Urinary Session 7 Flashcards
What can cause obstruction of the renal tract and increase the risk of developing a UTI?
BPH Pregnancy Uterine prolapse Stones Tumours
What is commonly seen as a cause of ascending infection in children with UTIs?
Ureteric reflux
What is ureteric reflux?
Abnormal or dysfunctional bladder valves, particularly seen in children
How should all children with a UTI be investigated?
Ultrasound
Which valves are likely to be involved in males and females with ureteric reflux?
Males: posterior urethral
Females: vesico-ureteric
What are bacterial factors which increase the likelihood of developing a UTI?
Fimbriae
K-antigen
Urease
Haemolysins
How does K-antigen allow a bacterium to cause a UTI?
Allows production of a polysaccharide capsule
How do haemolysins aid in the pathogenesis of UTI?
Damage host cell membranes and cause renal damage
Which two bacterial factors do G-ve UTI causative agents utilise to cause infection?
K-antigen
Haemolysins
What are coliforms?
G-ve, non spore forming bacilli that can ferment lactose
How do the majority of UTIs develop?
Transmission of coliforms across the perineum
What is secreted in between episodes of bladder voiding in order to reduce the risk of UTI?
Antibacterial secretions
After coliforms, what is a common causative agent of UTI in young women and hospitalised pts?
Coagulase -ve staph
What demonstrates irritation of the bladder in lower UTI?
Frequency and dysuria +/- low grade fever and urgency with a typical burning sensation
How does acute polynephritis present?
Fever, loin pain or pain in renal angle +/- dysuria and frequency
How can bacteraemia lead to acute polynephritis?
Becomes localised by filtration in the glomerular tuft
When is asymptomatic UTI significant and why?
In the mother during pregnancy –> premature birth
Can UTI progress to septicaemia +/- shock?
Yes, large cause of G-ve septicaemia in secondary care
Who fits into the uncomplicated UTI group?
Healthy women of child-bearing age
How are UTIs diagnosed in the uncomplicated UTI group?
Clinical diagnosis + dipstick
Who fits into the complicated UTI group?
Females of non-child bearing age
Males
Pregnant females
Pts who have failed to respond to UTI Tx
How are UTIs diagnosed in the complicated UTI group?
Dipstick and culture
What host factors promote the development of a UTI?
Shorter urethra in females
Obstruction
Neurological problems
Ureteric reflux
How can urine specimens be collected in diagnosis of UTI?
Mid stream urine (MSU) Clean catch (children) Collection bags Catheter sample Supra-pubic aspiration
Why do MSU samples have to be taken mid-stream?
So the first void can wash out flora
How are urine samples transported to the lab and why are these methods used?
@ 4 degrees Celsius to represent having just left bladder
+/- boric acid to preserve and restrict multiplication so a falsely raised pathogen count is not detected
What causes turbidity of urine to change in UTI?
WBC response to pathogen
Is using turbidity if urine to identify UTIs a good investigation to use?
Yes, it has high sensitivity so will identify +vex if you know there is an infection somewhere but you don’t know where
What is measured in dipstick testing?
Leucocyte esterase
Nitrite
Haematuria
Proteinuria
What do high levels of nitrite on a urine dipstick indicate?
Bacterial metabolism of urea
Which components of the urine dipstick test are good indicators for infection but do not specify the reason for WBCs in the urine?
Leucocyte esterase
Nitrite
Why do the haematuria and proteinuria components of a urine dipstick have low specifity?
There are a range of causes for both
When will microscopy be used to examine a urine sample?
Kidney disease
Suspected endocarditis
Children
What is examined during microscopy of a urine sample?
WBCs
RBCs
Bacteria
Casts
What are seen on microscopy of contaminated urine samples?
Squames
What is carried out if microscopy of a urine sample is +ve?
Culture
What can cause a non-significant culture following a +ve microscopy investigation for UTI?
Abx treatment for another infection e.g. URTI Urethritis Vaginal infection TB Appendicitis
59% of adult women with a UTI have urethral syndrome. What can cause this?
Low count bacteriuria Fastidious organisms Vaginal infection/inflammation STIs --> urethritis Mechanical/physical/chemical e.g. Soaps
Why are only symptomatic catheterised pts treated for UTI?
They will always have a level of bacteriuria
What is the treatment for an uncomplicated UTI?
3-day trimethoprim/nitrofurantoin
What is the treatment for a complicated UTI?
7-day trimethoprim/nitrofurantoin with follow up for clearance of S/S and bacteriuria
What is the treatment for pyelonephritis and septicaemia due to UTI?
14-day ciprofloxacin/cefuroxime of IV gentamicin if necessary
What prophylactic treatment can be used for pts who experience 3 or more episodes of UTI per year?
Single nightly dose of trimethoprim/nitrofurantoin
Why is amoxicillin not used to treat complicated UTI?
Has 50% resistance
What general management strategies can be used for all UTIs?
Ensure voiding mechanism is correctly functioning
Stay hydrated
What is diuresis?
Increased formation of urine by the kidney
What is the symptom of diuresis?
Polyuria= >3l per day urine output
What is a diuretic?
A substance/drug that promotes a diuresis by increasing renal excretion of water and sodium (increased fraction excretion) and thus reducing ECF volume
What do diuretics that block sodium reabsorption by acting on ENaC also decrease?
K+ secretion
How can diuretics have a direct action on cells in the nephron?
Via secretion into the lumen of PCT –> flow downstream and directly bind to transporters
How do aldosterone antagonists work as diuretics?
Competitively inhibit aldosterone action therefore decrease ENaC sodium reabsorption and K+ sparing
How do osmotic diuretics work?
Modify filtrate content so small molecules are filtered by not reabsorbed and hence increase the osmolarity of filtrate
Are osmotic diuretics currently used clinically?
No
How does inhibiting carbonic anhydrase act as a diuretic?
Prevents CA activity on brush border of PCT therefore altering Na+ and HCO3- reabsorption
Are carbonic anhydrase inhibitors currently used clinically as diuretics?
No
Which drugs can be classified as K+ sparing diuretics?
Inhibitors of renal sodium channels - Amiloride
Aldosterone antagonists - Spironolactone
Why are loop diuretics very potent diuretics?
25-30% of filtered Na+ is reabsorbed in the loop of Henle and segments distal to this have limited capacity to reabsorb sodium resultant increase in sodium and water
Which diuretics act on the filtration barrier?
Osmotic diuretics
Which diuretics act on the PCT?
CA inhibitors
Where in the loop of Henle do loop diuretics act?
Thick ascending limb
What does the efficacy of CA inhibitors for diuresis in the PCT depend on?
HCO3- filtration, a lower lumen +ve potential causes decreased cation reabsorption
Where do thiazides act on the nephron to cause diuresis?
Distal tubule
What ion movements do thiazides cause?
Increases sodium loss and increases calcium reabsorption
Where do potassium sparing diuretics act in the nephron?
Collecting duct
Why are loop diuretics used to treat heart failure?
Due to diuretic, vaso- and venodilation effects to decrease after and preload
When are loop diuretics used to treat fluid retention and oedema?
In nephrotic syndrome, renal failure and cirrhosis of the liver if Spironolactone is not sufficient
How are loop diuretics used in the management of hypercalcaemia?
Furosemide and IV fluids are given to prevent dehydration
What is the clinical application of thiazide diuretics?
Used to treat hypertension due to vasodilation effects
Why are thiazide diuretics not used in renal failure?
Lack potency
What is a possible side effect of thiazide treatment?
Erectile dysfunction
What are the clinical applications of aldosterone antagonists?
Primary hyperaldosteronism
Ascites and oedema in cirrhosis
Survival benefit in chronic heart failure
Additional Tx for hypertension not controlled by ACEI, CCB and thiazide
What is the clinical application of ENaC blockers?
Used with loop diuretics/thiazide to minimise potassium loss
What is the clinical application of CA inhibitors?
Used in glaucoma to decrease aqueous humour in the eye
What is a possible side effect of carbonic anhydrase inhibitors?
Can cause metabolic acidosis due to decreased HCO3-
What is the clinical application of osmotic diuretics?
IV mannitol in cerebral oedema to increase plasma osmolarity
What is the pathogensis of nephrotic syndrome which leads to a condition requiring diuretic Tx?
Glomerular disease –> increase in GbM permeability –> proteins lost in urine –> decreased plasma albumin which liver cannot compensate –> decreased plasma p(oncotic) –> peripheral oedema –> decreased circulating volume –> RAAS stimulation –> ECF expansion
How does cirrhosis of the liver lead to a condition requiring diuretic Tx?
Decreased albumin synthesis –> RAAS stimulation –> ECF expansion
Portal hypertension –> increased p(venous) in GI –> decreased an
p(oncotic) –> transudation from peritoneal capillaries to cavity –> ascites
Why is Spironolactone Tx preferred for cirrhosis of the liver?
Does not cause hypokalaemia
Why can Spironolactone Tx lead to gynaecomastia?
Oestrogen-like molecule
How are the different adverse effects of diuretics monitored?
K+ disturbances - monitor electrolytes
Hypovolaemia - monitor weight and postural BP
Hyponatraemia - monitor electrolytes
What are the possible adverse effects shared by loop and thiazide diuretics?
Increased uric acid levels due to competition of transporters –> gout
Glucose intolerance due to insulin release interference
Raised LDL levels
How can cirrhosis of the liver lead to hepatic encephalopathy?
Liver cannot detoxify ammonia –> increased levels in blood
How does hepatic encephalopathy present?
Constructional apraxia (can’t draw a star) –> flapping tremors –> confusion –> coma
What creates a favourable lumen -ve potential for passive K+ secretion in the DCT and CD?
Rate of sodium reabsorption
How can loop and thiazide diuretics cause hypokalaemia?
Block sodium and water reabsorption in loop/early DT –> increased delivery to distal parts –> faster washing away of secreted K+ and increased reabsorption of sodium by principal cells creating favourable gradient –> more K+ in urine
How does the effect of diuretics on the RAAS lead to hypokalaemia?
Decrease ECF –> RAAS activation –> increased aldosterone –> increased sodium reabsorption and K+ secretion
How can diuretics lead to hyperkalaemia?
Aldosterone antagonists decrease activity of Na-K-ATPase and ENaC –> less sodium reabsorption –> less K+ secretion
ENaC inhibitors cause less sodium reabsorption –> less K+ secretion
What management strategies can be used to when choosing diuretics to minimise K+ changes whilst maintaining diuretic action?
Loop/thiazide with K+ sparing diuretic
Loop/thiazide with K+ supplement
What other substances not used for Tx have diuretic action?
Alcohol
Coffee
Lithium
Demeclocycline
How does alcohol act as a diuretic?
Inhibits ADH release
How does coffee act as a diuretic?
Increases GFR –> decreases tubular sodium reabsorption
How do lithium and demeclocycline act as diuretics?
Inhibit ADH action on CD
Which substances with diuretic action but are not Tx have pure water effects by changing osmolarity, not volume?
Alcohol
Lithium
Explain how some named diseases can cause diuresis.
DM: glucose in filtrate –> osmotic diuresis
DI (cranial): decreased ADH release –> high pure water loss
DI (neohrogenic): poor CD ADH repsonse –> high pure water loss
Psychogenic polysdipsia: high fluid intake
Give an example of each type of diuretic with the following mechanism of action: direct action on cells, aldosterone antagonists, osmotic diuretics, CA inhibitor.
Bendroflumethiazide
Spironolactone
Mannitol
Acetazolamide
