Baseline characteristics of patients
A total of 125 children with moderate to severe ARDS admitted to PICU were eligible from November 2016 to October 2019. Among them, there were 14 cases with less than 72h in PICU, and 6 patients were lack of appropriate acoustic window, 14 cases were pneumothorax and 21 patients were hypoxemia secondary to cardiac disease congenital cardiovascular disease or chronic cardiopulmonary disease. Finally, 70 children were enrolled in this study (Figure 1). The median age was 33 (10 - 52) months and 41 cases were male (58.57 %). The hospital mortality rate was 38.57 % (27/70). There were 37 patients in the CRRT group, and 33 patients in the None-CRRT group. The baseline characteristics and outcome of patients were summarized in Table 3. The PRISM III score, proportion of complication with AKI, OI, mechanical ventilation duration, length of PICU stay in the CRRT group were significantly higher than that in the Non-CRRT group (17 [15 - 20] vs. 15 [12 - 18], P = 0.016; 67.57% vs. 27.27%, P = 0.001; 13.15 [10.00 – 14.78] vs. 7.69 [6.46 – 9.50], P < 0.001; 8 [6 - 15] days vs. 6 [4 - 9] days, P = 0.012; 14 [10 - 20] days vs. 10 [6 - 17] days, P = 0.047, respectively), while PaO2/FiO2 was significantly lower in the CRRT group than the Non-CRRT group (123.00 [110.50 - 138.50] mmHg vs. 163.00 [142.50 - 175.00] mmHg, P < 0.001). There were no significant differences in age, gender, BMI, PaCO2 and hospital mortality (all P > 0.05).
Correlation of LUS score to PaO2/FiO2, OI, PaCO2, dynamic lung compliance and fluid balance
LUS score was negatively correlated with PaO2/FiO2 [1st: r2 = 0.619, P < 0.001; 2nd: r2 = 0.788, P < 0.001; 3rd: r2 = 0.298, P < 0.001; 4th: r2 = 0.228, P < 0.001] and dynamic lung compliance (Cdyn) [1st: r2 = 0.497, P < 0.001; 2nd: r2 = 0.751, P < 0.001; 3rd: r2 = 0.740, P < 0.001; 4th: r2 = 0.869, P < 0.001] based on 1st to 4th values after ARDS diagnosed. Positive relationships were observed between LUS score and OI [1st: r2 = 0.531, P < 0.001; 2nd: r2 = 0.674, P < 0.001; 3rd: r2 = 0.530, P < 0.001; 4th: r2 = 0.512, P < 0.001] during the first four days after ARDS diagnosed. The change in daily fluid balance volume was positively correlated with the change in LUS score during CRRT (the first day of CRRT: r2=0.333, P < 0.001; the second day of CRRT: r2=0.489, P =0.002) (Figure 2).
The median of LUS score (1st: 18 [16 - 20], 2nd:22 [18 - 25], 3rd: 18 [16 - 22], 4th: 14 [12 - 18]), PaO2/FiO2 (1st: 123.50 [111.00 - 139.25] mmHg, 2nd: 105.00 [91.00 - 121.00] mmHg, 3rd: 127.00 [109.00 - 148.00] mmHg, 4th: 160.00 [142.50 - 170.50] mmHg), OI (1st: 13.15 [10.00 - 14.78], 2nd: 15.85 [13.54 - 17.46], 3rd: 11.63 [10.24 - 14.47], 4th: 9.47 [8.63 - 10.50]), Cdyn (1st: 0.38 [0.31 - 0.58] ml/cmH2O/kg, 2nd: 0.40 [0.30 - 0.42] ml/cmH2O/kg, 3rd: 0.44 [0.38 - 0.56] ml/cmH2O/kg, 4th: 0.60 [0.51 - 0.66] ml/cmH2O/kg) in the CRRT group were significantly different during the first four days after identified ARDS (all P < 0.001). CRRT group displayed peak median value of LUS score, OI, and the lowest median value of PaO2/FiO2, Cdyn one day after diagnosis as ARDS. Thirty-six patients received CRRT on the second day after diagnosis (97.30%). In the Non-CRRT group, there were only significant difference in PaCO2 during the first four days (P<0.001) (Table 2).
Though the median of LUS score and OI in the CRRT group were higher than the Non-CRRT group during the first four days, but on the 4th day the difference between two groups decreased. The paired analysis revealed that PaO2/FiO2 (1st: 123.50 [111.00 - 139.25] mmHg vs. 163.00 [142.50 - 175.00] mmHg, 2nd: 105.00 [91.00 - 121.00] mmHg vs. 152.10 [143.00 - 179.00] mmHg, 3rd: 127.00 [109.00 - 148.00] mmHg vs. 160.00 [140.00 - 183.00] mmHg) and Cdyn (1st: 0.38 [0.31 - 0.58] ml/cmH2O/kg vs. 0.61 [0.46 - 0.72] ml/cmH2O/kg, 2nd: 0.40 [0.30 - 0.42] ml/cmH2O/kg vs. 0.61 [0.50 - 0.71] ml/cmH2O/kg, 3rd: 0.44 [0.38 - 0.56] ml/cmH2O/kg vs. 0.60 [0.44 - 0.68] ml/cmH2O/kg) in the CRRT group were significantly lower than that in the Non-CRRT group in first three days after diagnosis as ARDS (P<0.001) (Table 2). In the CRRT group, the PaO2/FiO2 and Cdyn increased after received CRRT and compared to Non-CRRT group, there were no significant difference between two groups on the 4th day (Figure 3). The representative images of LUS were presented as Figure 5.
The interval time between identified moderate to severe ARDS and CRRT initiation was 6.0 (3.0 - 10.5) hours, and the median duration of CRRT was 49.5 (45.0 - 53.5) hours. The median of LUS score [22 (18 - 25) vs. 15 (13 - 18)], PaO2/FiO2 [106.00 (96.00 - 121.50) mmHg vs. 160.0 (142.50 - 173.00) mmHg], OI [15.92 (14.07 - 17.73) vs. 9.49 (8.70 - 10.58)], and Cdyn [0.40 (0.30 - 0.42) ml/cmH2O/kg vs. 0.60 (0.51 - 0.65) ml/cmH2O/kg] were determined at initiation and after CRRT target weaned in the CRRT group. These results indicated that LUS score and OI after CRRT weaned were significantly lower, and PaO2/FiO2 and Cdyn were increased (P<0.001, Table 4). Otherwise, only the value of PaCO2 was decreased on the 4th day after ARDS diagnosis in the Non-CRRT group (P = 0.006, Table 4).