22. 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
Infectious
Complex – multiple myeloma
List renal causes of poor urinary output in the renal category
Vasculitides Haemolytic uraemic syndrome Thrombocytic thrombocytopenic purpura DIC Malignant hypertension Scleroderma
List renal causes of poor urinary output in the infectious category
Malaria
Legionnaire’s disease
Leptospirosis
List the main post-renal causes of poor urinary output affecting the ureters
Bilateral calculi
Abdominal/pelvic mass compressing the ureters
Retroperitoneal fibrosis
List the main post-renal causes of poor urinary output affecting the bladder
Neuropathic bladder
Anticholinergic and sympathomimetic drugs
Bladder stones or tumour
Ureterovaginal prolapse
List the main post-renal causes of poor urinary output affecting the 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
