Clinical Investigation and diagnosis

Question 1

How body concentrates urine?

High serum sodium and low urine osmolarity=diabetes insipidus, as peeing out loads of water and so sodium concentrates (as no ADH)

But in psychogenic polydipsia: There is low sodium as drinking lots which is why peeing lots

Answer 1

Question 2

CHF-supine position puts pressure on kidneys which increases urine output (get nocturia)

Differential diagnosis: polydipsia and polyurea:

Answer 2

Lithium prevent transporters in ascending limb from working properly

Heart failure and kidney failure cause fluid overload and stretch atria so lead to more ANP and less ADH

Question 3

Diagnostic approach to polyuria

Answer 3

Question 4

tests explained

Answer 4

Question 5

Don’t correct fluids too quickly ie less than 8mmol per day because otherwise can cause cerebral oedema. So don’t correct acutely. If it developed over a long time then give fluids even slower to correct slower

Answer 5

Question 6

What fluid should you give?

Answer 6

• Give everyone saline. Don’t give dextrose because sodium will fall too quickly and they’ll die
• Unless liver patient, then give dextrose. If cirrhosis you stop making albumin so to maintain BP you switch on RAS and retain sodium so you get oedema everyone. The cost is extra fluid so you have peripheral oedema and sky high aldosterone and so they go on spironolactone or anything to get rid of salt. Any salt you give them it takes ages to remove for cirrhotic patients. Everyone else, give dextrose