This blood gas report was taken from a lady hospitalised for recurrent urinary tract infections. She was transferred to the ICU because of nosocomial pneumonia.

Test

Value

Normal Range

FiO2

0.3

pH

7.53

7.35 – 7.45

pCO2*

31 mmHg (4  kPa)

35 – 45  (4.6 – 5.9)

pO2

83.7 mmHg (11 kPa)

80 – 110  (10.5 – 14.5)

Bicarbonate

25 mmol/L

24 – 32

Standard Base Excess*

3.3 mmol/L

-2.0 – +2.0

a)  Comment on the acid-base status.

b)  List 2 likely causes of the acid-base derangement in this patient.

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College Answer

a)  Comment on the acid-base status.

Mixed respiratory and metabolic alkalosis

b)  List 2 likely causes of the acid-base derangement in this patient.

Respiratory alkalosis from the hyperventilation due to the pneumonia

Metabolic alkalosis from vomiting or diuretic use

Discussion

 This question is identical to Question 6.1  from the first paper of 2013.