Renal and urology Flashcards
Define acute kidney injury (AKI)
Impairment of renal function over days or weeks, which often results in raised plasma urea/creatinine and oliguria (< 400 mL/day) and is usually reversible. The term acute kidney injury (AKI) represents the full spectrum of acute kidney dysfunction.
The resulting effects include impaired clearance and regulation of metabolic homeostasis, altered acid/base and electrolyte regulation, and impaired volume regulation.
Explain the aetiology / risk factors of acute kidney injury (AKI)
Risk factors:
Age >75, CKD, Cardiac failure, PVD, chronic liver disease, DM, drugs, sepsis, poor fluid intake/increased losses, urinary symptoms
Aetiology:
Commonest: ischaemia, sepsis and nephrotoxins (and prostatic disease)
- Pre-renal (40-70%)- reduced renal perfusion:
a. Hypovolaemic (acute haemorrhage, GI loss, renal loss (diuretics or osmotic diuresis), dermal loss (burns), sequestration of fluid (sepsis).
EXAMINATION: tachycardia, hypotension, reduced skin turgor, cold extremeties
b. Hypervolaemic, there is low effective circulating volume
(systolic heart failure–> cardiorenal syndrome, there are signs of HF; hypoalbuminaemia (decompensated liver disease)–> hepatorenal syndrome.
Renal artery obstruction- stenosis, embolism (see RAS below)
- Intrinsic renal (10-50%):
a. Tubular- acute tubular necrosis is most common cause of intrinsic renal AKI: ischaemia (from prerenal AKI), drugs (see below) and toxins (myoglobinuria in rhabdomyolysis), crystals (ethylene glycol poisoning, uric acid), and radiocontrast dye myeloma and raised Ca2+
b. Acute glomerulonephritis (see the condition)- autoimmune e.g SLE/HSP, drugs, infections, primary glomerulonephritides
c. Acute interstitial nephritis- drugs (see below), infiltration (lymphoma, infection, tumour lysis syndrome following chemo)
d. Small or large vessel osslusion: Renal artery/vein thrombosis, cholesterol emboli from angiography, vasculitis, malignant HTN, haemolytic microanipathy HUS/TTP, large vessel occlusion eg. dissection or thrombus
e. Other renal: Light chain (myeloma), urate (lympho- or myeloproliferative disorders, particaurlly after chemo/radiation induced cell lysis), pigment nephropathy (haemolysis/rhabdomyolysis, malaria), accelerated phase HTN (e.g. in pre-eclampsia)
3. Post renal (10-25%)- urinary tract occlusion. Most commonly due to BPH or prostate cancer in a male leading to frequent urination but slow urinary stream. Kidney stones stuck in ureter/urethra.
Luminal= stones, clots, sloughed papillae. Mural=malignancy, benign prostatic hyperplasia, strictures, blood clots, retroperitoneal fibrosis
Extrinsic compression=malignancy (esp. pelvic, prostate and bladder), retroperitoneal fibrosis
Summarise the epidemiology of acute kidney injury (AKI)
Epidemiology
Happens to 18% of hospital patients.
ATN counts for 45% of cases
Recognise the presenting symptoms of acute kidney injury (AKI)
(Rapid medicine:) Malaise, anorexia, nausea, vomiting, pruritus, drowsiness, convulsions, coma (caused by uraemia).
Recognise the signs of acute kidney injury (AKI) on physical examination
Palpable bladder, peripheral oedema, palpable kidneys (polycystic disease), abdo/pelvic masses, renal bruits, rashes
Identify appropriate investigations for acute kidney injury (AKI) and interpret the results
Outline the KDIGO staging for AKI
Blood: ABG, FBC, U&E (urea creatinine, Na+ and K+), LFT, ESR/CRP, Ca2+, clotting, culture, blood film: red cell fragmentation in HUS/TTP
Other BTs: CK (for rhabdomyolysis), urate, serum electrophoresis and autoantibodies
Urine: stick testing, haematuria, proteinuria (glomerulonephritis). Cukture and sensitivity, Bence-Jones protein (exclude myeloma.
Urine osmolality/Na+:
- Renal ARF: REDUCED urine osmolality (reduced urine concentrating ability), INCREASED urine Na+ (due to reduced resorptive ability), INCREASED fractional excretion of Na+ (PCr.UNa/PNa.UCr):>2%
- Pre-renal: i
Basic metabolic profile, ACR, urinalysis, urine culture, FBC, fractional excretion of sodium, fractional excretion of urea
KDIGO staging for AKI:
Stage 1: Increase serum creatinine 1.5x baseline in 48hr; urine output <0.5mL/kg/hr for >6 consec hours
Stage 2: Creatinine- increase 2-2.9 x baseline; urine output <0.5mL/kg/hr for >12 consec hours
Stage 3: Creatinine- increase >3 x baseline or commence RRT at any stage or urine output <0.3mL/kg/hr for >24hrs. Anuria (<100mLday)
Classified by whichever criteria puts them in the most severe stage of injury
Pre-renal AKI: bloods (urea and creatinine increased. Urea usually higher than creatinine) + urine (reduced urine outpout, reduced sodium and osmolalility)
Generate a management plan for acute kidney injury (AKI)
GENERAL:
Stop nephrotoxic drugs, stop metformin if creatinine greater than 150mmol/L
Aim for euvolaemia
Monitoring: aim for normal calorie intake (or more if catabolic, eg sepsis or burns) and protein 0.5g/kg/d. Consider nasogastric nutrition
Protect from hyperkalaemia by giving 10mL 10% calcium gluconate. IV insulin and dextrose to lower serum potassium if necessary, or salbutamol nebuliser, or IV sodium bicarb.
TREAT UNDERLYING CAUSE:
Pre-renal: correct hypovolaemia with fluids, sepsis with Abx
Post renal: catheterise and consider CTKUB… maybe cytoscopy and retrogade stends or nephrostomy
Instrinsic renal: refer to renal
RENAL REPLACEMENT THERAPY:
Haemodialysis (must be haemodynamically stable, and requires large-bore venous access e.g. internal jugular line. Usually done intermittently and good clearance of solutes)
Haemofiltration (often for ICU patients, much slower at clearing solutes, usually continuously performed)
Identify the possible complications of acute kidney injury (AKI) and its management
Hyperkalaemia, pulmonary oedema, uraemia (e.g. causing uraemic pericarditis - may require dialysis), acidaemia (may require dialysis)
Summarise the prognosis for patients with acute kidney injury (AKI)
Depends on early recognition and intervnetion
Can be as high as 80% mortality:
burns (80%), trauma/surgery (60%), medical illness (30%)
How do nephrotoxic drugs affect the kidney
Those causing acute tubular necrosis: paracetemol, aminoglycosides, amphotericin B, NSAIDs, ACEi and lithium
Those causing acute interstitial nephritis: NSAIDS, penicillins, thiazaide diuretics, sulphonamides, leptospirosis
How do burns affect the kidney
Reduce blood flow to them (even 20% of skin burns can do this)
Does BUN or creatinine increase more when GFR reduces, and why so?
BUN (=blood urea nitrogen)- because less is filtered AND because the filtrate moves more slowly though the PCT with reduced GFR, there is more time for BUN to be reabsorbed
Creatinine- only because less is filtered. Creatinine is not reabsorbed in the PCT, in fact it is actively secreted into the tubule in the DCT so the level of creatinine only increases due to reduced levels of filtration .
How can a BUN test be used to distinguish the cause of renal failure
In pre-renal renal failure, then the BUN will increase more than the creatinine (because BUN increases with reduced GFR due to less filtration and also more reabsorption, whereas creatinine just increases due to less filtration), so the BUN to creatinine ratio will INCREASE
In intrinsic renal failure, the BUN will only increase because less is being filtered out, NOT because it is being reabsorbed more. So the BUN will increase to the same extent as creatinine, so even though both values will increase, the ratio BUN: creatinine will stay the same.
Note that the normal BUN to creatinine ratio is between 10:1 and 20:1. Above this may mean there is not enough blood getting to the kidneys!
How can the urine osmolarity be useful to distinguish the cause of renal failure
In prerenal disease there is low perfusion of the kidneys resulting in reabsorption of Na+ and thus water, increasing the osmolarity of the kidneys (usually urine osmolairty above 500mOsm/kg suggests prerenal azotemia)
Typically, the Uosm in ATN is approximately 300 to 350 mOsm/kg, a value that is similar to the plasma osmolality (Posm) because the damaged tubules cannot reabsorb the Na+ and thus not absorb water. However, a Uosm of less than 500 mOsm/kg is often not diagnostically useful, because it can be seen in patients with ATN, prerenal disease, or underlying renal disease.
The SG of pre-renal renal failure also increases for this reason
Urine sodium concentration low in pre-renal failure too
Generally what factors can increase/decreased BUN and creatinine
Increase BUN: -Steroids, fever, GI bleeding, burns, Reduce BUN: -Liver failure Increase creatinine: -cimetidine and trimethoprim Reduce creatinine: -Having a small amount of muscle
What happens to sediment and FENa in pre-renal and renal AKI
Pre-renal: sediment -ve (unless progresses to ATN). FENa will be low because hardly any Na is excreted (kidney can reabsorb it), so usually <1%
Renal: sediment +ve due to dead cells. FENa higher because kidney cannot reabsorb the Na+, so usually >2%
What are the signs of ethylene glycol poisoning
confusion and dilated pupils
What might cause myoglobinuria
Recent crush injury
Signs in nephrotic syndrome and labs and somec causes
Signs: peripheral oedema, periorbital oedema, ascites
Labs: Proteinuria >3.5g/day Protein-to-creatinine ratio ?3g/g Hypoalbuminemia <3.5g/dL LDL >130mg/dL Triglyceride >150mg/dL. Lipiduria
Membranous nephropathy
Membranoproliferative glomerulonephritis
Signs in nephritic syndrome and labs and some causes
Signs: Arterial hypertension, peripheral edema
Labs:
Proteinuria 1-3g/day
5 dysmorphic RBCs/uL
Red cell casts
SLE Goodpastures disease (malaise, arthralgia, fever)
What is the most common cause of nephritic syndrome and how can it be investigated.
What are its signs
The most common cause of nephritic syndrome is poststreptococcal glomerulonephritis. It develops approximately 10 to 14 days after a group A beta-hemolytic streptococcal infection, most commonly of the upper respiratory tract but also of the skin.
Features of poststreptococcal glomerulonephritis include hematuria, edema, and hypertension. The condition is generally self-limited and resolves in a matter of weeks to months.
Anti-streptolysin O (ASO or ASLO) is the antibody made against streptolysin O, an immunogenic, oxygen-labile streptococcal hemolytic exotoxin produced by most strains of group A and many strains of groups C and G Streptococcus bacteria.
What are the signs of Immunoglobin A nephropathy
Immunoglobulin A nephropathy, or Berger’s disease, is the most common cause of glomerulonephritis worldwide (but note that the most common cause of nephritic syndrome is post-streptococcal glomerulonephritis) .
Asymptomatic, recurrent hematuria may occur 24~48hrs (not weeks, as in the case of ) following an upper respiratory infection or exercise.
Asymptomatic, recurrent hematuria may occur 24~48hrs (not weeks) following an upper respiratory infection or exercise. IgA levels may be elevated.
What is nephrotic syndrome
What constitutes proteinuria, and what about hypoalbuminaemia
A condition caused by damage to the glomeruli which makes them more permeable, and allows protein to escape.
The result is hypoalbuminaemia, proteinuria and peripheral and periorbital oedema
> 3.5g protein excreted per day
hypoalbuminaemia is <30g/L
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