Results
A total of 104 point of care US were performed to 66 infants at a median (IQR) GA 30 (29–31) weeks. Infants were classified into two groups based on the outcome of extubation trials; succeeded vs failed extubation. The two groups were comparable in demographic and clinical characteristics (Table 1). LUS differed significantly between the two groups (p=0.022) whereas LVEI did not differ between groups (Table 1).
Table 2 shows the respiratory characteristics of both groups; mean airway pressure, duration of mechanical ventilation and of oxygen therapy were significantly higher in group-2 compared to group-1. Other ventilator parameters were comparable between the two groups.
OSI was different between those who succeeded and failed extubation: 2.1 (1.5 - 2.6) vs 3.4 (2.7-4.7), respectively; p <0.0001. Duration of mechanical ventilation was significantly increased in infants who failed extubation: 5 (5 - 8) days vs 8.5 (8 - 9) days, p<0.0001. Comparisons of the study population based on LUS severity are presented in supplemental tables (Tables S1 and S2).
Multivariate logistic regression was performed with extubation success as the dependent outcome and LUS, LVEI and duration of mechanical ventilation as covariates. In this model, LVEI remained insignificant (p=0. 817).
LUS was able to predict extubation success at day3 (area under the curve 0.71, 95% CI: 0.55 – 0.88, p=0.023) and at day 7 (area under the curve = 0.92, 95% CI: 0.82 – 1.0, p<0.001) (Figure 3). Table 3 presents predictive values for extubation success with LUS cut off points at the highest sensitivity and specificity on days 3 and 7. LVEI did not predict extubation success in ROC analysis (area under the curve = 0.52, 95% CI: 0.32 – 0.71, p= 0.87) (Figure 3). The predictive values for extubation success with LEVI are presented in Table 3. Using DeLong test, the predictive values for LUS and LVEI were compared and was found insignificant (p=0.19).
LVEI, measured at end-systole, correlated with PAP (r=0.66, 95% CI: 0.50 – 0.78, p<0.001) and with internal diameter of the ductus arteriosus (r=0.25,95% CI: 0.01-0.46, p=0.04). (Supplement Figures S1-S4). A total of 32 infants had PPHN with PAP >35 mmHg. There was no difference in PAP among infants who succeeded and failed extubation (p=0.27), Table 1.