A total of 3775 children were admitted to the PICU during the research period, of which 654 patients were eligible for inclusion. During the CT image analysis, 301 children were excluded due to poor CT scan image quality, 49 children were excluded because their guardians or parents refused participation, and 42 children were excluded due to missing CT data. Ultimately, 262 children met the criteria and were included in the study, with a mean SMI of 37.75 ± 9.32 cm2/m2. Subgroup analysis was performed for 203 of these children with SMD data, with a mean SMD of 41.71 ± 6.83 HU. Figure 2 shows the flow chart of this study.
The cutoff values that best fit to estimate hospital mortality were 30.96 cm2/m2 for the SMI and 41.21 HUs for SMD. All patients were categorized into a normal SMI group (n = 209) and a low SMI group (n = 53) based on the cutoff value of the SMI. A total of 204 patients were categorized into a low SMD group (n = 86) and a normal SMD group (n = 117) based on the cutoff value of SMD.
Sample characteristics
The characteristics of all children are given in Table 1. Comparing the group characteristics, the following were shown: BMI was superior in the normal SMI group compared to the low SMI group (18.07 ± 4.44 vs. 15.99 ± 4.51, P = 0.004), and length of PICU stay (13.00 [7.50–20.00] vs. 16.00[8.50–32.50], P = 0.02) and in-PICU mortality (10.00% vs. 22.6%, P = 0.025) were greater in the low SMI group.
Table 1
Sample Characteristics comparsion between normal and low SMI group
Characteristics | Normal SMI group (n = 209) | Low SMI group (n = 53) | P |
Age, mon, IQR | 84(18–156) | 76(49–119) | 0.694 |
Height, cm, IQR | 120(88.75-159.75) | 120(105–143) | 0.715 |
Weight, kg, IQR | 26(13.63–51.5) | 20(14.5–31) | 0.186 |
Sex, % | 68.75% | 53.48% | 0.195 |
BMI, kg/m2, (mean ± SD) | 18.07 ± 4.44 | 15.99 ± 4.51 | 0.004 |
SMI, cm2/m2, (mean ± SD) | 40.36 ± 8.55 | 27.40 ± 2.59 | ༜0.001 |
PCIS, (mean ± SD) | 86.95 ± 9.74 | 87.21 ± 6.55 | 0.821 |
Length of PICU stay, day, IQR | 13.00(7.5–20) | 16.00(8.5–32.5) | 0.02 |
Hospital mortality, % | 10.0(21/209) | 22.6(12/53) | 0.025 |
Admission diagnosis, % | | | |
Respiratory | 10.0 (21/209) | 5.6 (3/53) | |
Neurologic | 23.9 (50/209) | 22.6 (12/53) | |
Post-surgery | 2.8 (6/209) | 3.7 (2/53) | |
Hematology | 11.5(24/209) | 18.9 (10/53) | |
Sepsis | 11.5(24/209) | 9.4(5/53) | |
Cardiovascular | 3.8(8/209) | 5.6(3/53) | |
Trauma | 18.2(38/209) | 7.5(4/53) | |
Other | 18.2(38/209) | 26.4(14/53) | |
BMI = body mass index, SMI = skeletal muscle index, PCIS = pediatric critical illness score |
Subgroup analysis showed that children with low SMD had a higher in-PICU mortality rate (25.6% vs. 7.7%, P < 0.001), were younger (36.00[12.00-120.00] vs. 84.00[47.50-147.50], P < 0.001) and had lower weights (16.40[10.93–37.25] vs. 23.00[16.00–45.00], P = 0.006). No discrepancy was detected between the two groups in the length of PICU stay (Table 2).
Table 2
Sample Characteristics comparsion between normal and low SMD group
Characteristics | Normal SMD group (n = 117) | Low SMD group (n = 86) | P |
Age, mon, IQR | 84 (47.5-147.5) | 36(12–120) | < 0.001 |
Height, cm, IQR | 120 (104–157) | 104.5 (79.5-139.7) | 0.001 |
Weight, kg, IQR | 23 (16–45) | 16.4 (10.9–37.2) | 0.006 |
Sex male, % | 53.0 (62/117) | 55.8 (48/86) | 0.776 |
BMI, kg/m2, (mean ± SD) | 17.3 ± 4.1 | 18.6 ± 5.1 | 0.053 |
PCIS, (mean ± SD) | 87.3 ± 9.4 | 85.5 ± 10.2 | 0.199 |
Length of PICU stay, day, IQR | 16.3 (14.8–18.9) | 17.1 (15.2–20.4) | 0.065 |
Hospital mortality, % | 7.7(9/117) | 25.6(22/86) | ༜0.001 |
BMI = body mass index, PCIS = pediatric critical illness score, SMD = skeletal muscle density |
Relationship between muscle condition and clinical outcomes
The Kaplan–Meier curve analysis of the SMI and SMD is shown in Figs. 3 and 4. The analysis results indicated that mortality was considerably greater in patients with a low SMD and prolonged hospital stay (log rank test P = 0.007). However, a trend was not found between the low SMI and normal SMI groups (log rank test P = 0.902).
The comparison of characteristics between survivors (n = 172) and nonsurvivors (n = 31) showed that nonsurvivors had a lower SMD (37.53 ± 8.09 vs. 42.47 ± 6.32, P < 0.001), a longer length of PICU stay (25.00[17.00–41.00] vs. 13.00[8.00-19.75], P < 0.001) and more severe illness (PCIS 78.48 ± 18.9 vs. 88.08 ± 5.96 P < 0.001) (Table 3).
Table 3
The comparsion of characteristics between survivors and non- survivors
Characteristics | survivors (n = 172) | non- survivors (n = 31) | P |
Age, mon, IQR | 65.5(24.2–132.0) | 84.0(24.0-132.0) | 0.655 |
Height, cm, IQR | 113 (93.2-152.2) | 120 (78–157) | 0.79 |
Weight, kg, IQR | 20.5 (13.5-40.75) | 21.3 (10.7–47) | 0.975 |
Sex male, % | 55.8 (96/172) | 45.2 (14/31) | 0.329 |
BMI, kg/m2, (mean ± SD) | 17.3 ± 4.1 | 18.6 ± 5.1 | 0.053 |
PCIS, (mean ± SD) | 88.1 ± 5.9 | 78.4 ± 18.9 | ༜0.001 |
Length of PICU stay, day, IQR | 13.0(8.0-19.7) | 25.0(17.0–41.0) | ༜0.001 |
SMD, HU, (mean ± SD) | 42.47 ± 6.32 | 37.53 ± 8.09 | ༜0.001 |
SMI, cm2/m2, (mean ± SD) | 38.29 ± 9.66 | 34.98 ± 8.75 | 0.76 |
BMI = body mass index, SMI = skeletal muscle index, PCIS = pediatric critical illness score, SMD = skeletal muscle density |
The factors we included in logistic regression analysis were sex, age, BMI, SMD, the SMI, and the PCIS, and the results showed that SMD (95% CI, 0.79–0.92; OR, 0.85) and the PCIS (95% CI, 0.83–0.94; OR, 0.88) were independent predictors for in-PICU mortality, which indicated that for every 1 HU decrease in SMD, the in-PICU mortality increased by 15% (Fig. 5).
Multivariate linear regression analysis demonstrated that age (β = 0.08, P = 0.002), SMD (β=-0.54, P = 0.005) and BMI (β=-0.73, P = 0.025) were considerably correlated with in-PICU mortality (Table 4).
Table 4
Linear regression analysis of risk factors associated with Length of PICU stay
Factors | Length of PICU stay |
B | 95% CI | P |
SMD | -0.544 | -0.919 to -0.169 | 0.005 |
SMI | -0.072 | -0.396 to -0.251 | 0.659 |
BMI | -0.731 | -1.370 to -0.093 | 0.025 |
PCIS | -0.108 | -0.356 to -0.141 | 0.395 |
Age | 0.081 | 0.030 to 0.132 | 0.002 |
Sex | -1.02 | -6.008 to 3.968 | 0.687 |
BMI = body mass index, SMI = skeletal muscle index, PCIS = pediatric critical illness score, SMD = skeletal muscle density |