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7. CP - Kidney and Urinary Tract Disease > (SDL) Renal function and hydration status > Flashcards

(SDL) Renal function and hydration status Flashcards

1
Q

What is in a steady state during health?

A

Intake + metabolic production = body volume = excretion

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2
Q

The concentration of any solute eg. urea/Na depends on what?

A

The amount of the solute present and the volume of solvent (water) in which it is dispersed

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3
Q

What are the functions of the kidney?

A
  • excretion eg. urea, uric acid
  • regulation eg. homeostasis, water, acid base
  • endocrine eg. renin, erythropoietin, 1,25-dihydroxycholecalciferol
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4
Q

What are the purposes of renal function tests?

A
  • detect renal damage
  • monitor functional damage
  • distinguish between impairment and failure
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5
Q

Imagining the kidney is like a filter, what are the inputs and outputs?

A 
Input = arterial
Output = venous + urine
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6
Q

How do you know the kidney isn’t functioning?

A
  • no urine
  • clinical symptoms
  • tests
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7
Q

Give examples of causes of kidney failure?

A
  • pre-renal eg. decreased ECFV or MI
  • renal eg. acute tubular necrosis
  • post-renal eg. ureteral obstruction
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8
Q

What does ECFV stand for?

A

Extracellular fluid volume

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9
Q

What are the laboratory tests for renal function?

A
  • GFR/eGFR (estimate)
  • creatinine clearance
  • plasma creatinine
  • plasma urea
  • urine volume
  • urine urea/sodium/protein/glucose
  • haematuria
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10
Q

What do you look for in the urine in renal function tests?

A
  • volume
  • urea
  • sodium
  • protein
  • glucose
  • blood
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11
Q

What is the normal urine volume in health?

A

750-2000 ml/24hr

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12
Q

What urine volume defines oliguria?

A
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13
Q

What urine volume defines anuria?

A
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14
Q

What urine volume defines polyuria?

A

> 3000 ml/24hr

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15
Q

Describe the usefulness of plasma urea in renal function tests?

A
  • quick, simple measurement
  • wide reference range (3-8mmol/L)
  • sensitive but non-specific index of illness
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16
Q

What are the factors that influence plasma urea concentration?

A
  • GIT protein + tissue protein = liver amino acids
  • kidney filtration
  • kidney reabsorption excretion
  • distribution volume
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17
Q

Where is urea filtered?

A

At the glomerulus

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18
Q

How much filtered urea is reabsorbed by renal tubules in health?

A

About 40%

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19
Q

More urea is reabsorbed if what?

A

If rate of tubular flow is slow

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20
Q

More urea is reabsorbed if rate of tubular flow is slow. Why might tubular flow rate be slow?

A

When there is renal hypoperfusion

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21
Q

What might cause increased plasma urea?

A
  • GI bleed
  • trauma
  • renal hypoperfusion (decreased RBF, ECFV)
  • acute renal impairment
  • chronic renal disease
  • post-renal obstruction (calculus, tumour)
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22
Q

Describe the usefulness of urea tests

A
  • useful test but must be interpreted with great care

- always consider input, output and patient’s fluid volume

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23
Q

What is the normal plasma creatinine levels?

A

50-140 umol/L

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24
Q

When does plasma creatinine increase in concentration?

A

As GFR decreases

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25
Q

Is plasma creatinine proportional to renal damage?

A

No

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26
Q

What is more important about plasma creatinine than the absolute value?

A

Change within an individual patient

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27
Q

What happens as GFR increases?

A

Plasma creatinine decreases

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28
Q

What may happen to plasma creatinine in chronic renal disease?

A

May increase to 1000umol/L

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29
Q

A plot of reciprocal plasma creatinine against time in chronic renal disease predicts what?

A

When intervention is required in end stage renal failure

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30
Q

When is GFR measured?

A

Seldom measured in clinical practice

  • kidney donors
  • dose of drug
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31
Q

What is GFR?

A

Clearance of [99Tc]-Sn-DTPA

32
Q

How is creatinine clearance measured?

A

(Ucreat x V)/Pcreat = Ccreat

33
Q

What is the normal creatinine clearance?

A

100-130mL/min

34
Q

What does Ucreat mean?

A

Urine creatinine concentration (mmol/L)

35
Q

What is V?

A

Urine volume (mL collected in 24 hours)

36
Q

What does Pcreat mean?

A

Plasma creatinine concentration (umol/L)

37
Q

How much higher than GFR is creatinine clearance in health?

A

10-30% higher than GFR

38
Q

How can tubular secretion of creatinine be altered?

A
  • tubular secretion increased in chronic renal disease

- tubular secretion inhibited by drugs eg. salicylate, cimetidine

39
Q

Why is creatinine clearance an unreliable test?

A
  • problems with incomplete collection

- tubular secretion can be increased in chronic renal disease and inhibited by drugs

40
Q

What plasma change occurs when creatinine clearance is 60-120ml/min?

A

None

41
Q

What plasma change occurs when creatinine clearance is 30-60ml/min?

A
  • increased creatinine

- increased urea

42
Q

What plasma change occurs when creatinine clearance is 20-30ml/min?

A
  • increased potassium

- decreased bicarbonate

43
Q

What plasma change occurs when creatinine clearance is 10-20ml/min?

A
  • increased phosphate

- increased uric acid

44
Q

What happens with creatinine clearance in progression of chronic renal disease?

A

Creatinine clearance decreases as chronic renal disease progresses

45
Q

How is eGFR calculated?

A

Calculated by the lab using an international formula, takes into account creatinine levels

46
Q

Is eGFR reliable?

A
  • lots of problems when first introduced (different formulas, creatinine tests different in different places)
  • now more standardised and reliable
47
Q

What are the different GFRs for different stages of CKD?

A 
stage 1 = GFR 90+ 
stage 2 = GFR 60-89
stage 3a = GFR 45-59
stage 3b = GFR 30-44
stage 4 = GFR 15-29
stage 5 = GFR
48
Q

Being on dialysis automatically means which stage CKD?

A

Stage 5

49
Q

Describe stage 1 CKD

A

Normal kidney function but urine findings or structural abnormalities or genetic trait but to kidney disease

50
Q

Describe stage 2 CKD

A

Mildy reduced kidney function + other findings (stage 1) point to kidney disease

51
Q

Describe stage 3 CKD

A

Moderately reduced kidney function

52
Q

Describe stage 4 CKD

A

Severely reduced kidney function

53
Q

Describe stage 5 CKD

A

Very severe, or endstage kidney failure

54
Q

What is endstage kidney failure also sometimes called?

A

Established renal failure

55
Q

What is the treatment for stage 1 CKD?

A

Observation, control of blood pressure

56
Q

What is the treatment for stage 2 CKD?

A

Observation, control of blood pressure and risk factors

57
Q

What is the treatment for stage 3 CKD?

A

Observation, control of blood pressure and risk factors

58
Q

What is the treatment for stage 4 CKD?

A

Planning for end stage renal failure

59
Q

What is the treatment for stage 5 CKD?

A

Treatment choices - dialysis/transplant

60
Q

What is skin turgor?

A

Skin’s ability to resist a change in shape and use elasticity to return to normal. Used to assess dehydration

61
Q

What may cause pre-renal oliguria/failure?

A

Low renal perfusion

  • dehydration (sodium/water)
  • haemorrhage
  • renal artery damage
  • hypotension

eg. patient with oesophageal stricture, not been drinking

62
Q

What results would you expect in pre-renal oliguria? (in dehydration)

A
  • GFR reduced
  • ADH increased (concentrated urine/low volume)
  • hypo-perfusion = renin secretion (functioning nephrons increase sodium reabsorption (aldosterone) so urine sodium low)
  • high plasma Na
  • high plasma urea
  • high plasma creat
63
Q

What plasma values would you test for?

A
  • Na
  • urea
  • creat
64
Q

What urine values would you test for?

A
  • Na

- urea

65
Q

What would you test about the urine?

A
  • volume
  • concentration
  • Na and urea levels
66
Q

What is lassitude?

A

State of physical or mental weariness; lack of energy

67
Q

What may cause renal oliguria/failure?

A

Intrinsic damage

  • tubular necrosis
  • chronic infection
  • immunological damage eg. SLE
  • toxic damage eg. drugs, heavy metals (Hg, Ur), poisons (paraquat)
68
Q

How might a patient with renal oliguria present?

A
  • increasing lassitude
  • shortness of breath
  • swelling of ankles
  • pale
  • hypertensive
69
Q

What plasma test results would you expect in renal oliguria?

A
  • high plasma Na
  • high plasma urea
  • very high plasma creatinine
70
Q

What urine test results would you expect in renal oliguria?

A
  • urine Na higher than in pre-renal
  • urine urea lower than in pre-renal
  • weak urine/low volume
71
Q

What would you expect the GFR to be in renal oliguria?

A

GFR reduced/normal

72
Q

How would you expect renal oliguria to affect renal renin secretion and what are the consequences?

A

Renal renin secretion may be raised

  • hypertension
  • but nephrons unable to reabsorb sodium
  • urine sodium is >40mmol/L
73
Q

What are some other clues pointing towards renal renal failure?

A
  • anaemia
  • haematuria
  • proteinuria
  • urine casts
74
Q

What are some other problems associated with renal renal failure?

A
  • calcium/phosphate

- bone disease

75
Q

What are the laboratory tests for renal function?

A
  • plasma creatinine
  • plasma urea
  • plasma sodium
  • urine volume
  • urine sodium
  • urine urea
  • creatinine clearance
  • urine dipsticks
76
Q

What is wrong with certain lab tests for renal function?

A
  • GFR = impractical
  • creatinine clearance = unreliable
  • plasma creatinine = specific but insensitive
  • plasma urea = subject to problems
  • urine volume = often forgotten
77
Q

How is oliguria differentiated between pre-renal and renal?

A

UNa mmol/L

PRU = 40

P/U urea ratio

PRU = >5 fold
RRF =

7. CP - Kidney and Urinary Tract Disease (5 decks)

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