Sodium and LFTs Flashcards
What condition does AST being more than double ALT suggest?
Alcoholic liver disease
What does raised ALP and GGT suggest?
Biliary/gall bladder pathology
How is synthetic liver function assessed?
Clotting factors- prolonged PT time
What liver function results would a known chronic alcoholic have?
Raised bilirubin Prolonged PT Hypoalbuminaemia
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
b} Pneumonia High CURB 65 score Pneunomia can cause euvolaemic hyponatraemia due to SiADH- mechanism unknown
What are the three types of hyponatraemia?
Euvolaemic
Hypovolaemic
Hypervolaemic
What are the causes of hypovolaemic hyponatreamia?
Excessive water loss
- Vomiting + diarrhoea
- Diuretics
What are the mechanisms that regulate sodium balance?
- ADH
- RAAS- Renin-angiotensin-aldosterone
- Natriuretic peptides- ANP/BNP
How does ADH regulate sodium balance?
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]
How does the RAAS cause regulation of sodium balance?
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
How do natriuretic peptides regulate sodium balance?
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
LFT summary table
What are the causes of hypernatraemia?
- Diabetes insipidus
- Uncompensated water loss
- Hyperaldosteronism-eg Conn’s
What happens if sodium is replaced too quickly in a hyponatraemic patient?
Cerebral pontine myelinolysis
Hyponatremia summary table
What are the causes of euvolaemic hyponatremia?
SiADH
Hypothyroidism
Adrenal insufficiency/Addisons
How does SiADH cause hyponatremia?
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]
What are the causes of SiADH?
Lung pathology- pneumonias
CNS pathology- meningitis, encephalitis, SAH
Drugs- opiates, PPIs, carbamazepine, TCAs, SSRIs
Tumours- ectopic ADH- esp small cell carcinoma
Surgery
Common
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
Hypernatremia
What are the causes of hypervolaemia?
Heart failure = low CO
Liver failure= vasodilation due to excess nitric acid
Kidney failure= reduced urine output
How does hypervolaemic hypernatremia work?
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
How does hypothyroidism cause hyponatremia?
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
How does adrenal insufficiency cause hyponatremia?
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
