44-year-old man has had a recent drinking binge. He has fallen several times (unclear whether this is syncope or not)
| 137 | 92 | 15 | 91 |
| 4.9 | 16 | 0.7 |
Arterial Blood Gas(midnight)
| pH | 7.45 |
| pCO2 | 30 |
| pO2 | 84 |
| c HCO3 | 21 |
What do you think his acid-base diagnosis is? What tests would you order?
{ 4 comments… read them below or add one }
Two possibilities:
It is a little difficult because of the six hour gap between the lytes and ABG which means therapy has started. Most commonly that gas is simple chronic respiratory alkalosis, altho it is suspicious that the chloride is not higher than it is. The acid base compensation is appropriate but generally there will be a relative hyperchloremia.
Alternatively there may be an acute metabolic acidosis, appropriate respiratory compensation and a secondary metabolic alkalosis (possibly from vomiting). The anion gap is high so the work-up should include sources of unmeasured anions, specifically lactate, ketones (alcoholic keotacidosis) and volatile alcohols ethylene glycol and methanol. It is disturbing that the potassium is normal.
The falling down must be a clue, and there are many possible hypothesis but it is not immediately obvious how it is related to the metabolic profile.
The patient has a very slight alkalosis at midnight. The arterial blood pCO2 is low, indicating that the alkalosis is respiratory. The bicarbonate is low, indicating either compensatory metabolic acidosis or mixed respiratory alkalosis and metabolic acidosis. The pO2 is low normal despite respiratory alkalosis which could indicate a mild pulmonary problem or a small a-v shunt.
The electrolytes from six hours earlier showed low chloride and low bicarbonate with normal sodium and potassium. The anion gap ([Na] – [Cl] – [HCO3]) was 29 mEq/L. Lactic acidosis is an unlikely cause. Alcohol-related ketoacidosis is possible given the history of binge drinking. This patient does not appear to be volume depleted (given the normal creatinine and urea nitrogen levels). The falls could have been caused by ethanol toxicity, hypoglycemia, or other problems not directly related to the binge drinking.
Needed tests: urinalysis, blood glucose monitoring, electrolyte monitoring (especially potassium), serum magnesium
From the electrolytes alone, the anion gap is +3, but the change in CO2 is -12. Therefore, there is a negative bicarbonate gap (or low delta ratio), which is caused by either non-anion gap metabolic acidosis or bicarbonate excretion in response to chronic respiratory alkalosis. The ABG, on the other hand, shows a combined and mild metabolic acidosis and respiratory alkalosis, which explains neither the anion gap nor the degree of bicarbonate deficit that is seen. Therefore, one must postulate an additional metabolic alkalosis. This leaves us with the triple disorder of respiratory alkalosis, anion gap metabolic acidosis and metabolic alkalosis. The possibility of increased unmeasured anions not contributing to acidosis (hypercalcemia, hypermagnesemia, myeloma protein) must also be considered. Need to check serum Ca, Mg, SPEP, urinary electrolytes, serum/urine osmolality.
Sorry, reading the electrolytes wrong. If Na is 137 Cl is 92 and CO2 is 16, then he has an anion gap of 29 and a bicarbonate gap of +6, delta ratio ~1.5. Combined anion gap metabolic acidosis and metabolic alkalosis. Taking the ABG into account, there is no compensatory bicarbonate excretion present. We end up with the same triple disorder diagnosis. The workup is the same, but need to focus on high-AG metabolic acidosis (toxic ingestions, etc.) rather than high-AG non-acidosis.