Nephrology Flashcards
How can we divide up the causes of AKI?
Prerenal
Lack of blood flow to the kidneys
Intrarenal
Intrinsic damage to the glomeruli, renal tubules or interstitium
Postrenal
Obstruction to the urine coming from the kidneys
What findings can be expected in AKI?
Reduced urine output (<0.5ml/kg/hour is termed oliguria)
Fluid overload
Rise in molecules that the kidney normally excretes/maintains balance of, e.g. potassium, urea and creatinine
Symptoms of AKI
Reduced urine output
Pulmonary/peripheral oedema
Arrhythmias (due to potassium levels)
Uraemia features (pericarditis/encephalopathy)
What should we test in all AKI patients?
U+Es
Urinalysis
When should we do a renal ultrasound in AKI?
If there’s no identifiable cause for the deterioration OR are at risk of a urinary tract obstruction
What commonly used drugs should be stopped in AKI?
Metformin Lithium Digoxin NSAIDs Aminoglycosides ACEi Diuretics Angiotensin II receptor antagonists
How should we treat hyperkalaemia should it arise in AKI?
IV calcium gluconate Combined insulin/dextrose infusion Nebulised salbutamol Loop diuretics Calcium resonium Dialysis (last line)
Blood supply of the kidneys?
Renal arteries + veins
What is the normal blood urea nitrogen (BUN):creatinine ratio?
Causes of pre-renal AKI
Decreased bloodflow due to:
Absolute loss of fluid - Major haemorrhage Vomiting Diarrhoea Severe burns
Relative loss of fluid -
Distributive shock
Congestive heart failure (blood pools in the venous system)
Local to the kidney -
Renal artery stenosis
Embolus
What is azotemia?
High levels of nitrogen containing blood
What happens to the RAAS system during AKI?
Kidneys activate the RAAS, causing adrenal glands to secrete aldosterone which tells the kidneys to reabsorb sodium
Sodium reabsorption results in increased water reabsorption AND urea reabsorption
Is urine more concentrated in pre-renal AKI?
Yes. There is more urea relative to water than usual
What is the BUN:creatinine ratio in pre-renal AKI?
> 20:1
What is the most common cause of intrarenal AKI?
Acute tubular necrosis:
What are causes of acute tubular necrosis?
Ischaemia to the tubular cells Nephrotoxins: Aminoglycosides Heavy metals (e.g. lead) Myoglobin (from damaged muscle) Ethylene glycol (anti-freeze) Radiocontrast dye Uric acid (tumour lysis syndrome during cancer treatment)
How can you prevent uric acid causing tubular necrosis during cancer treatment?
Make sure they stay well hydrated
Give medications: allopurinol, urate oxidase
Trying to reduce the effects of tumour lysis syndrome
What happens to the tubule during acute tubular necrosis?
For whatever reason there is cell death. These cells then go into the tubule lumen and plug the tubule. This increases the pressure and makes it harder for fluid to flow down the tubules, reduced eGFR
What do you get a build up of in the blood during acute tubular necrosis resulting in AKI?
Acid (metabolic acidosis)
Hyperkalaemia
What might you find in the urine of someone with an acute tubular necrosis?
Brown grannular casts (these are the clumps of dead cells from the necrosis)
What is glomerulonephritis?
Inflammation of the glomerulus causing a reduction in eGFR. It is often caused by the deposition of antigen-antibody complexes in glomerular tissue
What do the antigen-antibody complexes activate in glomerulonephritis?
The complement system. This then attracts macrophages and neutrophils to the site. These release lysosomal enzymes which then damage podocytes in the glomerulus
Function of podocytes
They are negatively charged and have small gaps in between them. As a result larger molecules cannot get through.
What happens when podocytes are damaged (e.g. by lysosomal enzymes from neutrophils etc.)
They allow larger molecules to pass through (e.g. proteins and red cells)
Fluid leakage also reduces pressure difference which means lower GFR
This causes fluid build up and therefore oedema and HTN
Which condition affecting the interstitium can cause AKI?
Acute interstitial nephritis
Pathology of acute interstitial nephritis
Type I or type IV hypersensitivity reaction, usually in response to medications: NSAIDs, penicillins, diuretics.
These cause infiltration of immune cells (neutrophils, eosinophils) which cause inflammation of the interstium
Symptoms of acute interstitial nephritis?
Oliguria
Eosinophiluria
Fever
Rash
Complications of acute interstitial nephritis + cause?
If you don’t stop the medications causing interstitial nephritis, you can get renal papillary necrosis
Symptoms of renal papillary necrosis?
Haematuria
Flank pain
Causes of renal papillary necrosis?
Untreated acute interstitial nephritis
DM
Sickle cell disease
Pyelonephritis
What can cause obstruction to the outflow (postrenal AKI)?
Compression:
BPH
Intra-abdominal tumors
Blockage:
Kidney stones
Pathology of post-renal AKI?
Fluid backs up in post-renal AKI reducing the difference between the pressure between the tubule/glomerulus, thus reducing GFR
Longer-term effects of post-renal AKI?
Increased pressure in the renal tubule over time causes damage to the epithelial cells, reducing the amount of reabsorption of urea/sodium into the blood.
This then makes the urine higher in urea and thus the BUN:creatinine ratio falls
Damage to these epithelial cells also reduces the amount of water reabsorbed, and thus you start to produce less concentrated urine.
What are renal cysts?
Fluid filled sacs found in the kidney
How can we classify renal cysts?
Simple
Well-defined, homogenous features
Very common in older patients (50% prevalence over 50)
Complex
Complicated structures - thick walls, septations, calcification, heterogenous enhancement on imaging
Risk of malignancy
Risk factors for renal cysts?
Increasing age
Smoking
HTN
Male
What is polycystic kidney disease?
An autosomal dominant kidney caused by PKD1 or PKD2 genes. They result in individuals having multiple renal cysts
What is polycystic kidney disease associated with?
Berry aneurysm formation, leading to subarachnoid haemorrhage
Mitral valve disease
Liver cysts
Clinical features of renal cysts?
Usually asymptomatic
Can cause flank pain/haematuria if they rupture/become infected
Can also present with HTN/flank mass
What is the main differential of a renal cyst?
Renal cell carcinoma should be ruled out
How do we investigate renal cysts?
CT/MRI imaging both with and without IV contrast
What scoring system can we use for renal cysts?
Bosniak scoring system
Management of cysts?
If asymptomatic, no follow up required
Symptomatic simple renal cysts - simple analgesia +/- needle aspiration
Complex cyst - bosniak stage + continued surveillance/potential surgical intervention
Where do simple renal cysts originate from?
Renal tubule epithelium
Diagnostic criteria for autosomal dominant polycystic kidney disease?
US showing:
Two cysts (<30 y.o)
Two cysts in both kidneys (30-59 y.o)
Four cysts in both kidneys (aged >60)