Baseline characteristic of patients
A total of 348 patients were admitted to our hospital. 28 and 32 patients were excluded due to cancelling scheduled surgery and incomplete data, respectively. Finally, 288 subjects were included in the analyses. The median age of these patients was 74 years (IQR 72-28), and 148 patients (51.4%) were male. Of the overall population, 49 (17%) developed POD, and median LOS was 14 days (IQR 10-21). In our study, the number of patients who underwent general, orthopedic and thoracic surgery were 189 (65.6%), 71 (24.7%) and 28 (9.7%), respectively.
The characteristics of the population as determined by the MNA-SF and GNRI
The characteristics of the patients screened by the MNA-SF and GNRI are shown in tables 1 and 2. According to the GNRI, 29.5% and 15.6% of patients were low risk and high risk, respectively. Based on the MNA-SF, 34% and 14.2% of patients were at risk of malnutrition and malnourished, respectively. There were significant differences in the Barthel Index, POD incidence, and LOS among different GNRI and MNA-SF categories. By a post-hoc comparison, we found that albumin levels was significantly lower in subjects who were malnourished and at risk of malnutrition compared to those who were well-nourished according to the MNA-SF.
Table 1 Characteristics of the studied population according to the Geriatric Nutritional Risk Index (GNRI)
Characteristic
|
Total
|
High Risk 92
(n = 45)
|
Low Risk 92-98
(n = 85)
|
No Risk > 98
(n =158)
|
P-value a
|
Age (years), median (IQR)
|
74 (72-78)
|
75 (73-79)
|
75 (72-78)
|
74 (71-77)
|
0.086
|
Male gender, n (%)
|
148 (51.4)
|
24 (53.3)
|
36 (42.4)
|
88(55.7)
|
0.134
|
Preoperative pain, n (%)
|
169 (58.7)
|
26 (57.8)
|
56 (65.9)
|
87 (55.1)
|
0.261
|
Depression, n (%)
|
19 (6.6)
|
4 (8.9)
|
5 (5.9)
|
10 (6.3)
|
0.79
|
CCI, n (%)
Mild (≤2)
Moderate (3-4)
Severe (≥5)
|
214 (74.3)
52 (18.1)
22 (7.6)
|
34 (75.6)
7 (15.6)
4 (8.9)
|
58 (68.2)
21 (24.7)
6 (7.1)
|
122 (77.2)
24 (15.2)
12 (7.6)
|
0.546
|
GNRI score, mean ± SD
|
98.98±8.46
|
85.09±5.45 b
|
95.12±2.17 b
|
105.01±4.49 b
|
<0.001
|
MNA-SF score, med (IQR)
|
12 (9-13)
|
9 (7-11)
|
10 (8-12)
|
12 (11-14)
|
<0.001
|
Barthel Index, median (IQR)
|
100 (90-100)
|
95 (72-100)
|
100 (87-100)
|
100 (95-100)
|
0.010
|
Postoperative delirium, n (%)
|
49 (17.0)
|
14 (31.1)
|
11 (12.9)
|
24 (15.2)
|
0.021
|
Length of stay, med (IQR)
|
14 (21-10)
|
17 (12-21)
|
17 (12-23)
|
13 (9-18)
|
<0.001
|
BMI body mass index, CCI Charlson Comorbidity Index, MNA-SF Mini Nutritional Assessment-Short Form.
Notes: a p values according to ANOVA, Kruskall-Wallis or Chi-square tests;
b Significantly different from the other groups by post-hoc comparison.
Table 2 Characteristics of the studied population according to the Mini-Nutritional Assessment Short Form (MNA-SF)
Characteristic
|
Malnourished 7
(n = 41)
|
At risk 8-11
(n = 98)
|
Well nourished 12-14
(n =149)
|
P-value a
|
Age (years), median (IQR)
|
76 (73-78)
|
75.5 (72-78)
|
73 (71-77)
|
0.078
|
Male gender, n (%)
|
22 (53.7)
|
49 (50.0)
|
77 (51.7)
|
0.921
|
Preoperative pain, n (%)
|
30 (24.1)
|
59 (60.2)
|
80 (53.7)
|
0.075
|
BMI (kg/m2), mean ± SD
|
19.45±2.55 b
|
21.42±3.07 b
|
23.70±2.88 b
|
<0.001
|
Albumin (g/L), mean ± SD
|
36.93±5.13 b
|
39.79±4.73 b
|
41.21±4.48 b
|
<0.001
|
MNA-SF score, med (IQR)
|
6 (5-7) b
|
10 (9-11) b
|
13 (12-14) b
|
<0.001
|
Barthel Index, median (IQR)
|
95 (77-100)
|
100 (88-100)
|
100 (95-100)
|
0.010
|
Postoperative delirium, n (%)
|
16 (39.0)
|
20 (20.4)
|
13 (8.7)
|
0.004
|
Length of stay, med (IQR)
|
19 (14-23)
|
14 (10-19)
|
14 (10-20)
|
0.022
|
BMI body mass index, CCI Charlson Comorbidity Index, GNRI Geriatric Nutritional Risk Index.
Notes: a p values according to ANOVA, Kruskall-Wallis or Chi-square tests;
b Significantly different from the other groups by post-hoc comparison.
Multivariable logistic regression and linear regression analysis
In the multivariable model, the malnourished category of the MNA-SF was independent risk factor for POD after adjustment of age, sex, preoperative pain, depression, Barthel Index and CCI, while the GNRI was not predictor for POD (Table 3). In the linear regression, prolonged LOS was significantly associated with low and high risk of the GNRI, but only with malnourished category by the MNA-SF after adjustment of age, sex, Barthel Index and preoperative pain (Table 3). When modeled as a continuous variable, MNA-SF was independent predictor of prolonged LOS and POD, while the GNRI (modeled as a continuous variable) was only significantly correlated with LOS.
Table 3 Multivariable logistic regression and linear regression analyses for the occurrence of postoperative delirium and length of stay
|
Postoperative delirium
|
|
Length of stay
|
|
Adjusted OR (95% CI)a
|
P-value
|
|
β (95% CI)b
|
P-value
|
GNRI categories c
|
|
|
|
|
|
No risk (>98)
|
Reference
|
|
|
Reference
|
|
Low risk (92-98)
High risk (<92)
|
0.61 (0.26-1.43)
2.22 (0.92-5.37)
|
0.255
0.077
|
|
4.91 (2.43-7.39)
4.10 (0.95-7.25)
|
<0.001
0.011
|
GNRI scores d
|
0.96 (0.92-1.00)
|
0.077
|
|
-0.24 (-0.37 to -0.11)
|
<0.001
|
MNA-SF categories c
|
|
|
|
|
|
Well nourished (12-14)
At risk (8-11)
Malnourished (≤7)
|
Reference
1.95 (0.86-4.39)
4.06 (1.62-10.18)
|
0.109
0.003
|
|
Reference
0.87 (-1.55 to 3.29)
4.23 (0.91-7.54)
|
0.48
0.013
|
MNA-SF scores d
|
0.82 (0.72-0.92)
|
0.001
|
|
-0.52 (-0.93 to -0.11)
|
0.014
|
OR odds ratio, CI confidence interval, GNRI Geriatric Nutritional Risk Index, MNA-SF Mini-Nutritional Assessment Short Form, CCI Charlson Comorbidity Index.
Notes: a Adjusted for age, sex, CCI, depression, Barthel Index and preoperative pain in multivariable logistic regression model;
b Adjusted for age, sex, Barthel Index and preoperative pain in linear regression model;
c Modeled as categories variables;
d Modeled as continuous variables.
ROC curve analysis
Based on the ROC curve analyses and Delong’s test, MNA-SF scores showed higher AUC in predicting POD than GNRI scores (Table 4, Fig. 1). In addition, the AUC of MNA-SF scores was significantly higher than GNRI scores (Delong’s test, P=0.006). Although the AUC of GNRI scores for prolonged LOS was better than MNA-SF scores (Table 4, Fig. 2), there was no significant difference in determining prolonged LOS (Delong’s test, P=0.079). As shown in Table 4, both MNA-SF< 8 and GNRI< 92 exhibited satisfactory specificity values (>60%) in predicting POD and prolonged LOS. However, the sensitivity values of the two categories were below adequate (<80%).
Table 4 Sensitivity, specificity, positive likelihood ratios (PLR), negative likelihood ratios (NLR) and area under the curve (AUC) of nutritional screening tools
|
Sensitivity
|
Specificity
|
PLR
|
NLR
|
AUC (95% CI)
|
P (AUC)
|
Postoperative delirium
|
|
|
|
|
|
|
GNRI
|
|
|
|
|
|
|
Scores <92
|
28.6%
|
87.0%
|
2.20
|
0.82
|
0.606 (0.52-0.69)
|
0.019
|
Scores ≤98
|
51.0%
|
56.1%
|
1.16
|
0.87
|
MNA-SF
|
|
|
|
|
|
|
Scores <8
|
32.7%
|
89.5%
|
3.11
|
0.75
|
0.718 (0.64-0.80)
|
<0.001
|
Scores <12
|
73.5%
|
56.9%
|
1.71
|
0.47
|
Prolonged length of stay
|
|
|
|
|
|
|
GNRI
|
|
|
|
|
|
|
Scores <92
|
16.9%
|
84.8%
|
1.11
|
0.98
|
0.611 (0.54-0.69)
|
0.006
|
Scores ≤98
|
61.5%
|
59.6%
|
1.52
|
0.65
|
MNA-SF
|
|
|
|
|
|
|
Scores <8
|
23.1%
|
88.3%
|
1.97
|
0.87
|
0.533 (0.45-0.62)
|
0.421
|
Scores <12
|
50.8%
|
52.5%
|
1.07
|
0.94
|
CI confidence interval, GNRI Geriatric Nutritional Risk Index, MNA-SF Mini-Nutritional Assessment Short Form.