Poor Urinary Output Flashcards
What is important to ask if you find a patient with poor urinary output?
- trend in urine output: suddenly stopped or gradually decreased? checked catheter not blocked by flushing it
- obs of patient: HR, BP, Resp rate, O2 sats, and temp to see how unewell
What is the urine output of a healthy adult roughly?
1mL/kg/hour
What is oliguria?
reduced urine output
How is oliguria defined?
<400mL/day
<0.5mL/kg/hr
<30ml/hr
What does anuria refer to?
complete absence of urine output
Why does decreased urine output need to be taken seriously?
could be first and only sign of impending acute renal failure
What can happen to untreated patients of poor urinary output?
die due to
- hyperkalaemia
- profound acidosis,
- pulmonary oedema as kidneys not doing usual role
What does normal urine output require?
- Adequate blood supply to kidney
- Functioning kidneys and
- Flow of urine from kidneys, down ureter, into the bladder and out via urethra
What are the pre-renal (i.e. inadequate blood supply to kidney) causes for poor urinary output?
- Hypovoleamia
- Hypotension
- Hear failure
- Reduced local perfusion of kidneys
What can cause hypovolaemia?
decreased circulating volume due to e.g. dehydration, haemorrhage
What can cause hypotension?
decreased vascular resistance due to e.g. sepsis, pancreatitis
What can cause reduce local perfusion of kidneys?
e.g. dissecting aneurysm, renal emboli
What are the renal (i.e. damage resulting in impaired kidney function) causes of poor urinary output?
1, Tubular causes
- Glomerular causes
- Interstitial causes
- Vascular causes
- Infectious causes
- Complex mechanism
What are the tubular causes of poor urinary output?
acute tubular necrosis
What are the glomerular causes of poor urinary output?
glomerulonephritis
What are the interstitial causes of poor urinary output?
interstitial nephritis (caused by drugs e.g. NSAIDs and antibiotics)
What are the vascular causes of poor urinary output?
- Vasculitides
- Haemolytic uraemic syndrome
- Thrombocytic thrombocytopenic purpura
- Disseminated intravascular coagulation
- Malignant hypertension
- Scleroderm
What are the infectious causes of poor urinary output?
- Malaria
- Legionnaires’ disease
- Leptosipirosis
What are the complex mechanism causes of poor urinary output?
multiple myeloma
What are the post-renal (i.e. obtstruction to urinary flow) causes for poor urinary output?
- ureter
- bladder
- urethra
What are the ureter causes of poor urinary output?
- Abdominal/pelvic mass (e.g. tumour) compressing ureters
- Complication of pelvic surgery
- Bilateral calculi
- Retroperitoneal fibrosis
What are the bladder causes of poor urinary output?
- Neuropathic bladder
- Anticholinergic or sympathomimetic drugs
- Bladder stones or tumour
- Uterovaginal prolapse (women)
What are the urethra causes of poor urinary output?
- BPH
- Blocked catheter
- Prostate cancer
- Urethral stricture
- Posterior urethral valve
- Trauma
- Infection (e.g. herpes simplex making it painful to pass urine)
What 5 things must you check to establish cause of poor urinary output?
- fluid balance chart
- surgical opt notes
- drug chart
- blood test results
- PMHx
What do you check on the fluid balance chart?
- Adequate intake
2. Positive balance
What is the adequate intake of fluid for patients?
- 30-50mL/kg/day (roughly 3L)
- febrile patients require an extra 500mL for every 1 degree above 37 degree to compensate for increased loss of fluid from evaporation and increase RR
What does positive balance mean?
at least as much fluid going in (IV or oral) as comes out (urine, fluid feaces, NG tubes, vomit, stomas, drains
What do you check in surgical operative notes?
- type of surgery
2. blood loss
What type of surgery do you look out for in poor urinary output?
- pelvic surgery could damage urinary tract
- surgery to urinary tract could damage
- laparotomies esp long times can cause dehyrdration
Why do you check blood loss?
- if not replaced blood loss, could be hypovolaemic so kidneys cannot work as not well perfused
- even if adequately replaced, can have temporary ischaemic damage to underperfused kidneys (ischaemic acute tubular necrosis) so that kidneys no longer function properly
What drugs can be nephrotoxic?
- NSAIDS
- ACE inihibtiors diuretics
- some antibiotics (gentamicin, vancomycin)
- some IV contrast
What do you do if patients are taking these nephrotoxic drugs and have olguria or worsening renal function?
stop them or switch to alternative antibiotics
What blood tests do you do for poor urinary output?
- Haemolglobin
2. Renal function
How should you analyse haemoglobin results?
- compare pre and post-operative results in case pre-existing anaemia
- acute blood loss results in delayed drop in haemoglobin
How do you analyse renal function in poor urinary output?
compare pre and post-operative results as may have prexisting renal impairement
What result would suggest AKI?
50% increase in baseline creatinine
Why is AKI relevant in poor urinary output?
points towards pathology resulting in renal hypoperfusion (prerenal) or potenially renal aetiology
What comordities do you look for with poor urinary output? and why?
- cardiac disease can be more vulnerable to developing acute renal failure
- can provide clues to cause as more likely to be prerenal if heart failure
What questions should you ask patients with poor urinary output?
- Feel thirsty?
- Any pre-exisiting renal disease?
- Any symptoms of conditions that cause renal disease?
Why do you check if patient feels thirsty?
- prerenal disease
- symptom of dehydration + hypovolaemia
What are examples of symptoms of conditions that cause renal disease?
- haematuria (glomerulnephritis)
- swollen ankles or frothy urine (nephrotic syndrome)
- rashes and arthralgias suggestive of multisystem vasculitis or SLE
How do you check for postrenal obstruction with the patient?
catheterise patient to see if obstruction was problem, or if not cathertirised ask about lower UTI symptoms
What are some lower UTI symptoms?
- hesitancy
- frequency
- strangury
- poor stream
- terminal dribbling
What are the steps of examination for poor urinary output?
- Check catheter bag
- Signs of dehydration
- Signs of heart failure (fluid overload)
- Signs of urinary retention due to post renal obstruction
What do you look for in catheter bag?
- any output since last entry
- colour for hydration status
- blood, suggesting clot retention
What are signs of dehydration?
- dry lips
- mouth
- tongue
- dizzy on standing
What are the signs of a hypovolaemic patient?
- tachycardia
- narrow pulse pressure
- eventually low BP
- prolonged capillary refill time
- cool peripheries
What are the signs for intravasulcar hydration?
- pulse
- BP
- cap refill time
- JVP
Is it possible for patient to be overloaded with fluid in extravascular compartment, but fluid depleted intravascularly?
yes e.g. septic shock
What are signs of heart failure?
- raised JVP
- displaced apex beat
- gallop rhythm (third heart sound)
- bilateral and basal lung crepitations
- dependent oedema (sacrum if in bed)
What should you be careful with odematous patients?
their intravascular volume may be depleted with potential for renal hypoperfusion
How do you check signs of urinary retention due to post renal obstruction?
- palpable, distended bladder that is dull to percussion (as it is filled with fluid)
- pressing may stimulate urge to urinate
What may be suggested if bilateral basal lung crackles but no other signs of heart failure?
atelectasis
What is atelectasis?
post op, small areas of alveolar collapse that are common after surgery (esp abdominal surgery with poor postoperative analgesia)
If you suspect reduced urinary output due to hypovolemia what investigations do you order?
- check catheter has been flushed
- VBG
- bloods
- fluid challenge
- if not catheterised, US
Why do you order a VBG?
- quick way to get electrolyte balance (esp K+)
- acid-base status
- haematocrit
What bloods do you order?
renal function + haemoglobin
What would a raised urea suggest?
hypovoleamia
What would a raised urea and creatinine suggest?
renal injury (e.g.acute tubular necrosis)
What is fluid challenge?
give 250-500mL of crystalloid solution, monitor urine output and basic obs and if improved and stays it worked, if improved but goes back to bad give more fluids
What should you check with fluid challenge?
SOB and JVP raises suggest fluid overload e.g. congestive heart failure
Why do you order an US?
to exclude postrenal obstruction (if dilated ureter or renal pelvis/calyces)
What maintenance fluids are used for when prerenal hypovolemia is cause of poor urinary output?
- Volume: 25-30mL/kg/day (based of ideal weight if the patient is obese)
- Electrolytes: 1mmol/kg/day of K,Na,Cl
- Glucose: 100g/day (simply to prevent starvation)
