T4: Electrolyte Disorder

Question 1

What electrolytes are measured on U&Es?

Answer 1

We measure:
	- Sodium 
	- Potassium 
	- (chloride)
	- (bicarbonate)
	- Urea
	- Creatine
	It is important in terms of CVD - Sodium depletion will lead to low blood pressure and it can lead to renal disease. Poor electrolytes will lead to disturbance in the electrophysiology in the heart and so issues with potassium can lead to arrhythmias.  Electrolytes are also important for cellular homeostasis.

Question 2

How is sodium and potassium distributed in bodily fluid?

Answer 2

Normally inside the cell - sodium concentration is low and potassium is high, the opposite is true in plasma.

ECF Sodium is around 1`40mmol/L and Potassium concentration is around 5 mmol/L.

ICF Sodium concentration is around 10 mmol/L and Potassium concentration 150 mmol/L.

Question 3

What happens in a loss of hypotonic solution for example in diabetes?

Answer 3

Water is pulled out by osmosis and the cells shrink. There is a greater loss from ICF than ECF. There is a small increase in sodium concentration. There is fluid redistribution between the ECF and ICF.

Question 4

What happens when you gain hypotonic solution?

Answer 4

Hypotonic solution - with water nothing else. This dilutes the patient so the sodium concentration decreases. The water goes into the cells. You would see oedema. They would be water logged. Dextrose drips have water. A common mistake is putting a dextrose drip instead of a sodium dip - without a sodium drip the kidneys become over clogged - the brain can die central pontine myelinolysis. They can die of a stroke.

Question 5

What are compensatory mechanisms for loss of hypotonic solution?

Answer 5

Physiology: 
	- Thirst 
	- ADH 
	- Renin/Angiotensin System 
Therapeutic 
	- IV therapy 
	- Diuretics 
	- Dialysis 
ADH

Question 6

What is the role of ADH?

Answer 6

Produced by the median eminence in the brain and releases when osmolarity rises. It then decreases renal water loss and increases thirst.
Simple tests to ascertain ADH status:
- Measure plasma and urine osmolarity - in high ADH the plasma osmolarity will be high
- Urine > plasma suggests ADH is active - really concentrated water
- Measure plasma and urea area
Urea&raquo_space; plasma suggests water retention

Question 7

What is the role of Renin-Angiotensin System?

Answer 7

Vasoconstriction - increase blood pressure using renin from the kidney, angiotensin from the lungs and aldosterone from the kidney.

Question 8

Diagnose the following problem:

Patient 1
Patient is dry and has been treated for CCF

Plasma
Na - 120 (135-145 mmol/L)
Urea - 15 (3.0 - 8.0 mmol/L)

Urine
Na - 50 mmol/L
Urea - 150 mmol/L

Answer 8

It is concentrated looking at the urea. The urine would be dark and so the kidneys are working. You can tell this as the urine urea is greater than the plasma urine. The ratio is 10:1. However the kidney should not be letting the sodium through. They are on diuretics for cardiac failure - these let the sodium through. They are dry as they have too much diuretic and are dehydrated.

Reduced sodium reabsorption means they have sodium diuresis - water loss. The urea gets concentrated and vascular volume gets increased and ADH gets fired up giving concentrated urine.

Question 9

Diagnose the following problem:

Patient 2:
Patient is thirsty but well hydrated

Plasma
Na 119 (135-145 mmol/L)
Urea 2.5 (3.0 - 8.0 mmol/L)
Osmols 250

Urine
Na 40 mmol/L
Urea 70 mmol/L
Osmols 800

Answer 9

Normal osmolarity is normally 300. They are not concentrated. They have low concentrations. They are diluted, everything full of water. The urine osmolarity is very high, they have an inappropriate production of ADH.

Question 10

Diagnose the following problem:

Patient 3:
Patient is dry and has difficulty swallowing

Plasma
Na	150	(135-145 mmol/L)
Urea	15	(3.0 - 8.0 mmol/L)

Urine
Na 25 mmol/L
Urea 150 mmol/L

Answer 10

There urine is concentrated 10:1, the kidneys are working. They cannot clear the water down.