Genitourinary Flashcards
(432 cards)
Define Nephrolithiasis
Renal stones, or nephrolithiasis, is the presence of stones, or calculi, within the urinary system.
Epidemiology of Renal stones
- Typically occurs in 30-60 year olds
- M>F
- More than 50% lifetime risk of recurrence once you’ve had them
RF for renal stones
- Dehydration
- Previous kidney stone
- Stone-forming foods: chocolate, rhubarb, spinach, tea, and most nuts are high in oxalate, and colas are high in phosphate
- Genetic: cystinuria (Dent’s disease; cysteine stones), renal tubular acidosis (calcium phosphate stones)
- Systemic disease: Crohn’s disease (calcium oxalate stones)
- Metabolic:hypercalcaemia, hyperparathyroidism, hypercalciuria (calcium stones)
- Kidney disease-related: medullary sponge kidney, AD polycystic kidney disease
-
Anatomical abnormalities that predispose to stone formation e.g. duplex,
obstruction or trauma - Drugs: loop diuretics and acetazolamide can cause calcium stones; protease inhibitors (HIV medication) cause radiolucent stones
- Exposure: cadmium or beryllium
- Other: gout and ileostomies (uric acid stones)
- Family history
Pathophysiology of renal stones
Kidney stones form when solutes in the urine precipitate out and crystalise. These most commonly form in the kidneys themselves, but they can also form in the ureters, the bladder, or the urethra.
Urine is a combination of solutes and water (the solvent). If levels of the solvent is low (dehydration) or levels of the solute is high causing supersaturated urine. The solutes can precipitate and form a nidus. More solutes can precipitate around this nidus, forming a kidney stone.
Substances like magnesium and citrate inhibit crystal growth and aggregation, preventing kidney stones from forming.
Composition of renal stones and risk factors:
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Calcium oxalate: most common. Results in a black or dark brown coloured stone that is radio-opaque on an x-ray (shows up as white spot on x-ray). More likely to form in acidic urine.
- Risk factors: hypercalcaemia (due to increased Ca2+ absorption or hyperparathyroidism), hypercalciuria (impaired reabsorption in kidney), hyperoxaluria (due to genetic defect, defect in liver metabolism, increased intestinal resorption due to GI disease e.g. Crohn’s, or diet heavy in oxalate e.g. rhubarb, spinach, chocolate, nuts)
-
Calcium phosphate: dirty white in color and also radiopaque on an X-ray. More likely to form in alkaline urine.
- Risk factors: hypercalcaemia (due to increased Ca2+ absorption or hyperparathyroidism), hypercalciuria (impaired reabsorption in kidney)
-
Uric acid: red-brown in color and radiolucent under an x-ray.
- Risk factors: food high in purines e.g. shellfish, anchovies, red meat or organ meat, as uric acid is a breakdown product of purine
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Struvite: infection stones which are a composite mix of magnesium, ammonium, and phosphate. These form when bacteria e.g. Proteus mirabilis, Proteus vulgaris, and Morganella morganii use the enzyme, urease, to split urea into ammonia and carbon dioxide. The ammonia makes the urine more alkaline and favors precipitation of magnesium, ammonium, and phosphate into jagged crystals called “staghorns.” The stones are dirty white and usually radiopaque under an X-ray
- Risk factors: urinary tract infections, vesicoureteral reflux and obstructive uropathies
- Cystine stones: amino acid cysteine which sometimes leaks into the urine to crystalise and form a yellow or light pink colored stone that is radiolucent under X-ray.
- Xanthine: just like uric acid stones, they are a byproduct of purine breakdown. Red-brown in color and radiolucent under an X-ray.
Renal stone present with severe loin-to-groin pain. The characteristic renal colic pain is due to the peristaltic action of the collecting system against the stone. It is caused by the dilation, stretching, and spasm caused by obstruction of the ureter, and is typically worse at the ureteropelvic junction and down the ureter, and subsides once the stone gets to the bladder.
Signs of renal stones
- Flank or renal-angle tenderness
- Fever
- Hypotension and tachycardia: may indicate urosepsis / a septic stone
Symptoms of renal stones
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Acute, severe flank pain (renal colic)
- Classically ‘loin to groin’ pain
- Pain lasts minutes to hours and occurs in spasms (with intervals of no pain or dull ache)
- Fluctuating in severity as the stone moves and settles
- Nausea and vomiting
- Urinary urgency or frequency
- Haematuria: microsopic or macroscopic
- May present with oliguria
- Fever: suggests a septic stone or pyelonephritis
Primary investigations for renal stones
- Primary investigations
- Focused history and examination
- Urinalysis:microscopic haematuria +/- pyuria (high WCC in urine) if pyelonephritis present; culture if septic stone
- Inflammatory markers:elevated WBCs and CRP may suggest superimposed infection
- U&Es: raised creatinine suggests AKI due to obstruction
- Bone profile and urate: elevated calcium may suggest hyperparathyroidism as aetiology
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Non-contrast CT kidney, ureter, bladder (CT KUB): high sensitivity (97%) and specificity (95%) for ureteric stones
- Considered thegold standard; to be performed within14 hoursof admission**
- If the patient is septic, has one kidney, or the diagnosis is unclear, perform a CT KUBimmediately
- Indinavir-induced renal stonesare not visualised on non-contrast CT KUB and require acontrast-enhanced CT(CT urogram)
Other investigations for renal stones
- X-ray KUB:a renal tract ultrasound and/or X-ray KUB may suffice if a known stone former, particularly if a CT KUB has been performed in the last 3 months
- Renal tract ultrasound:considered if radiation needs to be avoided e.g. pregnancy and children; 40% sensitivity and 90% specificity
- 24-hour urine monitoring:assess for pH, sodium, uric acid, calcium, and other solutes.Not usually performed in the acute setting but may help evaluate stone aetiology
- Blood cultures: if temperature >38°C or features of sepsis
- Coagulation profile: if percutaneous intervention is planned
Differentials for renal stones
- Ruptured abdominal aortic aneurysm
- Appendicitis
- Ectopic pregnancy
- Ovarian cyst
- Bowel obstruction
- Diverticulitis
Acute management for renal stones
- IV fluids and anti-emetics
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Analgesia: an NSAID by any route is considered first-line;
- PR diclofenac is commonly used in clinical practice but the increased risk of cardiovascular events should be considered (e.g. diclofenac, ibuprofen)
- IV paracetamol is used if NSAIDs are contraindicated or ineffective
- Antibiotics: if infection is present
Conservative/medical management for renal stones
- Watchful waiting: stones <5mm should pass spontaneously and followed up in clinic
- Medical expulsive therapy (MET):Alpha-blocker, e.g.tamsulosin, for ureteric stones 5-10mm to help passage. Not indicated for renal stones.
Surgical management for renal stones
Depends on the size, location, and characteristic of the stone
- Ureteroscopy (URS): pass a ureteroscope through the urethra and bladder up to the ureter (retrograde) and retrieve the stone or fragment it with intracorporeal lithotripsy
- Extracorporeal shock wave lithotripsy (ESWL): utilises high energy sound waves to break the stone into tiny fragments; uncomfortable, requires analgesia and can cause organ injury. Contraindicated in pregnancy due to risk to the foetus (perform URS instead)
- Percutaneous nephrolithotomy (PCNL): accessing the renal collecting system percutaneously via a surgical incision in the back for intracorporeal lithotripsy or stone fragmentation
- Ureteral stenting: insertion of a plastic tube to assist drainage under ureteroscopic guidance; stents can be left in place for 4 weeks
- Percutaneous nephrostomy: insertion of a rubber tube into the kidney via the skin to drain urine and decompress the urinary tract (usually under local anaesthetic)
- Open surgery
Advice for recurrent stones
- Increase oral fluids
- Reduce dietary salt intake
- Reduce intake of oxalate-rich foods for calcium stones (e.g. spinach, nuts, rhubarb, tea)
- Reduce intake of urate- rich foods for uric acid stones (e.g. kidney, liver, sardines)
- Limit dietary protein
Summary of kidney stones management
Ureteric:
Smaller than 5mm - Watchful waiting
5-10mm - Medical expulsive therapy: ESWL then URS
10mm or larger - URS then ESWL
Kidney stones:
Smaller than 5mm - watchful waiting
5-10mm - ESWL then URS
10-20mm - URS or ESWL then PCNL
20mm or bigger - PCNL then URS
Septic stone - Antibiotics and ureteric stenting OR Antibiotics and percutaneous nephrostomy (both options equally effective)
Complications of renal stones
Urological:
Obstruction and hydronephrosis: acute kidney injury and renal failure
Urosepsis: an infected, obstructing stone is a urological emergency and requires urgent decompression
Procedure-related:
Ureteric injury
Bleeding
Sepsis
ESWL haematoma
Prognosis for renal stones
50% of first-time stone formers experience recurrence at 5 years and 80% at 10 years. Recurrence is greater in patients that do not comply with lifestyle modifications, such as remaining well hydrated, reducing protein and salt intake, and weight loss.
Stones <5mm generally pass spontaneously within 4 weeks, but ensure all patients have adequate follow-up.
Define AKI
- Acute kidney injury (AKI) is defined as a sudden decline in renal function over hours or days.
- A decline in renal function can lead to dysregulation of fluid balance, acid-base homeostasis and electrolytes.
Epidemiology of AKI
- AKI is a common medical condition affecting up to 15% of emergency hospital admissions
- The mortality associated with severe AKI can be up to 30-40%
- Common in the elderly
RIFLE classification for AKI
- RIFLE describes three levels of renal dysfunction (RIF) and two outcome
measures (LE) - these criteria indicate an increasing degree of renal damage
and have a predictive value for mortality - Criteria:
- Risk
- Injury
- Failure
- Loss
- End-stage renal disease
KDIGO classification for AKI
Kidney Disease: Improving Global Outcomes’ (KDIGO) criteria defines AKI based on one of the following parameters:
- An increase in serum creatinine by ≥ 26.5 micromol/L within 48 hours
- An increase in serum creatinine to ≥ 1.5 times baseline within 7 days
- Urine output < 0.5 mL/kg/hr for six hours
Aetiology of pre renal AKI
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Hypoperfusion: due to hypovolaemia, may also be due to hypervolaemia e.g. reduced cardiac output due to cardiac failure or due to hypoalbuminaemia due to liver disease, systemic vasodilation e.g. sepsis, arteriolar changes e.g. secondary to ACE-inhibitor or NSAID use.
- Renal hypoperfusion causes ischaemia of the renal parenchyma. Prolonged ischaemia can lead to intrinsic damage.
Aetiology of intrinsic renal AKI
- Structural damage: to vasculature, glomerular or tubulo-interstitial
- Vascular: can be due to atherosclerotic disease, thromboembolic disease and dissections (e.g. aortic). Other important causes include renal artery abnormalities such as renal artery stenosis and renal artery thrombosis.Small vessel disease can occur secondary to vasculitides, thromboembolic disease, microangiopathic haemolytic anaemias (e.g. disseminated intravascular coagulation) and malignant hypertension.
- Glomerular: may be primary or secondary (associated to systemic disease). Can lead to nephritic or nephrotic syndrome.
- Tubulo-interstitial: usually due to acute tubular necrosis (ATN). Other tubulointerstitial causes include acute interstitial nephritis that can occur secondary to medications (e.g. NSAIDs, PPI’s, penicillins) and infections. This typically leads to damage to the renal parenchyma that can lead to scarring and fibrosis in the long-term.
Aetiology of Post renal AKI
Typically due to obstruction e.g. urinary stones (urolithiasis), malignancy (inc. intraluminal, intramural and extramural tumours), strictures and bladder neck obstruction (e.g. benign prostatic hyperplasia).
RF for AKI
- Age(> 65 years old)
- History of AKI
- CKD
- Poor fluid intake/ increased loss
- Urological historye.g. stones
- Cardiac failure
- Peripheral vascular disease
- Diabetes mellitus
- Sepsis
- Hypovolaemia
- Nephrotoxic drug use e.g. NSAIDS and ACE inhibitors
- Liver disease
- Cognitive impairment
- Contrast agents e.g. during CT