Question 24.2

A 40-year-old patient with a background of alcohol abuse presents with a history of 8 days of diarrhoea and vomiting.

The following results are obtained:

Parameter	Patient Value	Adult Normal Range
Sodium	116 mmol/L*	137 – 146
Potassium	2.9 mmol/L*	3.5 – 5.0
Chloride	67 mmol/L*	95 – 110
Bicarbonate	14 mmol/L*	24 – 31
Urea	2.9 mmol/L*	3.0 – 8.5
Creatinine	46 µmol/L*	60 – 120
Glucose	6.8 mmol/L	3.0 – 7.8
Osmolality	254 mOsm/kg*	274 – 295
Phosphate	0.6 mmol/L*	0.7 – 1.4
Magnesium	0.7 mmol/L	0.7 – 1.05
Calcium corrected	2.3 mmol/L	2.1 – 2.6
Albumin	44 g/L	36 – 52
Bilirubin	13 µmol/L	0 – 18
Aspartate transferase	80 U/L*	0 – 30
Alanine transferase	67 U/L*	0 – 30
Alkaline phosphatase	148 U/L*	30 – 100
g-Glutamyl transferase	480 U/L*	0 – 35

a) What is the acid-base disturbance in this patient? (20% marks)

b) What are the likely causes in this context? (30% marks)

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College answer

a)
Metabolic acidosis- Anion gap= 116-(67+14) = 35 Delta ratio= 23/10=2.3
HAGMA with metabolic alkalosis OR Increased SID

b)
Metabolic alkalosis – due to vomiting- Acid loss and contraction alkalosis. HAGMA-
Lactic acidosis from hypovolaemia or bowel obstruction/sepsis, Ketoacidosis from starvation/alcohol.

Discussion

In some sort of a structured fashion:

The bicarbonate is low, suggesting a metabolic acidosis
The anion gap is (116-67-15) = 34
The delta ratio is therefore (34-12)/(24-15) = 2.44;
in other words, this is a mixed HAGMA and metabolic alkalosis.
The calculated osmolality is (116 × 2) + 2.9 + 6.8 = 241.7, and so the osmolar gap is minimal (254-241.7 = 12.3)

Causes of HAGMA appropriate to this scenario include:

Toxic alcohol ingestion (classically, methanol) - though the low osmolar gap makes this less likely
Alcohol-induced or starvation-associated ketoacidosis (more likely)
Lactic acidosis due to the hypovolemic state, and the failure of the liver to metabolise it

The metabolic alkalosis can be attributed to the vomiting and diarrhoea, and more directly to the aldosterone excess which develops in states of volume depletion.

References

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