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What is a normal BUN and what function is it measuring?
What is a normal serum creatinine and what is it measuring?
- 0.7-1.5mg/dL (> in males)
What is the normal BUN/Cr ratio and what is it measuring?
What is the normal creatinine clearance and what is it measuring?
Name the SERUM tests for renal function, hint they all measure GFR
- BUN/Cr ratio
- Cr clearance
What is the normal urine proteinuria (albumin) and what does it measure?
What is the normal urine specific gravity and what does it measure?
- Renal Tubular function
What is the normal urine osmolarity and what does it measure?
- Renal tubular function
What is the normal urine sodium and what does it measure?
- Renal tubular function
What is the normal glycosuria level? What does this measure?
- Renal tubular function
What is normal GFR?
125ml/min or 180L/day
Uremia will typically occur when GFR falls below...
Where does urea come from?
breakdown of proteins in liver, deamination of amino acids
BUN is only a useful measurement in what type of condition?
BUN only useful as measure of GFR if protein breakdown is constant and normal
What things will effect the reliability of BUN measuring GFR, making the BUN INCREASED?
- Volume status (Hypovolemia)
- High protein diet (high protein breakdown)
- High metabolic rate
- GI bleed (blood breakdown)
All of these are independent of renal function
What happens to the BUN in the setting of hypovolemia?
- Typically 40-50% of whatever gets filtered gets reabsorbed by renal tubules but that amount will be increased in hypovolemia as a compensatory mechanism.
- So in that case the BUN will be higher, in the hypovolemic pt unrelated to actual functioning of the nephrons.
What things will effect the reliability of BUN measuring GFR making the BUN DECREASED?
If the BUN is greater than ____, there is likely renal involvement (regardless if hypovolemic, etc. is providing a false elevation)
Why is the creatinine usually greater in males than in females?
Because of the differences in muscle mass. We know it comes from the breakdown of creatine, which is a product of muscle metabolism.
Why is Creatinine a better indicator of GFR than BUN?
- Creatinine that’s produced will get filtered but not reabsorbed, unlike urea.
- The serum creatinine should be directly proportional to muscle mass and inversely proportional to GFR
- if serum creatinine doubles, then we’ve decreased GFR by ½.
What types of things can give you a falsely elevated Creatinine?
- Due to a large meal
- Cimetidine therapy it inhibits creatinine secretion by the renal tubules)
- Ketoacidosis (acetoacetate will interfere w/lab testing measures for creatinine)
Why could the elderly have a false normal creatinine level?
- Muscle mass declines w/age (5% per decade) the decline in GFR that will occur w/age isn’t really reflected in serum creatinine levels.
- Creatinine normal, in elderly, could be false normal.
- Small bump in creatinine could be more significant, just not appreciated because muscle mass is lower.
What if the BUN/Cr is elevated? (say like 20:1)
Likely a pre-renal problem (hypovolemia)
What is the MOST ACCURATE measure of renal function?
How can we estimate the creatinine clearance from a serum creatinine level?
- (140-age) x lean body weight (kgs)
- divided by 72 x plasma creatinine.
- If it’s female, multiple by 0.85 to accommodate for decrease in muscle mass.
What is mild renal impairment according to creatinine clearance?
Mild renal impairment: 40-60 or 50-80 ml/min (depending on source, different ranges)
What is moderate renal impairment according to creatinine clearance?
Moderate dysfunction: 25-40 and another was less than 25ml/min
What is renal failure (anephric) where dialysis is required according to creatinine clearance?
Renal failure (anephric) requiring dialysis is less than 10ml/min
Specific gravity is really reflective of osmolarity. So a specific gravity of 1.0101 will correspond to urine osmolarity of _____
1st morning specific gravity of _______ is usually considered to be indicative of adequate urine concentrating ability.
In the absence of diuretics and glycosuria, what does osmolarity and specific gravity tell us?
normal concentrating ability and tubule function
Lower specific gravity and increased plasma osmolarity is indicative of....
What is the average urine osmolarity?
After we've fasted all night, we expect the urine osmolarity to be higher, how high would we expect it to be compared to the plasma osmolarity?
expect 3x the serum osmolarity
Proteinuria, can be transient, orthostatic or persistent. If it’s persistent, usually means
there is significant renal disease
Microalbuminemia is early sign of
ARF is loss of renal function over hours or days, and has about ___% mortality risk
______________ is the single most reliable predictor of postoperative renal dysfunction
Preoperative renal function
Preoperative cardiac dysfunction is another important predictor of postoperative ARF
Why is advanced age a factor contributing to risk of acute renal failure?
- Advanced age associated with reduced GFR, RBF and renal reserve.
- Also more likely to have cardiac disease
Name some factors that contibute to risk of acute renal failure?
- Any hypoperfused states (blood loss, burns, septic pt, trauma patient,CHF)
- Could also be acute obstruction of a renal artery.
- Surgeries (AAA repair, CV surgery (bypass), kidney or liver transplant surgery.
- Advanced age.
- Diabetics at high risk.
- Any pt w/myogloinbura, jaundice, scleroderma.
- Pretty much anything that influences renal perfusion and oxygenation.
What drugs can be helpful in reducing risk of acute renal failure?
Loop diuretics, mannitol. Dopamine: no really no data in literature supporting it.
Peri-op ARF accounts for ___ of the acute cases of hemodialysis and then kidney disease is the ___ leading cause of death.
GFR will vary w/
age (declines w/age), size, gender
Pt w/ GFR that’s greater or equal to ___% of normal are usually asymptomatic.
Anybody with a GFR between __-___% may not need hemodialysis but these are definitely at risk for nephrotoxic insults
GFR less than ___% of normal is associated w/End stage renal disease and hemodialysis is usually required.
Name the 5 exogenous categories of nephrotoxins found in the hospital setting
- Anesthetic agents
- Contrast Media
What antibiotics are nephrotoxic?
Aminoglycosides, cephalosporins, amphotericin, vancomycin
What anesthetic agents are nephrotoxic
Sevoflurane (risk of compound A)
What NSAIDs are nephrotoxic?
ASA, ibuprofen, naproxen, indomethacin, ketorolac
Name some chemotherapeutic or immunosuppresive agents that are nephrotoxic
Cisplatinum, cyclosporin A, methotrexate, mitomycin, nitrosoureas, tacrolimus
Name the 7 endogenous nephrotoxins
- Uric acid (hyperuricemia, hyperuricosuria)
- Myoglobin (rhabdomyolysis)
- Hemoglobin (hemolysis)
- Bilirubin (obstructive jaundice)
- Oxalate crystals
retention of nitrogenous waste products from metabolism of proteins & amino acids
What exactly are the nitrogenous waste products??
How long does it take for acute renal failure to occur?
hours to day
How much does the serum creatinine increase in acute renal failure?
- Means in increase in serum creatinine of greater than 0.5mg/dL over whatever the baseline was.
- Correlates with 50% decrease in GFR or decrease renal function requiring dialysis.
what is the difference between oliguric and non-oliguric acute renal failure?
- oliguric is u/o less than 400ml/day, not getting to obligatory urine volume
- non-oliguric meaning more than 400ml/day.
What is acute on chronic renal failure?
Pre-existing chronic renal disease that now has worsened and is deteriorating acutely.
List all the s/s of acute renal failure
- N/V, anorexia
- Fatigue, altered mental status
- Volume overload (Peripheral edema & pulmonary edema)
- Hyperkalemia, metabolic acidosis
Name the types of patients at risk for acute renal failure
CKD, HTN, cardiac dz., PVD, DM, liver dz., over age 60
What are the cardiovascular complications of renal failure?
- Systemic HTN
- Pulmonary edema
What are the CNS complications of renal failure?
- Seizure activity
- Autonomic dysfunction
What are the GI complications of renal failure?
- N & V
- GI bleed
What are the infectious complications of renal failure?
Do we see hypo or hyper kalemia in renal failure? What is the pathophys behind it?
- Poor excretion, transcellular shifts d/t acidemia and insulin deficiency
What are the s/s and tx of hyperkalemia?
- Weakness, parathesias, peaked T waves, ST depression, prolonged PR, wide QRS, sine wave, VF
- IV calcium stabilizes myocardium, NaBicarb, insulin/dextrose, hyperventilation (shifts K intracelllularly), HD
Do we see hypo or hyper calcemia in renal failure? What is the pathophys behind it?
- Elevated parathyroid hormone
What are the s/s of hypocalcemia and the tx?
- usually well tolerated, can cause tetany, seizures if sudden or severe
- Vit D and Ca+ supps
Do we see hypo or hyper magnesium in renal failure? What is the pathophys behind it?
- Poor excretion
What are the s/s of hypermagnesemia and the tx?
- usually well tolerated, can cause hypoventilation, altered MS,prolonged NMB if severe
- Avoid magnesium containing medications, HD
What type of acid base imbalance do we see in renal failure? what is the pathophys behind it?
- metabolic acidosis
- Inadequate H+ excretion
What are the s/s of the metabolic acidosis associated w/RF and the tx for it?
- Respiratory distress, hypotension, cardiac arrhythmias, hyperkalemia
- Hyperventilate, NaBicarb, HD
What is the major cause of pre-renal azotemia?
- Decreased renal perfusion
- Hypovolemia, hypotension (anesthetic agents)
- Decreased CO
- Shock (all types)
- Intrarenal vasoconstriction.
- Renal artery embolism
- So anything that impairs blood flow going through the kidney
What is the cause of the majority of RF (pre-renal, post-renal, etc)
What exactly is happening in pre-renal azotemia? (What is going on in the kidney?)
So what happens is that waste products are filtered at glomeruli but rate of filtration is those will get reabsorbed instead of excreting in urine
Why does the level of BUN increase faster than the creatinine in pre-renal failure?
Different in size, urea is smaller and easier to reabsorb than creatinine.
Is pre-renal failure reversible?
yes if you tx the underlying cause
What needs to happen for pre-renal failure to be reversible?
As long as the renal blood flow doesn’t fall below 20% of normal and cause is corrected before there is cellular damage
Will there be a high or low urine Na in pre-renal azotemia? What will the urine osmolarity be?
- a low urine Na
- Concentrated urine, meaning a urine osmolarity greater than 500mOsm/L
How do you treat pre-renal azotemia?
- Increase renal perfusion, increase BP back to normal, restoring intravascular volume
- Renal dose Dopamine (? Whether it actually does anything)
Name the causes of renal (intrarenal) azotemia and their associated percentages
- Ischemia – 50%
- Nephrotoxicity – 35%
- Acute tubular interstitial nephritis or acute glomerular nephritis – 15%
In total, renal (intrarenal) azotemia is about ___% of cases of renal failure
ATN is a cause of renal (intrarenal) azotemia. What is that caused by?
- As a result of hypoperfusion for more than 30-60min is most common
- Also sepsis, something r/t contrast media, other nephrotoxic drugs and trauma.
Post-op ATN accounts for 20-25% of all hospital acquired acute kidney failure. (CV bypass is a risk)
Can acute renal (intrarenal) azotemia be reversed
it’s not this can’t be reversed as long as there is not cellular death. As long as ischemia is not prolonged and/or severe.
What is the primary site of injury in acute renal (intrarenal) azotemia
- Renal vessels
- Renal tubules
What is post-renal azotemia caused by?
- Really d/t urinary tract obstruction.
- Might be something like prostatic hypertrophy, abdominal mass or pelvic mass putting pressure on ureters or a kidney stone.
- All of this can be reversed as long as dx promptly and underlying cause is tx quickly
Describe the urine Na, fractional excretion of Na (FENa), urine osmolarity and BUN/Cr ratio in pre-renal failure.
- Urine sodium: < 20 mEq/L (< 10 mmHg)
- FENa: < 1%
- Urine osmolarity: > 400 mOsm/L (> 500 mOsm/L)
- BUN/Creatinine ratio: > 15:1 (> 20:1)
Describe the urine Na, fractional excretion of Na (FENa), urine osmolarity and BUN/Cr ratio in intrarenal failure.
- Urine sodium: >40mEq/L (>20mmHg)
- FENa: >2%
- Urine osmolarity: 250-300mOsm/L (<350mOsm/L)
- BUN/Creatinine ratio: <10:1 (=10)
How can we tell if it is post-renal azotemia?
- To exclude post, need to visualize urinary tract to see if there is obstruction.
- Once that’s done look at labs to see if it’s pre or renal.
How do we calculate the fractional excretion of Na?
Calculated by dividing the urine Na by the plasma Na
In general normal urine Na is less than 40, represents good tubular reabsorption. What does it mean if it's less than 20?? What does it mean if it's high??
- If urine Na is less than 20, that would secondary to decreased renal perfusion and decreased GFR (d/t decreased renal perfusion)
- If there was a high urine Na that means decreased tubular function and the tubules can’t reabsorb Na
According to the RIFLE classification, what is the RISK category in terms of serum creatinine, u/o, and associated mortality?
- Serum creatinine: Increased by 1.5 X or Cr increased > 0.3 mg/dl
- U/O: < 0.5 ml/kg/hr X 6 hrs
- Mortality: 8.8 – 20
According to the RIFLE classification, what is the INJURY category in terms of serum creatinine, u/o, and associated mortality?
- Serum creatinine: Increased 2x
- U/O: <0.5ml/kg/hr x12hr
- Mortality: 11.4-45.6
According to the RIFLE classification, what is the FAILURE category in terms of serum cr)eatinine, u/o, and associated mortality?
- Serum creatinine: Increased 3x or Cr≥4mg/dL (acute rise ≥0.5mg/dL)
- U/O: <0.4ml/kg/hr x24hr or anuric
- Mortality: 26.3-56.8
According to the RIFLE classification, what is the LOSS category in terms of serum creatinine?
Serum creatinine: Complete loss of renal function > 4 wk
According to the RIFLE classification, what is the ESRD category in terms of serum creatinine?
End Stage Renal Disease
Management of Acute Perioperative Oliguria
- Fluid challenge
- possibly more fluid
(follow chart in notes)