Urinary obstruction in small animals Flashcards
Describe LMN bladder
- flaccid
- overdistended bladder
- easy to express
- urine leakage
- congenital (manx cats)
- cauda equina syndrome
- lumbo sacral dz
- vertebral fractures and dislocations
Describe UMN bladder
- firm, tense bladder
- difficult to express
- lesions cranial to sacral nn segments
- IVDD, tumours, luxations, fractures
CS - obstruction
DEPENDS ON: complete/partial, acute/chronic, underlying cause:
- usually inability or difficult in passing urine
- anuria, dysuria, stranguria, tenesmus
- can be mistaken for constipation in cats
- others: vulval/penile bleeding, haematuria, vomiting
- mistaken for other dz if animal presents collapsed
PE findings - obstruction
- full bladder (beware no bladder if ruptured)
- inability to pass catheter (not reliable)
- possible mass palpable on digital pelvic and urethral exam
- other non-specific findings: abdominal pain, depression, unproductive straining, abdominal distension
Pathophysiology - obstruction
- similar regardless of underlying cause
- urethral obstruction serious effects on: bladder, kidneys, secondary changes affect systemically
- upper urinary tract obstruction: less life threatening unless both kidneys involved
- ultimate outcome death
Describe obstructive uropathy
- increased ureteral and eventually tubular pressure
- increased pressure in bowman’s space
- GFR falls
- reduction in renal BF d/t vasoactive hormones maintains low GFR–>ischaemic nephropathy may result in permanent nephron loss and kidney shrinkage
- azotaemia d/t urethral obstruction may be reversible no matter how severe
Effects on bladder of overdistension
- depends on bladder capacity and compliance and rate or urine production
- increased intravesical pressure prevents ureteral emptying and may allow ureteral reflux
- ischaemia, oedema, aemorrhage and mucosal sloughing (may cause another obstruction)
How might blocked animals present?
hypovolaemic (as haven’t been eating/drinking) and hypotension
Biochemical changes - obstruction
- azotaemia
- hyperglycaemia
- acidaemia
- hyperphosphataemia
- hypocalcaemia
- hyperkalaemia
Describe ECG changes associated with hyperkalaemia
- prolonged PR interval
- tall or peak T waves (t waves should normally be 1/4 amplitude of R wave)
- bradycardia
- sino-ventricular rhythm
- ventricular arrhythmias
- changes more characteristic in dogs than in cats
- (in cats) don’t confuse with ventricular complexes if t waves merge with QRS
How quickly do blocked animals die?
usually within 72 hours
Emergency management of obstruction
- Priority is to ID and correct life-threatening hyperkalaemia:
- blood sample
- IV catheter + IVFT
= ECG if hyperkalaemic, or if unknonw {K+]
Tx - hyperkalaemia in obstructionfq
- IVFT
- calcium gluconate must be IV otherwise bad reaction: doesn’t alter [K+] but stabilises myocardium and improves arrhythmias so then safer to anaesthetise
- relieve obstruction
Outline pros/cons decompressive cystocentesis
PROS: allows stabilisation d/t temporary ‘effective’ relief of obstruction, allows a new grad time, reduced hydrostatic pressure within bladder facilitates catheterisation, obstructed cats almost always have sterile urine so the risk of septic peritonitis v low
- CONS: avoid unless only option, risk of urine leaking into abdominal cavity –> septic peritonitis + death. If necessary: empty bladder completely, don’t put off GA, consider ABs
Method - relieving obstruction and emptying bladder
- only when stable
- sedation/GA unless moribund
- urethral catheter: lubrication, penile massaage, flushing, care with cats, generally try and avoid catheter with a stylette, avoid walpole’s solution
What catheter to use
- ensure long enough in cats
What to do after unblocking a cat?
- save some urine or urine plug for analysis
- bladder lavage: warm saline, flush until urine clear, when removing catheter express bladder and evaluate urine stream
- if required, place indwelling catheter and closed closed collection system
Should you give ABs when an animal has a catheter?
NO - only at removal and afterwards. Resistance WILL develop if there is a UTI present.
Outline post-obstructive diruesis
- keep ins with outs with IVFT
- measure urine output
- diuresis may be profound (d/t osmotic effect of retained solutes and damage to tubular cells)
How is K+ affected after unblocking?
- -> hypokalaemia
- check electrolytes
- supplement via IVFT
- oral supplementation in food
What to monitor for after unblocking
- UTI
- detrusor atony resulting from excessive distension
- bladder outflow obstruction resulting from a blood clot or sloughed mucosa
- stricture formation
- struvite stones (females > males)
Pharamcological therapy after obstruction
- SMOOTH MUSCLE RELAXANTS: alpha-adrenergic blockers (phenoxybenzamine or prazosin)
- SKELETAL MUSCLE RELAXANTS: dantrolene or diazepam
Whaat further investigations are useful post-obstruction?
- not always done with first occurrence of obstruction, especially cats
- can r/o specific lesions
- plain and contrast radiography mainstay of investigation
- ultrasound and endoscopy also useful
Outline management of urinary tract obstruction
- different techniques
- depends on: cause/dx, 1st episode/recurrent problem, owners wishes
- options: sx, minimally invasive techniques / flushing, medical/conservative management, new cutting edge techniques/ technologies
Describe retrograde hydropulsion
- rarely fails
- aim to flush urethral calculi back into bladder which are then removed via cystotomy/ laparoscopic assisted cystoscopy
- preferred method of managing urethral calculi in male cats and dogs - always try first
- easily combined with urethrography
- 2 people
- if unable to pass catheter may have to combine with cystocentesis
Outline urinary diversion - CYSTOSTOMY
= tubes placed into blader across body wall
- allow urine to drain and by pass urethra
- indicated: to allow urine to drain if catheter cannot be placed, to protect urethra after sx/injury, as palliative tx for severe urethral dz
- short term (1 week) or long term (years)
What methods can be used to remove calculi/some other obstructing lesion?
- cystotomy
- urethrotomy (avoid, better to flush stone into bladder then do a cystotomy)
Outline urethrotomy
- avoid!!
- indicated ONLY when urethral calculi cannot be returned to bladder with hydropulsion
- incidence of complications > cystotomy
- usually performed pre-scrotally but can, if required, be performed at other sites
- primary closure a good option provided excellent sz technique and suitable materials used
What are the 2 neurogenic causes of urine retention?
- LMN bladder
- UMN bladder
Outline urinary diversion - URETHROSTOMY
- permanent sx opening into urethra
- used to bypass obstruction or to facilitate passage of stones/ sediment
- salvage procedure
- must be performed cr to obstruction
- common sites: scrotal (dog), perineal (cat), prepubic (last resort)
What are the sx options for managing upper urinary tract obstructio?
- KIDNEY: nephrotomy or pyelolithotomy
- Other rarely used methods: urethral resection and anastomosis, vagino-urethroplasty
Outline causes of urinary tract obstruction
- urethral obstruction most common and immediately life-threatening, usually secondary to urolithiasis, may be secondary to other conditions (intra-urethral, mural or extra-urethral lesions), organ displacement
- upper urinary tract obstruction less common. Azotaemia only if bilateral problem. Most likely calculi/ trauma
- UTO may be associated with urinary tract disruption and urine leakage.
Describe urinary tract obstruction
- UPPER UT: kidneys, ureters
- LOWER UT: bladder, urethra
Examples of intra-urethral causes of obstruction
- calculi
- tumours
- inflammatory dz
- FBs (rare)
Examples: extra-urethral causes of obstruction
- bladder masses
- pelvic masses
- prostatic dz
- trauma (penile, pelvic, iatrogenic = perineal rupture repair or TPO = triple pelvic osteotomy)
- others
Causes: bladder displacement
- retroflexion: perineal rupture
- Displacement: abdominal wall ruptures/ pelvic fractures
- bladder torsion
What is functional urethral obstruction?
= aka = reflex dysynergia
- rare
- dogs > cats
- animals dysuric, typically passing small spurts of urine and having a large residual volume
- characteristics: no anatomic reason for obstruction, suspected functional dysynergia b/w detrusor contraction and urethral relaxation
- objective proof rare and hard to get
- medical management: to relax urethra, not always succesful
List sx options for management of urethral obstruction
- REMOVE CALCULI/ OTHER OBSTRUCTING LESION: cystotomy or urethrotomy
- URINARY DIVERSION: cystostomy tube placement, permanent urethrostomy (scrotal urethrostomy in male dogs, perineal urethrostomy in male cats), vagino-urethroplasty
- SURGERY TO RE-ESTABLISH URETHRAL PATENCY: end to end anastomosis (including approach to pelvis)
List some cutting edge techniques and their indications
- urethral stenting (strictures, tumours)
- balloon dilations (strictures)
- endoluminal lithotripsy (calculi)
- endoluminal resection/ ablation (tumours, polyps)
List different ureteral surgeries
- ureteronephrectomy
- ureterotomy
- ureteral anastomosis
- ureteroneocystostomy (+/- psoas cystopexy, +/- renal descensus)
- implants (SC ureteral bypass system = SUB, ureteral stent, nephrostomy tube)
