Overview

Acute kidney injury (AKI) (formerly acute renal failure) is the syndrome arising from a rapid fall in GFR (over hours to days). It is characterized by retention of both nitrogenous (including Urea and Creatinine) and non-nitrogenous waste products of metabolism, as well as disordered electrolyte, acid– base, and fluid homeostasis.

Epidemiology

Develop in 5- 20% of hospitalised patients and a significant contributor to morbidity and mortality in the critically ill

Anatomy and Physiology

Renal Anatomy

The urinary system consists of:

• Kidneys
• Ureters
• Bladder
• Urethra

The kidneys are retroperitoneal bean shaped organs thats sits between veretbral levels T11-L3, the left kidney sitting slightly higher then the right kidney.

The kidneys is divided into three sections:

• Renal cortex – renal arches and renal columns
• Renal Medulla – pyramids, papillae, major calyx, minor calyx
• Renal Sinus – Pelvis, renal vessels and lymphatics

Arterial Supply

• Aorta → Renal artery (L2) → Segmental artery → Interlobular artery → Cortical radiate artery → Afferent Arteriole → GLOMERULUS

Venous Drainage

• GLOMERULUS → Efferent arteriole (has branches forming the Vasa recta) → Arcuate vein → Interlobar vein → Renal Vein → Inferior vena cava

Nephrons 

• Functional units of Kidneys
• Nephron’s are structurally divided into two types:
  • Cortical
  • Juxtamedullary

Ureters are narrow muscular tube that transport urine to the bladder. There are three narrowed areas of each ureter:

• Ureteropelvic junction
• Ureteral segment
• Ureterovesical junction

Bladder is a muscular organ which holds urine. The wall of the bladder comprises of four layers:

• Adventitia
• Detrusor muscle
• lamina propria
• Urothelium – specialised transitional cell epithelium (can stretch)

Urethra Arisis from the base of the bladder and is the passageway through which urine is discharged from the body. The female urethra is much shorter (3-4cm) than the male urethra (18+cm)

Renal Physiology

• Regulation of plasma ionic composition
• Regulation of plasma volume
• Regulation of plasma osmolarity
• Regulation of plasma hydrogen ion concentration (pH)
• Removal of metabolic waste products and foreign substance from the plasma.

Classification

Aetiology and Prevention

The aetiology of acute kidney injury can be simply divided into pre-renal, renal and post renal causes.

Pre-renal – Sepsis and hypotension:

• Severe sepsis
• Haemorrhage
• Dehydration
• Cardiac failure
• Liver failure
• Renovascular insult

Intrarenal

• Toxicity:
  • Nephrotoxic drugs
  • Iodinated radiological contrast
• Parenchymal kidney disease:
  • Glomerulonephritis
  • Tubulointerstitial nephritis
  • Rhabdomyolysis
  • Haemolytic uraemic syndrome
  • Myeloma
  • Malignant hypertension

Post renal Obstruction:

• Bladder outflow
• Stones
• Tumour
• Surgical ligation of ureters
• Extrinsic compression (lymph nodes)
• Retroperitoneal fibrosis

Investigations

• Urine Dipstick
• FBC
• Clotting profile
• Group and save – if anaemia
• CRP/ESR
• Blood smears
• EUC
• LFTs
• CK – rhabdomyolysis?
• Urate – tumour lysis syndrome?
• Lactate – tissue ischaemia?
• Blood culture
• Arterial blood gas
• CMP

Screening for nephritis/nephrotic syndromes

• Anti-ANA
• ANCA
• Anti-GBM
• Anti-streptolysin O tites
• Protein electrophoresis
• Immunoglobuins (IgG, IgA and IgM
• Rheumatoid factor
• Viral serology – HIV, HBV, HCV
• Antiphospholipid syndrome

Imaging

• Renal ultrasound
• Chest X-ray – pulmonary oedema? pulmonary infection?
• Renal scans
  • MAG 3 scan
• Renal biopsy

Management

Overview Initial treatment should focus on correcting fluid and electrolyte balances and uremia while the cause of acute renal failure is being sought. A volume-depleted patient is resuscitated with saline. The main electrolyte disturbances in the acute setting are hyperkalemia and acidosis.

General

• Fluid Replacement – The key to achieving euvolaemia is repeated clinical assessment of a patient’s volume status
• Review medications and stop nephrotoxins
• Monitor and adjust diet

Treat underlying cause

• Prerenal
• Intrarenal
• Postrenal

Treat complications 

• Hyperkalaemia
  • Calcium gluconate – it does not ↓potassium but is cardioprotective
  • Insulin and glucose
  • Sodium bicarbonate
  • B2 agnoists – Salbutamol
  • Urinary K+ wasting: diuretics
  • Gut K+ wasting: exchange resins

• Pulmonary Oedema
  • Sit patient up
  • Oxygen
  • Opiates
  • Nitrates
  • Diuretics
• Hyperphosphataemia
  • Dietary restriction of phosphate
  • PO4 removal through dialysis or haemofiltration.
  • Oral phosphate binder (calcium carbonate)
• Hypocalcaemia
  • Calcium is supplemented orally

• Hypomagnesaemia
  • Magnesium supplement
• Anaemia – Bleeding?
• Infections – Antibiotics

Summary

Complications

• Electrolyte imbalance
  • Hyperkalaemia
• Pulmonary oedema
• Uraemic complications
• Reduced conscious level