My Clinical Notes

• A significant deterioration in renal function occurring over hours or days
• Clinically there may be no symptoms or signs but oligouria (urine vol <400ml/24hr ) is common
• Biochemically there is rising plasma urea and creatine
• It may arise as an isolated problem but more commonly it occurs in the setting of circulatory disturbances;
  • Severe illness
  • Sepsis
  • Trauma
  • Surgery
• Or in the context of nephrotoxic drugs

Causes

• Pre-renal and ATN account for >80% of cases
  • Pre-renal causes;
    • Due to renal hypoperfusion;
      • Hypovolaemia
      • Sepsis
      • CCF
      • Liver cirrhoss
      • Renal artery stenosis
      • NSAIDs or ACEI
  • Intrinsic causes;
    • Acute tubular necrosis
      • This is caused by ischaemia or nephrotoxins;
        • Drugs - amphotericin B, gentamycin, tetracylines
        • Radiological contrast agents
        • Uric acid crystals
        • Haemoglobinuria
        • Myeloma
    • Other causes;
      • Vascultitis
      • Malignant hypertension
      • Cholesterol emboli
      • Haemolytic uraemic syndrome
      • Thrombotic thrombocytopenic purpura
      • GN
      • Interstitial nephritis
      • Hepatorenal syndrome
  • Post renal
    • Obstruction

Tests

• Bloods - U&Es, FBC, LFTS, clotting, CK, ESR, CRP
• Consider ABG, blood cultures and hepatitis serology is dialysis is being considered
• If the cause is unclear - serum Ig, electrophoresis, complement levels (C3/C4), autoantibodies (ANA, ANCA, anti-dsDNA, anti-GBM) and anti-streptolysin O titre
• Urine - dipstick for leucocytes, nitrite, blood, protein, glucose
• Microscopy for RBC, WBC, crystals, casts and culture and sensitivity
• Measure urine U&Es, creatine, osmolality, Bence-Jones protein
• CXR - pulmonary oedema
• ECG - signs of hyperkalaemia
• Renal ultrasound - renal size or obstruction?

Distinguishing pre-renal failure and ATN

• In pre-renal failure urine is concentrated and sodium is reabsorbed by working ubular cells. This fails to happen in ATN

Management of acute renal failure

• Get specialist help and make sure you have recent U&Es and urine microscopy results to hand
• Treat precipitating causes e.g. blood loss or sepsis
• If shock is the cause resuscitate - after catheterising and starting fluid balance chart give a challenge of 250-500ml of colloid or saline over 30min,  repeat if still rehydrated. Aim for a CVP of 5-10cm
  • Once fluid replete continue fluids at 20ml per hour plus previous hours urine output
  • If volume overloaded consider urgent dialysis. A nitrate infusion, furosemide or ‘renal dose’ of dopamine may help in the short term
• Do urgent US scan - check for a palpable bladder
• Stop nephrotoxic drugs - NSAIDs, ACEI, gentamycin, vancomycin, amphotericin B, stop metformin if creatinine >150mmol/L
• Are there signs of vasculitis - do autoantibodies
• Find and treat exacerbating factors - e.g. hypovolaemina, sepsis, hypertension
• If in doubt about fluid status insert a CVP line
• Monitoring
• Consider transfer to HDU or ITU
• Pulse, BP, CVP, urine output hourly
• Daily fluid balance and weight chart
• Match input to loss + 500ml of insensible losses
• Correct volume depletion
• If patient is septic take cultures and treat empirically
• Monitor nutrition - aim for normal calorie intake (more if catabolic) and protein ~0.5g/kg/d

Treat complications

• Hyperkalaemia
  • Tall tented T waves, small or absent P waves, increased PR interval, widened QRS complex, later there may be a sine wave pattern followed by asystole
  • Treat with;
  • IV calcium 10ml of 10% into a large vein over 2min - repeated until ECG improves
  • IV glucose and insulin - 10U Actrapid + 50ml of 50% glucose IV over 30mins - stimulates uptake of K+
  • Salbutamol 5mg nebulisor
  • Consider calcium resonium 15g/8hr PO or PR to bind K+ in the gut
  • Haemodialysis or haemofiltration is usually required if anuric

• Pulmonary oedema
  • Sit up and give high flow O2
  • Venous vasodilator - e.g. morphine 2.5mg IV (plus antiemetic)
  • Furosemide 120-250mg IV over 1hr
  • If no response urgent haemodialysis or haemofiltration may be required
  • Consider CPAP
  • IV nitrates have a role

• Pericarditis and tamponade

• Bleeding
  • Impaired haemostasis due to rasied urea may be compounded by the precipitating cause. In patients with ARF who are actively bleeding give;
  • FFP and platelets as needed
  • Blood transfusion to maintain HB >10g/dL and haemocrit >30%
  • Desmopressin to increase Factor VIII activity

Indications for acute dialysis;

• Refractory pulmonary oedema
• Persistent hyperkalaemia K+>7mmol/L
• Severe metabolic acidosis (pH<7.2 or BE <10)
• Uraemic encephalopathy
• Uraemic pericarditis

This entry was posted on Wednesday, February 11th, 2009 at 8:13 am and is filed under Kidney. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.