1. Philip Kiely pcdk1e08@soton.ac.uk
Acute Kidney Injury
Philip Kiely

2. Outline The kidneys - structure and function GFR and eGFR Clearance
Acute Kidney Injury

3. Anatomy The kidneys are retroperitoneal organs
Surrounded by a fibrous capsule and perirenal fat
Situated opposite L1-L3
Supplied by the renal artery, and drain via the renal vein

6. Function Removal of metabolic waste products Regulation of:
(i) Salt and water
(ii) Blood pressure
(iii) Acid-Base Balance
(iv) Synthesis of red blood cells
(v) Calcium and bone mineralisation

8. Glomerular Filtration Rate
Filtration at the glomerulus is a passive process
Net Filtration Pressure = Glomerular Hydrostatic Pressure - (Tubular Hydrostatic Pressure + Oncotic Pressure)
Generates an ultrafiltrate of plasma that is normally free of proteins and cells
Value is typically estimated at 125 mL/min

9. Clearance = (Urinary Concentration x Volume)
Is defined as the apparent volume of plasma from which a solute is completely removed per unit time during passage through the kidneys
Clearance = (Urinary Concentration x Volume)
Plasma Concentration
This will depend on the solutes handling by the kidney i.e. filtration, secretion, reabsorption

10. Creatinine Clearance
Creatinine is a substance that is produced endogenously by the breakdown of creatine in skeletal muscle
For a given individual its plasma concentration is at a steady state
Is freely filtered at the glomerulus and is neither secreted nor reabsorbed
Therefore provides a reasonable estimate of GFR

11. Cockcroft-Gault Equation
eGFR (mL/min) = (140 - age) x (weight in kg)
(72 x plasma creatinine (mmol/L))
- remember to multiply this value by 0.85 for women

12. Acute Kidney Injury - DAPSICAMP
AKI is defined as a rapid decrease in renal function sufficient to produce a uraemia
This causes an increase in plasma creatinine and urea and is often associated with oliguria (urine output < 0.5 mL/kg/min)
May be seen on a background of chronic renal failure - so-called acute-on-chronic renal failure

13. Pre-renal Renal Post-renal DAPSICAMP Hypovolaemia
Decreased Cardiac Output
Renovascular Disease
Acute Tubular Necrosis
Glomerulonephritis
Outflow Obstruction
Glomerular Hydrostatic
Pressure
Tubular Hydrostatic
Pressure

14. DAPSICAMP Oliguria Leg Swelling Breathlessness
Chest Pain - pericarditis
Anorexia
N + V
Lethargy
Uraemia

15. DAPSICAMP Urine dip Urine microscopy Bloods - FBC, U + Es
Imaging - USS to rule out obstruction

16. Cardiovascular - arrhythmias, acute myocardial ischaemia, hypertension
DAPSICAMP
Cardiovascular - arrhythmias, acute myocardial ischaemia, hypertension
Neurological - confusion, seizures
Gastrointestinal - haemorrhage
Systemic - infection

17. (i) Is the renal failure acute?
DAPSICAMP
Answer 3 questions:
(i) Is the renal failure acute?
(ii) Is there urinary tract obstruction?
(iii) Is there something rare that might be causing ARF?

18. DAPSICAMP
As an FY1 you should:
(i) Carefully fluid resuscitate
(ii) Take bloods and cultures
(iii) Order an USS
(iv) Put in a catheter in order to monitor urine output
(v) Stop all nephrotoxic drugs
Call for help

19. Mortality is 5-10% in those patients with isolated renal failure
DAPSICAMP
Mortality is 5-10% in those patients with isolated renal failure
This rises to 50-70% when ARF is precipitated by other organ failure
Renal replacement therapy if the following do not respond to treatment: fluid overload, hyperkalaemia, hypocalcaemia, metabolic acidosis, uraemic symptoms

20. RIFLE Criteria