Acute Renal Injury Flashcards
What is the traditional definition of acute renal failure?
The rapid loss of glomerular filtration and tubular function over hours-days
What are the features of acute renal failure according to the traditional definition?
Retention of urea/creatinine due to a failure of homeostasis
Can be oliguric or non-oliguric
Potentially recoverable
What are the problems with the traditional definition of acute renal failure?
Lack of standardisation
Absolute creatinine, changes in creatinine, urine output and need for dialysis are not determined
Creatinine is an insensitive and late marker
RRT is a hard end-point but very late marker
There is a wide spectrum of renal injury
What are the features of acute renal failure according to the current definition (KDIGO)?
Increase in serum creatinine by ≥ 0.3 mg/dl (25.5mol/l) within 48 hours or
Increase in serum creatinine by ≥ 1.5 times the baseline, which is known or presumed to have occurred within the prior 7 days, or
Urine volume < 0.5 ml/kg/hour for 6 hours
In normal/increased risk stages of acute kidney injury outcome, what measures should be taken?
Preventative
Once damage and progression occur to the kidneys, what should the treatment strategy be focussed on?
Managing the disease
How many hospital admissions are complicated by acute kidney injury?
Between 1/7 and 1/5
What is the mortality in hospital with dialysis-requiring AKI? In what patients is the mortality worse?
45-75%
Worse in older patients and in those with multi-organ failure
What is the mortality in hospital of non-dialysis requiring AKI? (AKIN classification)
2% of people
8% with AKIN 1
25% with AKIN 2
33% with AKIN 3
What is the incidence of long-term renal replacement therapy (RRT) following AKI?
Around 20% at 90 days post-discharge of those who had RRT
5/100 per year with AKI
What is the incidence of long-term chronic kidney disease following AKI?
8/100 per year with AKI (both with and without dialysis)
What are pre-renal causes of AKI?
Drugs
- NSAIDs
- ACEIs/ARBS
- Beta-blockers
- Diuretics
- Immunosuppressants
Problems with the blood flow to the kidney
- Sepsis
- Hypovolaemia e.g. haemorrhage, burns
- Hepatorenal syndrome
- Congestive cardiac failure
- Hypotension
- Renal artery occlusion/vasoconstriction
What are renal causes of AKI?
Damage to renal parenchyma
- Acute tubular injury e.g. haemoglobinuria, rhabdomyolysis
- Tubulointerstitial injury
- Glomerulonephritis
- Myeloma
- Vasculitis
What are post-renal causes of AKI?
Obstruction to urine exit
- Kidney stones
- Prostatic hypertrophy
- Tumours
- Retroperitoneal fibroids
What can happen in pre-renal AKI?
There is reduced effective circulation volume due to volume depletion, hypotension, cardiac failure etc. and arterial occlusion
What can happen in renal AKI?
Acute tubular necrosis
Acute interstitial nephritis
Acute glomerulonephritis
Intra-renal vascular obstruction e.g. vasculitis, thrombotic microangiopathy
What can happen in post-renal AKI?
Obstruction
- Intraluminal e.g. calculus, clot
- Intramural e.g. malignancy, ureteric stricture
- Extramural e.g. malignancy
What is the most common cause of AKI?
Poor perfusion leading to established tubule damage
How does damage occur in pre-renal AKI?
There is failure of the circulation to provide sufficient plasma flow to maintain blood chemistry due to volume/pressure loss, and fluid imbalance occurs
What can pre-renal AKI lead to if sustained?
Intrinsic renal failure (acute tubular necrosis)
What is intrinsic renal failure exacerbated by?
Toxic injury e.g. drugs
What are the stages in the course of acute kidney injury?
Initiation
Maintenance
Recovery
What happens in initiation of AKI?
Exposure to toxic/ischaemic insult
Real parenchymal injury evolves
Potentially preventable
What happens in maintenance of AKI?
Established parenchymal injury
Usually maximally oliguric at this stage
Typical duration of 1-2 weeks (can be up to several months)
What happens in recovery of AKI?
Gradual increase in urine output
Fall in serum creatinine
If GFR recovers more quickly that tubular resorptive capacity excessive diuresis may result
What are potential sources of harm to the kidneys?
Drugs e.g. ACEI, NSAIDs
Toxins e.g. drugs, radiocontrast
Sepsis
Myeloma
What is radiocontrast nephropathy?
AKI following administration of iodinated contrast agent
What happens in radiocontrast nephropathy?
Usually transient renal dysfunction, resolving after 72 hours
May lead to permanent loss of function
What are small reductions in renal function associated with?
Significant increase in mortality
What are the risk factors for radiocontrast nephropathy?
Diabetes mellitus Renovascular disease Impaired renal function Paraprotein High volume of radiocontrast
What is myeloma?
Cancer arising from plasma cells - monoclonal proliferation of plasma cells producing an excess of immunoglobulins and light chains
Second most common haematological malignancy
What is the median age of diagnosis of myeloma and the median survival?
Median age of diagnosis - 68
Median survival - 5 years
What are the clinical features of multiple myeloma?
Anaemia Back pain Weight loss Fractures Infections Cord compression Markedly elevated ESR Hypercalcaemia
How is myeloma diagnosed?
Bone marrow aspiration (> 10% clonal plasma cells)
Serum paraprotein +/- immunoparesis
Urinary Bence-Jones protein
Skeletal survey
List the causes of AKI
Cardiac failure Haemorrhage Sepsis Vomiting and diarrhoea Prostate disease Tumours Stones Glomerulonephritis Vasculitis Radiocontrast Myeloma Rhabdomyolysis Drugs
What investigations are done for AKI?
U&Es Bicarbonate LFTs Bone scan FBC Clotting screen Blood gas ANCA Urine dipstick Urine PCR/ACR if indicated Renal biopsy Ultrasound X-ray
What are important features of the history when suspecting AKI?
PMH of systemic disease New rash, nose bleeds, sore eyes, joint pain Drug exposure Uraemic symptoms Timing of symptoms
What are some common complications of AKI?
Acidosis Electrolyte imbalance Intoxication Overload Uraemia complications
What is the management of AKI?
Remove or treat cause if possible
Pre-renal - consider fluid replacement, BP support
Renal - remove precipitant if possible
Post-renal - consider catheterisation
Volume resuscitation or fluid restriction (deplete vs overload) Treat sepsis Vasopressors Stop nephrotoxic drugs e.g. NSAIDs, ahminoglycosides Dopamine Furosemide Atrial natriuretic peptide IGF 1
What are the “five Rs for IV prescribing” in AKI?
Resuscitation Routing maintenance Replacement Redistribution Reassessment
What are some of the possible ECG changes in hyperkalaemia?
Peaked T waves Tall tented T waves Widened and flattened P wave Lengthened PR segment P waves eventually disappear Prolonged QRS interval
What is the treatment of hyperkalaemia?
Stabilise myocardium - calcium gluconate
Shift potassium intracellularly - salbutamol, insulin-dextrose
Remove - diuresis, dialysis, anion exchange resins
What indications for dialysis in AKI are particularly important?
Decreased HCO3-
Increased K+
Pulmonary oedema
Pericarditis
What is haemodialysis?
Solute removal by diffusion
Intermittent therapy with sessions lasting 3-5 hours
What is haemofiltration?
Solute removal by convection
Larger pore size
Continuous therapy
What concepts are important in dialysis?
Ultrafiltration
Diffusion
Osmosis
What is ultrafiltration?
Solution moves by pressure gradient, blood enters glomerulus at a high pressure
What are the advantages of haemodialysis?
Rapid solute removal
Rapid volume removal
Rapid correction of electrolyte disturbances
Efficient treatment of hypercatabolic patients
What are the disadvantages of haemodialysis?
Haemodynamic instability
Concern if dialysis is associated with hypotension - may prolong AKI
fluid removal only during short treatment time
What are the advantages of continuous renal replacement therapy?
Slow volume removal associated with greater haemodynamic stability
Absence of fluctuation in volume and solute control over time
Greater control over volume status
What are the disadvantages of continuous renal replacement therapy?
Need for continuous anticoagulation
May delay weaning/mobilisation
May not have an adequate clearance in hypercatabolic patients
What are the risk events for AKI?
Post-surgery Volume depletion Hypovolaemia Hypotension Rhabdomyolysis Radiocontrast Sepsis Toxins
What are patient-related AKI risk factors?
Age > 75 Previous AKI Heart failure Liver disease Chronic kidney disease Vascular disease Cognitive impairment Acutely unwell e.g. MI Co-morbidities e.g. diabetes mellitus
How can you reduce the risk from contrast?
Saline hydration
Sodium bicarbonate
N-acetyle cysteine
Osmolarity of radiocontrast
