Sodium and LFTs

Question 1

What condition does AST being more than double ALT suggest?

Answer 1

Alcoholic liver disease

Question 2

What does raised ALP and GGT suggest?

Answer 2

Biliary/gall bladder pathology

Question 3

How is synthetic liver function assessed?

Answer 3

Clotting factors- prolonged PT time

Question 4

What liver function results would a known chronic alcoholic have?

Answer 4

Raised bilirubin Prolonged PT Hypoalbuminaemia

Question 5

The patient is Selma Bouvier, a 42 year old female. She has been a chronic heavy smoker since her teenage years. She is admitted to hospital confused, her observations and lab results are as follows: She has respiratory acidosis Na: 128 K: 4.4 Urea: 9 Creatinine: 109 Temp: 38.1°C HR: 109 bpm BP: 94/66 RR: 30 SaO2: 100% on 15L O2 What is the likely underlying diagnosis? Small cell lung cancer Pneumonia Heart failure Diarrhoeal illness AKI

Answer 5

b} Pneumonia High CURB 65 score Pneunomia can cause euvolaemic hyponatraemia due to SiADH- mechanism unknown

Question 6

What are the three types of hyponatraemia?

Answer 6

Euvolaemic

Hypovolaemic

Hypervolaemic

Question 7

What are the causes of hypovolaemic hyponatreamia?

Answer 7

Excessive water loss

• Vomiting + diarrhoea
• Diuretics

Question 8

What are the mechanisms that regulate sodium balance?

Answer 8

• ADH
• RAAS- Renin-angiotensin-aldosterone
• Natriuretic peptides- ANP/BNP

Question 9

How does ADH regulate sodium balance?

Answer 9

ADH is triggered by:

Reduced blood volume- [baroreceptors- carotid sinus]

Reduced Na+ concentration- [chemoreceptors- hypothalamus]

Increase volume

Doesn’t take up sodium- priority is fluid restoration

= Therefore causes hyponatraemia

[Sodium is excreted, while water is taken up]

Question 10

How does the RAAS cause regulation of sodium balance?

Answer 10

Renin is produced by juxtaglomerular cells- when reduced blood volume/hypotension detected

Produces angiotensin I

ACE makes angiotensin II

Stimulates aldosterone

Aldosterone reabsorbs Na and excretes K

However aldosterone doesn’t change CONCENTRATION of sodium because water reabsorbed too

Question 11

How do natriuretic peptides regulate sodium balance?

Answer 11

Natriuretic peptides= ANP and BNP

Detect high blood volume

Excrete sodium and water follows- decreasing blood volume

Prevents overloading of heart

Do not change the concentration of Na- just the absolute amount

Question 12

LFT summary table

Answer 12

Question 13

What are the causes of hypernatraemia?

Answer 13

• Diabetes insipidus
• Uncompensated water loss
• Hyperaldosteronism-eg Conn’s

Question 14

What happens if sodium is replaced too quickly in a hyponatraemic patient?

Answer 14

Cerebral pontine myelinolysis

Question 15

Hyponatremia summary table

Answer 15

Question 16

What are the causes of euvolaemic hyponatremia?

Answer 16

SiADH

Hypothyroidism

Adrenal insufficiency/Addisons

Question 17

How does SiADH cause hyponatremia?

Answer 17

SiADH causes excess reabsorption of water and loss of Na

This causes hypervolaemia and hyponatremia]

RAAS is activated, reduces hypervolaemia- but sodium concentration remains the same- so hyponatremia maintained

[From Year Two notes: ANP then is activated and excretes the water, but also excretes the sodium

This causes hyponatreamia]

Question 18

What are the causes of SiADH?

Answer 18

Lung pathology- pneumonias

CNS pathology- meningitis, encephalitis, SAH

Drugs- opiates, PPIs, carbamazepine, TCAs, SSRIs

Tumours- ectopic ADH- esp small cell carcinoma

Surgery

Common

Question 19

Patty Bouvier is a 42 year old female who has bipolar disorder. She successfully manages her condition using the mood stabiliser, Lithium. After a routine blood test, her doctor suspects she has diabetes insipidus.

Which of the following describes the effect of diabetes insipidus of blood sodium?

a) Normonatraemic
b) Hypovolaemic hyponatraemia
c) Euvolaemic hyponatraemia
d) Hypervolaemic hyponatraemia
e) Hypernatraemia

Answer 19

Hypernatremia

Question 20

What are the causes of hypervolaemia?

Answer 20

Heart failure = low CO

Liver failure= vasodilation due to excess nitric acid

Kidney failure= reduced urine output

Question 21

How does hypervolaemic hypernatremia work?

Answer 21

In heart and liver failure:

Excess fluid has leaked into third space- reduced circulatory volume:

Detected by baroreceptors

Therefore increase in ADH

Therefore- decrease in sodium as ADH takes up water + loses sodium

[In heart failure- ANP and BNP are also activated due to strain on the heart, which causes further natriuresis and hyponatremia

• This is still not enough to make the patient euvolaemic however]

In kidney failure/nephrotic syndrome:

Excess fluid in blood because can’t be excreted

Same amount of sodium

Dilutional hyponatremia

Cannot be compensated

Question 22

How does hypothyroidism cause hyponatremia?

Answer 22

Hypothyroidism leads to a decrease in cardiac output

Reduced blood volume detected via baroreceptors at the carotid sinus

Decreased sodium concentration sensed by chemoreceptors

ADH is increased to retain water

Loses sodium in process

Question 23

How does adrenal insufficiency cause hyponatremia?

Answer 23

Decreased aldosterone=

Decreased uptake of sodium- natriuresis

Also decreased water uptake= hypovolaemic/hypotensive

Reduced blood volume and decreased blood volume detected

ADH released

Increases water and blood volume but not sodium= hyponatremia