Med C - Renal Flashcards
What is AKI
Acute kidney injury (AKI) refers to a rapid drop in kidney function, diagnosed by measuring the serum creatinine. Acute kidney injury is most common in acutely unwell patients (e.g., infections or following surgery).
What are the NICE guidelines (2019) criteria for diagnosing an acute kidney injury are:
- Rise in creatinine of more than 25 micromol/L in 48 hours
- Rise in creatinine of more than 50% in 7 days
- Urine output of less than 0.5 ml/kg/hour over at least 6 hours
Risk factors that would predispose to developing acute kidney injury include
- Older age (e.g., above 65 years)
- Sepsis
- Chronic kidney disease
- Heart failure
- Diabetes
- Liver disease
- Cognitive impairment (leading to reduced fluid intake)
- Medications (e.g., NSAIDs, gentamicin, diuretics and ACE inhibitors)
- Radiocontrast agents (e.g., used during CT scans)
Causes of AKI
TOM TIP: Whenever someone asks you the causes of renal impairment, start with, “the causes are** pre-renal, renal or post-renal**”. This will impress them and allow you to think through the causes more logically.
**Pre-renal **
- Dehydration
- Shock (e.g., sepsis or acute blood loss)
- Heart failure
**Renal **
- Acute tubular necrosis
- Glomerulonephritis
- Acute interstitial nephritis
- Haemolytic uraemic syndrome
- Rhabdomyolysis
**Post-renal **
- Kidney stones
- Tumours (e.g., retroperitoneal, bladder or prostate)
- Strictures of the ureters or urethra
- Benign prostatic hyperplasia (benign enlarged prostate)
- Neurogenic bladder
What does pre renal, renal and post renal mean in AKI
- Pre-renal causes are the most common. Insufficient blood supply (hypoperfusion) to kidneys reduces the filtration of blood.
- Renal causes are due to intrinsic disease in the kidney.
- Post-renal causes involve obstruction to the outflow of urine away from the kidney, causing back-pressure into the kidney and reduced kidney function. This is called an obstructive uropathy.
What is Acute Tubular Necrosis
Acute tubular necrosis refers to damage and death (necrosis) of the epithelial cells of the renal tubules. It is the most common intrinsic cause of acute kidney injury
Acute Tubular Necrosis
Damage to the kidney cells occurs due to:
- Ischaemia due to hypoperfusion (e.g., dehydration, shock or heart failure)
- Nephrotoxins (e.g., gentamicin, radiocontrast agents or cisplatin)
________ _______ _______ on urinalysis confirm acute tubular necrosis. _________ _____ epithelial cells may also be seen.
Muddy brown casts on urinalysis confirm acute tubular necrosis. Renal tubular epithelial cells may also be seen.
Investigations for AKI
Urinalysis assesses for protein, blood, leucocytes, nitrites and glucose:
- Leucocytes and nitrites suggest infection
- Protein and blood suggest acute nephritis (but can be positive in infection)
- Glucose suggests diabetes
Ultrasound of the urinary tract assesses for obstruction when a post-renal cause is suspected.
Acute kidney injury is often preventable by:
- Avoiding nephrotoxic medications where appropriate
- Ensuring adequate fluid intake (including IV fluids if oral intake is inadequate)
- Additional fluids before and after radiocontrast agents
Treating an acute kidney injury involves reversing the underlying cause and supportive management, for example:
- IV fluids for dehydration and hypovolaemia
- Withhold medications that may worsen the condition (e.g., NSAIDs and ACE inhibitors)
- Withhold/adjust medications that may accumulate with reduced renal function (e.g., metformin and opiates)
- Relieve the obstruction in a post-renal AKI (e.g., insert a catheter in a patient with prostatic hyperplasia)
- Dialysis may be required in severe cases
- Input from a renal specialist
TRUE OR FALSE
ACE inhibitors are bad in AKI
FALSE
Calling ACE inhibitors nephrotoxic is incorrect. ACE inhibitors should be stopped in an acute kidney injury, as they reduce the filtration pressure. However, ACE inhibitors have a protective effect on the kidneys long-term. They are offered to certain patients with hypertension, diabetes and chronic kidney disease to protect the kidneys from further damage.
Complication of AKI
- Fluid overload, heart failure and pulmonary oedema
- Hyperkalaemia
- Metabolic acidosis
- Uraemia (high urea), which can lead to encephalopathy and pericarditis
What is CKD
Chronic kidney disease (CKD) describes a chronic reduction in kidney function sustained over three months. It tends to be permanent and progressive.
Kidney function naturally declines with age. Factors that can speed up the decline and cause CKD include:
- Diabetes
- Hypertension
- Medications (e.g., NSAIDs or lithium)
- Glomerulonephritis
- Polycystic kidney disease
Most patients with CKD are asymptomatic. Signs and symptoms as the renal function worsens may be non-specific:
- Fatigue
- Pallor (due to anaemia)
- Foamy urine (proteinuria)
- Nausea
- Loss of appetite
- Pruritus (itching)
- Oedema
- Hypertension
- Peripheral neuropathy
Investigations for CKD
- (eGFR)
- Proteinuria with a urine albumin:creatinine ratio (ACR).
- Haematuria with a urine dipstick or microscopy.
- Renal ultrasound helps identify obstructions
- Blood pressure (for hypertension)
- HbA1c (for diabetes)
- Lipid profile (for hypercholesterolaemia)
The __ ______ is based on the eGFR. The A score is based on the ___________ _______ ratio.
The G score is based on the eGFR. The A score is based on the albumin:creatinine ratio.
CKD
A diagnosis can be made when there are consistent results over three months of either:
- Estimated glomerular filtration rate (eGFR) is sustained below 60 mL/min/1.73 m2
- Urine albumin:creatinine ratio (ACR) is sustained above 3 mg/mmol
Whar is Accelerated progression in CKD
Accelerated progression is a sustained decline in the eGFR within one year of either 25% or 15 mL/min/1.73 m2.
Complications of CKD
- Anaemia
- Renal bone disease
- Cardiovascular disease
- Peripheral neuropathy
- End-stage kidney disease
- Dialysis-related complications
The _______ ______ ______ _______ can be used to estimate the 5-year risk of kidney failure requiring dialysis.
The Kidney Failure Risk Equation can be used to estimate the 5-year risk of kidney failure requiring dialysis.
The NICE clinical knowledge summaries (May 2023) suggest referral to a renal specialist when
- eGFR less than 30 mL/min/1.73 m2
- Urine ACR more than 70 mg/mmol
- Accelerated progression (a decrease in eGFR of 25% or 15 mL/min/1.73 m2 within 12 months)
- 5-year risk of requiring dialysis over 5%
- Uncontrolled hypertension despite four or more antihypertensives
CKD
Treating the underlying cause involves:
- Optimising diabetic control
- Optimising hypertension control
- Reducing or avoiding nephrotoxic drugs (where appropriate)
- Treating glomerulonephritis (where this is the cause)
BP targets for people with CKD
The blood pressure target is less than 130/80 in patients under 80 with CKD and an ACR above 70 mg/mmol.
Medications that help slow CKD disease progression are:
- ACE inhibitors (or angiotensin II receptor blockers)
- SGLT-2 inhibitors (specifically dapagliflozin)
Reducing the risk of CKD complications involves:
- Exercise, maintain a healthy weight and avoid smoking
- Atorvastatin 20mg for primary prevention of cardiovascular disease (in all patients with CKD)
Management of CKD complications involves:
- Oral sodium bicarbonate to treat metabolic acidosis
- Iron and erythropoietin to treat anaemia
- Vitamin D, low phosphate diet and phosphate binders to treat renal bone disease
Management of end-stage renal disease involves:
- Special dietary advice
- Dialysis
- Renal transplant
ACE inhibitors are offered to all CKD patients with:
- Diabetes plus a urine ACR above 3 mg/mmol
- Hypertension plus a urine ACR above 30 mg/mmol
- All patients with a urine ACR above 70 mg/mmol
The serum potassium needs close monitoring, as both CKD and ACE inhibitors can cause hyperkalaemia.
Which SGLT-2 Inhibitor is offered to CKD patients with Diabetes and a urine ACR above 30 mg/mmol
Dapagliflozin
Dapagliflozin is considered for patients with:
Dapagliflozin is considered for patients with:
- Diabetes plus a urine ACR or 3-30 mg/mmol
- Non-diabetics with an ACR of 22.6 mg/mmol or above
What is erythropoietin
a hormone that stimulates the production of red blood cells
CKD results in lower erythropoietin and a drop in red blood cell production. What disease does this cause?
CKD results in lower erythropoietin and a drop in red blood cell production.
It causes a** normocytic (normal sized) normochromic (normal colour) anaemia**.
Anaemia in Chronic Kidney Disease can be treated with?
erythropoiesis-stimulating agents, such as recombinant human erythropoietin. Blood transfusions can sensitise the immune system (allosensitization), increasing the risk of future transplant rejection.
BUT treat iron deficiency first
Renal bone disease is also known as chronic kidney disease-mineral and bone disorder (CKD-MBD). It involves:
- High serum phosphate
- Low vitamin D activity
- Low serum calcium
Reduced phosphate excretion by diseased kidneys results in ______ _____ _______
Reduced phosphate excretion by diseased kidneys results in **high serum phosphate. **
WHat is renal dialysis?
Dialysis is a method for performing the filtration tasks of the kidneys artificially. It is used in patients with end-stage renal failure or complications of acute kidney injury. It involves removing excess fluid, solutes and waste products.
What are the indications for renal dialysis
The “AEIOU” mnemonic can be used for the indications for short-term dialysis:
- A – Acidosis (severe and not responding to treatment)
- E – Electrolyte abnormalities (particularly treatment-resistant hyperkalaemia)
- I – Intoxication (overdose of certain medications)
- O – Oedema (severe and unresponsive pulmonary oedema)
- U – Uraemia symptoms such as seizures or reduced consciousness
- End-stage renal failure (CKD stage 5) is the main indication for long-term dialysis.
There are two options for dialysis in patients requiring it long-term:
Haemodialysis
Peritoneal dialysis
What is haemodialysis?
With haemodialysis, patients have their blood filtered by a haemodialysis machine. Regimes can vary, but a typical regime might be 4 hours a day, three days per week.
Blood is taken out of the body, passed through the dialysis machine, and pumped back into the body. The blood passes along a series of semipermeable membranes inside the dialysis machine. Solutes filter out of the blood, across the membrane and into a fluid called dialysate. The concentration gradient between the blood and the dialysate fluid causes water and solutes to diffuse out of the blood and across the membrane. Anticoagulation with citrate or heparin is necessary to prevent blood clotting in the machine and during the process.
Haemodialysis requires good access to an abundant blood supply. Two tubes are needed, one to remove the blood and one to put the blood back in. The options for longer-term access are:
Tunnelled cuffed catheter
Arteriovenous fistula
What are Tunnelled Cuffed Catheter
A tunnelled cuffed catheter is a tube inserted into the subclavian or jugular vein with a tip in the superior vena cava or right atrium. It has two lumens, one for blood exiting the body (usually red) and one for blood entering the body (usually blue). They can stay long-term and be used for regular haemodialysis.
A ________ cuff surrounds the Tunnelled Cuffed catheter. The cuff promotes healing and adhesion of tissue, making the catheter more permanent and providing a barrier to infection.
A Dacron cuff surrounds the catheter. The cuff promotes healing and adhesion of tissue, making the catheter more permanent and providing a barrier to infection
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What is the main complications of Tunnelled Cuffed Catheter
The main complications are infection and blood clots within the catheter.
What is Arteriovenous Fistula
An AV fistula is an artificial connection between an artery and a vein. It bypasses the capillary system and allows blood to flow under high pressure from the artery directly into the vein. This provides a permanent, large, easy-access blood vessel with high-pressure arterial blood flow. Creating an A-V fistula requires a surgical operation and a maturation period of 4-16 weeks before it can be used.
What are types of Arteriovenous Fistula
- Radiocephalic fistula at the wrist (radial artery to cephalic vein)
- Brachiocephalic fistula at the antecubital fossa (brachial artery to cephalic vein)
- Brachiobasilic fistula at the upper arm (less common and a more complex operation)
AV fistula features to examine in an OSCE are:
- Skin integrity
- Aneurysms
- Palpable thrill (a fine vibration felt over the anastomosis)
- A “machinery murmur” on auscultation over the fistula
Complications of AV fistula include:
Aneurysm
Infection
Thrombosis
Stenosis
STEAL syndrome
High-output heart failure
What is STEAL syndrome
occurs when there is inadequate blood flow to the limb distal to the fistula. The AV fistula “steals” blood from the rest of the limb. Blood is diverted away from the part of the limb it was supposed to supply, leading to ischaemia. Instead, it flows through the fistula and into the venous system.
