Following  laparotomy  for haemoperitoneum,  a patient  is transferred  to ICU.
Blood biochemistry  and arterial blood gas analysis on admission  to ICU are as follows:

Test

Value

Normal Range

Sodium*

147 mmol/L

135 – 145

Potassium

3.6 mmol/L

3.2 – 4.5

Chloride*

124 mmol/L

100 – 110

Haemoglobin*

106 G/L

115 – 155

pH

7.32

7.35 – 7.45

pCO2*

32.4 mmHg (4.3 kPa)

35 – 45  (4.6 – 5.9)

pO2*

63 mmHg (8.4 kPa)

80 – 110  (10.5 – 14.5)

Bicarbonate*

16.0 mmol/L

24 – 32

Standard Base Excess*

-9.0 mmol/L

-2.0 – +2.0

a)  Describe the acid-base status.

b)  What is the likely cause of this disturbance?

c)  What is the underlying biochemical mechanism?

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College Answer

a)  Describe the acid-base status.
Normal anion gap metabolic acidosis with appropriate respiratory compensation

b)  What is the likely cause of this disturbance?
Resuscitation with large volume saline infusion.

c)  What is the underlying biochemical mechanism?
ECF dilution by fluid with strong ion difference of zero

Discussion

 This question is identical to Question 6.3  from the first paper of 2013.