🥵 HARD

I’m labelling FEB questions as hard because I really think they can mess with you.  It took me a very long time to get around to writing these, and to thinking about it.  But, sadly, whether med or surgery is your call … you need to know about Na, K and Ca derangements.  This quiz in particular covers sodium changes.  Good luck! 

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FEB - Part One

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Question 1
What is the threshold for hypernatraemia?
A
Serum Na+ >145mmol/L
B
Serum Na+ >135mmol/L
C
Serum Na+ >125mmol/L
D
Urine Na+ >145mmol/L
E
Urine Na+ >135mmol/L
Question 2
Which conditions can be diagnosed by monitoring changes in urine osmolality?
A
Cushing's syndrome
B
Conn's Syndrome
C
Nephrogenic DI
D
Central DI
E
Excessive IV Na therapy
Question 2 Explanation: 

Urine osmolality is a measure of the concentration of urine. Diabetes insipidus produces large volumes of urine that have low concentrations of solutes - they have low urine osmolality.

How do changes help with diagnosis?

When these patients are deprived of water, the urine does not concentrate (as you would expect from a healthy individual). The cause can either be central (when the body isn't producing/releasing ADH - anti-diuretic hormone) or in the kidneys themselves (nephrogenic, where the kidneys do not respond to ADH).

If the patient is then given desmopressin (a synthetic version of ADH), the urine will start to concentrate (osmolality will increase). This means the cause of the DI is central/cranial as the kidneys can still respond to ADH.

Question 3
Raised urine osmolality may be caused by which of the following?
A
Stroke
B
Nephrogenic DI
C
Vomiting
D
Excess 5% dextrose
E
Diarrhoea
Question 3 Explanation: 
Vomiting and diarrhoea can lead to dehydration; the kidneys will concentrate the urine to compensate for the loss of fluid and therefore the urine osmolality will increase. As explained above, diabetes insipidus will make the urine less concentrated, and excess 5% dextrose can do the same: once the dextrose (glucose) is absorbed into the cells, the fluid will remain in the patient and need to be excreted in the urine.
Question 4
Which figure correlates to the serum threshold of hyponatraemia?
A
<145mmol/L
B
<125mmol/L
C
<135mmol/L
D
<115mmol/L
E
<105mmol/L
Question 5
What is the most serious side effect when correcting hyponatraemia?
A
Cerebral oedema
B
Peripheral oedema
C
Bibasal rales
D
Central pontine demyelination
E
Autonomic dysfunction
Question 5 Explanation: 
If hyponatraemia is corrected too rapidly, there can be fatal demyelination of nerves, especially in the pons of the brainstem (see here). Details about emergency management of severe hyponatraemia are available from the Society of Endocrinology.
Question 6
The hyponatraemic patient undergoes serum osmolality screening and is found to have:
A) a hypotonic state B) Elevated extracellular fluid volume

Which diagnoses best match this profile?
A
CHF
B
Cirrhosis
C
AKI
D
CKD
E
SIADH
Question 6 Explanation: 
Hypervolaemic hypotonic states suggest heart, liver and kidney failure. The patient may have signs of pleural or peripheral oedema.
Question 7
The patient undergoes serum osmolality screening and is found to have:
A) Hypotonic serum B) Normal extracellular fluid volume 

Which diagnoses best match this profile?
A
Cirrhosis
B
GI loss
C
Third spacing
D
SIADH
E
Hypothyroid
Question 7 Explanation: 
The isovolaemic hypotonic hyponatraemic patient is most likely due to SIADH or thyroid deficiency.
Question 8
The patient undergoes serum osmolality screening and is found to have:
A) an hypotonic state B) low extracellular fluid volume

Which diagnoses best match this profile?
A
Diuretics
B
Adrenal insufficiency
C
Burns
D
SIADH
E
AKI
Question 8 Explanation: 
The hypovolaemic hypotonic hyponatraemic patient is more likely to have GI, third space loss or diuresis. The patient will likely appear dehydrated with dry skin and mucous membranes, and tachycardia.
Question 9
Where is antidiuretic hormone synthesised?
A
Anterior pituitary gland
B
Hypothalamus
C
Posterior pituitary gland
D
Adrenal gland
E
Pineal gland
Question 9 Explanation: 
ADH is synthesised in the hypothalamus and released via the posterior pituitary gland. It helps to increase blood pressure and water in the body by stimulating the kidneys to reabsorb more water. When released in excess, as with SIADH (syndrome of inappropriate ADH), it causes hyponatraemia due to too much water being reabsorbed, but the urine will be more concentrated. I.e. they will be euvolaemic, hyponatraemic but with increased urine osmolality.
Question 10
Which of the following differentials match to hypovolaemic hyponatraemia?
A
GI loss
B
Water loading
C
SIADH
D
Addison's
E
Brain tumour
Question 11
Which of the following differentials match to euvolaemic hyponatraemia?
A
Diarrhoea
B
Diuretics
C
Ascites
D
Addison's
E
SIADH
Question 12
Which of the following differentials match to hypervolaemic hyponatraemia?
A
Burns
B
Lung cancer
C
Head injury
D
Renal failure
E
Paralytic ileus
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