Sun28November0628PM 25

An arterial blood gas is taken from a normal, non-labouring woman at term.

Which set of results is most likely to belong to this patient?

Option pH PaCO2 HCO3 PaO2

A 7.35 28 mmHg (3.73 kPa) 27 mmol/L 104 mmHg (13.8kPa)

B 7.43 32 mmHg (4.27 kPa) 21 mmol/L 104 mmHg (13.8kPa)

C 7.44 36 mmHg (4.8 kPa) 27 mmol/L 104 mmHg (13.8kPa)

D 7.45 40 mmHg (5.33 kPa) 21 mmol/L 104 mmHg (13.8kPa)

E 7.46 44 mmHg (5.87kPa) 21 mmol/L 104 mmHg (13.8kPa)

(Please select 1 option)

B This is the correct answer

A Incorrect answer selected

D

C

E

Explanation

Minute ventilation at term is increased by about 50% primarily due to an increased tidal volume with little change or at most a slight increase in respiratory rate. Progesterone, oestradiol and prostaglandins are thought to influence hypothalamic function. This causes a mild compensated respiratory alkalosis.

As a result of this increased alveolar ventilation at term maternal PaCO2 is usually decreased to about 32 mmHg (4.27 kPa). The impact of a maternal alkalosis is lessened by a compensatory decrease in serum bicarbonate from 27 to 21 mmol/L by renal excretion.

Reference:

Bedson R. Physiology of pregnancy: clinical anaesthetic implications. Contin Educ Anaesth Crit Care Pain. 2014;14(2):69-72.

Answer Statistics

1

48%

2

23%

3

5%

4

22%

5

4%

Times answered: 242