Plasma and red blood cell concentrations of zinc, copper, selenium and magnesium in the first week of paediatric critical illness

Background & aims: Critically ill children are at risk of micronutrient deficiencies, which might lead to poor clinical outcomes. However, the interpretation of micronutrient concentrations in plasma is complicated due to age-dependent and critical illness-dependent changes. Certain red blood cell (RBC) concentrations might reflect the overall body status more reliably than plasma levels in the presence of systemic inflammatory response. This study longitudinally examined micronutrient concentrations in both plasma and RBC in critically ill children.

Methods: This secondary analysis of the PEPaNIC RCT investigated the impact of early versus late initiation of parenteral macronutrient supplementation in critically ill children. All children received micronutrients when EN was insufficient (<80 % energy requirements). Blood samples were obtained on days 1, 3, 5 and 7 of Paediatric Intensive Care Unit (PICU) admission. Inductively coupled plasma mass spectrometry was used to measure zinc, selenium, and copper in plasma and selenium, copper, and magnesium in RBCs. Plasma magnesium was measured with colorimetric detection. Micronutrient concentrations were compared with age-specific reference values in healthy children and expressed using Z-scores. Changes in micronutrient concentrations over time were examined using the Friedman and post hoc Wilcoxon signed-rank tests.

Results: For 67 critically ill children, median (Q1; Q3) age 9.5 (5.5; 13.2) years, PIM3 score -2.3 (-3.1; -0.8), samples were available at various time points during their PICU stay. For 22 patients, longitudinal samples were available. On day 1, the median plasma Z-score for zinc was -5.2 (-5.2; -2.9), copper -1.6 (-2.9; -0.2), selenium -2.6 (-3.8; -1.0), magnesium -0.2 (-1.6; 1.3), and median RBC Z-score for copper was 0.5 (-0.1; 1.3), selenium -0.3 (-1.1; 0.7), magnesium 0.2 (-0.4; 1.3). In the longitudinal analysis, plasma zinc was significantly higher on day 5 (Z-score -3.2 (-4.6; -1.4)) than on day 1 (Z-score -5.2 (-5.2; -3.0), p = 0.032), and plasma magnesium was significantly higher on day 3 (Z-score 1.1 (-0.7; 4.0)) than on day 1 (Z-score -0.3 (-1.6; 0.5), p = 0.018). Plasma copper and selenium remained stable, and the RBC concentrations of all micronutrients remained stable during the first five days.

Conclusions: Most patients had low plasma zinc, copper and selenium concentrations in the first week of their PICU stay, whereas they had normal to high RBC concentrations. More research is needed to examine the relationships between micronutrients and clinical outcome.