The effect of different forms of heparin on point-of-care blood gas analysis

Abstract

Background. Point-of-care blood gas analysis plays an integral role in the management of critically ill and injured patients presenting to the emergency department (ED). While the use of specially manufactured syringes containing electrolyte-balanced dried heparin is recommended when processing these specimens, alternatives including manually self-prepared syringes washed with liquid heparin or heparin vacutainers are still often used.

Objectives. To assess the effect of two concentrations of liquid heparin and the use of heparin vacutainers on the reliability of blood gas analysis results compared with the recommended standard of dried heparin syringes in the ED setting.

Methods. Blood samples were drawn from 54 patients attending a tertiary-level hospital ED. Individual samples were distributed equally among each of four different collection devices: a dried heparin syringe, self-prepared syringes washed separately with 1 000 IU/mL and 5 000 IU/mL liquid heparin, and a heparin vacutainer. Results obtained from the standard dried heparin syringes were compared with those from the other three methods.

Results. For both the liquid heparin cohorts, partial pressure of carbon dioxide (pCO2), potassium (K⁺), sodium (Na⁺), ionised calcium (iCa²⁺) and haemoglobin had >20% of results falling beyond the total allowable error. iCa²⁺ and K⁺ results were most affected in the 5 000 IU/mL cohort and iCa²⁺ and Na⁺ in the 1 000 IU/ml cohort. pCO2, pH and iCa²⁺ were the most significantly affected in the heparin vacutainer cohort.

Conclusions. Use of liquid heparin can result in significant negative bias in the majority of blood gas analytes, especially electrolytes. Heparin vacutainer use can result in unacceptable variations in the respiratory analytes. While standard dried heparin syringes may not always be available, it is of vital importance that practitioners be aware of these biases and limitations when using substitutes.