Renal/urology Flashcards
Haemoglobinuria / myoglobinuria in UA
No RBCs on microscopy but dipstick pos for blood
Confirm with urine ammonium sulfate test - precipitates haemoglobin but not myoglobin
HUS pathophysiology
- Thrombotic microangiopathy
- Most commonly by Shiga toxin (esp E Coli aka typical HUS)
- Less commonly by activation of alternate complement pathway (aka atypical HUS)
Non AKI causes of creatinine variations
- Low in infants
- Low in kids with low muscle mass (DMD, spina bifida)
- High in muscular adolescents
- High in rhabdomyolysis
- Drugs - probenecid, cimetidine, trimethoprim (high Cr due to impaired secretion)
Fractional excretion of sodium (FENa)
= [(UNa x PCr) / UCr x PNa)] x 100
- Measures % Na excreted in urine
- Can’t be accurately interpreted in setting of diuretics (consider FE-Urea in that case - <30%=azotemia)
- If <1% -> due to prerenal azotaemia
- If >1% -> due to intrinsic causes of AKI
Total body water
70-80% term infants
60% at 1 yr
50% for females after puberty (M stay at 60%)
Osmolarity v osmolality
- Osmolarity - number of osmotically-active particles (osmoles) PER VOLUME of solute (Osm/L)
- Osmolality - number of osmoles PER WEIGHT of solution (Osm/kg)
- Normal serum osmolality ~280 mOsm/kg
ADH
- Secreted by posterior pituitary
- Acts on late distal tubule and CD to increase water permeability
- Regulated by (among others)
1) Osmoreceptors in hypothalamus
2) Volume (stretch) receptors in left atrium and blood vessels - Strongest stimulant = low volume aka hypovolaemia
Clinical clues to hypovolaemia
Tachycardia
Narrowed pulse pressure
Orthostatic hypotension
Orthostatic tachycardia (increase of 15-20 beats)
Prolonged CR
Resting tachycardia with hypotension
Low central venous pressure
Liddle syndrome
Primary Na retention (affects principal cells of distal tubule and CD)
-> low renin and aldosterone levels
-> HTN
-> hypokalaemia metabolic alkalosis
Bartter and Gitelman - common features
Severe Na+ losses -> hypovolaemia
-> Elevated renin/aldosterone levels
-> Hypokalaemia and alkalosis
Rarely hypertensive due to increased prostaglandin production causing vasodilation of renal arterioles
Bartter syndrome
- AR inheritance
- Abnormal solute transport in thick aLOH
- Lose Na, Cl, Ca and Mg in urine
- Similar labs to LOOP DIURETICs
- Type 4 is associated with deafness
- Sometimes presents with stones or nephrocalcinosis in neonatal period or early childhood due to Na wasting and hypercalciuria
Gitelman syndrome
- Defect in Na/Cl cotransporter in early distal tubule
- Similar labs to THIAZIDE DIURETICs, but also have severe Mg wasting
- Symptoms milder than Bartter
- Usually present later in life with muscle weakness, cramps, sapsms
Bartter v Gitelman
- Both cause hypokalaemic metabolic alkalosis & salt wasting WITHOUT HTN
- Bartter - affects aLOH, sometimes associated with deafness, HYPERcalciuria, NORMAL/LOW Mg, clinically = LOOP diuretics
- Gitelman - affects distal convoluted tubule, HYPOcalciuria, HYPOmagnesaemia, clinically = THIAZIDE diuretics
Thiazide diuretics - urinary Ca
DECREASES urinary Ca (can be used to treat kidney stones) and INCREASES serum Ca
Loop diuretics - affect on urinary Ca
INCREASES urinary Ca and DECREASES serum Ca (can be used to treat hypercalcaemia)
RTA type 1
Defective H+ SECRETION from DISTAL tubule
- Low K+, sometimes low Na
- Hypercalciuria
- +ve urinary anion gap (Na + K - Cl)
- AR and AD forms
RTA type II
Inability to reabsorb HCO3 in PROXIMAL tubule
- Low K+, normal Na+
- Normal urine Ca
Anion gap equation
Na - (HCO3 + Cl)
Causes of HAGMA - MUDPILES
Methanol
Ureamia
DKA
Propylene glycol
Iron/isoniazide/inborn error
Lactic acidosis
Ethylene glycol
Salicylates
PUV - overview
- Obstructing membranous folds within the lumen of the posterior urethra.
- Caused by disruption in the normal embryologic development of the male urethra.
- Most common cause of chronic renal disease due to urinary tract obstruction in children.
PUV - presentation
- Usually antenatal - bilateral hydronephrosis, dilated bladder, dilated posterior urethra
- Postnatal - newborn with UTI, abdo distension, resp distress (lung hypoplasia)
- Infant - FTT, urosepsis, poor urinary stream, straining while voiding
- Older - UTIs, day and night incontinence, voiding dysfunction
PUV - complications
- VUR
- Bladder dysfunction
- Increased risk of CKD
PUV - diagnosis
Micturating cystourethrogram (MCUG)
PUV - mgmt
- Urgent urology consult
- IDC (NGT, not balloon)
- Manage sepsis, UEC abnormalities, uraemia, acidemia, fluid imbalance
- Ablation