Haemorrhage Associated Acute Kidney Injury

Haemorrhage associated acute kidney injury is loss of kidney function following acute blood loss from trauma, surgery, gastrointestinal bleeding, obstetric haemorrhage or ruptured aneurysm. It combines hypovolaemic renal hypoperfusion with ischaemia reperfusion tubular injury, the effects of vasopressors, transfusion related inflammation and, in massive resuscitation, abdominal compartment syndrome.

Loss of more than 15% of blood volume reduces renal blood flow through sympathetic and angiotensin II activation. Loss of 30% to 40% causes hypotension; when mean arterial pressure falls below 60 mmHg autoregulation fails and filtration declines. Established tubular necrosis follows prolonged ischaemia and leads to recovery over 1 to 3 weeks if the patient survives.

Additional mechanisms:

• Haemoglobin and iron release from stored red cells and haemolysis
• Contrast exposure during angiography for bleeding control
• Intra-abdominal hypertension (pressure above 12 mmHg) or abdominal compartment syndrome (pressure above 20 mmHg with new organ dysfunction) from massive transfusion and retroperitoneal haematoma
• Rhabdomyolysis in crush injury
• Coagulopathy, hypothermia, acidosis (the lethal triad) and hyperkalaemia from stored blood

Obstetric haemorrhage can cause bilateral cortical necrosis, a patchy and often irreversible injury.

• Acute blood loss: tachycardia (above 100/min), hypotension, cool peripheries, pallor, confusion, oliguria
• Class of haemorrhage: class III is 30% to 40% loss (heart rate above 120/min, hypotension, urine output 5 to 15 mL/h); class IV is above 40% loss (anuria, collapse)
• Visible haematemesis, melaena, vaginal bleeding, wounds, expanding haematoma
• Abdominal distension and tense abdomen with rising airway pressures in compartment syndrome
• Dark urine in crush or haemolysis
• Persisting oliguria after resuscitation suggests tubular necrosis

Red flags: shock index (heart rate:systolic pressure) above 1.0, lactate above 4 mmol/L, base excess of minus 6 or lower, anuria, potassium above 6.0 mmol/L, bladder pressure above 20 mmHg, coagulopathy.

• Immediate: haemoglobin (may be normal early), lactate, base excess, group and crossmatch, coagulation screen, fibrinogen, viscoelastic testing, platelets, ionised calcium, potassium
• Urea, creatinine, urine output hourly; BUN:creatinine ratio above 20:1 in upper gastrointestinal bleeding
• Urinalysis and sediment: muddy brown casts support established tubular injury
• Imaging directed to the bleeding source: CT angiography, endoscopy, focused ultrasound in trauma
• Intra-abdominal pressure via bladder measurement (normal below 12 mmHg)
• Creatine kinase in crush injury

Differentials: pure prerenal azotaemia (recovers within 48 to 72 hours), sepsis, rhabdomyolysis, haemolytic transfusion reaction, contrast injury, cardiogenic shock.

Control bleeding and resuscitate

• Haemorrhage control first: direct pressure, tourniquet, surgical or endovascular control, endoscopic therapy.
• Damage control resuscitation: red cells, plasma and platelets in a 1:1:1 ratio; use crystalloid sparingly. Cryoprecipitate or fibrinogen concentrate to keep fibrinogen above 1.5 g/L (above 2 g/L in obstetric bleeding). Platelets above 50 x 10^9/L (above 100 x 10^9/L in head injury or central nervous system bleeding).
• Tranexamic acid 1 g intravenously over 10 minutes within 3 hours of injury or onset, then 1 g over 8 hours.
• Calcium chloride 1 g (or calcium gluconate 3 g) after the first 4 units of red cells; keep ionised calcium above 1.1 mmol/L.
• Permissive hypotension in trauma (systolic pressure 80 to 90 mmHg) until bleeding is controlled; avoid in head injury or spinal injury.
• Transfusion threshold after control: haemoglobin 70 g/L (80 g/L with cardiovascular disease).
• Keep temperature above 36 degrees Celsius.

Renal protection

• Restore mean arterial pressure at least 65 mmHg; noradrenaline 0.05 to 0.5 microg/kg/min after volume.
• Avoid NSAIDs, aminoglycosides, vancomycin and unnecessary contrast, but do not withhold angiography needed to control bleeding.
• Treat hyperkalaemia with calcium gluconate 10% 10 mL intravenously over 10 minutes, insulin 10 units with glucose 25 g and salbutamol 10 to 20 mg nebulised.
• Rhabdomyolysis: crystalloid 1 to 2 L/h initially, with urine output target 200 to 300 mL/h until creatine kinase is below 1000 U/L.

Abdominal compartment syndrome. Sedation, neuromuscular blockade, nasogastric and rectal decompression, paracentesis, and urgent surgical decompression when pressure is above 20 mmHg with new organ failure.

Renal replacement therapy for refractory hyperkalaemia, acidosis (pH below 7.15), overload impeding ventilation or uraemic complications; prefer continuous techniques in unstable patients.

Obstetric haemorrhage. Uterotonics (oxytocin 5 units slow intravenous then 40 units in 500 mL at 125 mL/h; carboprost 250 microg intramuscularly every 15 minutes up to 8 doses), tranexamic acid, uterine balloon tamponade, surgical control. Watch for oliguria below 0.5 mL/kg/h for 6 hours.

Follow up. Creatinine and albumin:creatinine ratio at 3 months; nephrology review if not recovered by 90 days.