Online OSCEs - Station TWO - Arterial Blood Gas Interpretation

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A 15 year old schoolgirl is brought to A+E. On arrival, she is extremely unwell.

The doctor is concerned by her breathlessness, and performs an arterial blood gas analysis. The patient was not on supplemental oxygen at the time.

pH: 7.29

PaO₂: 13.6 kPa

PaCO₂: 2.3 kPa

Bicarbonate (HCO₃^-): 6 mmol/l

Base excess (BE): -10 mmol/l

Question 1: Does the patient have a problem with oxygenation? (1 mark)

Question 2: Describe the acid-base abnormality. (2 marks)

Question 3: The following blood results are then returned:

Na⁺: 146 mmol/l

K⁺: 4.2 mmol/l

Cl^-: 92 mmol/l

HCO₃^-: 6 mmol/l

Urea: 12.2 mmol/l

Creatinine: 87 umol/l

Calculate the anion gap. (2 marks)

Question 4: Give four causes for the above acid-base disturbance. (4 marks)

Question 5: The patient is found to have diabetic ketoacidosis, and is commenced on intravenous fluids and insulin.

Which electrolyte requires careful monitoring during treatment? (1 mark)

Answer 1:

Does the patient have a problem with oxygenation?

No. The PaO₂ is entirely appropriate for a patient breathing room air that comprises 21% oxygen. (1 mark)

Answer 2:

Describe the acid-base abnormality.

Answer 3:

The following blood results are then returned:

Na⁺: 146 mmol/l

K⁺: 4.2 mmol/l

Cl^-: 92 mmol/l

HCO₃^-: 6 mmol/l

Urea: 12.2 mmol/l

Creatinine: 87 umol/l

Calculate the anion gap.

The anion gap is calculated as follows:

Answer 4:

Give four causes for the above acid-base disturbance.

Diabetic ketoacidosis
Renal failure
Lactic acidosis
Salicylate poisoning
Methanol poisoning
Ethylene glycol (antifreeze) poisoning

(1 mark for each correct answer from above list to a maximum of 4. Any other correct answer also acceptable)

Answer 5:

The patient is found to have diabetic ketoacidosis, and is commenced on intravenous fluids and insulin.

Which electrolyte requires careful monitoring during treatment?