Plasma and Serum Electrolyte Levels Correlation in the Pediatric ICU

Background: Patients in the intensive care unit (ICU) are susceptible to develop electrolyte imbalance resulting in increased mortality rate. Electrolyte measurements especially for sodium and potassium are frequently required in critically ill patients. The purpose of the present study was to compare sodium and potassium concentrations between serum from venous blood and plasma from arterial blood in order to decrease the number of needle punctures required in children admitted to the ICU. Materials and Methods: Thirty-five patients admitted to the pediatric intensive care unit (PICU) were enrolled in this study; hypotensive patients were excluded. Two cc venous and 1cc arterial blood samples were taken for serum and plasma measurement of sodium and potassium. Venous samples were analyzed within 15 minutes in the hospital laboratory and arterial samples were immediately auto-analyzed in the PICU for sodium and potassium concentrations. Results: Mean serum concentrations of sodium (NaV=137.1±5.5) and potassium (KV=4.1±0.7) were higher than plasma concentrations of sodium (NaA=133.1±11.1) and potassium (KV =3.1±0.7); (p < 0.02 and p < 0.001 respectively). Linear regression showed NaV=106+0.23 Na A for sodium; (p=0.005), and KV= 1.96+0.69 KA; (p < 0.001) for potassium. Conclusion: Serum concentrations of sodium and potassium were higher than their plasma levels and could be calculated using the plasma sample and the formula given above.