Systems Pathology: Disordered Fluid And Electrolyte Balance Flashcards Preview

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Flashcards in Systems Pathology: Disordered Fluid And Electrolyte Balance Deck (13)
0

Fluid compartments

Total body water 45l osmolality 285-295mmol/kg
Extra cellular 15l (1/3)-> sodium 135-145 mmol/l, potassium 3.5-5.3
-> intravascular 5l
-> intersitial 10l
Intracellular 30l (2/3)-> Na 9 K 150
1100l of fluid transferred daily between plasma and interstitial fluid
ECF fluid largely determined by total body sodium
Distribution determined by hydrostatic pressure, colloid osmotic pressure, capillary

1

Water regulation

Water intake->Thirst centre in hypothalamus-> sensitive to osmolality and blood volume changes
Water loss-> ADH-> high osmolality and low blood volume-> increases permeability of distal tubule-> increased water reabsorption, vasoconstriction-> increased blood pressure
-> RAA sensitive to change in renal blood flow-> aldosterone-> increase Na reabsorption in exchange for H and K
Net renal loss-> 1.5l water and 100mmol Na

2

Dehydration causes

Reduced fluid intake-> unavailability, impaired thirst mechanism, Dysphagia
Increased loss-> sweating, burns, hyperventilation, diuretics, diabetes mellitus and insipidus, adrenal failure, renal failure

3

Dehydration clinical features

Tachycardia
Hypotension
Thirst
Rapid weight loss
Loss of skin elasticity
Oliguria
-> severe-> confusion, coma, renal failure

4

Dehydration managment

Fluid +- electrolyte replacement
Treat cause

5

Dehydration case study

High plasma sodium-> water loss exceeds electrolyte loss
High urine osmolality-> hypernatremia triggers ADH relase-> increased water reabsorption
Low urine Na-> dehydration causes decrease ECF volume-> decreased renal blood flow-> RAA-> aldosterone-> sodium reabsorption
Loosing Na via vomiting-> don't be mislead by high plasma Na-> only because of water loss

6

Dilutional Hyponatraemia

Post op IV dextrose-> water moves out of cells-> dilution
Fluid overload
Hyperglycaemia-> high blood glucose-> increased osmolality-> water out of cells
Hypovolomic-> low blood pressure-> water moves out of cells
Diuretics, antidepressants, anticonvulsants, ACEis

7

Fluid overload causes

Excessive fluid intake
Impaired excretion
-> renal impairment
-> failure of regulatory mechanisms

8

SIADH

Some cancers secrete ectopic hormones
Eg small cell carcinoma of lung-> ADH, ACTH
Unregulated ADH release-> water retention-> hypervolaemia-> Dilutional Hyponatraemia
All body fluid compartments effected
Hypervolaemia inhibits RAA-> high urine Na >20mmol/l
-> high urine osmolality >200 (inability to produce dilute urine)
Response to water restriction
Other causes-> cerebral trauma or infection, pulmonary embolus, drugs

9

Conns syndrome

Aldosterone secreting tumour or adrenal Hypertrophy
Increased aldosterone-> sodium and therefore water retention-> K loss
Hypernatremia and hypokalaemia
Increased ECF-> hypertension

10

Pseudo Hyponatraemia

Excessive proteins or lipids causes dilution
Total body water and sodium unchanged
Normal plasma osmolality

11

Clinical features of fluid over load

Dependent oedema
Raised central venous pressure
Pulmonary oedema
Rapid weight gain
Abdo cramps
Weakness
Impaired conciousness
Hypertension

12

Treatment of fluid overload

Fluid restriction
Diuretics
Treat cause

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