Acute renal failure
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What is the definition of acute renal failure?
Worsening of kidney function over hours to days, resulting in the retention of nitrogenous waste and Cr in the blood, creating an inability to maintain acid-base, fluid, and electrolyte balance
What is azotemia?
Retention of nitrogenous wastes (urea nitrogen) and Cr in the blood
What is oliguria?
Urine output <500cc/day or <20cc.hour
What is anuria?
Urine output <20cc/day
What is the RIFLE criteria?
Which RIFLE classes are associated with an increased risk for in-hospital mortality?
What is pre-renal failure?
Decreased renal perfusion leading to lower GFR, renal parenchyma is NOT damaged
What is the msot common cause of renal failure?
What causes pre-renal failure?
- Kidneys not seeing enough arterial volume
- Decreased circulating volume due to GI loss, dehydration, hemorrhage, pancreatitis, burns, and excessive diuresis
- Low CO (CHF, cardiac tamponade, massive PE, cardiogenic shock)
- Altered system resistance: sepsis, anaphylaxic, cirrhosis (systemic vasodilation)
What are clinical features of pre-renal failure?
Signs of dehydration
Describe labs in a pre-renal pt:
(Urine Na, FeNa, BUN/Cr, UA)
- Urine Na <20 (body is holding onto it to hold water)
- BUN/Cr>20:1 (reflection of hemoconcetration, people are dry)
- UA; benign or hyaline casts
What is FeNa?
Fractional excretion of Na, used to help ascertain etiology of renal failure
What is the FeNa forumula?
(Urine Na/Plasma Na)/(Urine Cr/Plasma Cr)
When is FeNa most helpful? (Oliguric or non-oilguric)
What can alter a FeNa measurement?
- Use of diuretics in the past 12-24 hours
- Acute glomerulonephritis
- Therefore use urine urea for UNa
What are the FeNa classes?
- <35%: prerenal
- >35%: intrinsic
How do you tx pre-renal failure?
- Replete volume
- Low CO: inotropes (dobutamine), pericardiocentesis, lytics
- Dec SVR: Replete vascular volume, add vasoconstrictor (Norepi)
- Monitor lytes, avoid nephrotoxins
When might pre-renal failure not correct quickly?
When ischemia has occured, which may progress to ATN
What is intrinsic renal failure?
Dz of the kidney itself, affecting mostly the glomerulus or tubule, renal parenchyma IS damaged
Name 4 causes of intrinsic renal failure
- Dz of glomeruli or microvasculature (Glomerulonephritis and vasculitis, TTP/DIC/Hemolytic uremic syndrome)
- ATN (ischemia caused by hypotension, Toxins)
- Acute Interstitial Nephritis
What things can cause renovascular obstruction in intrinsic renal failure?
- Atherembolic (cholesterol crystals)
- Renal artery thrombosis
- Renal artery dissection (stenotic or occlusive lesions)
What puts a person at risk for atheroembolic obstruction?
- >50 yo
- Hx of recent manipulation of the aorta
- anticoagulated pts
What are clinical findings of a pt with intrinsic renal failure caused by atherosclerosis?
- Livedo reticularis
- Gangrenous toes
- UA nl (may see casts or eosinophilia)
- Low completement levels
How do you tx intrinsic renal failure caused by atherosclerosis?
No tx has been proven efficacious
What predisposes someone to renal artery thrombosis?
Hx of afib, recent AMI
What are clinical findings of someone with intrinsic renal failure caused by renal artery thrombosis?
- Flank pain
- elevated LDH
- nl transaminases
How do you tx someone with intrinsic renal failure caused by renal artery thrombosis?
What predisposes someone to renal artery dissection?
HTN pts with underlying atherosclerotic, firbomuscular dysplasia
What are the m/c causes of glomerulonephritis?
- Post infectious GN due to GABHS#1
- Goodpastures #2
What are sx of malignant HTN?
- pulmonary edema,
- neurologic dysfunction
What does UA show in malignant HTN?
- red cells and red cell casts
What can cause ischemic ATN?
- Prolonged hypotension
- cardiac arrest
When is the liklihood of ischemic ATN increased?
When renal failure persists after restoration of BP
muddy brown granular casts
- Ischemic ATN
- Toxin induced ATN
What does a U/A show lab wise in an ischemic ATN pt?
- BUN/Cr <20:1
- FeNa >1%
- UNa >20
- SG < 1.015
How do you tx ischemic ATN?
- Restore perfusion and maintain BP
- Avoid nephrotoxins, tx electrolytes
- Dialysis if needed
What is the med class most commonly causing toxin-induced ATN?
When does contrast nephropathy occur?
24-48 hours after receiving dye, peaks 3-5 days, resolives in 1 week
How can you prevent contrast dye nephropathy?
- Hydration, pretreatment with mucomyst or HCO3 contianing IVF
- Results mixed
What other meds aside from aminoglycosides can acuse ATN?
What do labs show in toxin-induced ATN?
- BUN/Cr <20:1
- FeNa > 1%
- UNa >20
What can cause myoglobinuria?
- Crush injuries
- Prolonged unconsciousness
What are signs/sx of myoglobinuria?
- Weakness, pain, edema in affected muscles
- N/V/confusion, arrhythmias
- severe cases: hypotension, DIC, shock, compartment syndrome
What do rhabdo pts' labs look like?
- Hyperkalemia, hyperphosphatemia, hyperuricemia
- Hypocalcemia (it's deposited in the muscle)
How do you tx rhabdo pts?
- Goal UO: 1.5cc/kg/hr
- Can use loops to ensure good urine output (even though you are flushing pt with fluids)
What causes hyperuricemic renal failure?
Tumur lysis syndrome
Who gets hyperuricemic renal failure?
- pts with high cellular burden following chemo (1-3 days)
- NHL, leukemia
What is hyperuricemic renal failure?
Rapid relase of tumor cellular markers that overwhelm metabolic pathways that cause tubular obstruction and ARF
What are s/sx of hyperuricemic renal failure?
- Weakness, lethargy
- Muscle cramps, tetany
- Fluid overload
What does hyperuricemic renal failure labwork show?
- Same as rhabdo
- Hyperkalemia, phosphatemia, and uricemia
How do you tx hyperuricemic renal failure?
- Vigorously hydrate
- Allopurinol (prevents further high levels of uric acid)
- Rasburicase (lowers level of uric acid)
- Urinary alkalizatoin with metabolic acidosis
- Tx electrolytes
What is acute interstitial nephritis?
Infiltration of tubulointerstitium by granulocytes (eosinophils) and macrophages
What is the m/c cause of acute interstitial nephritis?
What infections can cause acute interstitial nephritis?
What are clinical findings of acute interstitial nephritis?
- Acute/subacute N/V/ malaise,
- fever, maculopapular rash
- Triad: fever, rash, eosinophils
What does a U/A show in a acute interstitial nephritis pt?
- White cells, white cell casts, red cells
- Eosinophiluria (>1% of WBC cells on Hansel stain)
What is the gold standard for dx acute interstitial nephritis?
renal biopsy, only done in severe cases
How do you tx acute interstitial nephritis?
- D/c offending agent and monitor
- Sever cases: short corse of steroids
What are mortality rates like in acute interstitial nephritis?
20-50% in hospital, 70% with comorbid illness
What is postrenal failure?
Urinary flow from B/L kidneys are obstructed, or a single functioning kidney is obstructed
What is the m/c cause of postrenal failure?
Describethe course of GFR in postrenal failure
Increases then decreases
What are s/sx of postrenal failure?
The same for BPH/what you would expect for an obstruction
What do postrenal failure labs show?
- Early: resemble prenal (low FeNa and Una, high urine osm) as tubules aren't damaged
- Later: (tubules damaged, can't concentrate urine)
- BUN/Cr >20:1
- UNa >20
- Low Uosm
What is the best way to image postrenal failure?
- renal ultrasound
- NON CONTRAST Ct if needed
How do you tx postrenal failure?
- Place foley
- Relieve obstruction
- After obstruction resolved, expect post-obstruction Diuresis and hydrate to avoid volume depletion
What are complications of ARF?
- Metabolic acidosis
What are sx of uremia?
- Cardiac pericarditis
- Asterixis, confusion, coma, seizures
- Bleeding diathesis
What are the indications for dialysis?
- Electrolyeimbalance (hyperkalemia, not mag, phos, etc)
- Ingestions (ASA, methanol)
- O: volume overload
- U: uremia causing end-organ damage (pericarditis, encephalopathy)
What is general tx of ARF?
- Avoid nephrotoxins
- Adjust meds to GFR
- Anticipate changes in electrolytes and tx accordingly
- Consult renal in a timely fashion
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