Renal & Urology Overview Flashcards
What are the functions of the kidney?
- regulation of blood pressure & volume via RAAS
- acid-base balance
- electrolyte balance
- production of new RBCs stimulated by Epo
- contains 1-alpha-hydroxylase, which is needed to produce the active form of vitamin D
- acts as a filter for the excretion of water-soluble waste products
How is the kidney involved in bone metabolism?
- the prohormone, 25(OH)D is produced in the liver
- the kidney contains 1-alpha-hydroxylase, which will hydroxylate the prohormone to produce the active hormone
- active vitamin D leads to increased calcium absorption in the gut and the bone
How is renal function measured?
renal function = flow rate from the glomerulus into the Bowman’s capsule
- this is the glomerular filtration rate (GFR)
- it is a measure of the volume of blood being filtered by the glomerulus each minute
- any value of GFR > 90 ml/min is considered normal
- this means that the glomerulus is filtering 90ml of blood each minute
- GFR typically reduces at a rate of 1 ml/min/year
What is the gold standard measurement of GFR?
- the only way that GFR can be measured is with inulin clearance
- inulin is freely filtered by the glomerulus, not secreted or reabsorbed in the tubules and is not synthesised or metabolised by the kidney
- calculations involve concentrations of inulin in the urine and serum
How can blood urea be used as an endogenous marker of GFR?
- urea is a by-product of protein metabolism that is freely filtered at the glomerulus
- it has variable reabsorption (30-60%) depending on nutritional state, hepatic function and GI bleeding
- e.g. GI bleed can raise serum urea
- raised serum urea can indicate poor kidney function
How can serum creatinine be used to estimate GFR (eGFR)?
What equation is used to work this out and what factors does it take into account?
- creatinine is derived from muscle cells, freely filtered at the glomerulus and not reabsorbed
- the Cockcroft-Gault equation is used to estimate creatinine clearance and eGFR
- this estimates how much creatinine is being cleared from the blood
- creatinine clearance is affected by age, sex, ethnicity and weight
- more creatinine is produced when there is more muscle mass
What would a normal urea : creatinine ratio be?
- urea is reabsorbed by the tubules, but creatinine is not
- normal urea to creatinine ratio is 40:1 to 100:1
- this ratio is used when looking at different types of kidney injury
What is the problem with the Cockroft-Gault equation?
- it is used to measure creatinine clearance as a measure of eGFR
- it often overestimates the true GFR, especially when < 30 ml/min
If both of these people have a serum creatinine of 100, why is it important to measure eGFR?
- creatinine clearance (eGFR) is important to measure when giving drugs that are renally cleared
- if the drugs are not being cleared sufficiently, it can lead to renal toxicity
500ml of 0.9% saline over 15 minutes
- this looks like a pre-renal AKI
- need to give an IV fluid bolus and maintenance fluids
-
hold nephrotoxic medications
- metformin
- NSAIDs
- ACE-inhibitors
What mnemonic can be used to remember the nephrotoxic drugs?
DAMN
- D - diuretics
- A - ACEi / ARBs
- M - metformin (can predispose to lactic acidosis)
- N - NSAIDs
What is meant by acute kidney injury?
Why does it occur and how is it measured?
- a rapid decline in renal function over hours to days
there is failure to maintain homeostasis of:
- fluid - leading to oliguria** or **volume overload
- electrolytes - leading to hyperkalaemia
- acid-base balance - leading to metabolic acidosis
- it is measured by looking at urea and creatinine
What are 2 easy ways to spot an AKI?
Is it reversible?
- the easiest way to recognise AKI is that the patient stops peeing
- look at creatinine** as this will be **acutely raised
- it is potentially reversible
What is meant by chronic kidney disease?
How is it diagnosed?
- this is a chronic and irreversible process with 5 stages
- there must be impaired renal function for > 3 months based on:
- abnormal structure or function
- or GFR < 60 ml/min for > 3 months
- +/- evidence of kidney damage
- this is progressive and irreversible, ending in end-stage renal failure
- it is monitored by looking at eGFR
What symptoms may someone with an AKI present with?
symptoms depend on underlying cause, but typically:
-
oliguria / anuria
- abrupt anuria suggests a post-renal cause
- nausea & vomiting
- dehydration
- shortness of breath
-
confusion
- encephalopathy from uraemia (build-up of urea in the brain)
What signs might someone with AKI present with?
- hypertension
-
distended bladder
- typically seen with an obstructive cause
- postural hypotension due to dehydration
- if they have fluid overload - raised JVP, peripheral / pulmonary oedema
- i.e. in cirrhosis, heart failure, nephrotic syndrome
- if they have vascular disease - bruising, rash, pallor
What classification system is used for AKI?
KDIGO classification system
- need to check the patient’s baseline creatinine to determine whether a rise is significant
Stage 1:
- 1.5x rise in creatinine compared to baseline
- OR urine output <0.5 ml/kg/hr for > 6 hours
Stage 2:
- 2x rise in creatinine compared to baseline
- OR urine output <0.5 ml/kg/hr for > 12 hours
Stage 3:
- 3x rise in creatinine compared to baseline
- OR urine output < 0.3 ml/kg/hr for > 24 hours
- OR anuria for > 12 hours
What are the risk factors for AKI?
What mnemonic can be used?
CHARD CH
- C - chronic kidney disease
- H - hypovolaemia
- this is the most common cause of AKI
- A - age > 75
- R - renal transplant
- D - diabetes
- C - contrast administration
- H - heart ailure
What is meant by a pre-renal cause of AKI?
What 4 states can lead to pre-renal AKI?
there is inadequate perfusion to the kidney
when there is decreased blood flow to the glomerulus, there is decreased blood filtration
- this is most commonly due to hypovolaemia
- systemic vasodilatation (e.g. in sepsis)
- decreased cardiac output
- intrarenal vasoconstriction
What is meant by renal and extrarenal losses leading to hypovolaemia and pre-renal AKI?
Renal loss:
- loss of fluid from diuretic overuse
- osmotic diuresis (e.g. diabetic ketoacidosis)
Extrarenal loss:
- vomiting and/or diarrhoea
- burns
- sweating
- blood loss
What can cause systemic vasodilatation or decreased cardiac output leading to pre-renal AKI?
Systemic vasodilatation:
- sepsis
- neurogenic shock
Decreased cardiac output:
- heart failure
- myocardial infarction
What can cause intra-renal vasoconstriction leading to pre-renal AKI?
- cardiorenal syndrome
- hepatorenal syndrome
- renal artery stenosis
What are the consequences of pre-renal AKI?
What will happen to the urea:creatinine ratio and why?
-
reduced urine output
- if there is no bloodflow to the kidney, urine cannot be produced
- urea is raised much higher than creatinine so urea:creatinine > 100:1
- this is due to dehydration and urea resabsorption by the kidneys
- urea is still being reabsorbed as the kidneys themselves are not damaged
What is involved in the inital management of pre-renal AKI?
What factors need to be monitored?
- start with NEWS monitoring and observe for life-threatening complication
- should be able to identify hyperkalaemia / hypovolaemia
- need to treat hypovolaemia
- catheterise the patient to monitor fluid balance
- need to monitor K+, lactate (for signs of sepsis) and daily creatinine
What is involved in investigations for pre-renal AKI?
Urine dipstick:
- proteinuria and/or haematuria could be a sign of glomerulonephritis
USS:
- should be performed within 24 hours unless there is an obvious cause
VBG:
- check electrolytes, glucose & lactate
- check platelets to rule out thrombotic cause like HUS or TTP
- if AKI does not improve, consider investigations for intrinsic renal disease
What is involved in the management of pre-renal AKI?
- bolus fluid and maintenance fluid
- treat the underlying cause e.g. sepsis
- stop nephrotoxic medications
-
stop / change medications that are heavily renally excreted
- e.g. LMWH
- if eGFR < 30 then use another form of prophylactic VTE
- avoid radiological contrast
Which class of antibiotics are known to be nephrotoxic?
aminoglycosides
(e.g. amikacin, gentamicin)
these can cause acute tubular necrosis
What causes a renal AKI?
What are the 4 different types?
- this is caused by cellular / intrinsic damage to the kidney
- the different types depend on where the damage is located
- tubular
- glomerular
- interstitial
- vascular
What is the main tubular cause of renal AKI?
What causes this?
acute tubular necrosis
- ischaemia
-
drugs
- NSAIDs
- paracetamol
- ACE inhibitors
-
toxins
- contrast
- myoglobulinuria in rhabdomyolysis
- these cause death of the tubular epithelial cells than form the renal tubules of the kidneys
How are the renal tubular epithelial cells damaged in acute tubular necrosis?
-
prolonged hypoperfusion state leading to ischaemia
- this can be due to pre-renal AKI from sepsis that has not been treated and has progressed
- systemic vasodilation - sepsis, DIC
- exogenous and endogenous nephrotoxic agents
How does acute tubular necrosis cause AKI?
- death of renal tubular epithelial cells leads to sloughing of these cells and obstruction of the tubules
- there is increased hydrostatic pressure within the tubules, which leads to reduced GFR
- there is reduced filtration / reabsorption
- this leads to reduced urine output
What are exogenous and endogenous nephrotoxins that can cause ATN?
Exogenous (drugs):
- aminoglycosides
- NSAIDs
- contrast media
- cisplatin
- calcineurin inhibitors
- amphotericin B
Endogenous:
- myoglobinaemia (rhabdomyolysis)
- haemoglobinuria
- uric acid crystals
- IgG light chains in myeloma
What urine findings would you expect to see in ATN?
- muddy brown granular casts of epithelial cells
- myoglobinuria and haemoglobinuria
What features of renal AKI would you expect to see in ATN?
How would urea : creatinine be affected?
- raised urea
- raised creatinine
- raised potassium
- metabolic acidosis
- in renal causes of AKI, urea : creatinine is < 40 : 1
- the kidney itself is not functioning, so urea cannot be reabsorbed
Hyperkalaemia is a complication of renal AKI.
What is involved in the management of this condition?
- medical emergency so escalate senior help and start ABCDE approach
- hyperkalaemia carries risk of cardiac arrhythmias + cardiac arrest
- continuous cardiac monitoring + baseline ECG + IV access
- stop any nephrotoxic drugs
- give 10ml 10% calcium gluconate** IV over **10 mins
- this protects the myocardium but onset is 4 hours
- give 100ml 20% dextrose** with **8U insulin** over **15 mins
- give 10-15mg nebulised salbutamol
- sodium bicarbonate 1.26% over 6 hours to correct acidosis
- monitor ECG changes
- (insulin and salbutamol both work to drive K+ back into cells and out of the blood)*
What ECG changes are associated with hyperkalaemia?
- tall tented T waves
- small / absent P waves
- broad QRS complex
- increased PR interval
- bradycardia
- VT
What is the main cause of glomerular renal AKI?
glomerulonephritis
- this is inflammation of the glomeruli and nephrons
- there are many different types of glomerulonephritis with different aetiologies
- e.g. postinfectious
How does glomerulonephritis show up on urine dipstick and BP?
- blood pressure can range from normal to malignant hypertension
- proteinuria and haematuria will be present on urine dipstick
What are the consequences of glomerular inflammation on renal function?
How do these present?
Loss of barrier function:
- when podocytes are damaged and the barrier is lost, there is loss of protein and blood
- proteinuria (mild to nephrotic syndrome)
- haematuria (mild to macrocytic)
Loss of filtering capacity:
- reduced excretion leads to accumulation of waste products and AKI
What is the interstitial cause of renal AKI?
interstitial nephritis
- this is caused by drugs, infection and infiltration
- it involves inflammation of the renal interstitium (fluid surrounding the renal tubules)
- there will be eosinophils in the urine
What are the vascular causes of renal AKI?
- this is caused by vessel obstruction
- thrombosis
- vasculitis
- haemolytic microangiopathy
In order to make urine, how many layers do the solutes have to pass through?
- blood enters glomerulus via an afferent arteriole
- within the glomerulus, solutes must then pass through the wall of the Bowman’s capsule
- endothelial cells
- glomerular basement membrane
- slit diaphragms of podocytes
- solutes (urea, electrolytes, waste products) are then within the urinary space
- they will then pass into the renal tubules that lead to the collecting ducts
What is meant by acute pyelonephrititis?
- inflammation of the renal pelvis of the kidney
- it is a form of upper urinary tract infection that is usually caused by bacteria
What is the difference between a lower and an upper urinary tract infection?
- a lower UTI affects the urethra and the bladder
- an upper UTI affects the ureters and the kidneys
- an upper UTI is usually caused by ascending infection
- bacteria begin by colonising the urethra / bladder and then make their way up the ureter to the kidney
What are the risk factors for an upper UTI?
the risk factors for upper UTI are very similar to those of a lower UTI
- female sex
- sexual intercourse
- indwelling catheter
- diabetes
- urinary tract obstruction
- vesicoureteral reflux (VUR)