Study design

We conducted an interrupted time series study of all patients who received fluid resuscitation at our PED. Data was collected during two time periods: January 1, 2018, to December 31, 2019, when NS was the primary resuscitation fluid (NS cohort), and March 1, 2022, to February 28, 2024, when RL became the primary fluid (RL cohort). Data collection between 2020 and early 2021 was excluded due to the SARS-CoV-2 pandemic.

Data were collected retrospectively for the 2018–2019 cohort and prospectively for the 2022–2024 cohort. The study was approved by the hospital’s institutional review board (Helsinki SZMC-21–0198), which also waived the requirement for informed consent.

Population

The cohorts included all patients aged 0–18 years who were admitted to the ED and resuscitated with 30 ml or more of fluids per kilogram. We excluded patients with diabetic ketoacidosis, traumatic brain injury, or hyponatremia, as treatment protocols for these conditions require the use of NS.

Data collection

Data were extracted from electronic health records (EHR). The following information was collected:

Demographics: Age, sex, and weight at admission.

Clinical Information: Indication for fluid resuscitation (e.g., fluid losses from vomiting, diarrhea, poor intake), sepsis or septic shock, acute kidney injury (AKI) defined as creatinine levels above age-specific normal limits [13], vital signs, amount of fluids administered per kilogram, department of admission from PED, length of stay, and need for oxygen or respiratory support (e.g., high-flow nasal cannula or intubation).

Biochemical results: (from the blood draw taken on arrival at the PED)

o

Values on admission: pH, pCO2 (mmHg), HCO3⁻ (mmol/L), sodium (mEq/L), potassium (mEq/L), chloride (mEq/L), creatinine (mg/dL), and blood urea nitrogen (BUN, mg/dL).

o

Minimal pH, pCO2, HCO3−, and BUN during admission.

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Maximal sodium, potassium, chloride, creatinine, and BUN during admission.

Outcomes

The primary outcome was the length of hospital stay, being the more significant outcome in the current literature. Secondary outcomes included differences in acidosis, renal functions (adjusted for age), and metabolic abnormalities. These outcomes were evaluated for the entire cohort and, in addition, for a subset of patients from both cohorts who had AKI upon admission to PED.

Statistical analysisMatching

We matched patients in the treatment groups on a one-to-one basis using k-nearest neighbors without replacement and a caliper of 0.15 on the propensity score. Exact matching on the department of admission was also applied to improve group balance. Variables used for matching included age, sex, weight, indication for fluid resuscitation, fluid dose, and biochemical results on admission to ED (BUN, sodium, and creatinine). Baseline covariate balance was assessed using standardized mean differences (SMD), with SMD > 0.25 indicating significant imbalance.

Statistical methods

Continuous descriptive data are presented as means ± standard deviation (SD) or medians (interquartile range), while categorical data are presented as frequencies and percentages. Groups were compared using Student’s t-test, Wilcoxon rank-sum test, χ2 test, or Fisher’s exact test, as appropriate. Adjusted means were calculated for each group to interpret main effects, and post hoc pairwise comparisons were conducted using Bonferroni correction to control for Type I error. A p-value < 0.05 was considered significant. All analyses were performed using RStudio version 4.3.2.

Ethics approval

This study was approved by the SZMC review board in accordance with the Declaration of Helsinki (SZMC-21–0198).