# Question 9.2

A 21-year-old patient presents with fainting spells and lethargy.

a) Explain the following results and provide a rationale for the abnormalities.    (40% marks)

 Parameter Patient Value Adult Normal Range FiO2 0.21 pH 7.51* 7.35 – 7.45 pO2 72 mmHg (9.5 kPa) pCO2 69.0 mmHg (9.1 kPa)* 35.0 – 45.0 (4.7 – 6.0) SpO2 97% Bicarbonate 55.0 mmol/L* 22.0 – 26.0 Lactate 1.0 mmol/L 0.5 – 1.3 Sodium 128 mmol/L* 135 – 145 Potassium 2.0 mmol/L* 3.5 – 5.0 Chloride 71 mmol/L* 95 – 105 Glucose 4.4 mmol/L 3.5 – 6.0 Urea 15.2 mmol/L* 3.0 – 8.0 Creatinine 82 μmol/L 45 – 90

Not available.

## Discussion

The abnormalities are:

• The A-a gradient is actually negative: (713 × 0.21) - (69  / 0.8) - 72 = -8.52. This is usually an error of measurement (eg. excess air bubbles in the sample).
• There is alkalaemia
• There is a metabolic alkalosis; the SBE is not offered, but the bicarbonate is 55.
• The CO2 is excessive. We cannot apply the SBE equation here, but empirical rules for respiratory compensation in metabolic alkalosis suggest the CO2 should be (0.7×55)+20 = 58.5 mmHg, i.e. there is also a respiratory acidosis here.
• There are also electrolyte abnormalities:
• Hyponatremia
• Hypokalemia
• Hypoglycaemia
• Lastly, the urea and creatinine suggest dehydration.

The possible differentials include:

• Bartter syndrome
• Laxative abuse
• Diuretic abuse