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Azotemia
- Elevation in nitrogenous waste products
- (ex. urea and creatinine)
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Uremia
- Symptoms assoc. w/ azotemic accumulations
- fatigue, anorexia, nausea, vomiting, pruritus, mental status changes, etc.
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Normal Urine Output
1-1.5 L / 24 hrs
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Non-oliguria
> 500 mL/day
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AKI
Any sudden onset injury or impairment of the kidney
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Pre-renal
- Hypoperfusion d/t:
- Intravascular volume depletion
- Reduced effective circulatory volume
- Vascular occlusion
- Drug induction
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Intrinsic: General
Direct renal damage
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Intrinsic: Vascular
- thrombotic thrombocytopenic purpura
- hemolytic uremic syndrome
- renal artery thrombosis
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Intrinsic: Glomerulus
- SLE
- glomerulonephritis
- post-infection
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Intrinsic: Acute, allergic interstitial nephritis (AIN)
- Inflammatory, immunologic reaction within the
- renal interstitium resulting from drugs, infections or autoimmune disorders
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Intrinsic: Acute tubular necrosis (ATN)
- Causes 85% of intrinsic AKI
- Can result from extending pre-renal states or exposure to direct toxins
- uric acid, aminoglycosides, contrast media
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Post-renal
- An obstruction of the urinary collection system
- BPH, improper catheter, cancers, fibrosis, nephrolithiasis
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AKI Risk Factors
- Age (>65 y/o)
- Pre-existing renal dysfunction
- Volume depletion or dec. circulating volume
- Serious infections
- Comorbidities
- Exposure to nephrotoxins
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KDIGO: Stage 1 SCr
- 1.5-1.9 times baseline
- OR
- ≥ 0.3 mg/dL increase
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KDIGO: Stage 1 UO
< 0.5 mL/kg/h for 6-12 hours
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KDIGO: Stage 2 SCr
2.0-2.9 times baseline
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KDIGO: Stage 2 UO
< 0.5 mL/kg/h for ≥ 12 hours
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KDIGO: Stage 3 SCr
- 3.0 times baseline
- OR
- Increase in SCr to ≥ 4.0
- OR
- Initiation of renal replacement therapy
- OR
- In patients < 18 years: dec. in eGFR to < 35
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KDIGO: Stage 3 UO
- < 0.3 mL/kg/h for ≥ 24 hours
- OR
- Anuria for ≥ 12 hours
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Limitations of Dx & Staging
- Need a baseline Scr level
- May be 1 to 2 day delay in SCr increase after injury
- Urine output can be variable
- Studied/validated in critically ill pop.
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Lab Data
- Serial BUN, SCr, K+, BUN:SCr
- U/A
- Urine Na
- FENa
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Fractional Excretion of Sodium Equation
FENa = (Urine Na x SCr / Serum Na x Urine Cr) x 100
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AKI Diagnostic Procedures
- Renal ultrasound
- Catheter
- Kidney-ureter-bladder (KUB) X-ray
- Cystoscopy with retrograde pyelography
- Renal biopsy
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Pre-renal Parameters
- PE: Hypotension, dry mucus membranes, dec. CO, edema, ascites, etc.
- Urine Sediment: Normal
- Urine Na: <20
- FENa: <1
- BUN/SCr ratio: ≥ 20:1
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Intrinsic Parameters
- PE: Variable
- Urine Sediment: Granular and epithelial casts; RBCs; WBCs may be present in AIN
- Urine Na: >40
- FENa: >2
- BUN/SCr ratio: < 20:1
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Post-renal Parameters
- PE: Prostatic enlargement, bladder distension, etc.
- Urine Sediment: Variable; cellular debris, RBCs, or crystals possible
- Urine Na: >40
- FENa: Variable
- BUN/SCr ratio: ~ 15:1
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Non-Pharm Prevention
- Avoidance of nephrotoxins
- Maintain hemodynamic stability to avoid
- hypotension, hypovolemia, etc.
- ID and avoid risk factors when possible
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Contrast Media-induced Nephrotoxicity(CIN)
Pharm Prevention
Sodium bicarbonate + hydration (Alkalinizing agent)
N-Acetylcysteine (NAC) + hydration (Antioxidant effect / Neutralizes urine)
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Goals of AKI Tx
- Rapid identification of cause
- Removal or reduction of causative agents
- Prevent further kidney injury
- Prevent complications
- Regain renal function
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AKI Supportive Care
- Stop nephrotoxic drugs
- Maintain adequate hemodynamic status
- Maintain glucose control
- Manage complications
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Dopamine Tx
- vasodilation; increase U/O
- not recommended
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Fenoldopam Tx
- vasodilation; increase U/O
- some use in crit. ill pts
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Loop Diuretic Tx
- Inc. UO; Dec. renal ishemia risk
- Contoversial: harm/ototoxicity vs. minimal benefit
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Ca Channel Blocker Tx
- Dec. vasoconstriction; natriuretic
- weak evidence for renal transplant pts
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N-acetylcysteine (NAC)
- antioxidant; dec. vasoconstriction
- weak evidence v. CIN w/hydration
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Ascorbic acid
- Antioxidant
- weak evidence in CIN
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Erythropoietin
- May dec. ishemia risk
- needs more study
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Natriuretic peptides
- Inc. vasodilation and perfusion
- may dec. need for dialysis
- needs more study
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Indications for Renal Replacement Tx
- A – Acid-base abnormalities
- E – Electrolyte imbalance
- I – Intoxications
- O – Overload of fluids
- U – Uremia
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Fluid Overload
- Minimize fluid intake
- Loop diuretics (Furosemide; also torsemide & bumetinide)
- Strategies to reduce diuretic resistance
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AKI Furosemide Dosing
- Initiate @ 40-100 mg x 1 --> 200-1500 mg/day
- Cont. Infusion @ 10 mg/h dec. resistance and avoids high peaks
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Strategies to reduce diuretic resistance
- Identify and eliminate/reduce potential cause
- Increase dose or use continusous infusion
- ADD Thiazide diuretics (Chlorothiazide 250–500 mg IV q12h)
- ADD Thiazide-like diuretics (Metolazone 5–10 mg PO q24h)
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Causes of Diuretic Resistance
- Excessive sodium intake
- Inappropriate diuretic dose/regimen
- Reduced bioavailability
- Reduced renal blood flow
- Drugs (NSAIDs, ACE inhibitors)
- Hypotension
- Intravascular depletion
- Increased sodium reabsorption
- Nephron adaptation to chronic diuretic Tx
- NSAIDs
- Heart failure
- Cirrhosis
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Hyperkalemia
- Most common complication of AKI
- Sx: Parasthesias, weakness, paralysis
- EKG changes: peaked T waves (5.5-6.0 mEq/L); prolongation of PR and QRS intervals (6.0-7.0 mEq/L); disappearance of P wave/merger with QRS and T wave (> 7.0 mEq/L)
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Hypernatremia
Treat via Na restriction
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Infection
- Most common cause of death
- Sepsis often leads to AKI
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CV Complications
- HTN with intermittent hypotension
- CHF, arrythmias, and pulmonary edema
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GI Complications
- Inc. bleed risk
- Stess ulceration
- N/V
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Neurologic Complications
- Altered mental status
- Seizures
- Somnolence
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Calcium gluconate
(1st Line)
- Cardioprotective; stabilizes membrane voltage
- 10 mL 10% soln. IV push
- 1-3 min onset; 30 min duration
- 20-30 min infusion w/digoxin
- incompatible w/ Ca & Bicarb
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Insulin (plus glucose)
- Redistribution: inc. cellular K+ & dec. plasma K+
- 10 U IV bolus w/50 mL D5W
- 10-30 min onset; 2-6 hr duration
- no D5W if BG > 250
- monitor BG closely
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Β-adrenergic agonists (eg, albuterol)
- Redistribution: inc. cellular K+ & dec. plasma K+
- 10-20 mg neb over 10 min
- 10-30 min onset; 2-4 hr duration
- 25% of pts do not respond
- tachycardia common
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Sodium polystyrene sulfonate
(Kayexalate; SPS)
- elim. K+ in gut (exchanged for Na+)
- 15 g PO in sorbitol soln. 1-4 times/day OR
- 30-50 g retention enema in sorbitol (retain 30-60 min)
- 1-3 hr onset; 4-6 hr duration
- Sorbitol minimizes constipation but may -> bowel necrosis
- Enema has faster onset
- 1g binds ~ 1 g K+
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