Arterial Blood Gases Interpretation Definition Values respiratory metabolic

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1 Arterial Blood Gases Interpretation Definition A blood gas test measures the amount of oxygen and carbon dioxide in the blood. It is also useful in determining the ph level of the blood. The test is commonly known as a blood gas analysis or arterial blood gas (ABG) test. Values There are 3 values to look at when trying to find out if the patient is in respiratory or metabolic acidosis or alkalosis. The values are as follow: ph: CO2: (if this is abnormal, it indicates a respiratory issue) HCO3: (if this is abnormal, it indicates a metabolic issue) For ph, anything less than 7.35 is an acid and anything greater than 7.45 is a base. For CO2, (NOTE: it is the opposite) anything less than 35 is a base and anything greater than 45 is an acid. For HCO3, anything less than 22 is an acid and anything greater than 26 is a base.

2 Tic-Tac-Toe Method In order to use the tic-tac-toe method to interpret ABGs, first draw the tic-tac-toe grid. Label each column as acid, normal and base. It should look like this: Here is an example: ph: 7.26, paco2: 32, HCO3: 18 First, determine where the values should be written on the tic-tac-toe chart. In this example, the solution is as follows: ph of 7.26 is LOW = ACID, so place ph under Acid paco2 of 32 is LOW = BASE, so place paco2 under Base HCO3 of 18 is LOW = ACID, so place HCO3 under Acid Your chart should look like this:

3 Now, notice which value matches up in the same column with ph. In this example, HCO3 is in the same column as ph. HCO3 is considered Metabolic, and both are under Acid, so this example displays Metabolic Acidosis. The last step is to determine if the ABG is Compensated, Partially Compensated, or Uncompensated. Here is the trick to memorize: 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 example is METABOLIC ACIDOSIS, PARTIALLY COMPENSATED.

4 Sometimes you will have a ph that is within normal range, but will lean towards either a high abnormal or low abnormal. For example: ph of 7.44 (within normal range, but closer basic (alkalosis). paco2 30 HCO3 21 ABGs Practice Questions 1. The nurse reviews the arterial blood gas results of a client and notes the following: ph 7.45, Pco2 of 30 mm Hg, and HCO3 of 20 meq/l. The nurse analyzes these results as indicating which condition? A. Metabolic acidosis, compensated B. Respiratory alkalosis, compensated C. Metabolic alkalosis, uncompensated D. Respiratory acidosis, uncompensated Rationale: The normal ph is 7.35 to In a respiratory condition, an opposite effect will be seen between the ph and the Pco2. In this situation, the ph is at the high end of the normal value and the Pco2 is low. In an alkalotic condition, the ph is elevated. Therefore the values identified in the question indicate a respiratory alkalosis that is compensated by the kidneys through the renal excretion of bicarbonate. Because the ph has returned to a normal value, compensation has occurred. 2. A client who is found unresponsive has arterial blood gases drawn and the results indicate the following: ph is 7.12, Pco2 is 90 mm Hg, and HCO3 is 22 meq/l. The nurse interprets the results as indicating which condition? A. Metabolic acidosis with compensation B. Respiratory acidosis with compensation C. Metabolic acidosis without compensation D. Respiratory acidosis without compensation Rationale: The acid-base disturbance is respiratory acidosis without compensation. The normal ph is 7.35 to The normal Pco2 is 35 to 45 mm Hg. In respiratory acidosis the ph is decreased and the Pco2 is elevated. The normal bicarbonate (HCO3) level is 22 to 27 meq/l. Because the bicarbonate is still within normal limits, the kidneys have not had time to adjust for this acid-base disturbance. In addition, the ph is not within normal limits. Therefore the condition is without compensation. The remaining options are incorrect interpretations. 3. The nurse reviews the blood gas results of a client with atelectasis. The nurse analyzes the results and determines that the client is experiencing respiratory acidosis. Which result validates the nurse's findings? A. ph 7.25, Pco2 50 mm Hg B. ph 7.35, Pco2 40 mm Hg C. ph 7.50, Pco2 52 mm Hg D. ph 7.52, Pco2 28 mm Hg

5 Rationale: Atelectasis is a condition characterized by the collapse of alveoli, preventing the respiratory exchange of oxygen and carbon dioxide in a part of the lungs. The normal ph is 7.35 to The normal Pco2 is 35 to 45 mm Hg. In respiratory acidosis, the ph is decreased and the Pco2 is elevated. Option 2 identifies normal values. Option 3 identifies an alkalotic condition, and option 4 identifies respiratory alkalosis. 4. The nurse plans care for a client with chronic obstructive pulmonary disease (COPD), understanding that the client is most likely to experience what type of acid-base imbalance? A. Metabolic acidosis B. Metabolic alkalosis C. Respiratory acidosis D. Respiratory alkalosis Rationale: Respiratory acidosis is most often caused by hypoventilation in a client with COPD. Other acid-base disturbances can occur in a client with COPD during exacerbation of the disease, but the most likely imbalance is respiratory acidosis. The remaining options are incorrect. COPD is a respiratory condition, not a metabolic one. Respiratory alkalosis is associated with hyperventilation. 5. The nurse reviews the arterial blood gas results of an assigned client and notes that the laboratory report indicates a ph of 7.30, Pco2 of 58 mm Hg, Po2 of 80 mm Hg, and Hco3 of 27 meq/l. The nurse interprets that the client has which acid-base disturbance? A. Metabolic acidosis B. Metabolic alkalosis C. Respiratory acidosis D. Respiratory alkalosis Rationale: The normal ph is 7.35 to Normal Pco2 is 35 to 45 mm Hg. In respiratory acidosis, the ph is low and Pco2 is elevated. Options 1, 2, and 4 are incorrect interpretations of the values identified in the question.