8.12 Salt, Water & Potassium Flashcards
Hyponatriaemia
- low Na in blood serum
- excessive water intake
1. Low salt
2. Add lots of water
RF
- less well trained athletes
- long race times
- weight gain during race (because of water gain)
- females, low body mass, younger age
Symptoms
- confusion
- weight gain
- seizures
- resp distress
Prevention
- education (don’t drink too much water)
Water compotition in man and women
M: 60%
W: 50%
ICF: 20L (2/3)
⬆️ K
Bigger vol
⬇️pH
ECF: 10L (1/3)
⬆️ Na
Osmolarity is same ICF & ECF: osmotic forces very powerful, cell membrane full of channels (290-300 mOsm/kg)
How is osmolarity meassured?
- depression of freezing point
- with solutes: will not freeze at 0
- the more solutes the lower the freezing point (-1)
salt lowers freezing point
How does water move across membrane?
- Permeability
- Driving force (concentration difference)
Driving forces:
- concentration
- electrical
- pressure
What force is the strongest force?
Osmotic force
Why are most of the potassium inside our cells?
Inside of cells are ➖ charged and hold potassium inside
Why is most of sodium outside the cell?
The cell membrane has no permeability for sodium; so stays outside
What 2 factors determine ICF?
P osmolarity
Concentration of Na (ICF vol)
What is ECF determined by?
Na+ content
What happens if give pt 1L of pure water?
- dilute blood (water gets into cells)
Regulation of Na+
- by kidney
GO ON WITH SLIDE 22
What determines the permeability of collecting duct?
ADH
Stimuli of ADH
VASOPRESSIN
- physiologic - SLIDE
- non- physiologic - CNS, lung disease, ectopic cancers, drugs, anxiety, pain, nausea
How does the body responds to osmolarity (Na concentration) changes?
Via water intake and output
Water, thirst, ADH
How does the body responds to ECF volume (Na content) changes?
Sodium intake & output
(Renin-angiotensin-aldosterone)
Acute hyponatraemia
- less than 48hrs
**Causes:* acute water overload (hypotonic iv fluids in hospital, ectasy, marathons, psychogenic polydipsia)
Dangers: brain swelling and herniation (coma, seizures, death)
Chronic hyponatraemia
- more than 48hrs
Causes
- Na loss ± water gain
- ADH present & prevents water excertion
- hypovolaemia, drugs, CNS, lung disease
Dangers
- osmotic demyelination from too-rapid correction
- serious neurological damage
What are the normal values of potassium?
ECF: 4mmol/L (in blood test)
ICF: 150 mmol/L
What are the signs of Hyperkaleamia on ECG?
- Tall peaked T waves
- loss of p waves
- widening QRS complexes
- sine waves, ventricular arrythmias, asystole
What keeps K inside cells?
- electrical charge ➖
- Na/K ATPase
What leads to a negative K balance?
- ⬇️ input
- ⬆️ output
How does acidosis cause hyperkalemia?
- Acidosis cause: diabetic acidosis or lactic acidosis (this is normal!!)
Therefor this statement is not entirely true. Acidosis doesn’t really cause hyperkalemia
Only when body is confronted with abnormal acid; acidosis will cause Hyperkalemia
Therefor depends ON NATURE OF ACID
How does the body handle usual dietary K+ load?
- we absorb all the potassium we ate -> that we need to excrete
- K+ parked in Liver -> redistributed to rest of body
- kidney will excrete it slowly over time
- use insulin to push potassium into cells (this is only temporarily)
What should you consider if you have pregnant pt with hypokalemia?
Geophasia
