Practice Problems Acid-Base Imbalances interpretation of Arterial Blood Gases (ABG) RESP

Getting an arterial blood gas sample

Ulnar Artery Radial Artery

Blood Gas Report Acid-Base Information pH PCO2 HCO3 [calculated vs measured] Oxygenation Information PO2 [oxygen tension] SO2 [oxygen saturation]

PRIMARY AND SECONDARY ACID-BASE DERANGEMENTS [HCO3-] pH = 6.1 + log --------------------------------- PCO2 + 0.225 Acid-Base Disorder Primary Change Compensatory Change Respiratory acidosis PCO2 up HCO3 up Respiratory alkalosis PCO2 down HCO3 down Metabolic acidosis HCO3 down PCO2 down Metabolic alkalosis HCO3 up PCO2 up

Steps for interpretation of ABG Know normal values of pH, (PCO2), and (HCO3-). Look at the patient's ABG's to determine what's abnormal high or low. Correlate the abnormal values of PCO2 and HCO3- to the abnormality of pH. Name the disorder, the cause, and the source of any compensation.

1- Normal values for ABG's: 2- Evaluate the patient's ABG's: is the pH normal? Is it too high or too low? Is it acidosis or alkalosis? Is the HCO3- normal? Is it too high or too low? Will it cause acidosis or alkalosis? Will it correct acidosis or alkalosis? Is the CO2 normal? Is it too high or too low? Will it cause acidosis or alkalosis? Will it correct acidosis or alkalosis?

3-Correlate the abnormal values: If only one of the two parameters (CO2 or HCO3-) is abnormal, then its value should be consistent with the pH (for example, if the CO2 is high, since that causes a drop in pH, the pH should be low). If both of the parameter are abnormal, then usually one is CAUSING the problem, and the other is trying to CORRECT (COMPENSATE FOR) the problem. (For example, if the CO2 is high, and is causing the pH imbalance, then the pH must be low, since CO2 behaves as an acid. If HCO3- level is also abnormal, then usually it will be high, to compensate for the low pH, since it is a base.)

Respiratory acidosis (with or without renal compensation) 4- Name the disorder: Respiratory acidosis (with or without renal compensation) Respiratory alkalosis(with or without renal compensation) Metabolic acidosis (with or without respiratory compensation) Metabolic alkalosis (with or without respiratory compensation) 5- Suggest a possible cause For example, a cause of chronic respiratory acidosis is emphysema.

Practice Problem 1 ABG's: pH 7.31 PCO2 55 mm Hg HCO3- 26 mEq/L Normal values for ABG's: pH range 7.35 - 7.45 PCO2 35 - 45 mm Hg HCO3-, 22 - 26 mEq/L pH is too low - acidosis;  PCO2 is too high, would cause acidosis or correct alkalosis; HCO3- is normal, neither causing nor correcting imbalance high PCO2 is correlated with low pH, which is consistent with patient's report because PCO2 is causing the problem, this is respiratory acidosis; because bicarbonate is normal, there is no compensation

Practice Problem 2 ABG's: pH 7.31 PCO2 55 mm Hg HCO3- 35 mEq/L pH – low = acidosis PCO2 – high = respiratory acidosis HCO3 - high = renal compensation

Practice Problem 3 ABG's: pH 7.31 PCO2 35 mm Hg HCO3- 20 mEq/L pH – low = acidosis HCO3 - low = metabolic acidosis PCO2 – normal; no compensation

Practice Problem 4 ABG's: pH 7.31 PCO2 25 mm Hg HCO3- 20 mEq/L pH – low = acidosis HCO3 - low = metabolic acidosis PCO2 – low = respiratory compensation

Practice Problem 5 ABG's: pH 7.48 PCO2 25 mm Hg HCO3- 24 mEq/L pH – high = alkalosis PCO2 – low = respiratory alkalosis HCO3 - normal; no compensation

Practice Problem 6 ABG's: pH 7.48 PCO2 25 mm Hg HCO3- 20 mEq/L pH – high = alkalosis PCO2 – low = respiratory alkalosis HCO3 - low = renal compensation

Practice Problem 7 ABG's: pH 7.48 PCO2 40 mm Hg HCO3- 33 mEq/L pH – high = alkalosis HCO3 – high = metabolic alkalosis PCO2 – normal; no compensation

Practice Problem 8 ABG's: pH 7.48 PCO2 55 mm Hg HCO3- 33 mEq/L pH – high = alkalosis HCO3 – high = metabolic alkalosis PCO2 – high = respiratory compensation