Acid base teaching – Case 4

A 62 year old woman with a long history of respiratory disease was being treated for oedema, with the diuretic frusemide. On admission she was confused and weak.

Her results were:

[H+] = 32 nmol/L   pH = 7.5
PaCO2= 9.3 kPa
[HCO3] = 53 mmol/L
[Na+] = 135 mmol/L 
[K+] = 2.6 mmol/L
[CI] = 59 mmol/L

Question 1

What is the patient’s acid base disturbance?

FALSE – Metabolic acidaemia presents with high [H+], significantly low [HCO3-] and low PaCO2.

TRUE – Loop diuretics inhibit resorption of [Na+] and [Cl-] and produce loss of [K+] and therefore they cause a metabolic alkalaemia but this is not the only acid base disorder in this case.

FALSE – Respiratory alkalaemia usually occurs due to hyperventilation of the lungs and results in significant low PaCO2 and a fall in [H+].

FALSE – This is a metabolic alkalaemia with compensated respiratory acidaemia.

TRUE – The history suggests a chronic compensated respiratory acidaemia with increased PaCO2 and increased [HCO3-]

The history suggests that she may have a chronic compensated respiratory acidaemia. In this the expected results are a raised PCO2 with the initially raised [H+] brought back to normal (or nearly so) by an increased bicarbonate level. But the [H+] is actually slightly low, which suggests something else is also going on. Loop diuretics such as frusemide inhibit resorption of [Na+] and [Cl-] and produce loss of [K+] through increased [Na+]/[K+] exchange. They therefore cause a (usually mild) metabolic alkalaemia. So in this case the [HCO3-] is raised by two mechanisms – renal compensation of the chronic respiratory metabolic acidaemia, and a superimposed metabolic alkalaemia caused by the frusemide. The confusion and muscle weakness are signs of hypokalaemia.

 


Question 2

Please answer A, B, C or D for each question – each answer should be used once:

A – High PaCO2
B – Increase in renin release
C – Rise in bicarbonate level
D – Hypokalaemia

A – High PaCO2
B – Increase in renin release
C – Rise in bicarbonate level
D – Hypokalaemia

A – High PaCO2
B – Increase in renin release
C – Rise in bicarbonate level
D – Hypokalaemia

A – High PaCO2
B – Increase in renin release
C – Rise in bicarbonate level
D – Hypokalaemia

A – High PaCO2
B – Increase in renin release
C – Rise in bicarbonate level
D – Hypokalaemia