Renal

• Renal system


  • Help maintain homestasis
  • Regulate the balance of water, sodium, potassium, hydrogen ions and other water soluble substances
  • Produce hormones
• Kidney


  • Each kidney is a collection of 1.2 million nephrons
  • A nephron is a long tube lined with epithelial cells
  • At the proximal entrance are glomerulus and the other end opens into the renal pelvis
  • Fluid that passes through the sieve is called filtrate
  • Filtrate moves along the nephron useful substances pass back into the blood stream; while metabolic waste stays in the nephron to be excreted
• Kidney Blood Flow


  • The kidneys receive ~25% of the 5 litres of cardiac output
  • Every hour the kidneys process ~60 litres of fluid
• Kidneys and blood pressure

  • The flow through the glomerular capillaries is auto-regulated; as the blood pressure rises and falls the intrarenal arterioles constrict and dilate to keep the blood flowing at a constant rate
  • If the MAP falls below 80 mmHg auto-regulation is lost and urine outputs starts to fall
  • THE KIDNEYS HEALTH IS AT RISK
• How the kidneys maintain their GFR


  1. Sufficient perfusion pressure to force fluid from the blood through the glomerular membrane to form the filtrate

  2. If the blood flow through the kidneys decreases it can temporarily compensate for this by leaving the inflow arteriole wide open; while constricting the outflow arteriole

  3. This results in the blood damming up in the glomerulus

  4. Angiotensisn II and noradrenergic nervous system mediate outflow shutdown
• Kidneys and blood pressure


  • In a healthy person glomerular filtration stops and urine output ceases once the MAP falls below 60 mmHg
  • In patients with vascular disease (e.g. diabetes or long-term smokers) glomerular filtration rates ceases at mean blood pressures higher than 60 mmHg because of the existing aetiology of the vessels
• Causes of Chronic Renal Failure


  • Diabetes (30%)
  • Hypertension (24%)
  • Glomerulonephritis (17%)
  • Chronic pyelonephritis (5%)
  • Polycystic renal disease (4%)
  • Unknown Cause (20%)
• Chronic renal failure


  • A multisystem disease
  • These patients often have very complex medical histories and require poly-pharmacies
• Chronic renal failure


  • Broken down into 5 stages
  • These patients require extensive pre-operative planning
• Drugs in chronic renal failure


  • Drugs safe in CRF
  • Drugs safe in limited/reduced doses
  • Drug contraindicated
• Renal transplants


  • The treatment of choice for patients with stage 5 CRF
  • A successful renal transplant will greatly improve the quality of life for the patient
• Anaesthesia in a patient with a renal transplant


  • The implanted kidney will never function as well and has only ½ the normal amount of nephrons
  • The drugs given to prevent rejection of the organ (immunosuppressant's) further impair renal function
  • The immunosuppression makes these patients incredibly vulnerable to infection/sepsis
  • Depression of the CVS may compromise renal function; hypotension and hypovolaemia should be avoid
  • Avoid nephrotoxic drugs
  • Transplanted kidney is superficial in the abdomen
• Risk factors for Acute Renal Failure/Acute Kidney Injury (AKI)


  • Patients over 65
  • Patients with exiting severe arterial disease
  • Diabetics
  • Surgery involving cross clamping of the aorta
  • Patients with pre-existing renal disease
  • Patients undergoing major vascular surgery; especially if a blood transfusion is required
  • Patients taking NSAIDs
  • Patients with sepsis
  • Patients undergoing bowel surgery
  • Pre-eclampsia
  • Trauma/crush injuries
• AKI classification system


  • Risk – UO <0.5 mL/kg/h for 6 h, serum creatinine rise x 1.5 or GFR decreases > 25%
  • Injury - UO <0.5 mL/kg/h for 12 h, serum creatinine rise x 2 or GFR decreases > 50 %
  • Failure - UO <0.3 mL/kg/h for 24 h or anuria serum creatinine rise x 3 or GFR decreases > 75 %
  • Loss of function = persistent ARF which is complete loss of renal function for > 4 weeks
  • ESRD
• AKI classification


  • Pre-renal acute renal failure
  • Intrinsic acute renal failure
  • Post-renal acute renal failure
• AKI - Treatment


  1. Monitor hourly urine output if a catheter is in-situ ensure that a free flowing bag is replaced with a urometer. If no catheter is in-situ ensure accurate fluid balance is monitored.

  2. Assess volume status and restore normovolaemia

  3. Maintain MAP > 70 mmHg (higher if the patient is normally hypovolaemic)

  4. Optimise cardiac output

  5. Treat life-threatening complications e.g. hyperkalemia
• The kidneys are essential for maintaining homeostasis
• The kidneys are extremely sensitive to changes and are a extremely good indicator of deterioration
• A number of considerations need to be made when managing a patient with a renal compromises
• If a patient develops renal impairment intra-operative this needs treating aggressively to avoid permanent damage