Here are some initial labs:
Looks like we have (at least 1) acid-base disturbance ! Let’s follow the steps below to see what they are:
Would you describe this patient’s arterial blood pH as acidemic or alkalemic?
Alkalemic
The normal range for arterial blood pH is 7.35 – 7.45. A pH greater than 7.45 would be alkalemic. Try again!
Acidemic
That’s right! The normal range for arterial blood pH is 7.35 – 7.45. This pH less than 7.35 is acidemic.
What is the primary acid-base disturbance here?
Respiratory
A respiratory acidosis would be the consequence of a high PCO2. In this case the PCO2 is lower than normal (40 mm Hg), meaning it is not the primary process driving the acidemia. Try again!
Metabolic
That’s correct! The bicarbonate level is lower than normal (24 mEq/L) with an acidemic pH – thus, we have a primary metabolic acidosis.
Is there appropriate compensation?
Yes
Correct! The expected pCO2 based on Winter’s Formula would be 1.5 (bicarbonate) + 8 = 1.5 (9) + 8 = 21.5. So our expected PCO2 should be between 19.5 – 23.5 mm Hg if there is adequate compensation.
No
Check your math one more time – this patient does not seem to have an appropriate compensation based on Winter’s Formula.
Which best describes this patient’s acid/base disturbance (s)?
Non- anion gap metabolic acidosis
Not quite, try again! Hint: what’s the anion gap here?
Anion gap metabolic acidosis
That’s correct! This patient has a high anion gap (Na – Cl – HCO3 = 30), with adequate respiratory compensation (so there is no respiratory acid-base disturbance)
Anion gap metabolic acidosis + respiratory alkalosis
Close, though we do have adequate respiratory compensation here so there is no additional respiratory acid-base disturbance.
Anion gap metabolic acidosis and respiratory acidosis
Not quite, try again! Hint: what would be the expected PCO2 for a patient with a respiratory acidosis?
Non-anion gap metabolic acidosis and respiratory acidosis
Not quite, try again! Hint: the anion gap can be calculated using the following equation: AG = Na – Cl – HCO3
Non-anion gap metabolic acidosis and respiratory alkalosis
Not quite, try again! Hint: the anion gap can be calculated using the following equation: AG = Na – Cl – HCO3
Which of the following is the most likely etiology of this patient’s acid-base disturbance?
Salicylate toxicity
Pulmonary embolism
Methanol toxicity
Lorazepam infusion
Propofol infusion
Septic shock
Pyroglutamic acidosis
Penicillin toxicity
Starvation ketoacidosis
Isopropyl alcohol toxicity
Which of the following are the highest yield tests to uncover the etiology of this patient’s acid-base disturbance?
Lactic acid
1.0 mmol/L. This is an important test to send in any patient with a metabolic acidosis.
Urine ketones + serum ß-hydroxybutyrate
Nice! There are no ketones detected in the urine and the serum ß-hydroxybutyrate is within normal limits.
Serum osmolality
Excellent! The serum osmolality is 275 mosm/kg. Is there an osmolal gap? What does that tell you?
Serum 5-oxoproline
Good choice – though will take a few days for this one to come back.
Triglycerides
Good choice. The triglyceride level is 135 mg/dL.
D-lactic acid
This patient does not have clear risk factors for a D-lactic acidosis (e.g. short bowel syndrome). Let’s start with a few higher yield tests!
Computed tomography with angiography (CTA) of the chest
A CTA may reveal a pulmonary embolism (PE), though this patient does not have clear risk factors for PE *we might find a respiratory alkalosis in a patient with a PE
So…which of the following is the most likely etiology of this patient’s acid-base disturbance?
Salicylate toxicity
Pulmonary embolism
Methanol toxicity
Lorazepam infusion
Propofol infusion
Septic shock
Pyroglutamic acidosis
Penicillin toxicity
Starvation ketoacidosis
Isopropyl alcohol toxicity
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NephSIM