Acute Kidney Injury

Essentials

• In acute kidney injury (AKI) the ability of the glomeruli to filtrate deteriorates, which leads to a disturbed acid-base and fluid balance as well as to the accumulation of end products of nitrogen metabolism.
• Within 24 to 48 hours of the onset of the injury the serum creatinine concentration will rise and urine output fall.
• AKI should be identified before the creatinine concentration is markedly increased and the estimated glomerular filtration rate (eGFR) falls.
• A typical patient is an elderly individual with pre-existing renal impairment who, for example, contracts acute diarrhoea or receives nephrotoxic drugs (e.g. NSAIDs, ACE inhibitors), i.e. acute-on-chronic kidney disease.
• Hypovolaemia is the most common cause of oliguria and can be reversed with fluid therapy. The urine output of a seriously ill patient must be monitored.
• Urinary retention must be identified and treated.
• The concomitant administration of an ACE inhibitor, diuretic and NSAID Nsaids and Risk of Acute Renal Failure increases the risk of AKI.

Aetiology

• Pre-renal causes
  • Impaired renal perfusion: hypovolaemia, hypotension, circulatory problems
    • For example: diarrhoea, sweating, bleeding, surgical procedures, burns, severe congestive heart failure , drugs (ACE inhibitors, angiotensin II receptor blockers, NSAIDs Nsaids and Risk of Acute Renal Failure)
• Renal (intrinsic) causes
  • Ischaemic injury: sepsis , prolonged pre-renal cause
  • Toxic injury: intravenous contrast media, drugs (e.g. aminoglycosides, ciclosporin), poisons (ethylene glycol, poisonous mushrooms), myoglobin in rhabdomyolysis , haemoglobin
  • Vascular diseases: emboli , thrombotic microangiopathy
  • Nephritis: including pyelonephritis Urinary Tract Infections, epidemic nephropathy , drug-induced interstitial nephritis, glomerulonephritis Glomerulonephrites.
• Post-renal causes
  • Prostatic hyperplasia Benign Prostatic Hyperplasia (the most common cause of urine flow obstruction and urinary retention), tumour, urinary tract calculi Urinary Calculi, bladder dysfunction, etc.
• Risk factors
  • Existing impairment of renal function (eGFR < 60 ml/min, plasma creatinine > 100 µmol/l) Treatment of Chronic Renal Failure or other underlying disease, such as diabetes, cardiovascular disease
  • Advanced age
  • Diabetes
  • Vascular diseases
  • Nephrotoxic drugs
  • Surgical procedures in elderly individuals
  • Intravenous contrast media
  • Serious acute illness, such as sepsis, rhabdomyolysis

Clinical picture

• Oliguria (< 30 ml/hour or < 400 ml/24 hours) or anuria (< 100 ml/24 hours); however, urine output may also be normal
• Total anuria is usually suggestive of an obstruction to the urine flow resulting in a large, usually palpable bladder.
• Hypovolaemia is characterised by low blood pressure and cool limbs
• Hypervolaemia is characterised by oedema, particularly of the lower limbs, increased blood pressure and raised jugular venous pressure.
• Nausea, loss of appetite
• Dull pain and percussion tenderness over the kidneys are signs of acute nephritis
• Deteriorating general health (may be the only sign in an elderly individual)
• Fever signifying an infection (e.g. sepsis , pyelonephritis Urinary Tract Infections or epidemic nephropathy )
• Skin changes (e.g. livedo reticularis in cholesterol embolism after a vascular procedure, purpura in vasculitides)

Diagnosis

• Laboratory tests
  • Urinalysis immediately, urinary cell count and bacterial culture
    • A dark colour and a positive urine strip test to Hb are suggestive of rhabdomyolysis - check CK.
    • Proteinuria, haematuria and casts are suggestive of an intrinsic kidney disease.
  • Creatinine and eGFR , plasma electrolytes (sodium, potassium, calcium, phosphate) and, if possible, blood gas analysis
    • Re-check creatinine concentration without delay if it is unexpectedly increased.
    • Hyperkalaemia is the most serious complication of AKI.
    • Acidosis worsens hyperkalaemia.
  • CRP, blood count with platelets, glucose
• ECG (hyperkalaemia?) and chest x-ray (congestion/oedema?)
• Palpation of the bladder, determination of residual urine Determining the Volume of Residual Urine by Ultrasonography and digital rectal examination, especially in men.
• Ultrasonography of the kidneys and urinary tract
  • Hydronephrosis is suggestive of a post-renal obstruction.
  • Oedematous kidneys are suggestive of an acute parenchymal disease.
  • Shrunken kidneys are suggestive of an underlying chronic kidney disease (acute-on-chronic).
• Kidney biopsy is carried out in specialist care when acute glomerulonephritis is suspected (heavy proteinuria, haematuria, red cell casts).
• Classification of acute kidney injury: see table T1

Treatment Intermittent Versus Continuous and Intensity of Continuous Renal Replacement Therapy for Acute Kidney Injury in Adults, Nutritional Support for Acute Kidney Injury

• It is not possible to treat AKI with medication.
• Stop potentially nephrotoxic medications.
• Monitoring of urine output: catheter if the patient is unable to pass urine
  • Hourly urine measurements
  • In anuria, the catheter should be removed due to the risk of infection.
• Urinary retention, or other obstruction to urine flow, with a palpable bladder
  • A sudden cessation of urine output without hypovolaemia
  • An indwelling catheter or percutaneous cystostomy
  • The underlying cause should be corrected.
• Oxygen therapy as required (SpO₂> 94%)
• Management of dehydration
  • A patient with cool extremities, low systolic blood pressure (below 90 mmHg), and no audible rales on pulmonary auscultation (for example, an elderly patient with diarrhoea)
  • Ringer's acetate solution 1 000 ml as an infusion 15 ml/kg/hour or 1 000-2 000 ml over 2-4 hours. The infusion is continued until the symptoms of hypovolaemia improve and diuresis recommences.
  • The target blood pressure (systolic) is above 100 mmHg. If needed, inotropic drugs (e.g. noradrenaline).
  • Observe the patient for excessive fluid overload and pulmonary oedema (in which case CPAP is indicated).
  • The use of colloids Hydroxyethyl Starch (Hes) Versus other Fluid Therapies: Effects on Kidney Function or albumin Albumin for Resuscitation and Volume Expansion in Critically Ill Patients is not recommended.
• Hyperkalaemia and acidosis must be corrected.
  • Mild hyperkalaemia (plasma K < 6.0) with no ECG changes
    • Usually requires no specific treatment. Any medication inducing hyperkalaemia should be stopped.
  • PlasmaK HASH(0x2e59d78) 6.0: see
• Furosemide
  • Can be tried in gradually increasing doses (20-40-80 mg i.v.; large doses administered as an infusion over 15-20 minutes), after it has been verified that the patient is not hypovolaemic.
  • If urine output increases, treatment may continue with repeated doses (4-6 times daily) or a continuous infusion (10-15 mg/hour).
  • No evidence is available on the benefit of furosemide , and it does not improve renal function Furosemide to Prevent or Treat Acute Renal Failure in Adults.
• Renal replacement therapies (dialysis, continuous filtration) should be considered in the following situations:
  • overhydration
  • hyperkalaemia (plasma K > 6.5 mmol/l)
  • metabolic acidosis (pH < 7.2; HCO₃< 15 mmol/l)
  • persistent oliguria (urine output < 200 ml/12 hours) or a markedly increased urea (> 35 mmol/l) and creatinine (> 500 µmol/l ) concentration.
• In AKI, the patient's medication list should always be examined and the possible nephrotoxicity of the drugs in use checked in an appropriate database as needed.

Arrangement of treatment

• Treatment is usually carried out in specialist care.
• An elderly patient with gastroenteritis can in most cases be treated in a general ward.

Prophylaxis when using intravenous contrast media

• Important particularly in high-risk patients (see above)
• The greatest risk is associated with investigations necessitating intra-arterial administration.
• Nephrotoxic drugs and diuretics should be stopped 24 hours before the investigation.
• It is crucial to ensure the adequate hydration of patients in the high risk groups: an infusion of 0.9% NaCl 1 ml/kg/hour, 6-12 hours before and after the investigation. The fluid regime should be agreed on in good time with the unit carrying out the investigation.
• In emergency situations (in a hospital), administer 500 ml of 0.9% NaCl as a rapid infusion before the investigation and 1 ml/kg/hour after the investigation for 6-12 hours.
• Sodium bicarbonate appears to be as effective as 0.9% NaCl.
  • 1.4% sodium bicarbonate is given 3 ml/kg over one hour before the investigation, and after the investigation 1 ml/kg/hour is continued for at least 6 hours.
• Contrast media used in magnetic resonance imaging are (usually) not nephrotoxic.
• Plasma creatinine should be checked in high-risk patients 2 days after the procedure.

References

• Solomon R, Werner C, Mann D, D'Elia J, Silva P. Effects of saline, mannitol, and furosemide to prevent acute decreases in renal function induced by radiocontrast agents. N Engl J Med 1994 Nov 24;331(21):1416-20. [PubMed]