Poor Urinary Output Flashcards
How much urine do normal adults produce per hour?
1 ml/kg/hour
What urine output would be considered as oliguria?
< 0.5 ml/kg/hour
What important condition can decreased urine output be the first sign of?
Impending acute renal failure
What are the major complications of AKI that could be fatal?
Hyperkalaemia
Acidosis
Uraemia
Pulmonary oedema
What are the three main requirements for normal renal function?
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
List the main pre-renal causes of poor urinary output.
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)
List the main renal causes of poor urinary output.
- 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
List the main post-renal causes of poor urinary output.
- 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
What must you look for on fluid balance charts?
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
Describe how the fluid requirement of febrile patients is different from afebrile patients.
Febrile patients require an extra 500 ml per 1 degree above 37
What must you look for on the surgical operative notes?
Pelvic surgery may damage the urinary tract
Laparotomies cause a lot of fluid loss leading to dehydration
Blood loss (usually poorly estimated)
List some nephrotoxic drugs that you would look for on the drug charts of a patient with AKI.
NSAIDs ACE inhibitors Diuretics Some antibiotics (e.g. gentamycin, vancomycin) IV contrast
Why does acute haemorrhage cause a delayed drop in Hb?
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
Why is it important to compare pre-operative and post-operative blood test results?
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)
What is an important comorbidity that increases the risk of the patient developing AKI?
Cardiac disease – can lead to inadequate renal perfusion
Which question would you ask the patient to screen for a pre-renal cause of poor urinary output?
Have you been feeling thirsty?
This is sensitive for hypovolaemia
Which questions would you ask to check for renal disease as a cause of poor urinary output?
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))
Patients with post-renal causes of poor urinary output tend to have lower urinary tract symptoms (LUTS). List some of these symptoms.
Hesitancy Frequency Strangury Poor stream Terminal dribbling
What should you check the catheter bag for when examining the patient?
Volume of urine
Colour of urine (dark/light)
Blood in urine
List some signs of dehydration.
Dry mucosal surfaces (e.g. mouth) Tachycardia Narrow pulse pressure Delayed capillary refill Cool peripheries Postural drop Low blood pressure
List some signs of heart failure.
Raised JVP Displaced apex beat Bilateral basal crepitations S3 gallop Peripheral oedema
List some signs of post-renal obstruction.
Palpable, distended bladder that is dull to percuss
Pressing the bladder may stimulate the urge to urinate
List three key investigations for pre-renal causes of poor urinary output.
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)
State a key difference between acute urinary retention and chronic urinary retention.
Acute – painful
Chronic - painless
Describe the appearance of the prostate in a patient with BPH.
Smooth, symmetrical and enlarged
Central sulcus is palpable
The immediate management of a patient with urinary retention involves catheterisation. How can the volume of urine voided help you figure out the pathogenesis?
Volume > 1 L suggests chronic retention
Acute retention rarely produces a volume > 1 L
What should be monitored to get an idea of the patient’s renal function?
Urea, creatinine and electrolytes
Urine output
Why should you avoid ordering a PSA in patients with acute retention?
PSA is elevated in acute urinary retention with or without prostate cancer
What is TWOC and when is it indicated?
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
What are the possible outcomes of TWOC?
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)
Describe the typical presentation of cauda equina syndrome.
Lower back pain Urinary retention Lax anal tone Perianal numbness Lower motor neuron signs in the lower limbs
What can cauda equina syndrome be caused by?
It is caused by compression of the cauda equina (e.g. by a centrally prolapsing intervertebral disc)
