Renal Failure (Acute Kidney Injury), Emergency Medicine

Basics

Description

The disorder is now known as acute kidney injury (AKI); the term renal failure is outdated.
Changes in glomerular filtration rate (GFR) and urine output (UO) encompassing a spectrum ranging from normal physiologic response to end-stage renal disease (ESRD) and measured by accumulation of nitrogenous by-products.
Defined by the RIFLE criteria:
- 3 stages of renal injury:
  - Risk: Increased creatinine (Cr) 1.5 or GFR decrease >25%, UO <0.5 mL/kg/h >6 h
  - Injury: Increased Cr 2 or GFR decrease >50%, UO <0.5 mL/kg/h >12 h
  - Failure: Increased Cr 3 or GFR decrease >75% or Cr ≥4 mg/dL (acute rise of ≥0.5 mg/dL), UO <0.3 mL/kg/h 24 h or anuria 12 h
- 2 stages of outcome:
  - Loss: Loss of renal function >4 wk
  - ESRD: Loss of renal function >3 mo
The most severe marker defines stage.
AKI based upon changes within last 48h; however, must often base on most recent data.
Higher RIFLE stages correlate with higher 1 and 6 mo mortality rates for hospitalized patients.

Etiology

Prerenal AKI:
- Caused by renal hypoperfusion
- Renal tissue remains normal unless severe/prolonged hypoperfusion.
Intrarenal AKI:
- Caused by diseases of the renal parenchyma
Iatrogenic AKI causes include:
- Aminoglycoside antibiotics
- Radiocontrast material administration
- NSAIDs
- ACE inhibitors
- Angiotensin receptor blockers
Postrenal AKI:
- Due to urinary tract obstruction (e.g., prostatic hypertrophy, prostatitis)

Diagnosis

Signs and Symptoms

Acute Kidney Injury

Often asymptomatic and commonly diagnosed with incidental lab findings
Oliguria (<400 mL/d urine production)
Fluid overload:
- Dyspnea
- Hypertension
- Jugular venous distention
- Pulmonary and peripheral edema
- Ascites
- Pericardial and pleural effusion
Nausea/vomiting
Pruritus/skin changes
Confusion/mental status changes

Prerenal AKI

Absolute or relative volume deficit
Dry mucous membranes
Hypotension
Tachycardia
Low cardiac output
Congestive heart failure
Systemic vasodilation (e.g., sepsis, anaphylaxis)

Intrinsic AKI

Allergic Interstitial Nephritis:
- Fever
- Rash
- Recent myocardial infarction
Renal vein thrombosis:
- Nephrotic syndrome
- Can be associated with pulmonary embolus
- Flank or abdominal pain
Glomerulonephritis, vasculitis
Hemolytic uremic syndrome (HUS)
Thrombotic thrombocytopenic purpura (TTP):
- Mild elevation of BUN/Cr
- Fever
- Altered mental status
- Anemia & thrombocytopenia
- Neurologic: Coma, seizure, headache, altered mental status
Allergic interstitial nephritis fever:
- Rash
- Arthralgias

Postrenal AKI

Abdominal or flank pain
Distended bladder
Oliguria or anuria

Complications of AKI

Uremic syndrome:
- Altered mental status
- Asterixis
- Reflex abnormalities
- Focal neurologic abnormality
- Seizures
- Restless leg syndrome
- Pericarditis
- Pericardial effusion/cardiac tamponade
- Ileus
- Platelet dysfunction
- Pruritus
Hematologic disorders:
- Anemia
- Increased bleeding time & platelet dysfunction
- Leukocytosis

History

Prior history of AKI
Medication history including nephrotoxins
Weight change

Physical Exam

Mental status changes/confusion
Eyes: Fundoscopy
CV exam: Jugular venous distention, S3
Lungs: Rales, crackles
Abdomen: Flank tenderness, palpable kidneys
Edema
Skin changes

Prone to prerenal AKI
Cr will vary by body mass index, so a "normal " range in elderly may represent an elevation.
Increased risk of contrast- and medication-induced AKI

Prerenal AKI a concern in neonates
Anatomic abnormalities

Intrinsic renal azotemia
Pre-eclampsia/eclampsia
Ischemia: Postpartum hemorrhage, abruptio placentae, amniotic fluid embolus
Direct toxicity of illegal abortifacients
Postpartum TTP, HUS

Essential Workup

Electrolytes including Ca, Mg, PO4
BUN/Cr
Urinalysis (UA):
- Centrifuged specimen helps to distinguish different etiologies of AKI.
- Exam for casts, blood, WBCs, and crystals
Fractional excretion (FE) of Na and/or urea
CBC: Anemia common with chronic disease
Postvoid residual volume (>100 mL suggests obstruction) OR
Ultrasound to rule out obstruction " especially in older men (e.g., prostatic hypertrophy, prostatitis)
ECG

Diagnosis Tests & Interpretation

Lab
Prerenal
UA:

Specific gravity >1.018
Osmolality >500 mmol/kg
Sodium <10 mmol/L
Hyaline casts
BUN/Cr ratio >20
FENA <1%
Rapid recovery of renal function when renal perfusion normalized

Intrarenal

BUN/Cr ratio <10 " 15
FENA >2%
Glomerulonephritis, vasculitis:
- UA with red cell or granular casts
- Complement and autoimmune antibodies
HUS or TTP:
- UA normal
- Anemia
- Thrombocytopenia
- Schistocytes on blood smear
Nephrotoxic acute tubular necrosis (ATN):
- UA:
  - Brown granular or epithelial cell casts
  - Specific gravity = 1.010
  - Urine osmolality <350 mmol/kg
  - Urine Na >20 mmol/L
Ethylene glycol ingestion:
- UA: Calcium oxalate crystals
- Anion gap metabolic acidosis
- Osmolar gap
Rhabdomyolysis:
- Elevated serum K+, PO4, myoglobin, creatine phosphokinase, uric acid
- Decreased serum Ca2+
Tubulointerstitial disease
Allergic interstitial nephritis:
- UA with WBC casts, WBCs, RBCs, and proteinuria
- Peripheral eosinophilia

Postrenal
UA:

Usually normal
May have some hematuria but no casts or protein
FENA often >4%
Urine osmolality usually <350 mmol/kg

Imaging

US:
- 98% sensitive for excluding obstruction
Helical CT scan:
- Without contrast sensitive for obstruction
- May detect intrarenal changes
Duplex scan for:
- Renal artery or vein thrombosis
Renal arteriogram:
- Definitive diagnosis of renal artery thrombosis
Inferior vena cava and renal vessel venogram for renal vein thrombosis
IV pyelogram

Diagnostic Procedures/Surgery
ECG:

Hypertension secondary to volume overload may cause ischemia.
Sensitive for significant, acute electrolyte changes

Treatment

Pre-Hospital

Airway, breathing, and circulation (ABCs):
- Supplemental oxygen for hypoxia
IV NS for volume depletion

Initial Stabilization/Therapy

ABCs:
Supplemental oxygen for hypoxia
IV NS for volume depletion
Correct electrolyte disturbances
Indications for emergent dialysis:
- Intractable hypertension
- Intractable volume overload
- Uremic encephalopathy, bleeding, or pericarditis
- BUN >100 mg/dL
- Intractable metabolic acidosis (pH <7.2)
Avoid nephrotoxic drugs.
Monitor UO.

Ed Treatment/Procedures

Prerenal AKI

Treat hypoperfusion with IV NS
Packed RBC for blood loss or anemia after lack of response after 2 boluses
Invasive cardiac monitoring if unable to assess cardiac failure vs. hypovolemia
Response to NS good indicator of the degree to which hypovolemia is a factor

Administer NS fluid challenge cautiously to avoid fluid overload in liver failure with ascites.
Intrarenal AKI

Glomerulonephritis:
- Glucocorticoids or plasma exchange
ATN:
- Volume replacement
Hyponatremia: Free water restriction
Hyperkalemia:
- Sodium polystyrene sulfonate (SPS) or calcium polystyrene sulfonate (CPS) for asymptomatic patient with K+ >5.5 mEq/L
- For K+ >6.5 mEq/L or ECG abnormalities consistent with hyperkalemia:
  - Albuterol via nebulizer
  - Dextrose and insulin
  - Furosemide if patient not anuric
  - Calcium stabilizes myocardium in severe hyperkalemia
  - Calcium gluconate for awake patient
  - Calcium chloride for patient without pulse
  - Dialysis for intractable hyperkalemia
Metabolic acidosis:
- Consider sodium bicarbonate for pH <7.2 or HCO3 <15 mEq/L in chronic disease
- Hyperphosphatemia:
  - Calcium carbonate
  - Aluminum hydroxide
- Myoglobinuria " aggressive fluid resuscitation with NS

Calcium is only indicated by ECG for widened PR, QT, or QRS intervals. Peaked T waves alone are not an indication.
Sodium bicarbonate is a considerable sodium load; use caution in anuric/oliguric patients.

Medication

Albuterol: 10 " 20 mg via nebulizer
Aluminum hydroxide (amphojel): 0.5 " 1.5 g PO
Calcium carbonate (Os-Cal): 0.250 " 3 g PO
Calcium gluconate: 10 mL of 10% solution over 5 min IV (may repeat q5min)
Calcium chloride: 10 mL of 10% solution
Dextrose: D50W 1 amp (50 mL or 25 g) (peds: D25W 2 mL/kg) IV
Furosemide: 20 " 400 mg IV push
Insulin: 0.1 U/kg regular IV with dextrose (decrease dose by 50% for severe renal and/or liver disease)
Sodium bicarbonate: 1 " 2 mEq/kg IV
SPS (Kayexalate) or CPS: 1 g/kg up to 15 " 60 g PO or 30 " 50 g retention enema in sorbitol q6h

Diuretics (in the absence of volume overload) and dopamine are not recommended in AKI.

Follow-Up

Disposition

Admission Criteria

New-onset AKI
Hyperkalemia/significant electrolyte abnormalities
Fluid overload with hypoxia/congestive heart failure
Uremia
Altered mental status

Discharge Criteria

Stable
Normal electrolytes

Issues for Referral
Refer to primary physician for progressive AKI in an otherwise stable patient.

Pearls and Pitfalls

Insulin dose for hyperkalemia should be reduced for significant liver or renal disease so as to avoid hypoglycemia.
NSAIDs to be avoided with any degree of AKI
SPS has a considerable sodium load; CPS is preferred when volume overload is a concern.
Avoid contrast if possible in AKI, as it may worsen renal function.

Additional Reading

Andreoli S. Acute kidney injury in children. Pediatr Nephrol. 2009;24:253 " 263.
Kellum JA. Acute kidney injury. Crit Care Med. 2008;36(suppl):S141 " S145.
Rahman M, Shad F, Smith MC. Acute kidney injury: A guide to diagnosis and management. Amer Fam Physician. 2012;86(7):631 " 639.

Codes

ICD9

584.5 Acute kidney failure with lesion of tubular necrosis
584.9 Acute kidney failure, unspecified
997.5 Urinary complications, not elsewhere classified
584.8 Acute kidney failure with other specified pathological lesion in kidney
283.11 Hemolytic-uremic syndrome
585.6 End stage renal disease

ICD10

N17.0 Acute kidney failure with tubular necrosis
N17.9 Acute kidney failure, unspecified
N99.0 Postprocedural (acute) (chronic) kidney failure
N17.8 Other acute kidney failure
D59.3 Hemolytic-uremic syndrome
N18.6 End stage renal disease

SNOMED

14669001 Acute renal failure syndrome (disorder)
35455006 Acute tubular necrosis (disorder)
36225005 Acute renal failure due to procedure
429489008 Acute renal failure due to obstruction
111407006 Hemolytic uremic syndrome (disorder)
301814009 Post-renal renal failure
46177005 End stage renal disease (disorder)

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