Effects of lithium heparin concentration on whole blood analytes measured on a multichannel blood gas/electrolyte system

Background: Current-generation multichannel blood gas electrolyte analyzer systems (MBGES) have the ability to measure blood gases and electrolytes simultaneously. The proposed volume of sample required to achieve this is as little as 1.8 mL. Previous studies have identified inaccuracies and imprecision of blood gas and electrolyte results caused by anticoagulants and small sample size. However, the effects of these two variables on measured analyte parameters have not been addressed for simultaneous measurements on current-generation MBGES. We designed a prospective study to quantify errors introduced into blood gas and electrolyte measurements by sample size and concentration of dry lyophilized heparin during simultaneous analysis using a Corning 288 MBGES. Methods: Arterial blood was collected from an arterially cannulated 33-year-old healthy Caucasian man. Seventy samples of blood were removed, comprising 10 randomly ordered sets of 0.2, 0.4, 0.6, 0.8, 1.0, 2.0, and 3.0 mL of blood; the resulting specimens contained ~ 250, 125, 83, 63, 50, 25, and 17 IU of lithium heparin to 1.0 mL of blood, respectively. Sodium, potassium, ionized calcium, pH, P(aO2), P(aCO2), and total hemoglobin were all measured according to criterion standard for arterial blood gas analysis, collection, and calibration. Results: Using analysis of variance and the Scheffe test, small sample volumes/high heparin concentrations resulted in lower sodium (p < 0.001) and ionized calcium (p < 0.001) and higher P(aO2) (p = 0.03) values. No variations were found in potassium, P(aCO2), or total hemoglobin. Sodium and ionized calcium concentrations are underestimated in sample volumes of < 0.6 mL with lithium heparin concentrations > 83 IU/mL. Conclusion: When standard samples are used with MBGES, we recommend a minimum 0.6-mL sample size for accurate and precise blood gas and electrolyte values.