Acid-base parameters in venous blood - agreement between values from safePICO syringes and lithium-heparin vacutainer tubes

Venous blood is considered an acceptable alternative to arterial blood for assessment of metabolic acid-base disorders. Also, venous sampling using lithium-heparin (Li-Hep) tubes is advantageous to arterial sampling using PICO syringes, the risk of complications being lower. Usage of partly filled tubes without firm knowledge about the clinical consequences is, however, a pre-analytic consideration. The study evaluated primary acid-base parameters (pH, standardized hydrogen carbonate (HCO₃), standardized base excess (SBE), lactate) and co-determined parameters in venous blood stored at room temperature up to 60 min in Li-Hep tubes vs. venous blood in PICO syringes analyzed immediately. Also, 50% filled tubes stored up to 30 min were compared to filled tubes analyzed immediately. Significant differences were generally observed. Stability was parameter and time dependent (filled tubes: 30 min: pH, (preferably 15 min for optimal stability), SBE, potassium and lactate, 60 min: HCO₃, hemoglobin, methemoglobin (MetHb), carbon monoxide hemoglobin (COHb), sodium, chloride, glucose and creatinine; 50% filled tubes: 15 min: lactate, 30 min: HCO₃, hemoglobin, MetHb, COHb, potassium, sodium, chloride, glucose and creatinine). In conclusion, storage in filled Li-Hep tubes for 30 min generates comparable results to blood in PICO syringes for all parameters, except pCO₂, pO₂ and sO₂. Storage in 50% filled Li-Hep tubes is not acceptable for pH, pCO₂, pO₂, sO₂ and SBE, and lactate is only stable for 15 min.