Early cardiopulmonary fitness impairment across stages of pediatric chronic kidney disease

Abstract Background Children with chronic kidney disease (CKD) are at high cardiovascular risk, yet cardiopulmonary fitness is rarely assessed in this population. Maximal oxygen uptake (VO2max) is a powerful prognostic marker, and Z-score–based evaluations may improve risk stratification. Methods In this prospective multicenter study, children aged 6–17 years with CKD stages 2 to 5 were categorized according to KDIGO criteria. Cardiopulmonary exercise testing (CPET) was performed using a standardized cycle ergometer protocol. VO2max was expressed as Z-scores based on contemporary pediatric reference values. Impaired fitness was defined as VO2max Z-score –1.64. Multivariable linear regression identified predictors of VO2max. Results Eighty-eight patients (mean age 11.8 ± 3.8 years, 67% male) were enrolled; 77 completed valid CPET. Mean VO2max Z-score was –1.8 ± 2.1 and 56% had impaired fitness. A significant, stage-dependent decrease in VO2max was observed across CKD stages (Jonckheere–Terpstra trend test, P 0.001). In multivariable analysis, higher VO2max was independently associated with lower hypertension risk, higher diastolic blood pressure, better pulmonary function (FEV1), lower VE/VCO2 slope, and higher ventilatory anaerobic threshold (VAT). These parameters explained 80% of VO2max variability. Conclusion Cardiopulmonary fitness is significantly reduced in children with CKD with a stage dependent effect, even at early stages. VO2max impairment is linked to clinical and functional parameters that are commonly assessed by CPET and amenable to therapeutic intervention. These findings support early screening and the development of tailored rehabilitation strategies, including hybrid, multidisciplinary programs targeting hypertension, ventilatory efficiency, and physical deconditioning in pediatric CKD.