Acute Kidney Injury Flashcards
What is the definition of acute kidney injury?
It is a clinical syndrome characterised by a rapid reduction in renal excretory function due to several different causes:
- Pre-renal (85% - reduced renal perfusion)
- Renal (10%)
- Post-renal (5% - obstruction)
What are the common causes of AKI?
Pre-Renal (85%) = reduced renal perfusion
- Dehydration
- Sepsis
- Hypotension
- Shock
- Hepatomegaly syndrome
- Severe heart failure
- Intra-abdominal hypertension/compartment syndrome
Renal (10%)
- NSAIDs
- ACE inhibitors
- ARBs
- Gentamicin
- GN/Vasculitis
- Contrast
- Interstitial nephritis
- Myeloma
- Rhabdomyolysis (death of muscle tissue)
Post-Renal (5%) = obstruction
- Prostate enlargement
- Renal stones
- Pelvic cancer
What are the key points in a history and examination to cover with reference to a patient with AKI?
- AKI RISK FACTORS:
- Age > 65
- History of AKI
- CKD
- Symptoms/history or urological obstruction/conditions that may lead to obstruction
- Chronic conditions (HF, liver disease, diabetes)
- Neurological/cognitive impairment or disability (may limit fluid intake)
- Sepsis
- Hypovolemia
- Oliguria
- Nephrotoxic drug use within the last week (i.e. NSAIDs, ACE, ARBs, diuretics)
- Exposure to iodinated contrast agents within past week - POTENTIAL CAUSES FOR AKI:
- Reduced fluid intake
- Increased fluid losses
- Urinary tract symptoms
- Recent drug ingestion
- Sepsis - SYSTEMIC CLINICAL FEATURES:
- Fever
- Rash
- Joint pain - CLINICAL EXAMINATION SHOULD INCLUDE:
- General (rash, uveitis, joint swelling)
- Assessment of volume status (drowsy/yawning/thirsty, core temperature, CRP, HR, BP, JVP)
- Signs of renovascular disease (audible abdo bruits, impalpable peripheral pulses)
- Abdo exam (palpable bladder)
What investigations would you perform in a patient with AKI and why?
Patient has AKI 3 and is confused, has 1 week history of diarrhoea
- Chest x-ray -> look for pulmonary oedema or pneumonia
- Urine dipstick -> look for dipstick blood + protein’
- Urine culture -> look for urine infection
- Renal tract US -> look for obstructed kidneys (hydronephrosis), kidney size
- Stool culture -> pathogens causing diarrhoea
What is the importance of a urine dipstick in AKI?
> 3+ proteinuria = intrinsic renal disease
If blood + protein positive = glomerulonephritis
Positive for blood + no RBC = myoglobin
Send urine PCR/MSU if dipstick positive
If negative likely excludes intrinsic renal disease
Name 4 complications of AKI that if not resolved requires dialysis
- Hyperkalemia
- Pulmonary oedema
- Metabolic acidosis
- Uraemic encephalopathy (confusion, myoclonic jerks, seizures, coma) OR uraemic pericarditis (inflammation of pericardial sac)
What do kidneys do?
- Reduce salt + water in the body
- Remove waste from the blood into the urine
- Regulate BP
- Create erythropoietin to control production of RBCs
- Activate vitamin D
- Remove drugs from the body
How many nephrons are damaged with a decrease in GFR?
50%
What is the natural history of AKI?
There are 4 possible processes:
- Full recovery
- AKI -> CKD (AKI that persists for more than a few months)
- Acute on chronic kidney disease
- AKI -> ESRD (end stage renal disease; requiring dialysis or transplant)
Define the staging of AKI
Stage 1:
1.5-1.9x baseline Creatinine OR ≥ 26umol/L increase
<0.5ml/kg/hr for 6-12h
Stage 2:
2-2.9x baseline increase in Creatinine
<0.5ml/kg/hr for ≥12h
Stage 3:
>3x baseline increase in Creatinine OR ≥354umol/L increase OR initiation of RRT OR if under 18y, eGFR < 35ml/min
<0.3ml/kg/hr for ≥24h OR anuria for ≥12h
What do you do if you suspect AKI?
Think “SALFORD”!
- Sepsis + other causes - treat!
- ACE/ARB + NSAIDs - suspend/review
- Labs - repeat creatinine within 24h
- Fluid assessment + response (daily weights if hypovolemic give bonus IV 250ml + reassess)
- Obstruction - USS should be performed within 24h in non-resolving AKI 3 of unknown cause
- Renal/critical care referral - non-resolving AKI 3, possible intrinsic disease requiring specialist tx, CKD 4-5, renal transplant, severe AKI complications
- Dip urine
Name 4 causes of fluid overload and dehydration
Overload:
- Iatrogenic (too much IV fluid)
- Cardiac failure
- Renal failure
- Increased ADH secretion
Dehydration:
- Diabetes
- Diarrhoea + vomiting
- Fever
- Drugs (i.e. diuretics)
- Insufficient replacement fluid
- Hemorrhage
- Sepsis
What bloods will be elevated in AKI?
Urea»_space; creatinine
Albumin
Hematocrit (Hct)
What needs to be reviewed in a patient with altered hydration status?
- Fluid balance chart
- Observations chart
- Drug kardex
- Bloods
- Chest x-ray
Outline what you’re looking for in a hydration status examination
End of Bed:
- Body habituate, breathlessness, oedema
- IV lines, NGT, NBM (nil by mouth), food/drink (“into patient”)
- Catheter, vomit bowel, drains, Tomas (“out of patient”)
Hands:
- Warm, CRT, skin turgor, pulse, lying/standing BP (significant difference > 20mmHg)
Neck:
- Carotid, JVP
Head:
- Temperature, sunken eyes, dry mouth
Chest:
- Parasternal heave (RH dilatation), displaced apex beat (LH dilatation), 3rd heart sound (HF)
Back/Legs:
- Lung bases (crackles - LHF)
- Sacral/pedal oedema (RHF)
Extras:
- Review charts, suggest daily weights
- Bloods (LFTs, FBC)
- Chest x-ray
- Specific gravity of urine (for dehydration)
What is the management of underloaded or fluid overloaded patients?
Underloaded/dehydrated:
- IV fluids (250-500ml Hartmann’s or 0.9% NaCl)
Overloaded:
- Nitrates
- Diuretics
- CPAP
What changes are seen in ECG in hyperkalemia?
- Peaked T waves (tented)
- Small/indiscernible P waves
- Broad QRS complexes
- Slurring of QRS into ST component
What causes acute tubular necrosis? Histology? Treatment?
Usually a result of a combination of factors which have caused renal ischemia + toxicity (i.e. hypotension, dehydration, sepsis, associated nephrotoxic drugs)
The histology shows laughing of the renal tubular epithelium causing dilation and obstruction of tubules and some mild leukocyte infiltration
Treatment is supportive + withdrawal of nephrotoxic agents + treatment of associated sepsis.
Usually there’s recovery after 2-3 weeks (max 6wks). 50% mortality b/c of associated illness. Only a very small proportion of people are left with CKD.
What are the 3 phases of ATN?
- Oligouric Phase
- Kidneys produce less than 500ml of urine/day. Patients in this phase are vulnerable to fluid overload + electrolyte imbalance especially potassium. Creatinine levels usually rise quite rapidly during this phase - Maintenance Phase
- The patient is no longer oligouric and this increased urinary output helps maintain fluid + electrolyte balance. Creatinine levels are usually stable or rise very slowly - Polyuric Recovery Phase
- Kidneys produce large quantities of dilute urine, so large that patients can become hypovolemic and unwell. Number of causes for this phase but one explanation is that the distal tubules and collecting ducts recover last and in particular their aquaporin channels. These damaged aquaporin channels don’t allow water to be reabsorbed and thus high quantities of dilute urine are produced. Patients are also susceptible to electrolyte loss (i.e. hypokalemia) in this phase. Creatinine levels fall swiftly.
What is creatinine a marker of?
Glomerular filtration + levels rise in the blood when the kidney is damaged
GFR is proportional to 1/Creatinine
** Creatinine is the favoured marker of pre-renal failure compared to urea
What is the difference between urea and creatinine?
Urea:
- Derived from proteins, amino acids, ammonia
- Liver converts ammonia -> urea
- Urea excreted via kidneys or the GI tract
..Kidney tubules re-absorb some urea back into blood
..Rumen + colon = site where urea recycling can occur
Creatinine:
- Muscle breakdown product (not muscle breakdown marker tho - that’s creatine kinase - CK)
- Freely filtered into urine from kidney
What ions are absorbed at different portions in the nephron?
PCT (65% of absorption happens here)
- NA+, amino acids, glucose, H20 absorbed
Loop of Henle
- Descending Limb
- NO ions are reabsorbed, just H20 via passive transport - Ascending Limb
- NA+, Cl-, K+ absorbed but NO H2O via active transport
DCT:
- NA+, Cl- absorbed
Collecting Tubule:
- Urea reabsorbed to maintain osmolarity in medulla to drive H2O reabsorption in the Loop of Henle (urea recycling)