Had the respiratory compensation been appropriate, the pCO 2 should have dropped by the same number of points as the bicarbonate. (A normal pCO 2 is 40 mm Hg, and this patient’s pCO 2 is 20 mm Hg. Notice that the pCO 2 is too low by 20 points. Look back at the ABG above and focus on the pCO 2. Step 3: look at the arterial blood gas and see if the partial pressure of carbon dioxide (pCO 2) is dropping in proportion to the drop in the bicarbonate level (c) another yet-to-be-identified acid-base disturbance (because I told you it was going to be a triple acid-base disorder!).
(b) a metabolic alkalosis (from Step 2) and, (a) a high anion gap metabolic acidosis (from Step 1) and, You know, again without even looking at the ABG (!), that this patient has: Ĭongratulations! So far, you’ve solved two thirds of this patient’s triple acid-base disorder. So this patient also has a metabolic alkalosis on top of his high anion gap metabolic acidosis. A higher than expected bicarbonate in a patient with no past medical history suggests a metabolic alkalosis. Here, however, the bicarbonate is 16 mEq/L, which is 8 points higher than the expected 8. So you’d expect the serum bicarbonate to be 8 mEq/L (24- 16 = 8). In any event, since the patient’s anion gap was too high by 16 points, the patient’s bicarbonate should be similarly low by 16 points. (That’s just something you absolutely need to have committed to memory!). Therefore, you should expect the serum bicarbonate to be similarly 16 points below normal.Ī normal serum bicarbonate is 24 mEq/L. Recall from the previous step that, in this case, the anion gap is too high by 16 points (27-11 = 16). Step 2: see if the serum bicarbonate (HCO 3 –) is dropped in proportion to the degree to which the anion gap rose
Remember the number 16 because you will need it for the next two steps. It’s supposed to be 11, but it is 27, so it is too high by 16 points (27-11 = 16). This patient’s anion gap is too high by 16 points. You know (or should know!) that the normal anion gap is 11 so this patient has a high anion gap metabolic acidosis. Congratulations! You solved one third of this triple acid-base disorder problem without lifting a finger and without even looking at the ABG!īefore proceeding to the next step, however, please pay attention to how high above normal this patient’s anion gap actually is because you will need this number for the steps that follow.
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