Water and sodium balance Flashcards
Where sodium goes water follows
Where sodium goes water follows
What hormone regulates water balance?
ADH
Where is water found in the body?
All body compartments and can move freely between them.
What does ADH do?
Increases water reabsorption in renal tubules
What causes ADH release?
Increasing osmolality
How is urine conc measured?
Osmolality
What does a high osmolality indicate?
Conce urine
What does a low osmolality indicate?
Dilute urine
What are the extremes of urine osmolality range?
40 and 1200
What hormone controls Na balance?
Aldosterone
What is the physiological range of Na?
135-145 mmol/l
What fluid compartment is Na mainly found in?
ECF
How does aldosterone work?
Causes reabsorption of Na in renal tubules and lose K instead.
How is aldosterone regulated?
RAAS
Explain RAAS
Renin released from kidneys in response to drop in BP
Renin converts angiotensinogen to angiotensin I
ACE converts angiotensin I to angiotensin II
Angiotensin II causes release of aldosterone from adrenal glands
What are the two major fluid compartments in the body and what are their volumes?
Extracellular fluid- 14L
Intracellular fluid- 28L
What are the two components of the ECF and what are their volumes?
Plasma- 3.5L
Interstitial fluid- 10.5L
What are the two pathologies of Na/water?
Hyponatraemia
Hypernatraemia
What two things can cause hyponatremia?
Low Na
High fluids
What two things can cause hypernatremia?
High Na
Low fluids
When is hyponatraemia serious?
<120 mmol/L
When is hypernatraemia serious?
> 160 mmol/L
When might a normal range of sodium be serious?
If it changes fast
What effect does decreasing Na have on fluid compartments?
Decrease ECF only. Large drop as only lost from here.
What can cause Na decrease?
Reduced Na intake
Na loss in vomiting/diarrhoea, burns, kidney damage
Addison’s disease
How does low sodium present?
Tachycardia Dry membranes Sunken eyes Loss of consciousness Decreased urine output and BP
How do you treat a low sodium?
Give sodium
What effect does increasing fluid have on fluid compartments?
Small increase in all as it spreads throughout body.
What can cause a fluid increase?
Increased fluid intake (compulsive drinking)
Decreased fluid loss- SIADH (V common)
How do you treat a high fluid?
Fluid restrict
How do you diagnose high fluid?
Someone with low sodium who doesn’t look dehydrated
What effects does increasing sodium have on fluid compartments?
Large increase in ECF as fluid gain restricted to here only.
What can cause high sodium levels?
Increased Na intake
Near drowning in salt water
poisoning with salt
How does high sodium present?
Coughing, SOB, tiredness, pulmonary oedema, pleural effusion, weak heart, ascites, oedema
How do you treat high sodium?
Remove sodium with loop diuretics
What effects does decreasing fluid have on fluid compartments?
Small decrease in whole body volume as lost from whole body
What causes low fluid levels?
Increased fluid loss (DI) or decreased fluid intake
How do you treat low fluid levels?
Give water- as 5% dextrose to maintain osmolality so don’t damage RBC
Collides- Plasma expanders
What is pseudohyponatremia?
Increase in blood proteins and lipids reduces apparent blood volume and sodium when they’re actually normal.
When should you suspect pseudohyponatremia?
If have really low sodium but no clinical features.
What is syndrome of inappropriate ADH?
Release of ADH in response to low blood volume when actually have enough fluid
What regulates ADH release?
Blood osmolality
Hypovolemia/hypotension
What happens in SIADH?
Fluid leaks out of vessels due to lack of albumin
BP drops
ADH released to restore volume
Cycle continues
How do you treat SIADH?
Loop diuretics to lose fluid and Na
What happens to plasma osmolality during an abnormal water deprivation test?
Increases due to fluid loss
Why is it better to undertreat than overtreat with desmopressin?
Because overtreatment can lead to very dangerous side effects
How can glucose cause pseudohyponatremia?
By drawing water into extracellular compartments therefore diluting Na content
How do you calculate normal urea production?
1ml/kg/hr
What is classed as polyuria?
More than 50% greater than normal urine production
How do you calculate osmolality?
2[Na+K]+Glucose+Urea
What are some endocrine causes of hypertension?
Cushing’s
Conn’s
Phaeocytocratoma
Acromegaly
What is another cause of SIADH?
Patho too much ADH release
Ectopic ADH production- SCLC
How does SIADH present?
Low Na and K
Oedema
High BP
How do you treat SIADH?
Treat underlying cause
Fluid restrict
Loop diuretics
