Fluid Accumulations and Adverse Outcomes in Critically Ill Pediatric Patients

Fluid overload in critically ill pediatric patients has been associated with adverse outcomes in a variety of conditions and age groups. Mortality rates, ventilator days, pediatric intensive care unit (PICU) length of stay (LOS), and hospital LOS have all been shown to be affected by fluid accumulation (FA).¹ To date, however, the threshold of FA that increases these risks has not been definitively determined. Gelbart et al sought to investigate the association between FA as a continuous exposure and worsening patient-centered outcomes and whether a threshold for these outcomes could be determined.²

In this retrospective cohort study, the authors looked at the records of critically ill children admitted to a tertiary-care PICU over a 5-year period. Children were eligible for the study if they were mechanically ventilated for at least 24 hours, commencing within the first 24 hours of PICU admission, and if they weighed between 2 and 150 kg. Children with a diagnosis of chronic renal failure on admission were excluded. The authors collected demographic and clinical information, including daily fluid totals, duration of respiratory support, hospital and PICU LOS, and mortality. Risk Adjustment for Congenital Heart Surgery (RACHS) and Pediatric Index of Mortality (PIM3) scores were followed when appropriate.

FA was calculated as the net daily fluid balance in liters divided by the admission weight, then multiplied by 100. Cumulative FA was calculated within the first 7 days of of PICU admission, and the day that the maximum FA occurred was recorded. Patients who underwent cardiopulmonary bypass (CPB) had their fluid values determined starting on the first postoperative day. The primary outcome was the determination of maximum cumulative FA during the first 7 days of PICU admission. The secondary outcome was the determination of thresholds of percentage FA that was associated with adverse outcomes.

In this study, 1636 children met the criteria and were enrolled, including 623 who had undergone CPB and 674 from the general PICU. In the CPB group, the median maximum FA was 6.5% and each 1% increase in maximum FA was associated with decreased ventilator days and PICU LOS but not hospital LOS or mortality. Factors associated with higher FA in the CPB population included younger age, PIM3 and RACHS scores, and the need for extracorporeal membrane oxygenation (ECMO). In the general PICU group, the median maximum FA was 8.0%, and each 1% increase in maximum FA was associated with decreased ventilator days and PICU and hospital LOS but not mortality.

Some factors associated with higher maximum FA were younger age and the need for ECMO but not PIM3 score. In both groups together, FA occurred in 1507 subjects (92%). The median maximum FA was 7.5%, which occurred at a median of 4 days after PICU admission. In multivariable analyses, each 1% increase in maximum FA was associated with longer duration of mechanical ventilation, increased PICU and hospital LOS, and increased mortality. The threshold at which continuously collected maximum FA was associated with decreased ventilator days and PICU and hospital LOS was greater than 20%, which was also true for both groups separately.

The authors demonstrated that FA was common in critically ill mechanically ventilated children within the first 7 days of admission. They showed that higher FA was associated with adverse outcomes but that only greater than 20% FA was associated with worse outcomes. They demonstrated that no harmful associations were found when they excluded FA values greater than 10%. The authors acknowledged limitations to the study, including the inability to establish causality between FA and poor outcomes and the limited duration to only the first 7 days of a PICU stay. However, the authors’ findings are consistent with previous studies,¹ and the finding of a threshold FA level is novel. Clearly not all FA is associated with poor outcomes in critically ill ventilated pediatric patients, and clinicians should personalize the treatment plans for each patient, although this study can serve as an initial guide.

References

1. Alobaidi R, Morgan C, Basu RK, et al. Association between fluid balance and outcomes in critically ill children: a systematic review and meta-analysis. JAMA Pediatr. 2018 Mar 1;172(3):257-268. https://pubmed.ncbi.nlm.nih.gov/29356810/
2. Gelbart B, Serpa Neto A, Stephens D, et al. Fluid accumulation in mechanically ventilated, critically ill children: retrospective cohort study of prevalence and outcome. Pediatr Crit Care Med. 2022 Dec 1;23(12):990-998. https://pubmed.ncbi.nlm.nih.gov/36454001/