Question 23.1

A 52-year-old patient with a history of chronic alcohol abuse was brought to the Emergency Department with a reported change in mental state for 3 – 4 days. They were drowsy and lethargic but communicated appropriately when roused. They did not appear dehydrated. The following are the blood results on presentation:

Parameter

Patient Value

Normal Adult Range

Sodium

116 mmol/L*

135-145

Potassium

2.9 mmol/L*

3.5-5.0

Chloride

67 mmol/L*

95-110

Bicarbonate

14 mmol/L*

22-32

Urea

2.9 mmol/L*

3.0-8.0

Creatinine

46 µmol/L

45-90

Glucose

6.8 mmol/L

3.5-6

Phosphate

0.60 mmol/L*

0.65-1.45

Magnesium

0.51 mmol/L*

0.70-1.05

Calcium adjusted

2.31 mmol/L

2.10-2.60

Albumin

34 g/L*

36-52

Bilirubin total

13 mmol/L

< 18

Alanine aminotransferase

67 U/L*

< 35

Aspartate transaminase

80 U/L*

< 40

Alkaline phosphatase

148 U/L*

30-110

g-Glutamyl transferase

480 U/L*

< 40

Lipase

492 U/L*

< 95

Amylase

189 U/L*

< 130

Free T4

14.2 pmol/L

12.0-31.0

Thyroid stimulating hormone             

0.65 mU/L

0.50-5.00

Cortisol

1440 nmol/L*

150-700

b-Hydroxybutyrate

4.4 mmol/L*

< 0.4

Osmolality

254 mOsm/kg*

275-295

Urine Chemistry

Sodium

< 20 mmol/L

Potassium

37 mmol/L

Osmolality

198 mOsm/kg

23.2.1    List the likely diagnosis with the rationale for your decision.    (2.5 marks)
23.2.2    Briefly outline your management of the hyponatraemia in this patient.    (2 marks)
 

[Click here to toggle visibility of the answers]

College Answer

Syllabus topic/section:
2.1.14 Environmental Injuries and Toxicology in ICU – L1.
2.1.21 Applied Pharmacology in Intensive Care.
Aim:
To explore the understanding of data interpretation, toxidromes and management of dysnatraemias.
Discussion:
Overall, this question scored highly but the answers were not as well structured as the other data question 19. Some candidates missed parts of the question, which was really the only way to 'fail' this repeat data interpretation. The management of hyponatraemia was frequently muddled by candidates with many stressing that the correction must be slow but then giving both a fluid restriction and iv hypertonic saline or normal saline. These candidates appeared to have remembered parts of the management but not fully applied it correctly.

Discussion

Quite right, this should have been hard to fail. Assessment drives learning, which means 99% of CICM exam candidates will be able to confidently make the diagnosis of pyroglutamic acidosis, and certainly all of them can interpret the absolute bejeesus out of sodium results, as hyponatremia questions have been repeated abundantly in historical exams. This SAQ is a repeat  of Question 13.2 from the second paper of 2016, and what follows is a direct copy of the discussion section from 2016. 

Let us analyse the results in some detail.

This guy is a drinker, and his GGT is elevated, so... he has been drinking. 

After a few days of decreased level of consciousness he is not dehydrated, so ... he has been drinking a lot.

The bloods demonstrate hypoosmolar hyponatremia with a low usine osmolality and a low urine sodium. There are only a few conditions which can give rise to this:

  • Beer potomania
  • Psychogenic polydipsia
  • Excess 5% dextrose administration (psychogenic polydipsia by proxy, you might say)

Beer potomania is a case of dietary solute deficiency. Your water intake is excessive, but you eat virtually nothing containing salt. Lets say you are a degenerate beer-fiend, and your total nutritional intake consists of carbohydrate-rich, sodium-poor beer. Vast volumes are happily ingested. The carbohydrate from the beer is metabolised preferentially, leading to a suppression of protein catabolism. Low protein catabolism results in low urea levels, and with the sodium dropping, what solute can you excrete? None. The volume of urine drops. Each day you will excrete as little as 4 litres of maximally dilute urine. Obviously if you drink more than 4 litres of beer a day, hyponatremia will ensue. This phenomenon is not limited to American college students; ovolactovegetarians and people trying to lose weight too fast are also susceptible.

This was the second question in the SAQ, but this time it was presented as the first in the series of three, and the question asks your to "list" the diagnosis rather than to "give" it, in order to maintain a predictable consistency with the college exam vocabulary. 

References

Hariprasad MK, Eisinger RP, Nadler IM, Padmanabhan CS, Nidus BD. Hyponatremia in psychogenic polydipsia. Arch Intern Med. 1980 Dec;140(12):1639-42.

Hilden T, Svendsen TL. Electrolyte disturbances in beer drinkers. A specific "hypo-osmolality syndrome". Lancet. 1975 Aug 9;2(7928):245-6.

Thaler SM, Teitelbaum I, Berl T. "Beer potomania" in non-beer drinkers: effect of low dietary solute intake. Am J Kidney Dis. 1998 Jun;31(6):1028-31.

Fox BD.Crash diet potomania. Lancet. 2002 Mar 16;359(9310):942.