Acute Kidney Injury

Question 1

Acute kidney injury

Answer 1

Abrupt loss of kidney function whereby the kidney cannot effectively remove waste products (urea) or regulate water or electrolyte balance
* Marked by increased serum creatinine or blood urea nitrogen concentration, oliguria

Question 2

Pathophysiology

Answer 2

Pre-renal: reduced renal blood flow (hypovolemia, HF, sepsis)

Intrinsic: conditions that affect the kidney, usually glomerulus or tubule (glomerulonephritis & tubular necrosis from drugs, toxins, inflammation)
* These conditions release vasocontrictors, causing ischemia

Post-renal: obstruction of the urinary tract that increases tubular pressure and reduces filtration drive (reduced GFR) - (urinary calculi, benign prostatic enlargement, prostate/cervical cancer)

Consequence
* Reduced RBF leads to ischemia, which causes a cascade of free radicals and cytokines, that initiate coagulation and apoptosis
* Cell injury continues despite restored RBF
* Tubular damage causes gap junction disruption, leading to filtrate to leak back (reduced GFR & oliguria)

Question 3

Phases of AKI

Answer 3

Oliguric: initial phase, lasts 10-14 days, UO < 400ml/day
* Signs of oedema may be present, the longer this phase, the worse the prognosis

Diuretic: lasts 1-3 weeks, varies from 1-3L/day
* High diuresis from high urea, but unable to concentrate urine (may develop hypovolemia) but starts to improve

Recovery: GFR increases which allows BUN & creatinine to stabilise and decline (may take up to 12 months)

Question 4

Manifestations

Answer 4

NB: many mild/moderate AKI patients are asymptomatic

• Oliguria
• Oedema
• N&V
• Fatigue/drowsiness, muscle twitching, seizures
• SOB, dyspnoea, chest pain
• High BUN & creatinine
• Hyperkalemia, arrythmias, CA

Question 5

Diagnostic investigations

Answer 5

• BUN, creatinine
• FBC (check for infection, anemia, blood loss)
• Urinalysis (indicators for aetiologies - brown/sediment for tubular necrosis, hematuria for intra-renal injury)
• Electrolyes
• US/CT (identify diseases or obstruction)
• Angiography (diagnose vascular disorders)
  *

Question 6

Management/Treatment

Answer 6

• Treat precipitating cause
• Maintain fluid balance based on weight, CVP, urine output, BP & avoiding fluid excess (e.g. pulmonary oedema)
• Address electrolyte imbalances (restrict sodium and phosphate, increase calcium, IV insulin or salbutamol to reduce K, reduce salt)
• In diuretic patients, these may be opposite & will need to be supplemented
• Enteral or parenteral nutrition - the metabolic impairment disregulaes macro and micronutrient balance, and patients often have critical illness that leads to protein breakdown and insulin resistance
• Dialysis or RRT

Question 7

Nursing management

Answer 7

• Strict FB to monitor injury progression & guide fluid replacement (this includes daily weight)
• Monitor urine specific gravity
• Assess for oedema
• Monitor HR, BP, CPV, JVP, RR (pt may be hypertensive and tachy)
• Lung auscultation for oedema
• Cardiac monitoring
• Monitor electrolyte status & signs of hyperkalemia (muscle weakness, cramping)
• LOC
• Skin care, infection control, psychological support

Question 8

Complications

Answer 8

• Fluid overload & pulmonary oedema
• Seizures (increased wastes)
• Hyperkalemia & arrhythmias & muscle weakness
• Chest pain from endocarditis
• Permanent kidney damage
• Death

Question 9

Haemodialysis

Answer 9

• Blood is removed from the body into a dialyzer machine and passes through a semipermeable membrane containing fibres that filters wastes out
• 3-4x a week, 4-5 hours
• Can cause low BP, dizziness, fatigue, chest pain, cramping from removing too much fluid
• Better for worse kidney injury, for those wanting HCT to control kidney care, better for obese patients or those with abdominal scarring

Question 10

Peritoneal dialysis

Answer 10

• Sterile glucose solution (dialysate) runs via a tube into the abdominal cavity, and the peritoneum acts as the semi permeable membrane which filters wastes by diffusion and osmotic drive
• When there is an equilibrium with the bodys fluids, it is drained and replaced with fresh dialysate
• More flexibility, cheaper, less risk of infection but requires more training

Question 11

Hemofiltration

Answer 11

• Similar to haemodialysis, but instead of by diffusion, it occurs by applying a pressure gradiant, whereby water moves across a very permeable membrane rapidly and drags with it many large molecular weight substances that are not able to be filtered with haemodialysis (more effective)
• Extra water and salt are then replaced with a substitution fluid