Why he had not peed in 2 days


Category : Acid-Base & Lytes, Attending Rounds

To restate:

A 55-year-old man comes to the ER for RUQ abdominal pain for the past week, getting worse, and diarrhea (4-6 semi-formed stools daily. His vital signs show tachycardia, normal respiratory rate, and a normal BP. He has a positive Murphy’s sign, but otherwise his abdomen just appears distended.


129 80 101 144
4.6 15 8.6 6.9


pH 7.27

pCO2 37

pO2 91

HCO3 17


When first presented with this story at morning report, these were my thoughts:

  1. Mild hyponatremia, will not address at this time
  2. Increased anion gap acidosis – 34 – must evaluate
  3. Metabolic alkalosis – ask for albumin level – 4.4 – expected gap is 13, actual gap is 34, therefore delta gap is 21.  21 + observed bicarb of 15 =36.  Therefore if we correct the anion gap, the patient will likely have a metabolic alkalosis.  We would expect volume contraction.
  4. Oliguria with acute kidney injury.  Ultrasound ordered and excludes hydronephrosis.  Urine electrolytes ordered = uNa = 25, uCr = 392.  FeNa = 0.4 – clear evidence of volume contraction.  The patient should respond to volume expansion.
  5. Hypocalcemia – not due to decreased albumin.  Let’s check the phosphate – 13.4.  That explains the anion gap and the hypocalcemia.  Both lactic acid and ketones were negative and serum osms showed no significant gap.

We then had further information.  An NG tube delivered 1.5 liters of bilious fluid.  Further history found a history of ciprofloxacin.  A presumptive diagnosis of C diff was confirmed 5 days later.  While the ultrasound just showed “gallbladder sludge” with normal common duct size, a HIDA scan showed a gallbladder EF of 20%.

The patient’s number totally corrected with volume expansion.  The C diff did not respond to metronidazole but did respond to oral vancomycin.  Our surgeon will re-evaluate next week, the patient may need an elective cholecystectomy.

I present this patient, because a careful assessment of the electrolytes and ABG allowed the housestaff to correct the AKI before the patient developed ATN.

If anything in this discussion does not make sense, please ask a question – I will answer to the best of my ability.


Comments (1)

With that explanation, this blood gas looks like a triple disorder to me. Good teaching blood gas for residents to see multiple disorders on one gas and the need for clinical story to interpret.
Primary- metabolic acidosis from diarrhea
Secondary -metabolic alkalosis, etiology not certain to me, volume contraction may be the cause or the effect, the large NG may certainly be the cause, and you didn’t say how much potassium replacement was necessary so that may have something to do with it.
Tertiary -there is a relative respiratory acidosis. One would expect with a low pH and a primary metabolic acidosis compensatory hyperventilation. There is not (pCO2 of 37 considered normal). This is mild and my guess likely a compensation to the secondary metabolic alkalosis.

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