, as shown in Fig. 4. After 500 bootstrap internal validations, the ROC curve showed an AUC of 0.793 (95% CI (0.7447–0.8422)), which indicated that the model had good discrimination (Fig. 5).
Calibration
Accuracy reflects the degree to which the model correctly estimates absolute risk, that is, whether the predicted value of the model is consistent with the actual value [8]. In this study, the calibration curve was established using the R language software package, and the Hosmer‒Lemeshow test was used for the internal test of calibration (Fig. 6). The x-axis represents the predicted probability of postoperative planned ICU transfer, and the y-axis represents the actual probability of postoperative planned ICU transfer. The ideal (diagonal) slope is 1, representing the ideal curve; apparent represents the uncalibrated prediction curve, and bias-corrected represents the calibrated prediction curve. The two curves fluctuate on the diagonal and do not deviate significantly from the ideal curve. The results of the Hosmer‒Lemeshow test showed that chi-square = 5.214611 (P = 0.8152131), and P > 0.1 indicated that the predicted value was in good agreement with the actual value, indicating that the prediction accuracy of this model was high.
Clinical Usefulness
Clinical practicability refers to the clinical net benefit of using the prediction model under a certain threshold probability, namely, DCA [ 9 ]. DCA obtains the net benefit value of using the model at the threshold by determining the relationship between the selected prediction probability threshold and the relative value of false-positive and false-negative results [ 10,11 ]. The net benefit is calculated by all possible risk thresholds between the two extremes, namely, zero and maximum risk estimates, representing all negative events and all positive events, respectively [ 12 ]. If DCA is higher than two extreme lines, it indicates that patients can benefit and have better clinical practicability [ 13 ]. The black horizontal line in the DCA curve of this prediction model indicates that when all patients after hip arthroplasty are not transferred to the ICU, the clinical net benefit is zero; the grey line indicates that when all patients with hip arthroplasty are transferred to the ICU after the operation, the clinical net benefit has a negative slope; the red curve is based on the curve related to the prediction model in this study. When the prediction probability P-m is between 12% and 80%, the red curve is above the two extreme lines, indicating that the model can benefit from the prediction, as shown in Fig. 7.
Model Rationality Re-evaluation
We compared the constructed nomogram prediction model with the seven factors in the model in terms of discrimination and clinical applicability. ROC curves and DCA curves were drawn to verify the rationality of the model (Figs. 8 and 9). The area under the ROC curve of the nomogram in Fig. 8 is larger than that of the other seven factors, indicating that this prediction model has the best discrimination among all models. The DCA curve of the nomogram in Fig. 9 is located at the outermost side of the internal factor curve, indicating that the clinical practicability of this prediction model is the best and worthy of clinical application.