A 45-year-old man is admitted unconscious to the Emergency Department. His electrolytes are as follows:
|
Parameter |
Patient Value |
Normal Range |
|
Sodium |
119* mmol/l |
135 – 145 |
|
Potassium |
5.5* mmol/l |
3.2 – 4.5 |
|
Chloride |
80* mmol/l |
100 – 110 |
|
Bicarbonate |
<5* mmol/l |
22 - 27 |
|
Urea |
10* mmol/l |
3.0 – 8.0 |
|
Creatinine |
105 µmol/l |
50 – 100 |
|
Glucose |
13.0* mmol/l |
3.0 – 6.0 |
|
Lactate |
8.8* mmol/l |
<2 |
|
Measured osmolality |
340* mOsm/kg |
275 – 295 |
|
Urine ketones |
Negative |
a) What are the abnormalities?
b) Give a possible diagnosis
c) What further tests would you consider to elucidate the cause of the acid base disturbance?
a) What are the abnormalities?
b) Give a possible diagnosis
c) What further tests would you consider to elucidate the cause of the acid base disturbance?
This is a straighforward question about high osmolar gap high anion gap metabolic acidosis.
The anion gap is (119) - (80 + 5) = 34, or 39.5 when calculated with potassium
The delta ratio, assuming a normal anion gap is 12 and a normal bicarbonate is 24, would therefore be (34 - 12) / (24 - 5) = 1.15, making this a pure HAGMA.
There is also a high osmolar gap of 79 (340- (119x2 + 10+ 13))
Hyperosmolar hyponatremia is not asked about, but is still interesting as an aside.
The causes of a metabolic acidosis with a raised anion gap and a raised osmolar gap are numerous, and well discussed in the literature. Specifically, methanol and the other toxic alcohols are a common cause, and are dealt with in detail elsewhere.
Alcoholic ketoacidosis is mentioned as a differential, although the urinary ketones are absent from the scenario sample. This may be because beta-hydroxybutyrate, the major ketone in alcoholic ketoacidosis, is not detected by urine dipsticks (which look for acetone and acetoacetate).
Smith SW, Manini AF, Szekely T, Hoffman RS.. Bedside detection of urine beta-hydroxybutyrate in diagnosing metabolic acidosis. Acad Emerg Med. 2008 Aug;15(8):751-6.
Kraut JA, Xing SX. Approach to the evaluation of a patient with an increased serum osmolal gap and high-anion-gap metabolic acidosis. Am J Kidney Dis. 2011 Sep;58(3):480-4.