22. 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

Infectious

Complex – multiple myeloma

Question 8

List renal causes of poor urinary output in the renal category

Answer 8

Vasculitides 
Haemolytic uraemic syndrome 
Thrombocytic thrombocytopenic purpura
DIC 
Malignant hypertension
Scleroderma

Question 9

List renal causes of poor urinary output in the infectious category

Answer 9

Malaria
Legionnaire’s disease
Leptospirosis

Question 10

List the main post-renal causes of poor urinary output affecting the ureters

Answer 10

Bilateral calculi
Abdominal/pelvic mass compressing the ureters
Retroperitoneal fibrosis

Question 11

List the main post-renal causes of poor urinary output affecting the bladder

Answer 11

Neuropathic bladder
Anticholinergic and sympathomimetic drugs
Bladder stones or tumour
Ureterovaginal prolapse

Question 12

List the main post-renal causes of poor urinary output affecting the urethra

Answer 12

BPH
Blocked catheter
Prostate cancer
Urethral stricture
Trauma 
Infection

Question 13

What must you look for on fluid balance charts?

Answer 13

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 14

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

Answer 14

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

Question 15

What must you look for on the surgical operative notes?

Answer 15

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

Question 16

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

Answer 16

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

Question 17

Why does acute haemorrhage cause a delayed drop in Hb?

Answer 17

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 18

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

Answer 18

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 19

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

Answer 19

Cardiac disease – can lead to inadequate renal perfusion

Question 20

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

Answer 20

Have you been feeling thirsty?

This is sensitive for hypovolaemia

Question 21

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

Answer 21

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 22

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

Answer 22

Hesitancy 
Frequency
Strangury
Poor stream
Terminal dribbling

Question 23

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

Answer 23

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

Question 24

List some signs of dehydration.

Answer 24

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

Question 25

List some signs of heart failure.

Answer 25

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

Question 26

List some signs of post-renal obstruction.

Answer 26

Palpable, distended bladder that is dull to percuss

Pressing the bladder may stimulate the urge to urinate

Question 27

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

Answer 27

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 28

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

Answer 28

Acute – painful

Chronic - painless

Question 29

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

Answer 29

Smooth, symmetrical and enlarged

Central sulcus is palpable

Question 30

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 30

Volume > 1 L suggests chronic retention

Acute retention rarely produces a volume > 1 L

Question 31

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

Answer 31

Urea, creatinine and electrolytes

Urine output

Question 32

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

Answer 32

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

Question 33

What is TWOC and when is it indicated?

Answer 33

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 34

What are the possible outcomes of TWOC?

Answer 34

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

Question 35

Describe the typical presentation of cauda equina syndrome.

Answer 35

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

Question 36

What can cauda equina syndrome be caused by?

Answer 36

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