ABG Sampling Errors PDF

ABG SAMPLING ERRORS Dilution error Air bubbles in sample Clotting Prolonged storage Venous blood contamination Temperature Correction DILUTION ERROR Too much NaCL flush solution with heparin in blood sample Discard at least 3 times the dead...

ABG SAMPLING ERRORS Dilution error Air bubbles in sample Clotting Prolonged storage Venous blood contamination Temperature Correction DILUTION ERROR Too much NaCL flush solution with heparin in blood sample Discard at least 3 times the dead space and check the catheter for exact amount of dead space to withdraw Always withdraw blood with appropriate electrolyte-balanced heparin Heparin is more acidic AIR BUBBLES IN SAMPLE Air bubbles should be expelled as soon as the sample is obtained. The bias results depends on the size of the air bubble, original PAO2, duration of exposure and extent of mixing. Avoid this error by  Visually inspecting sample  Remove air bubbles before mixing  Use blood gas samplers with vented tip caps that allows air to be vented and the sample sealed. AIR BUBBLES Push up on syringe until blood occupies the cap. AIR BUBBLES IN SAMPLE Comparison of 2 samples  Without Air in Sample With Air in Sample  PaO2 – 70 mm Hg 90 mm Hg  PaCO2 – 45 mm Hg 45 mm Hg  SaO2 – 94% 96% CLOTTING Mix sample immediately inspecting for air bubbles and expelling them. Clots will block syringe and prevent analyzing Cellular K increases Always use pre-heparinized with dry electrolyte-balanced heparin. Mix sample before putting it into blood gas machine PROLONGED STORAGE Analyze sample within 30 minutes If unable to analyze within 30 minutes put on ice. After 30 minutes in room temperature results may vary. TEMPERATURE CORRECTION Higher body temperature results in a higher PaCO2 and PaO2. Effect of temperature on normal ABG’s Get temperature of patient when obtaining the ABG. Set ABG machine at this temp and values will be adjusted. Cooler blood  CO2 becomes more soluable which reduces the PaCO2.  pH rises because Hb is principle buffer in blood and accepts more H ions when cooled.  When blood is rewarmed H ions are released from hemoglobin and returns blood to normal. EFFECT OF TEMPERATURE ON BLOOD GAS VALUES Temperature (° C) PO2 PCO2 pH 37 80 40 7.40 39 90 44 7.37 30 54 30 7.50 VENOUS BLOOD CONTAMINATION Getting venous blood in arterial sample. Venous blood contaminates the sample with a few drops of blood prior to entering artery Avoid these errors by Using self-filling syringes Use short-beveled needles and puncture at a 45 degree angle MIXED VENOUS BLOOD How do you know you have a mixed venous sample?  Color? Not a good clue  Clinic status and picture does not match the ABG sample. MIXED VENOUS SAMPLE Arterial sample will  Have flash of blood into the syringe  Auto fill syringe (because of blood pressure) Venous sample  Slow movement of blood into syringe Normal mixed venous gases  pH – 7.38  PvCO2 – 48 mm Hg  PvO2 – 40 mm Hg  SvO2 – 75% MIXED VENOUS SAMPLE Cross check with pulse oximetry Patient has a SpO2 of 90% ABG sample has a SaO2 (from ABG machine) of 78% then sample is mixed venous