J Pediatr Intensive Care 2024; 13(01): 080-086
DOI: 10.1055/s-0041-1736549
Original Article

Urinary Chloride Excretion Postcardiopulmonary Bypass in Pediatric Patients—A Pilot Study

Sophie Fincher
1   Department of Pediatric Intensive Care, Queensland Children's Hospital, Brisbane, Australia
2   Pediatric Critical Care Research Group, Brisbane, Australia
Kristen Gibbons
2   Pediatric Critical Care Research Group, Brisbane, Australia
3   Child Health Research Centre, The University of Queensland, Brisbane, Australia
Kerry Johnson
1   Department of Pediatric Intensive Care, Queensland Children's Hospital, Brisbane, Australia
2   Pediatric Critical Care Research Group, Brisbane, Australia
3   Child Health Research Centre, The University of Queensland, Brisbane, Australia
Peter Trnka
4   School of Medicine, The University of Queensland, Brisbane, Australia
5   Queensland Child and Adolescent Renal Service, Queensland Children's Hospital, Brisbane, Australia
Adrian C. Mattke
1   Department of Pediatric Intensive Care, Queensland Children's Hospital, Brisbane, Australia
2   Pediatric Critical Care Research Group, Brisbane, Australia
3   Child Health Research Centre, The University of Queensland, Brisbane, Australia
4   School of Medicine, The University of Queensland, Brisbane, Australia
› Author Affiliations
Funding The study received in-kind support from the Pediatric Intensive Care Unit, Queensland Children's Hospital, South Brisbane, Australia.


The aim of this study was to describe renal chloride metabolism following cardiopulmonary bypass (CPB) surgery in pediatric patients. A prospective observational trial in a tertiary pediatric intensive care unit (PICU) with 20 recruited patients younger than 2 years following CPB surgery was conducted. Urinary electrolytes, plasma urea, electrolytes, creatinine, and arterial blood gases were collected preoperatively, on admission to PICU and at standardized intervals thereafter. The urinary and plasma strong ion differences (SID) were calculated from these results at each time point. Fluid input and output and electrolyte and drug administration were also recorded. Median chloride administration was 67.7 mmol/kg over the first 24 hours. Urinary chloride (mmol/L; median interquartile range [IQR]) was 30 (19, 52) prior to surgery, 15 (15, 65) on admission, and remained below baseline until 24 hours. Plasma chloride (mmol/L; median [IQR]) was 105 (98, 107) prior to surgery and 101 (101, 106) on admission to PICU. It then increased from baseline, but remained within normal limits, for the remainder of the study. The urinary SID increased from 49.8 (19.1, 87.2) preoperatively to a maximum of 122.7 (92.5, 151.8) at 6 hours, and remained elevated until 48 hours. Plasma and urinary chloride concentrations were not associated with the development of acute kidney injury. Urinary chloride excretion is impaired after CPB. The urinary SID increase associated with the decrease in chloride excretion suggests impaired production and/or excretion of ammonium by the nephron following CPB, with gradual recovery postoperatively.


This study was performed at the Queensland Children's Hospital.

Ethical Approval

Ethical approval for this study was received from the Children's Health Queensland Human Research Ethics Committee (HREC/17/QRCH/310).

Publication History

Received: 06 June 2021

Accepted: 10 September 2021

Article published online:
22 October 2021

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