227 - Acute Renal Failure Flashcards
If this marker is high it suggests a poor prognosis / high mortality in AKI
High serum creatinine
What criteria is used for rating severity of AKI?
RIFLE criteria
GFR/Cr, urine output
Affected by age, DM, high BP, CCF
What extra-renal systems does AKI affect?
Pulmonary (pul oedema, ARDS, Leukocyte invasion, heamorrhage)
CNS (inflam reaction, altered conscious level, acidosis + electrolyte imbalence - confusion, convulsions, coma)
Cardiac (electrolyte imbalance, uraemic toxins, acidosis.. sympathetic NS - increase Bp, pericarditis, arrhythmias, Mi)
The causes of AKI are split into what 3 domains?
Pre-renal
Intrinsic
Post-renal
Describe how pre-renal issues can cause AKI
GFR reduced ↓ , due to haemodynamic disterbances - so causes ↓ globerular filtration.
No cellular injury
IF you reverse haemodynamic factors - should revert to ok
List 4 pre-renal causes of AKI
Intravascular vol depletion
↓ effective blood volume (burns)
Altered intrarenal haemodynamics (dehydration, sepsis)
3rd space sequestration (bowel obstruction)
List 3 intrinsic causes of AKI
Acute tubular necrosis (85%)
Radiocontrast nephropathy
Acute tubulo-interstial nephritis
What can cause acute tubular necrosis?
50% due to ischaemia - ↓bp, sepsis, cardiopulmonary arrest, bypass
35% nephrotoxic - drugs (aminoglycosides, radiocontrast, ACEi, NSAIDS) or pigment (Rhabdomyolysis, heamolysis)
How long does acute tubular necrosis last for?
Recover in 1 week due to proliferation and differentiation
Mortality linked with number of other failed organs
When might you be at risk of radiocontrast nephropathy?
When you need IV or intra-arterially injected contrast (special CT scans)
Not oral contrast or MRI contrast
Why can contrast cause nephropathy?
Contrast is hypertonic, so can induce transient vasodilation then constriction - can cause renal ischaemia.
How can you prevent contrast nephropathy?
Give lots of fluid - before and during
Use low osmolality contrast
What are the features of acute tubulo-interstitial nephritis?
An allergic reaction (so high mast cells and eosinophils)
Drug induced or infection mediated
- Get fever, rash, arthralgia, eosinophila
What investigation can confirm acute tubulo-interstitial nephritis?
A biopsy - will show cellular infiltrates
What can cause post renal AKI?
An obstruction
- stone, necrosis, clot, TCC, stricture, fibrosis, tumour, aortic aneurysm
What are the features of urine in someone with post-renal AKI?
Dilute (can’t be concentrated as well)
Acidification is imparied - high blood acid and alkaline urine
What are 2 life threatening complications of AKI?
Metabolic acidosis
Hyperkaleamia
Describe metabolic acidosis in AKI
Can have a normal anion gap (bicarb is lost) or increased anion gap (acid is overproduced)
Get muscle weakness, altered mental state, kasmail breathing, high potassium and low BP
Describe how hyperkalemia occurs in AKI
When the pH of blood is low, H+ moves intracellularly
K+ moves out of cells to help keep the + balance
-> too much K+ in the blood
= muscle weakness, cardiac issues, big T waves (lots of pot lots of tea), wide QRS, bradycardia
How do you treat hyperkaleamia in AKI?
Treat cause
Give fluids
Correct acidosis
Protect heart - IV Ca Gluconate
Shift K+ back into cells - IV dextrose insulin
Reduce K+ absorption in GI tract - cation exchange resin
What is Rhabdomyolysis?
AKI caused by muscle necrosis releasing intracellular constituents. The AKI then causes electrolyte imbalance
How does Rhabdomyolysis cause AKI?
Haem pigment casts obstruct tubules - proximal tubular injury by heam iron
+ volume depetion due to swelling of damaged muscle
What are the signs and blood abnormalities of rhabdomyolysis?
Red/brown urine (as pigmented granular casts and supernatant in)
High serum enzymes - CK and LDH
Hifh K+, phosphate and uric acid
Low Ca (as goes to damaged muscles)
What could it mean if Ca was high in someone with known rhabdomyolysis?
They might be recovering, the excess Ca taken up by damaged muscles is released as it heals
What can cause rhabdomyolysis?
Trauma - crush, struggle, immobilisation, compression
Non-traumatic - marathon, hot weather, low K+, convulsions, low phosphate, alcohol, opiates, statins, cyclosporin, infections, DKA
How can you prevent rhabdomyolysis from occurring?
Fluid repletion
Forced alkaline diuresis - if you increase the pH of urine then less myoglobin precipitates with tamm-horsfall protein - reduces free radical release - better
Mannitol forced diuresis - osmotic diuretic. help flush out.
What is myeloma kidney?
A plasma disorder characterised by monoclonal immunoglobulin proliferation + marrow infiltration
Causes heam abnormalities - anaemia
Immune paresis
Renal injury
How does myeloma kidney lead to renal injury?
Light chain Ig can be filtered by glomeruli and reabsorbed by the PCT, but they can block it - obstruction - AKI
The light chain Igs also can bind to tamm-horsfall protein and precipitate into the tubules - obstruction and ? rupture - AKI
What signs are seen in myeloma kidney?
bone pain, weight loss, pallor, hyperviscosity - headaches, high BP, visual issues, convulsions
- Renal failure, anaemia, high calcium and low platlets
What is the 1st line investigation for myeloma kidney?
SPEP electrophoresis
- look at the gamma antibody peaks - will see an abnormal high peak
What investigations can be done to confirm myeloma kidney?
SPEP electrophoesis (1st line) immunofixation Free light chain assay Kidney biopsy Bone marrow biopsy? Xray - see punched out lesions
What are the treatment options for myeloma kidney?
You try to target each issue:
- cast nephropathy - IV fluid, plasma exchange, or reduce production - chemo + steroids
- hyperuricaemia - xanthine oxidase inhibitors, urate oxidase, fluid
- hypercalcaemia - fluid + bisphosphonates
- Hyper-viscosity - fluid, plasma exchange
Many drugs affect the kidneys. Which can cause damage by volume depletion?
Excessive laxatives
Loop diuretics (furosemide, benetanide)
NSAIDS
Many drugs affect the kidneys. Which can cause damage by altering renal haemodynamics?
ACE inhibitors
A2RBs (angiotensin II receptor blockers
- have vasodilator effects on efferent glomerular arterioles
Many drugs affect the kidneys. Which can cause damage by causing hypercalcaemia?
Calcium preparations
Vit D in a toxic dose
Many drugs affect the kidneys. Which can cause damage by hyperuricemia?
Chemo for bulky tumours
Many drugs affect the kidneys. Which can cause damage by causing hyperkalemia?
ACEi A2RBs Spironolactone amiloride (K+ sparing diuretic) NSAIDS
Many drugs affect the kidneys. Which can cause damage by causing hypokalemia?
loop diuretics Thiazide diuretics (bendroflumethiazide)
Many drugs affect the kidneys. Which can cause damage by increasing serum creatinine?
Trimethoprim
Cimetridine
- block Cr secretion
Many drugs affect the kidneys. Which can cause damage by irreversibly damaging the kidneys?
Aminoglycosides (gentamicin)
NSAIDS
Many drugs affect the kidneys. Which can cause damage by increasing CK - causing rhabdomyolysis?
Statins + Calcineurin inhibitors (cyclosporin)
Particularly together
Renal failure affects drug processing.
Which drug is affected by: volume depletion ?
Gentamicin - has a small vol of distribution, so if volume depletion, big effect
Renal failure affects drug processing.
Which drug is affected by: altered protein binding?
Phenytoin - more free drug becomes available as proteins it usually binds to (albumin) are reduced, or other things (eg. urea) bind competitively to them.
Renal failure affects drug processing.
Which drug is affected by: a reduction in drug metabolism?
Insulin - as kidney is place of phase I and II drug metabolism - so less broken down, increased serum conc
Renal failure affects drug processing.
Which drug is affected by: reduced elimination
Renally excreted drugs - morphine
Increased half life - give lower dose
Renal failure affects drug processing.
Which drug is affected by: uraemia
uraemia alters bodys response to drugs
- increases sensitivities to CNS acting drugs (benzos)
- increases GI bleed risk (NSAIDS)
- increases hyperkalamia risk (K sparing diuretics - amiloride)
Renal failure affects drug processing.
Which drug’s effect is lost?
Nitrofurantoin - needs to be excreted into the urinary tract to work.
What can be checked in a urinalysis?
Chemical content
Protein content
Formed elements (Cells, RBCs, Fat, Casts)
Crystals
How are casts formed in urine?
Formed in the DCT and collecting ducts by tubular microproteins (eg. tamm-horsfall)
What makes casts in urine abnormal?
When cells get trapped in the casts
- eg. RBC casts due to glomerulonephritis
- WBC casts - pyelonephritis or interstitial damage
- Fatty casts - nephrotic syndrome
Name 4 crystals that can be found in urine?
Calcium oxalate
Triple Phosphate
Uric Acid
Cystine
What shape are calcium oxalate crystals?
envelope
? stones present?
What shape are triple phosphate crystals? Why do you get them?
Coffin lid - rectangle.
in a UTI + alkaline urine
What do uric acid crystals suggest?
Gout, hyperuricaemia
What is GFR?
Glomerular filtration rate
use a substance with constant levels that is only excrete by glomerular filtration - eg. urea or creatinine
Does urea give an over or underestimation of GFR?
Underestimates - some reabsorbed
Does creatinine over or underestimate GFR?
Overestimates.
It is freely filtered, but tubular secretion is altered by drugs (eg. trimethoprim)
If high muscle mass, more creatinine
What is eGFR?
estimated glomerular filtration rate
Serum creatinine put into equation
adjusted for age, wt, gender, race
What is hyponatremia?
Serum Na
What signs can you get with hyponatremia?
Asymptomatic?
Nausea, confusion, headache, lethargy, convulsions, coma.
What investigation findings would you find in someone with hyponatremia?
Low serum osmolality (usually)
High urine osmolality
If volume deplete, urinary Na 40
What are the 3 groups causes of hyponatremia fit into?
High ADH state
Low ADH state
High plasma osmolality
What high ADH states can cause hyponatremia?
Hypovolaemia - diarrhoea, vomiting, thiazide diuretics
Hypervolaemia - heart failure, liver cirrhosis, SIADH, ecstacy, pregnancy
What LOW ADH states can cause hyponatremia?
renal failure
Polydipsia
Beer drinkers
What high osmolality states can cause hyponatremia?
renal failure
hyperglycaemia
mannitol therapy
pseudohyponatramia
How can you treat hyponatremia?
Treat cause!
fluid restriction and salt replacement
if severe: vasopressin receptor antagonist (tolvaptam), loop diuretics
What can occur if you correct hyponatremia too quickly?
Osmotic demyelination syndrome
2-3 days later - dysarthria, dysphagia, paraparesis, confusion, behavioural issues.
Where is prorenin produced?
Juxtaglomerular cells
Where is renin stored?
Juxtaglomerular cells
Where is angiotensin I produced?
liver + kidney
Where is ACE produced?
Lung
Where is aldosterone produced?
Adrenal cortex
What prompts the release of renin?
Low renal blood flow
Increased sympathetic tone
What does angiotensin II cause?
efferent renal arteriolar contraction
Peripheral vasoconstriction
What does aldosterone do?
Activates Na/K pump in DCT - increases Na and water reabsoption
