Electrolyte Homeostasis Flashcards Preview

Year 2 EMS MoD > Electrolyte Homeostasis > Flashcards

Flashcards in Electrolyte Homeostasis Deck (80)
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31

What are 2 simple tests to ascertain ADH activity?

Measure plasma and urine osmolality
If urine>plasma this suggests ADH is active
or
Measure plasma and urine urea levels (urea is a good indicator of osmolality)
if urine>plasma this suggests water retention

32

How is the RAAS activated?

Reduction in intravascular volume and Na depletion

33

What does the RAAS cause?

renal Na retention (and thus water retention)

34

Give a simple test to measure RAAS activity?

Measure plasma and urine Na
if urine

35

What would happen to fluid and electrolyte levels if you replaced a 2L loss of isotonic fluid with 2L of isotonic fluid?

Fluid and electrolyte levels would return to normal
There would be no change in ECF [Na] and thus no fluid redistribution

36

What would happen to fluid and electrolyte levels if you replaced a 2L loss of isotonic fluid with 2L of hypotonic fluid?

ICF fluid levels 1L greater than normal
ECF fluid levels 1L less than normal
As you would get a reduction in ECF [Na] and thus fluid redistribution

37

What would happen to fluid and electrolyte levels if you replaced a 3L loss of hypotonic fluid with 3L of hypotonic fluid?

Fluid and electrolyte levels would return to normal
[Na] would be restored in ECF and you would get subsequent fluid redistribution

38

What would happen to fluid and electrolyte levels if you replaced a 3L loss of hypotonic fluid with 3L of isotonic fluid?

ICF fluid levels 2L less than normal (unchanged following loss)
ECF fluid levels 2L greater than normal (a 3L gain following loss)
ECF [Na] would be still be slightly increased compared and you would get no fluid redistribution

39

What is hyponatraemia and what 2 situations can cause this?

Reduced [Na] in ECF
Caused by:
Too little Na in ECF
Too much water in ECF

40

What is hypernatraemia and what 2 situations can cause it?

Increased [Na] in ECF
Caused by:
Too little water in ECF
Too much Na in ECF

41

What can dehydration refer to? 2

1) Water depletion
2) Fluid (Na and water) depletion

42

What are the 2 differential diagnoses for a patient with hyponatraemia and oedema?

1) CCF Cirrhosis
2) Nephrosis

43

What would be the diagnosis for hyponatraemia for a euvolaemic patient with a normal plasma osmolality?

Pseudo-hyponatraemia

44

What would the diagnosis for hyponatraemia for a euvolaemic patient with high plasma osmolality?

Hypertonic hyponatraemia

45

What would be the diagnosis for hyponatraemia in a euvolaemic patient with low plasma osmolality?

Water overload - You would then measure the urine sodium to determine the cause of water overload

46

In a patient found to have water overload causing hyponatraemia with a urine sodium of >20mmol/L what are the 3 possible reasons for water overload?

1) SIADH (syndrome of inappropriate ADH)
2) Drugs
3) CRF (chronic renal failure)

47

In a patient found to have water overload causing hyponatraemia with a urine sodium of

1) Stress post surgery
2) Endocrine: Hypothyroid

48

In a hypovolaemic patient with hyponatraemia and a urine sodium of >20mmol/L what are the 3 possible diagnoses?

1) diuretics
2) Addison's
3) Na losing nephritis

49

In a hypovolaemic patient with hyponatraemia and a urine sodium of

1) Vomiting
2) Diarrhoea
3) Skin loss

50

Describe the steps in the cycle of diuretics leading to hyponatraemia?

1) Decreased urine Na reabsorption
2) Leads to Na diuresis, causing increased renal water and Na loss and increased urine [Na] and decreased plasma [Na]
3) This all leads to a decreased intravascular volume (which not only causes increase in plasma [Creatinine] and [urea] due to reduced GFR) also leads to increased release of ADH
4) Increased ADH causes increased water intake which also leads to reduced plasma [Na]

51

Describe the steps in the cycle of SIADH leading to hyponatraemia?

1) Increased ADH leads to decreased urine volume which leads to increased urine [Na]
2) Increased ADH also leads to increased renal water reabsorption which also leads to increased urine osmolality
3) Increased renal water reabsorption also leads to increased IVV which leads to decreased renal Na reabsorption (due to RAAS) which also leads to increased urine [Na]
4) Increased IVV also leads to haemodilution which leads to decreased plasma osmolality, plasma [Na] and plasma [creatinine] and [urea]

52

Other than water retention what else does ADH cause?

Increased thirst

53

Describe the steps in decreased water intake leading to hypernatraemia?

1) Decreased water intake leads to haemoconcentration which causes increased plasma osmolality and increased plasma [Na]
(2) Decreased water intake also leads to increased ADH which causes decreased urine volume and increased urine osmolality)
3) Decreased water intake also leads to reduced IVV which reduces GFR which leads to increased plasma [creatinine] and [urea]
4) Decreased IVV also leads to increased Na retention via the RAAS which leads to increased plasma [Na]

54

If a patient is dry and has been treated for chronic cardiac failure, what is the most likely cause for their hyponatreamia?

Diuretics

55

If a patient is thirsty but well hydrated what is the most likely cause for their hyponatraemia?

SIADH (syndrome of inappropriate ADH)

56

If a patient is dry and has trouble swallowing what is the most likely cause of their hypernatraemia?

Decreased water intake

57

If a patient is dry and thirsty with a high blood glucose what is the most likely cause of their hypernatraemia?

Osmotic diuresis

58

Describe the steps in high blood glucose leading to hypernatraemia by osmotic diuresis?

1) Increased plasma [glucose] leads to osmotic diuresis leading to increased water loss (nb. it does lead to some sodium loss which causes increased urine [Na]) leading to haemoconcentration
2) Haemoconcentration leads to increased plasma [Na] and plasma osmolality which leads to increased ADH leading to increased urine osmolality
3) Increased renal loss of water also leads to decreased IVV which leads to decreased GFR leading to increased plasma [creatinine] and [urea]

59

What is the reference range for plasma [K] and what levels are considered dangerous?

3.6-5.0mmol/L
Values 6mmol/L are potentially dangerous

60

What are the potential dangers of high or low plasma [K]?

Cardiac conduction defects
Abnormal neuromuscular excitability