An arterial blood gas (ABG) is a blood test that measures the acidity (pH) and the levels of oxygen and carbon dioxide in the blood. Blood for an ABG test is taken from an artery whereas most other blood tests are done on a sample of blood taken from a vein. This test is done to monitor several conditions that can cause serious health complications especially to critically ill individuals. Every day, a lot of nursing and medical students assigned in acute areas encounter ABG results, which they may not necessarily be able to interpret with its knotty aspect. They struggle over the interpretation of its measurements, but they are not especially complicated nor difficult if you understand the basic physiology and have a step by step process to analyze and interpret them. There may be various tips and strategies to guide you, from mnemonics, to charts, to lectures, to practice, but this article will tell you how to interpret ABGs in the easiest possible way. And once you have finished reading this, you’ll be doing actual ABG analysis in the NCLEX with fun and excitement! Steps: 1. Know the Normal Values Know the normal and abnormal ABG values when you review the lab reports. 2. Check for Acidosis or Alkalosis The first thing you need to determine when checking ABG results is the acidity of the blood which is determined by the value of the pH. The pH level in a healthy human should be between 7.35 to 7.45. Your body is constantly striving to keep pH in balance. pH level below 7.35 is Acidosis pH level above 7.45 is Alkalosis 3. Determine If the Acid Base is Respiratory or Metabolic Next thing you need to determine is whether the acid base is Respiratory or Metabolic. paCO2 = Respiratory HCO3 = Metabolic 4. Remember ROME Still, it all boils down to mnemonics. The mnemonic RO-ME. Respiratory Opposite When pH is up, PaCO2 is down = Alkalosis When pH is down, PaCO2 is up = Acidosis Metabolic Equal When pH is up, HCO3 is up = Alkalosis When pH is down, HCO3 is down = Acidosis 5. Tic-Tac-Toe And yes, ABG problems work using the Tic-Tac-Toe method. All you have to do is make a blank chart a bit like a tic-tac-toe chart. 6. Mark the Chart Using the lab result values, mark them on your Tic-Tac-Toe chart. Now begin with this given example. pH 7.26, paCO2 32, HCO3 18 pH is LOW = ACID so place pH under Acid paCO2 is LOW = BASE so place paCO2 under Base HCO3 is LOW = ACID so place HCO3 under Acid Your chart should go like this: 7. Match It up In this step, look at which column matches up with the pH. In this case HCO3 goes with pH. HCO3 is considered Metabolic (shown in step 3), and both are under Acid, so this example implies Metabolic Acidosis. 8. Determine Compensation The last step is to determine if the ABG is Compensated, Partially Compensated, or Uncompensated. If pH is NORMAL, PaCO2 and HCO3 are both ABNORMAL = Compensated If pH is ABNORMAL, PaCO2 and HCO3 are both ABNORMAL = Partially Compensated If pH is ABNORMAL, PaCO2 or HCO3 is ABNORMAL = Uncompensated Therefore this ABG is METABOLIC ACIDOSIS, PARTIALLY COMPENSATED . By applying the steps above, interpret the following ABGs. pH 7.44, PaCO2 30, HCO3 21 pH is NORMAL = NORMAL so place pH under Normal PaCO2 is LOW = BASE so place PaCO2 under Base HCO3 is LOW = ACID so place HCO3 under Acid *Since the acidity of the blood is determined by the value of the pH, determine whether the normal pH is SLIGHTLY ACIDIC or SLIGHTLY BASIC. In this example, pH is NORMAL but SLIGHTLY BASIC therefore it is ALKALOSIS. Your chart should go like this: In this case PaCO2 goes with pH. PaCO2 is considered Respiratory (shown in step 3), and both are under Basic, so this example implies Respiratory Alkalosis. The HCO3 is also abnormal. When pH is NORMAL and PaCO2 and HCO3 are both ABNORMAL, it indicates FULL COMPENSATION. Therefore this ABG is RESPIRATORY ALKALOSIS, FULLY COMPENSATED. pH 7.1, PaCO2 40, HCO3 18 pH is LOW = ACID so place pH under Acid PaCO2 is NORMAL = NORMAL so place PaCO2 under Normal HCO3 is LOW = ACID so place HCO3 under Acid Your chart should go like this: In this case HCO3 goes with pH. HCO3 is considered Metabolic (shown in step 3), and both are under Acidic, so this example implies Metabolic Acidosis. The PaCO2 is normal. When pH is ABNORMAL, PaCO2 or HCO3 is ABNORMAL, it indicates UNCOMPENSATION. Therefore this ABG is METABOLIC ACIDOSIS, UNCOMPENSATED.
