Lung ultrasound scores are not associated with subcutaneous oedema or fluid balance in infants after cardiac surgery

Background Lung ultrasound may help to estimate extravascular lung water (EVLW). However, after paediatric cardiac surgery, the relationship of a lung ultrasound score (LUS) with subcutaneous oedema, fluid balance, or body weight is unknown. Methods A prospective, observational study was performed in mechanically ventilated infants following cardiac surgery. A clinical oedema score (COS), fluid balance (FB), body weight (BW) and LUS (based on a B-line scoring tool) were performed. Results We studied 53 infants with a median age of 8 days [IQR, 0–14]. EVLW, as estimated by the mean LUS, was 8.7 (SD 3.7) at baseline, 9.2 (SD 4.2) at 24 h, and 9.1 (SD 3.4) at 48 h, out of a maximum score of 24. However, LUS changes over time were small and infero-lateral lung zones had higher mean LUS compared to supero-anterior lung zones. Moreover, subcutaneous body oedema, as measured by a COS, change in BW, or FB, were not associated with the LUS. On multivariable, linear, mixed-effects modelling, accounting for repeated measures within children over time, there was no significant association between the COS and LUS (0.2 points [95% CI − 0.01–0.3]. Finally, in similar regression analyses, there was no significant association between each 100 gm increase in BW or 100 ml increase in FB and changes in LUS (BW, 0.3 [− 0.1–0.7] and FB, 0.1 [− 0.2–0.4]). Conclusions In infants following cardiac surgery, the lung ultrasound score was higher in infero-lateral lung zones compared to supero-anterior zones. However, it had no association with a subcutaneous oedema score or changes in fluid balance or body weight.