Poor Urinary Output

Question 1

How much urine do normal adults produce per hour?

Answer 1

1 ml/kg/hour

Question 2

What urine output would be considered as oliguria?

Answer 2

< 0.5 ml/kg/hour

Question 3

What important condition can decreased urine output be the first sign of?

Answer 3

Impending acute renal failure

Question 4

What are the major complications of AKI that could be fatal?

Answer 4

Hyperkalaemia
Acidosis
Uraemia
Pulmonary oedema

Question 5

What are the three main requirements for normal renal function?

Answer 5

Adequate blood supply to the kidney
Functioning kidneys
Unobstructed flow of urine from the kidneys, down the ureters to the bladder and out via the urethra

Question 6

List the main pre-renal causes of poor urinary output.

Answer 6

Hypovolaemia (e.g. haemorrhage, dehydration)
Hypotension (e.g. sepsis, pancreatitis)
Heart failure
Reduced local perfusion of the kidneys (e.g. renal emboli, renal artery dissection)

Question 7

List the main renal causes of poor urinary output.

Answer 7

• Tubular – acute tubular necrosis
• Glomerular – glomerulonephritis
• Interstitial – acute interstitial nephritis
• Vascular
  Vasculitides
  Haemolytic uraemic syndrome
  Thrombocytic thrombocytopenic purpura
  DIC
  Malignant hypertension
  Scleroderma
• Infectious
  Malaria
  Legionnaire’s disease
  Leptospirosis
• Complex – multiple myeloma

Question 8

List the main post-renal causes of poor urinary output.

Answer 8

- Ureters
Bilateral calculi
Abdominal/pelvic mass compressing the ureters
Retroperitoneal fibrosis
- Bladder
Neuropathic bladder
Anticholinergic and sympathomimetic drugs
Bladder stones or tumour
Ureterovaginal prolapse
- Urethra
BPH
Blocked catheter
Prostate cancer
Urethral stricture
Trauma 
Infection

Question 9

What must you look for on fluid balance charts?

Answer 9

Adequate fluid intake – average-sized adults should have 3 L of water per day (30-50 ml/kg/day)
Positive balance – make sure there is at least as much fluid going in as there is going out

Question 10

Describe how the fluid requirement of febrile patients is different from afebrile patients.

Answer 10

Febrile patients require an extra 500 ml per 1 degree above 37

Question 11

What must you look for on the surgical operative notes?

Answer 11

Pelvic surgery may damage the urinary tract
Laparotomies cause a lot of fluid loss leading to dehydration
Blood loss (usually poorly estimated)

Question 12

List some nephrotoxic drugs that you would look for on the drug charts of a patient with AKI.

Answer 12

NSAIDs
ACE inhibitors
Diuretics
Some antibiotics (e.g. gentamycin, vancomycin)
IV contrast

Question 13

Why does acute haemorrhage cause a delayed drop in Hb?

Answer 13

Acute haemorrhage will initially lead to an equal loss of serum and Hb meaning that the Hb concentration has not changed
However, serum will be replenished much quicker than Hb leading to a delayed drop in Hb

Question 14

Why is it important to compare pre-operative and post-operative blood test results?

Answer 14

Allows you to check for pre-existing anaemia and long-standing renal impairment
It allows you to check whether any abnormal changes are new or whether they have always been there (provides baseline values)

Question 15

What is an important comorbidity that increases the risk of the patient developing AKI?

Answer 15

Cardiac disease – can lead to inadequate renal perfusion

Question 16

Which question would you ask the patient to screen for a pre-renal cause of poor urinary output?

Answer 16

Have you been feeling thirsty?

This is sensitive for hypovolaemia

Question 17

Which questions would you ask to check for renal disease as a cause of poor urinary output?

Answer 17

Ask about pre-existing renal disease
Ask about symptoms of renal disease:
Haematuria
Swollen ankles and frothy urine (features of nephrotic syndrome)
Rashes and arthralgia (suggests multisystem disease (e.g. SLE))

Question 18

Patients with post-renal causes of poor urinary output tend to have lower urinary tract symptoms (LUTS). List some of these symptoms.

Answer 18

Hesitancy 
Frequency
Strangury
Poor stream
Terminal dribbling

Question 19

What should you check the catheter bag for when examining the patient?

Answer 19

Volume of urine
Colour of urine (dark/light)
Blood in urine

Question 20

List some signs of dehydration.

Answer 20

Dry mucosal surfaces (e.g. mouth)
Tachycardia 
Narrow pulse pressure 
Delayed capillary refill
Cool peripheries
Postural drop 
Low blood pressure

Question 21

List some signs of heart failure.

Answer 21

Raised JVP
Displaced apex beat
Bilateral basal crepitations 
S3 gallop
Peripheral oedema

Question 22

List some signs of post-renal obstruction.

Answer 22

Palpable, distended bladder that is dull to percuss

Pressing the bladder may stimulate the urge to urinate

Question 23

List three key investigations for pre-renal causes of poor urinary output.

Answer 23

Venous blood gas – check electrolyte balance, acid-base balance and haematocrit
Bloods – renal function (creatinine), dehydration (urea) and Hb
Fluid challenge – if hypovolaemia is suspected, give 250-500 mL crystalloid solution and monitor urine output and basic observations (watch out for signs of fluid overload)

Question 24

State a key difference between acute urinary retention and chronic urinary retention.

Answer 24

Acute – painful

Chronic - painless

Question 25

Describe the appearance of the prostate in a patient with BPH.

Answer 25

Smooth, symmetrical and enlarged

Central sulcus is palpable

Question 26

The immediate management of a patient with urinary retention involves catheterisation. How can the volume of urine voided help you figure out the pathogenesis?

Answer 26

Volume > 1 L suggests chronic retention

Acute retention rarely produces a volume > 1 L

Question 27

What should be monitored to get an idea of the patient’s renal function?

Answer 27

Urea, creatinine and electrolytes

Urine output

Question 28

Why should you avoid ordering a PSA in patients with acute retention?

Answer 28

PSA is elevated in acute urinary retention with or without prostate cancer

Question 29

What is TWOC and when is it indicated?

Answer 29

TWOC = Trial without catheter – patients with BPH are given an alpha blocker (e.g. tamsulosin) and a single dose antibiotic and then monitored to see whether they can urinate
Indicated if < 1 L is voided upon catheterisation and normal renal function

Question 30

What are the possible outcomes of TWOC?

Answer 30

CAN urinate = discharge with alpha blocker (e.g. tamsulosin) and 5-reductase inhibitor (e.g. dutasteride)
CANNOT urinate = discharge with alpha blocker and 5a-reductase inhibitor and indwelling catheter – if this fails then schedule a TURP (trans-urethral resection of the prostate)

Question 31

Describe the typical presentation of cauda equina syndrome.

Answer 31

Lower back pain 
Urinary retention 
Lax anal tone 
Perianal numbness
Lower motor neuron signs in the lower limbs

Question 32

What can cauda equina syndrome be caused by?

Answer 32

It is caused by compression of the cauda equina (e.g. by a centrally prolapsing intervertebral disc)