ABG Sampling Errors

ABG Sampling Errors

• Dilution Error: Too much saline flush with heparin in the blood sample. Discard at least 3 times the dead space in the catheter. Use the correct amount of dead space to withdraw blood. Always use heparinized electrolyte-balanced solution. Heparin is more acidic. Dilution lowers PCO2, increases pH, increases low partial pressure of oxygen (pO2), or decreases high partial of oxygen (pO2).

• Air Bubbles in Sample: Remove air bubbles as soon as the sample is obtained; the bias depends on the size of the bubble and duration of exposure. Visually inspect the sample, remove air bubbles before mixing, blood gas samplers with vented tip caps are helpful. Air lowers PCO2, increases pH, increases low partial pressure of oxygen (PO2), and decreases high partial of oxygen (PO2). Push up on syringe until blood occupies the cap.

• Clotting: Mix sample immediately and expel air bubbles. Clots block syringes, preventing analysis. Use pre-heparinized electrolyte-balanced heparin. Mix the sample before putting it into the blood gas machine. Clotting increases cellular potassium.

• Prolonged Storage: Analyze samples within 30 minutes. If unable to analyse within 30 minutes, place the sample on ice. After 30 minutes at room temperature, results may vary. Prolonged storage increases PCO2, decreases pH, and decreases the partial pressure of oxygen (PO2).

• Venous Blood Contamination: Avoid getting venous blood in arterial samples. Use self-filling syringes, short beveled needles, and a 45-degree puncture angle. Venous contamination increases PCO2, decreases pH, and significantly lowers the partial pressure of oxygen (PO2).

• Temperature Correction: Higher body temperature results in a higher PaCO2 and PaO2. Get the patient's temperature when obtaining the ABGs. Set the ABG machine to this temperature, and adjust the values accordingly. Cooler blood results in more soluble CO2, which decreases PaCO2. pH increases because hemoglobin acts as a buffer, accepting more H+ ions when cooled. When blood is rewarmed, H+ ions are released from hemoglobin, returning blood to normal. The table shows the effect of temperature on blood gas values.