pediatric emergency MCQ-No4

Question 4

A patient presents to the ED and has the following laboratory values: sodium 139 mEq/L, potassium 4.1 mEq/L, chloride 112 mEq/L, bicarbonate 15 mEq/L, BUN 22, creatinine 1.5, and glucose 180.

1)All of the following could be the etiology of these laboratory findings EXCEPT
A.Salicylates
B.Renal tubular acidosis, type II
C.Acute diarrhea
D.Uretero-sigmoidosto my
E.Pancreatic fistula

2)What is the calculated osmolarity for the patient?
A.157 mOsm/L
B.274 mOsm/L
C.296 mOsm/L
D.310 mOsm/L
E.347 mOsm/L

Answer & Comments
•1A •2C
•Comments:
–The anion gap (AG) is the difference between the measured sodium level and the sum of the measured chloride and HCO3 levels.
•Normal AG = 12 ± 4
–The etiologies of this patient’s normal AG (hyperchloremic) metabolic acidosis can be remembered by a helpful mnemonic,

HARDUP:
•H for hypo-aldosteronism (Addison’s disease),
•A for acetazolamide,
•R for renal tubular acidosis,
•D for diarrhea,
•U for uretero-sigmoidosto my,
•P for pancreatic fistula.
–Salicylate toxicity causes an elevated AG with a normal osmolar gap.
–Serum osmolarity is measured directly by determining the freezing point of the serum.
–It is calculated from the sodium, glucose, and BUN values with the following equation:

•Osmolarity = 2 (Na) + glucose mg/18 + BUN mg/2.8.

–The normal serum osmolarity is 275 to 296 mOsm/L.
–In this case, the calculate dserum osmolarity is 296 mOsm/L.
–A difference between the measured and calculated osmolarity (osmolol gap) of more than 10 mOsm/L indicates the presence of osmotically active substances (such as alcohols) in the blood.