Diagnostic Skills Cases

Question 1

Normal BUN and Cr indicates what?

Answer 1

Euvolemic (normal volume)

Question 2

Low Na+ 
Low Cl- 
Low osms plasma
High osms urine
What condition does this person have?

Answer 2

SIADH (syndrome of inappropriate ADH secretion)

• With such a low plasma osmolarity, you should be trying to get rid of water
• Probably due to small cell lung cancer

Question 3

What is the first question to ask with hyponatremia?

Answer 3

What is the patient’s volume status?

look at osms

Question 4

What is your BUN:Cr ratio if you’re hypovolemic?

Answer 4

Greater than 20!

Question 5

How do you manage SIADH?

Answer 5

• Fluid restrict patients
• Maybe give an ADH antagonist
• Maybe use 3% saline IV (not normal or they will get worse)

Question 6

-Hyponatremia
-Hypochloremia
-low urine Na+
-HIGH urine volume
-Low urine osm
What does the patient have?

Answer 6

Primary Polydipsia (person with schizophrenia) [maybe also tea and toast syndrome and/or beer potomania]

Question 7

What should you do to treat Primary Polydipsia?

Answer 7

Restrict fluid intake [this will also tell you difference between DI and primary polydipsia. If someone has DI they will still have very dilute urine after 24 hours - can’t concentrate urine!]

Question 8

-High Na+
-High Cl-
-High HCO3-
-BUN:Cr = 32:1.3
-High BUN, low Cr
-Low Na+ in urine
-High urine osmolarity
-Urine = 0.3 L/day
What does this patient have?

Answer 8

Severe Dehydration. Hypovolemia Hypernatremia. Cause by people not drinking (ex: someone who fell and broke their hip and has been lying on the floor for hours)

Question 9

What does high urine osmolarity tell us?

Answer 9

It serves as a marker for ADH. It tells us that ADH is being used/working in this person!

Question 10

What is the most appropriate treatment for severe dehydration?

Answer 10

Normal saline until in uvolemic state. It will expand the vascular system which is where you want the water! Then, you can correct the hypernatremic state.

Question 11

Low HCO3-
High BUN
High Cr
Very high BUN: Cr ratio
Anion gap = 22 (elevated)
Serum glucose = 520
Arterial pCO2 = 31 mm (low normal is 40)
What is this?

Answer 11

• High anion gap metabolic acidosis.

- Also seen in Diabetic Ketoacidosis!

Question 12

What treatment do you use for DKA?

Answer 12

INSULIN!!

Question 13

What are the causes of high anion gap metabolic acidosis?

Answer 13

MUDPILES!!

• Methanol (formic acid)
• Uremia
• Diabetic ketoacidosis
• Propylene glycol
• Iron tablets/Isoniazid
• Lactic acidosis
• Ethylene glycol (oxalic acid)
• Salicylates

Question 14

Why does DKA mess with potassium?

Answer 14

Metabolic acidosis causes K+ to leave cells. As you correct acidosis, K+ will fall (get re-sequestered by the cells). When K+ gets to about 4, you start supplementing.

Question 15

Low HCO3-
Low pH
Low CO2
High BUN
High Cr
High Osm
UA with several crystals

Answer 15

High anion gap = 25
Metabolic acidosis
Ethylene Glycol

Question 16

What does hyponatremia say about the volume in the body?

Answer 16

Too much water!

Question 17

What does urine osmolarity double the body plasma osmolarity suggest?

Answer 17

Inappropriately high level of Anti-diuretic Hormon (ADH).

Question 18

Why must serum sodium not be changed in either direction more than 10-12 mEq/L in 24 hours?

Answer 18

A more rapid change than this can increase the risk of Central Pontine Myelinolysis (CPM) –> irreversible