Lecture 6: Clinical Renal Failure Flashcards Preview

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Renal Failure

Reduction in Kidney Function/GFR
GFR normally 100ml/min (90-110) (think of renal failure as a % of kidney function)
Acute Kidney Injury or Chronic Kidney Disesase


When are blood tests needed re kidney failure?

Collection of non-specific symptoms dont hint to kidney failure w/o blood test evidence
Mainly measure Urea and Creatine levels


Plasma Urea

main excretory product from waste nitrogen
Formed in live from aa (urea cycle)
35g (600mmol) formed per day based on average protein intake
Urea is the major solute in urine contributing to urine osmolarity


What is the amount of Plasma urea dependant on?

Dietary protein intake
Protein breakdown (catabolism), increased by infections (septic), trauma, immobilisation
Bleeding into GIT (equivalent to high protein diet as blood breaks down, increasing protein levels)


Why could a body builder be referred to a GU specialist?

Lots of muscle = high creatine
Lots of protein in diet = high urea
- doctors think have kidney failure


Renal handling of urea

Urea is Freely filtered
Fraction of Urea reabsorbed in tubules (back diffusion)
Urea Back diffusion increases during slow flow rate (dehydrated patient)
Urea excretion rate DEPENDS on GFR but isnt exact (creatine is more accurate)


Plasma urea as a renal function test

Renal failure --> Decreased GFR --> Decreased urea filtered through glomeruli --> Increased Plasma Urea
Reflects rough index of glomerular function but creatine levels more accurate (as is effected by back diffusion (-ve vs filtration))
Plasma Urea levels Affected by factors other than renal function (protein diet, hydration status, intestinal bleeding)


Dehydrated patient

Dehydrated patient --> decreased volume --> decreased flow --> increased back diffusion --> increased urea reabsorption into tubules --> increased urea in blood
- urea levels rise more than creatinine in dehydration



Derived from creatine in muscle --> peoples levels change depending on the body size
Purely waste product (no biological function)
1% of muscle creatine converts spontaneously to creatine daily (irreversible)
- formation rate propn to muscle mass (8-20mmol/day)
Freely filtered
No tubular reabsorption of secretion --> Clearance rate of creatine is propn to GFR
Increase GFR --> increased filtration --> decreased plasma creatinine


Relationship b/w plasma creatinine and GFR

Increase GFR --> increased filtration --> decreased plasma creatinine
INSENSITIVE index of renal function, failing to detect early renal disease
Muscle mass varies widely in population
Serial plasma creatine measurements can be used to monitor the course of renal disease


Effect on meat and fish intake on creatinine and eGFR

normal creatinine 60-80umol/L
creatinine formation occurs in the meat/fish (esp during cooking) --> plasma creatinine rises by 10-30umol/L after meat/fish meal --> FALSE LOW eGFR (looks like lots of creatinine has been filtered into blood)
THEREFORE: blood sample for creatinine should be taken 12 hours after last consumption of meat/fish


Gold standard measurements of GFR

inulin clearance
51Cr-EDTA clearance (nuclear medicine scan, kidney donors)
- impractical for everyday clinical use (therefore use equations and blood tests)
eGFR estimates GFR via plasma creatinine levels


Factors in eGFR

1. Weight: 2x people with same large weight and same creatinine, Fat person would be more likely due to kidney failure rather than muscle mass
2. Age: Decreased muscle mass and possible reduction in nephron function (GFR 130 --> 80)
3. Gender: due to popn norms, woman tend to have less muscle mass than men


Creatinine as a surrogate measure

1. Quantity of waste product produced
2. Ability of the kidney to get rid of the waste product



normal GFR 100ml/min
Creatine better than urea in 2x ways re eGRF:
1. More accurate representation of kidney function
2. Accounts for muscle mass


Components of eGFR calculators

1. age
2. gender
3. race
4. creatinine
CKD-EPI equation requires: plasma creatinine, age, sex


Limitations of eGFR

eGFR is inaccurate if muscle mass is unusually low or high
- e.g. amputees (renal function looks dispropn good), muscle wasting, body builders
eGFR is only valid for patients in a steady state (stable creatinine levels)
- not valid if creatinine is rising (acute renal failure) or falling (Recovery from acute kidney injury) (good for chronic kidney disease?)


Creatinine levels if different body sizes

Small and v skinny: creatinine 80 = GFR 102
Body builder: creatinine 140 = GFR 102
Fat man: creatinine 140= GFR 60 (lower kidney function due to less muscle mass)


Acute Kidney Injury

Sudden rapid reduction in GFR (decreased blood flow due to other causes 70% of time)
reversible usually
70% due to non-renal causes
- something else bad has happened --> decreased blood flow to kidney --> acute kidney injury


Aetiology of AKI

PreRenal: blood supply has problem in body so cant get to kidneys
Renal: Intrinsic nephron problem
PostRenal: Blockage


Prerenal AKI

1. Dehydration
2. Septic shock (meningicocal infection --> increased cytokine release --> decreased BP --> AKI)
3. Haemorrhage (leg cut off)
4. Cardiogenic shock ( HF --> decreased CO --> decreased BP)
5. Severe Renal Artery Stenosis (Bilateral narrowing)
Causing: Decreased BP --> Not enough blood to kidneys:
Dehydration/sepsis/haemorhage/cardiogenic shock / RA stenosis --> Decreased BP --> brain/gut/heart/lungs receive prioritised blood supply --> Decreased/deficient blood supply to liver and kidneys --> acute as kidneys/liver are able to regenerate/repair themselves


AKI Clinicians response

1. History: Reasons for low BP (IG bleeding/vom, dehydration, infection, heart failure, recent surgery)
2. Urine Output: Oligouric: unusually low urine output initially (<1 L/day) (Note: "oligo"=less anurea=<100mL/day)
3. Blood Tests: High creatinine (defining test) Hyperkalaemia, high phosphate, calcium pot. low
4. Treatment: Fix underlying problem respectively (rehydrate, treat bleeding, fix heart, antibiotics for sepsis, ICU treatment for persistent low BP/NE)


Prerenal AKI Outcomes

1. Gets better (non-severe insult to kidneys)
2. Acute Tubular Necrosis (hypotensive for too long, necrosis of renal tubules in short time)


Renal AKI

1. 80% Acute Tubular Necrosis (ATN)
2. RPGN Rapidly Progressive Glomerulonephritis (10% of acute kidney injury in the renal form)



Acute Tubular necrosis (80% of Renal AKI)
- Mainly DUE to Prerenal (that hasnt been treated quickly or vigorously enough)
Persistent oliguria (Low urine output) and Renal Failure after correction of underlying pre-renal condition
May take 4-6 weeks to recover (regeneration)
Mainly necrotic changes
High creatinine and low urine output continues --> dialysis
High potassium sometimes too


ATN Treatment

Maintain normal BP
Treat underlying problem
If kidneys keep getting worse --> Dialysis (usually GFR <10ml/min)


ATN Recovery

95% gets better (decreased tubule function --> decreased ability to hold onto salt and water -(cannot concentrate urine) --> very dilute urine --> increased volume of urine --> massive decreased in body water levels)
Polyuric Phase in Recovery
- Tubules cant concentrate. Pee up to 20L of urine/day.
Tubules recover --> concentrate urine --> dont pee out much needed salt and hence water)


Causes of ATN

1. unresolved Pre-renal problems
2. Drugs (Pharmaceuticals, crack/heroine, angiogram contrast)
3. Toxins(severe reactions) (bee stings, snake venom)



Rapidly Progressive Glomerulonephritis
- Blood and/or protein in urine
- consider if exclude e.g. toxin
Renal AKI: due to glomerular disease
RPGN Diagnosis: Renal Biopsy --> important to diagnose as is a specific treatment


Post Renal AKI Causes

Blockage post kidneys --> back up of urine --> damage to kidneys --> post renal failure
1. Kidney Stones
2. Tumour
3. Prostate Hypertrophy
4. Urinary Retention