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Renal function basic data for students and residents

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Renal function- basic data. for students and residents. Department of Paediatrics. Section for Pediatric Nephrology. University Hospital Motol, Prague ... – PowerPoint PPT presentation

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Title: Renal function basic data for students and residents


1
Renal function- basic data for students and
residents
  • Department of Paediatrics
  • Section for Pediatric Nephrology
  • University Hospital Motol, Prague

2
Functions of the kidney
  • regulation e.g. homeostasis,
  • water, acid/base
  • excretion e.g. urea, creatinine
  • endocrine e.g. renin,
  • erythropoietin,
  • 1,25 dihydroxycholecalciferol- conversion only in
    kidney!

3
Renal function tests
  • detect renal damage
  • monitor functional damage
  • help determine etiology

4
Laboratory tests of renal function
  • urine protein
  • urine glucose
  • hematuria
  • osmolality
  • glomerular filtration rate (GFR)
  • plasma creatinine
  • plasma urea
  • urine volume
  • urine urea
  • minerals in urine

5
Kidney Function
  • A plumbers view

6
Kidney basic data
  • Urine excreted daily in adults cca 1.5L
  • Kidney only ca 1 of total body weight, despite
    it
  • The renal blood flow 20 of cardiac output
  • Plasma renal flow PRF ca 600 mL/Min./1.73 M2
  • Reflects two processes
  • Ultrafiltration (GFR) 180 L/day
  • Reabsorption gt99 of the amount filtered

7
How do you know its broken?
  • Decreased urine production
  • Clinical symptoms
  • Tests

8
Where can it break?
  • Pre-renal
  • Renal (intrarenal)
  • Post-renal (obstruction)

9
Causes of kidney functional disorders
  • Pre-renal e.g. decreased intravascular volum
  • Renal e.g. acute tubular necrosis
  • Postrenal e.g. ureteral obstruction

10
Tests of renal function
  • glomerular filtration rateGFR
  • plasma creatinine Pcr
  • plasma urea-Purea
  • urine volume V
  • urine urea- Uurea
  • cystatin C in plasma?
  • urine protein
  • urine glucose
  • hematuria
  • osmolality

11
Renal Function Tests- Urine volumes
  • Adults
  • 1.5 L/24 h typical in health,
  • oliguria lt 400 mL,
  • anuria lt 100 mL,
  • polyuria gt 3000 mL
  • Children ca 1.5 ml/Kg of b.w./1 hour!

12
Principle of of Clearance
  • Some substances when filtered enter the tubules
    are not reabsorbed and so 100 excreted GFR
    (inulin gold standard for GFR, creatinine (but
    this one partially reabsorbed, particularly in
    uremia, then clearance ltGFR
  • Some substances are filtered, enter tubules, and
    more of the substance is secreted enters the
    tubules by excretion. ClearancegtGFR
  • Some substances are filtered, enter tubules, but
    are completely reabsorbed, so they did not reach
    the final urine (e.g. cystatin C)

13
Glomerular filtration rate
  • Glomerular filtration major physiologic
    responsibility of kidney, GFR used as index of
    overall excretory function
  • Methods
  • clearence of inulin, creatinine, EDTA and DTPA
    (both derivates of acetic acid), cystatin C
  • GFR Ux x V (Vvolum of urine/ 1 minute or 1
    second)
  • P x x clearence of
    substance used

14
Glomerular filtration rate
  • Also service of nuclear medicine dptm.
  • Follow up the inulin clearence, EDTA or DTPA
    clearence labelling the substances with chromium
    or Tcm99
  • Where will you catch the activity with
    detectors?
  • Never in the kidney or bladder area!!

15
Glomerular filtration rate
  • GFR in children, value always adapted to the
    BSA!! Ideal BSA in adults is 1.73m2
  • Schwartz equation GFR v x 0.808

  • Pcr (umol/L)
  • How to assess easy if plasma creatinine is OK?
  • Pcr max Vcm x 0.61 (v body height in cm

16
Creatinine and Urea Plasma Concentration-
hyperbolic correlation
Tendency in individual patients is more important
than the one value, ever test if the hydration is
OK. In patients with CRI always note also the
BSA! Lower limit today not 80 ml/Min. /1.73 m2
but 90 ml/Min./1.73 m2
pCr, pUrea
Normal range-gt
140 mL/min (100)
0 mL/min (0)
GFR 50
17
Plasma urea (BUN)
  • BUN (blood urea nitrogen)
  • Urea product of protein catabolism
  • Synthesized by liver, majority excreted by
    kidney, partially reabsorbed in tubuli
  • Plasma concentration increases with decreased GFR

18
Urea cycle
aspartate
CO2 NH3
Urea Cycle
3 ATP
Urea
19
Enzymatic conductivity rate method for measuring
urea
Urea 3H2O
urease
Urease solution
HCO3 2NH4 OH
20
Urea in patients with kidney diseases
  • Useful test but must be interpreted with great
    care, urea plasma level is more than creatinine
    dependent on protein intake
  • Most useful when considered along with
    creatinine
  • High in high protein intake, low in severe liver
    dysfunction
  • Urea EF may be useful in pts. on diuretics

21
Plasma creatinine and renal functions
  • Creatine main storage compound of high energy
    phosphate needed for muscle metabolism.
  • Creatinine anhydride of creatine!

Creatine
Creatinine
(Waste product)
H2O
22
Plasma creatinine vs. GFR not linear, hyperbolic
correlation!
pCreat
Change within an individual patient is usually
more important than the absolute value
140 mL/min (100)
0 mL/min (0)
GFR
23
Jaffe reaction for measuring creatinine, simple,
but better is enzymatic method
Creatinine alkaline picrate solution
Bright orange/red colored complex absorbs light
at 485nm (many interfering substances in
blood Can be minimized using rate method)
24
Analytical methods (Cr)
  • Normal range Pcr
  • Male 0.6-1.2 mg/dL,
  • Female 0.5-1.0 mg/dL
  • Be careful in children!!
  • Remember the max. plasma creatinine value!!

25
BUN creatinine ratio
  • Pre-renal disorders
  • BUNCr ratio gt20
  • Renal disorders
  • BUN Cr nl but both elevated
  • Post-renal

26
Osmolality of urine
  • Measures urine concentrating ability
  • Depends on of particles, not size or charge
  • Largely due to ADH (anti-diuretic hormone)
  • Can reach maximum of 1200 mOsm/L
  • Normal range 300-900mOsm/L, plasma 28510
  • prior to collection, fluid intake restricted,
    first void submitted for evaluation
  • Measuring using the fact of freezing point
    depression

27
Standardized renal concentration capacity test
  • 1. Voiding completely at 9 p.m. (WC)
  • 2. Desmopressin administration (since 2006 as
    nasal spray). DDAVP is a Czech invention !!
  • 3. Collection of urine (9 p.m. 7 a.m.)
  • 4. Testing of urine osmolality in this sample
    (not the morning urine only!)
  • 5. The lower limit of normal value 950
    mOsm/kg of urine
  • 6. Short testing- Desmopressin, collection for
    4 hours only at least 900 mOsm/kg of urine

28
Urine dipsticks
  • Strip impregnated with reagents for the
    substances in question within a urine sample
  • Substance level can be altered in the setting of
    pathology within the urinary tract
  • Measured substances
  • Modern dipsticks with multiplied zones
  • Protein, hemoglobin, glucose, urobilinogen,
    nitrite, leukocytes, specific gravity, and pH
  • Should be a tool everywhere on the level of
    primary care!!!
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