Evaluation of pKa as a cause of discordance between calculated and measured bicarbonate in arterial and venous blood

ABSTRACT

Background: The measurement of bicarbonate level in blood is extremely common and often provides vitally important data used in the care of critically ill patients. The bicarbonate level in blood can be directly measured or derived from calculations using the Henderson-Hasselbalch equation; mostly adopted by the blood gas analyzers. Arterial blood gas (ABG) analysis is commonly performed for clinical evaluation, but the procedure has certain limitations in the form of reduced patient acceptability (because the procedure can be painful) and the potential to cause complications such as arterial injury, thrombosis with distal ischemia, hemorrhage, aneurysm formation, median nerve damage and, rarely, reflex sympathetic dystrophy. The aim of the study If there is discordance between arterial and venous blood gas parameters including pH, pCO2, bicarbonate, Sodium, Potassium, chloride and discordance between measured and calculated bicarbonate in both arterial and venous blood samples. Materials and methods: Comparison study involving 250 patients for whom clinical Judgment was made that arterial blood sample is needed for assessment of acid-base status. Both arterial and venous blood samples were collected using heparinized autosampler syringes PICO 50 as close in time as possible and were analyzed in Arterial Blood Gas analyzer ABL 80 flex. Results: There was a statistically significant difference between arterial and venous pO2 (126+48.5 vs 62+30.5, p= 0.001) and SO2 (95% vs 68%, p=0.03). Conclusion: According to the study results traditionally measured venous bicarbonate can be a Shanmugapriya Chandrasekaran, Poonguzhali Gopinath. Evaluation of pKa as a cause of discordance between calculated and measured bicarbonate in arterial and venous blood. IAIM, 2019; 6(3) 127-131. Page 128 convenient substitute for calculated arterial bicarbonate in critically ill ICU patients. However, more accurate assessments will require ABG for additional parameters. Besides, the present study design did not involve the collection of data on patient demographics, the severity of illness, and a requirement for inotropic support or prognosis.