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

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

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

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

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

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

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

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

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

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

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

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

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

(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?

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

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

RIFLE Criteria