Acute Renal Failure: The Response to Severe Injury and Hypovolemic Shock

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Acute Renal FailureThe Response to Severe
Injury and Hypovolemic Shock
TRAUMA-ICU NURSING EDUCATIONAL SERIES

• Bradley J. Phillips, M.D.
• Critical Care Medicine
• Boston Medical Center
• Boston University School of Medicine

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Renal Function and Failure

• Overview
• Renal Physiology
• Trauma and Renal Function
• Initial management of Oliguria
• Acute Renal Failure
• Key Management Issues

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Glomerular Architecture
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Physiology in Normal State

• Renal blood flow (RBF)
• 20-25 cardiac output
• distribution
• 85 outer cortical
• 15 inner cortex outer medulla
• lt1 inner medulla

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Physiology in Normal State

• Glomerular filtration
• 20 of plasma filtered as cell-free and
  protein-free
• normal GFR 125 ml/min
• calculate
• most accurate - insulin
• completely filtered/neither secreted or absorbed
• good estimation - creatinine
• (Cr Urine / Cr Plasma) x urine (ml/min)

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Glomerular Component Functions
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Renal Physiology after Trauma

• Class I Hemorrhage (10-15)
• autoregulation maintains GFR
• Class II Hemorrhage (15-30)
• exceeds autoregulation
• vasoconstriction at afferent efferent
• GFR decreases by 50-60
• Class III Hemorrhage (30-40)
• GFR decreases to less than 20

resuscitation relieves vasocontriction over hours
to days, afferent then efferent arterioles
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Oliguria after Trauma

• Rapid replenishment of the circulatory volume and
  cardiac output
• at least 3-4 L for every 1 L of blood loss
• Factors
• general anesthetic
• loss of renal autoregulation
• loss of systemic vasoconstriction

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Key Management Issue

• IV Fluid Resuscitation

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Renal Function and Trauma

• Postresuscitative oliguria
• even if MAP and CO restored
• persistant for several hours secondary to renal
  arteriole vasoconstriction
• shifting of fluid from plasma to interstitial
  space secondary to depletion during
  hypotension/hypovolemia
• Postresuscitative polyuria
• usually transient
• not excessive (lt 250 cc for 30-45 mins, lt 3 hrs)
• wash out effect of inner medulla
• use other parameters ( ie HR, base deficit)

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Postoperative Fluid Sequestration

• Obligatory extravascular sequestration
• Phase II (Lucas, Resuscitation of the Injured
  Patient Three Phases of Resuscitation, Surg Clin
  North Am, 1977)
• Last 12-36 hours
• Clinical signs
• tachycardia
• reduced pulse pressure
• oliguria
• weight gain
• some respiratory insufficiency
• Hormoral effect - ADH, aldosterone

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Fluid Mobilization Phase

• Phase III - mobilization and diuresis
• Water added to plasma faster than excreted
• Postresuscitation Hypertension
• Renal blood flow still remains decreased
• Caution with diuretics
• role in post elective surgery in elderly patient
  with CHF
• avoid in trauma patients
• can precipitate oliguria/renal dysfunction

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Mechanical Ventilation and Fluid Therapy

• Reduce renal blood flow
• even if zero PEEP
• PEEP reduces RBF more
• additional fluid may be required to maintain UOP

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Acid-Base Balance

• Hemorrhagic shock
• increased lactate acidosis
• metabolic acidosis persistent after intravascular
  volume repleted (hours)
• cell metabolism
• impaired renal excretion of acids
• Renal acid excretion
• absorb Na/HCO3, excrete PO, NH3
• normal excrete 70-80 mEq /day
• can excrete 4-5x normal with severe acidosis
• depends on GFR and RBF

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Renal Response to Sepsis

• Hyperdynamic state
• increased CO, increased RBF, decreased SVR,
  expanded ECF volume, increased UOP
• inappropriate polyuria
• vasodilators of sepsis
• wash out effect
• Hypodynamic state
• later stages of severe sepsis
• decreased CO, increased SVR, decreased GFR and RBF

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Key Management Issue

• IV Fluid Resuscitation

PEARL Check Urine Na. If less than 10
meq/L???
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Acute Renal Failure

• Mortality in posttrauma 50- 60
• acute oliguric gt 90
• contrast nonoliguric lt 20

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Terminology

• ARF - sudden, severe deterioration
• rule of thumb - Cr increasing gt 1.0 mg/dL/day
• Acute tubular necrosis (ATN) - form of ARF
• Oliguria UOP less than 400 ml/d
• 500 mOsm daily solute concentrated to 1200
  mOsm/kg
• Anuria UOP less than 50 ml/d
• Nonoliguric renal failure
• progressive azotemia despite UOP gt 400 ml/d
• High-output renal failure
• acute renal insufficiency with UOP gt 4 L/d

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Acute Renal Failure

• Etiology
• severe and prolonged hypotension
• severe sepsis
• massive blood transfusions
• compartment syndrome
• myoglobinuria/hemoglobinuria
• radiocontrast
• aortic cross clamping (gt 30 minutes)
• drug-induced
• postinfectious glomerulonephritis
• Contributing factors
• age
• pre-existing renal vascular disease
• pre-existing renal insufficiency

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Myoglobinuria/hemoglobinuria

• Muscle necrosis or RBC destruction
• Hypotension significant increase risk of ATN
• can occur even if renal perfusion well maintained
• Skeletal muscle (per kg of tissue)
• 40-45 meg K
• 730 ml of H2O
• 23 mmol of PO4
• 4 g myoglobin ( takes 100-150 mg/dL to discolor
  urine)
• Severe crush injury/muscle ischemia causes
  hyperkalemia, hyperphosphotemia,azotemia,
  hypocalemia, DIC, hypotension, and myoglobinuria

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Predictors of ARF ?

• Vivino G. Antonelli M. Moro ML. Cottini F. Conti
  G. Bufi M. Cannata F. Gasparetto A. Risk factors
  for acute renal failure in trauma patients.
  Intensive Care Medicine. 24(8)808-14, 1998 Aug
• prospective, consecutive 153 trauma patients
• CPK gt 10,000, PEEP gt 6, hemoperitoneum
• Loun B. Astles R. Copeland KR. Sedor FA.
  Adaptation of a quantitative immunoassay for
  urine myoglobin. Predictor in detecting renal
  dysfunction. American Journal of Clinical
  Pathology. 105(4)479-86, 1996 Apr.
• urine assay for myoglobinuria
• levels gt 20,000 mcg/L

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Key Management Issue

• Administer IV Fluid Resuscitation
• and
• Maintain UOP gt 100 cc/hr

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Rhabdomyolysis

• Treatment
• volume, volume, volume!!!
• shock and rhabdomyolysis renal failure
• maintain UOP gt 100 - 200 cc/hr
• ? role or sodium bicarbonate
• precipitation of myoglobin urine pH lt 5.6
• check urine pH
• consider if UOP marginal or severe hyperkalemia
• mannitol (avoid lasix if possible)
• volume expander, mild diuretic, free radical
  scavenger
• follow CPK levels (most sensitive)

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Drug-Induced ARF

• Pathogenesis depends on drug
• Predisposing factors
• volume depletion
• age
• pre-existing renal disease
• prolonged therapy
• other nephrotoxic agents

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Drug-Induced ARF

• Antibiotics
• aminoglycosides (most publicized)
• however use of cephalosporins and clindamycin
  potentate nephrotoxicity
• amphotericin B
• vancomycin
• PCN can cause hypersensitivity nephritis
• Limit nephrotoxicity
• low trough
• ? once a day dosing (proven to limit ototoxicity)
• avoid NSAIDS
• avoid combination of nephrotoxic antibiotics
• avoid hypotension

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Radiocontrast-Induced Nephropathy

• Incidence as high as 13
• Mechanisms
• direct toxicity
• renal ischemia (vasoconstriction)
• intratubular obstruction
• immunologic abnormality
• Clinical
• serum Cr elevation within 24 hours
• serum Cr peak day 3-5
• renal function normally returns by 10 days
• hemodialysis seldom needed

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Key Management Issue

• Administer IV Fluid Resuscitation

Only IV fluid hydration has been shown to reduce
incidence of IV contrast nephropathy (not lasix
or dopamine) Should maintain UOP 12 hours before
and 24 hours post procedure
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Classification of ARF

• Prerenal azotemia
• inadequate renal perfusion
• characterized by low urine Na/high urine Cr
• Postrenal azotemia
• complete obstruction bilateral ureteral or lower
  urinary tact
• Acute tubular interstitial nephritis
• usual drug-induced
• signs of hypersensitivity (check urine
  eosinophils)
• renal biopsy

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ARF - Clinical Changes

• Increase serum Cr (gt 1 to 1.5 mg/dL/d)
• directly related to decreased GFR
• Increase BUN (exceeds gt 25 mg/dL/d)
• related to decreased GFR and reabsorption
• Hyponatremia
• intake fluids gt UOP (particularly hypotonic
  solutions)
• increased endogenous water
• increased loss of urine sodium

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ARF - Clinical Changes

• Hyperkalemia
• reduced excretion from decreased GFR
• impaired renal tubules secretion
• faster if muscle protein breakdown due to
  ischemia or injury
• Metabolic acidosis
• accelerated protein catabolism
• decreased excretion of acid load
• Other electrolytes
• hyperPO4, hyperMg
• hypoCa

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Differential Diagnosis

• Postrenal azotemia
• rule out urinary tract obstruction
• Prerenal azotemia
• hypovolemia
• cardiac failure

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Hypovolemia

• Renal response to decreased blood flow
• normal - conserve H20 and Na
• ARF - impaired ability to concentrate/conserve
• Differentiation of Pre-renal vs ARF
• renal failure index
• fractional excretion of sodium

RFI Urine Cr / Plasma Cr
lt 1.0 prerenal azotemia
FE (U Na/P Na) / (U Cr/P Cr) x 100 lt 1.0
prerenal azotemia
SIMULATANEOUS SPOT PLASMA URINE SAMPLES
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Urinalysis

• Prerenal azotemia
• unremarkable
• Obstructive uropathy
• unremarkable
• Glomerular disease
• heavy proteinuria
• sterile pyuria
• mild microhematuria
• casts (granular/WBC)
• ? eosinophils

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Key Management Issue

• Fluid Challenge!!!!!

RULE OUT HYPOVOLEMIA 1. test response to fluid
challenge at least 500 to 1,000 cc (15-30
minutes) 2. consider CVP or pulmonary artery
monitoring
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Treatment of ARF

• Diuretics
• after hypovolemia ruled out
• if given soon after onset of oliguria may convert
  to non-oliguric renal dysfunction (better
  prognosis)
• types
• mannitol
• osmotic diuretic decrease proximal Na
  reabsorption
• dose 25 g IV bolus
• lasix
• inhibits active Na transport in loop of Henle
• dose 20-40 mg IV initial, then double every 30
  minutes if no response (max dose 500 mg)
• dopamine (low dose, 1-3 ug/kg/min)
• effects partially due to inhibition of ADH

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Sodium and Water Balance

• Fluid restriction is important treatment of ARF
• careful to maintain perfusion
• problem sometimes with initial hemodialysis
• Fluid requirements
• GI and renal loss plus 500 cc
• accurate daily weights and I/Os

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Metabolic Acidosis

• Hypercatabolic generation of acid loads
• Produces anion gap
• Best treated with reducing catabolism or
  hemodialysis, not sodium bicarbonate

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Hemodialysis

• Indications
• refractory pulmonary edema
• hyperkalemic crisis
• uremic complications
• severe metabolic acidosis

A E I O U Y
Acidosis Electrolyte disturbance Intoxication Over
load Uremia Why not
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Hemodialysis

• Ultrafiltration
• indicated in hemodynamically unstable patients
• continuous venovenous (CV VH) or
  arteriovenous(CAVH)
• filtrate removal of 500-800 ml/hr
• require often some heparinization
• Hemodialysis
• rapid correction of uremia, fluid overload,
  electrolyte disturbances, and acidosis
• prophylactic dialysis probably beneficial
• added benefit by providing for adequate calories
  and protein

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ARF - Special Consideration/Complication

• Adjustment of medications
• Coagulopathy
• platelet dysfunction in aggregation
• treatment with DDAVP (0.3 ug/kg)
• low antithrombin III levels
• microvascular thrombosis
• Hyperkalemia
• increased with blood transfusions, acidosis, and
  hyperosmolemia (ie treatment with diuretics)
• usual treatment (glucose insulin, calcium IV)
• avoid kayexelate (Na exchange for K)

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ARF - Special Consideration/Complication

• Anemia
• reduced EPO levels
• contributing factors include GI blood loss and
  hemodialysis (ie hemolysis)
• treatment with recombinant EPO/Fe replacement
• Stress gastritis
• more than 20 of ARF patients
• treatment
• AlOH antacids (also treats hyperphosphotemia)
• H2 blockers

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ARF - Special Consideration/Complication

• Pericarditis (uremia)
• with or without pleuritis
• presence of chest pain or friction rub
• some with fever with or without leukocytosis
• treatment with hemodialysis
• Nutritional support
• problems
• insulin resistance
• negligible free water and urea clearance
• ? high energy requirement

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ARF - Special Consideration/Complication

• Nutritional support
• treatment
• minimize free water
• do not restrict protein if needed unless unable
  to clear with hemodialysis

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Outcomes of ARF

• Oliguric ARF
• expect return of renal function in 3 weeks
• if enter diuretic phase, likelihood of survival
  greatly increased
• older patients progress to chronic renal failure
  much more often
• Non-oliguric ARF
• increasing secondary earlier and aggressive fluid
  resuscitation and conversion with diuretics
• easier to manage than oliguric
• only few require dialysis
• much lower mortality

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Questions ?