SAQ 74 – Metabolic – mixed acid-base disturbance and hypokalaemia

Question 7. mixed acid-base disturbance and hypokalaemia.

a. Useful calculations. (3 marks)

• Anion gap: 12.
• Delta gap: 0.
• Expected PCO2: 26.
• Expected potassium: 6.0.

b. Primary acid-base abnormality. (1 mark)

• Moderate normal anion gap metabolic acidosis.

c. Secondary acid-base abnormality. (1 mark)

• Mild respiratory acidosis.

d. Unifying explanation. (3 marks)

• Gastrointestinal losses with vomiting and diarrhoea causing dehydration.
• Dehydration leading to pre-renal renal failure.
• Possible aspiration contributing to low oxygen saturations and respiratory acidosis.
• Fatigue or respiratory muscle weakness from severe hypokalaemia contributing to respiratory acidosis.

e. Further key treatments. (3 marks)

• IV fluids, for example normal saline boluses if shocked, then titrated to MAP, heart rate, capillary refill, and mentation.
• Potassium replacement, for example 10 mmol over 30 to 60 minutes with repeat VBGs guiding further replacement.
• Oxygen.
• Renal replacement therapy if indicated.