Acute kidney injury Flashcards
What is AKI
- A rapid(within hours to days) fall in glomerular filtration rate (GFR) which impedes the kidney’s normal functions
AKI stage 1 serum creatinine criteria
- Increase in serum creatinine of 26 micromol/litre or more within 48 hrs or 1.5-2 fold increase from baseline
- Less than 0.5 ml/kg/hour urine for more than 6 hrs
AKI stage 2 serum creatinine criteria
- Increase in serum creatinine to more than 2 to 3-fold from baseline
- Less than 0.5 ml/kg/hour for more than 12 hrs
AKI stage 3 serum creatinine criteria
- Increase in serum creatinine to more than 3-fold from baseline OR serum creatinine more than 354 micromol/litre with an acute increase of at least 44 micromol/litre
- Less than 0.3 ml/kg/hour for 24 hours or anuria for 12 hrs
AKI stage 1 urine output criteria
Less than 0.5 ml/kg/hour for more than 6 hours*
AKI stage 2 urine output criteria
Less than 0.5 ml/kg/hour for more than 12 hours
AKI stage 3 urine output criteria
Less than 0.3 ml/kg/hour for 24 hours or anuria for 12 hours
What is creatinine
- A normal product of muscle turnover
- Non-toxic
- Transported by the blood and excreted by the kidneys
- Used as a surrogate marker for glomerular filtration.
- Less filtration => less creatinine removed => a creatinine rise
GFR is estimated from creatinine results
Urine output criteria - oliguria
<0.5ml/kg/hr urine output
Usually <500ml/24 hrs in adults
Urine output criteria - anuria
- officially would mean no urine output
- Softly defined as <100ml/24 hrs
AKI natural time course phases
Four Phases Onset phase Oliguric/Anuric phase Polyuric/Diuretic phase Recovery phase
AKI - onset phase
- Common triggering events: significant blood loss, burns, fluid loss, diabetes insipidus
- Renal blood flow 25% of normal
- Tissue oxygenation 25% of normal
- Urine output below 0.5 ml/kg/hr
AKI - onset phase duration
hours to days
AKI - oliguric(anuric) phase
- Urine output below 400 ml/day, possibly as low as 100 ml/day
- Increases in blood urea nitrogen (BUN) and creatinine levels
- Electrolyte disturbances, acidosis, and fluid overload(from kidney’s inability to excrete water)
AKI - oliguric phase duration
- 8-14 days or longer, depending on nature of AKI and dialysis initiation
AKI - diuretic phase
- Occurs when cause of AKI is corrected
- Renal tubule scarring and edema
- Increased glomerular filtration rate (GFR)
- Daily urine output above 400 ml
- Possible electrolyte depletion from excretion of more water and osmotic effects of high BUN
AKI - diuretic phase duration
- 7-14 days
AKI - recovery phase
- Decreased edema
- Normalisation of fluid and electrolyte balance
- Return of GFR to 70% or 80% of normal
AKI - recovery phase duration
- several months to 1 yr
Normal K+ levels
> 6.0 = bad
> 6.5 = medical emergency
ECG features of hyperkalaemia
- Reduced P wave with widened QRS complex
- Tented T wave
- ‘Sine wave’ pattern (pre-cardiac arrest)
Symptoms of fluid overload
- Breathlessness
- Orthopnea
- Limb swelling
Danger of fluid overload in AKI
The danger = pulmonary oedema -> severe tissue hypoxia
If your patient is oliguric/anuric – they won’t be able to get rid of this excess water
Indications for dialysis
- Refractory hyperkalaemia
- Pulmonary oedema
- Refractory acid/base disturbance
- Uraemic complications (coma, pericarditis)
Pre-renal causes of AKI
Decrease in perfusion pressure resulting in ischaemia or infarction
- Bleeding
- Septic shock
- Dehydration
- MI
- Iatrogenic
- Renal artery stenosis
Renal causes of AKI
Direct toxic effects
- Drugs
- Calcium and other metals
Overproduction leading to blockage of the tubules
- Rhabdomyolysis, myeloma
Inflammation in the kidney
- GN, interstitial nephritis, ATN
Post-renal causes of AKI
Plumbing problem/outflow obstruction:
- Stones
- Ureteric/urethral strictures
- BPH
- Prostate cancer
- Urinary retention e.g. neurogenic, constipation
Who is at risk of AKI - chronic
Elderly CKD Cardiac Failure Liver disease Diabetes Vascular disease Background nephrotoxic medications
Risk of AKI - acute risk
S - Sepsis and hypoperfusion
T - Toxins
O - Obstruction
P - Parenchyma
How do your predict/prevent AKI
The 4 ‘M’s
Monitor
Obs/NEWS, regular blood tests, fluid balance charts, pathology alerts
Maintain Circulation
Hydration, resuscitation, oxygenation
Minimise Kidney Insults
Nephrotoxic meds, surgery, contrast, hospital acquired infection
Manage the acute illness
Sepsis, heart failure, liver failure
AKI - red flags in history
Haemoptysis Rashes Joint pain/swelling ENT – crusting of nose/acute hearing impairment Significant acute limb swelling Noticable urine frothiness Jaundice
Initial fluid assessment
Focused history - Is the patient thirsty? Capillary refill time Mucus Membranes Skin turgor Pulse rate BP (relative and postural) Respiratory rate Central vs. Peripheral temp JVP Lung auscultation Oedema – peripheral and sacral CXR – pulmonary oedema/infiltrates Fluid balance charts/urine output Invasive methods – catheter, arterial line, central line
Drugs to avoid in AKI
ACE inhibitors Angiotensin Receptor Blockers NSAIDS: ibuprofen, diclofenac, naproxen Any diuretics Metformin (theoretically)
Causes of polyuria
Is a known and common phase of AKI of any cause
Post relief of obstruction
Diabetes mellitus
Pscyhogenic
Beer potomania
Rare endocrine causes (e.g. diabetes insipidus)
Management of polyuria
Encourage the patient to drink
Depending on your assessment of fluid balance
Provide iv fluids to match the output+/- additional input if dry
Once renal function is beginning to improve reduce to 75% of urine output
