Mini fluid challenge versus passive leg raising test for predicting fluid responsiveness in spontaneously breathing children.

BACKGROUND: Fluid responsiveness assessment is recommended in acutely ill patients to avoid fluid overload. However, pediatric evidence on which bedside tests to use and how to apply them remains limited, particularly in spontaneously breathing children. We compared passive leg raising (PLR) and the mini-fluid challenge (mini-FC), hypothesizing that mini-FC would show greater diagnostic performance. METHODS: Prespecified secondary analysis of a prospective multicenter cohort of spontaneously breathing children requiring fluid resuscitation. Patients underwent standardized PLR followed by a fluid challenge (FC) embedding a mini-FC (4 mL/kg). Stroke volume was measured by transthoracic echocardiography. Fluid responsiveness was defined as a stroke volume increase >15% after 20 mL/kg. Diagnostic performance was assessed using ROC analysis, high-specificity thresholds, gray-zone analysis, and age-predictor interaction models. RESULTS: Eighty-seven children were analyzed; 52.9% were fluid responders. Mini-FC showed good discrimination (AUC 0.84, 95% CI 0.75-0.92) whereas the PLR showed acceptable discrimination (AUC 0.77, 95% CI 0.67-0.87; DeLong p = 0.26). Youden-derived thresholds were 8% for mini-FC and 14.5% for PLR, closely approximating clinically driven high-specificity thresholds of 8% and 13.9%, respectively. At the clinically driven thresholds, mini-FC showed higher sensitivity than PLR (71.7% vs. 60.9%). Mini-FC also classified more patients outside the gray zone (63.2% vs. 50.6%) with fewer misclassifications. Unlike PLR, mini-FC performance remained stable across age. CONCLUSION: Mini-FC showed clinically useful diagnostic performance and appeared to provide more consistent classification across age groups than PLR in this cohort. IMPACT STATEMENT: In spontaneously breathing children, both passive leg raising and mini-fluid challenge predict fluid responsiveness, but the mini-fluid challenge provides greater diagnostic certainty and more consistent performance across ages. Evidence guiding fluid responsiveness assessment in pediatrics is scarce, and this study provides one of the first direct, head-to-head clinical comparisons of two bedside dynamic tests under identical conditions. By offering a simple, weight-indexed preload test, the mini-fluid challenge may help guide early fluid resuscitation while limiting the risks associated with unnecessary fluid overload.