Urinary obstruction in small animals

Question 1

Describe LMN bladder

Answer 1

• flaccid
• overdistended bladder
• easy to express
• urine leakage
• congenital (manx cats)
• cauda equina syndrome
• lumbo sacral dz
• vertebral fractures and dislocations

Question 2

Describe UMN bladder

Answer 2

• firm, tense bladder
• difficult to express
• lesions cranial to sacral nn segments
• IVDD, tumours, luxations, fractures

Question 3

CS - obstruction

Answer 3

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

Question 4

PE findings - obstruction

Answer 4

• 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

Question 5

Pathophysiology - obstruction

Answer 5

• 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

Question 6

Describe obstructive uropathy

Answer 6

• 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

Question 7

Effects on bladder of overdistension

Answer 7

• 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)

Question 8

How might blocked animals present?

Answer 8

hypovolaemic (as haven’t been eating/drinking) and hypotension

Question 9

Biochemical changes - obstruction

Answer 9

• azotaemia
• hyperglycaemia
• acidaemia
• hyperphosphataemia
• hypocalcaemia
• hyperkalaemia

Question 10

Describe ECG changes associated with hyperkalaemia

Answer 10

• 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

Question 11

How quickly do blocked animals die?

Answer 11

usually within 72 hours

Question 12

Emergency management of obstruction

Answer 12

• Priority is to ID and correct life-threatening hyperkalaemia:
• blood sample
• IV catheter + IVFT
  = ECG if hyperkalaemic, or if unknonw {K+]

Question 13

Tx - hyperkalaemia in obstructionfq

Answer 13

• 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

Question 14

Outline pros/cons decompressive cystocentesis

Answer 14

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

Question 15

Method - relieving obstruction and emptying bladder

Answer 15

• 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

Question 16

What catheter to use

Answer 16

• ensure long enough in cats

Question 17

What to do after unblocking a cat?

Answer 17

• 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

Question 18

Should you give ABs when an animal has a catheter?

Answer 18

NO - only at removal and afterwards. Resistance WILL develop if there is a UTI present.

Question 19

Outline post-obstructive diruesis

Answer 19

• 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)

Question 20

How is K+ affected after unblocking?

Answer 20

• -> hypokalaemia
• check electrolytes
• supplement via IVFT
• oral supplementation in food

Question 21

What to monitor for after unblocking

Answer 21

• UTI
• detrusor atony resulting from excessive distension
• bladder outflow obstruction resulting from a blood clot or sloughed mucosa
• stricture formation
• struvite stones (females > males)

Question 22

Pharamcological therapy after obstruction

Answer 22

• SMOOTH MUSCLE RELAXANTS: alpha-adrenergic blockers (phenoxybenzamine or prazosin)
• SKELETAL MUSCLE RELAXANTS: dantrolene or diazepam

Question 23

Whaat further investigations are useful post-obstruction?

Answer 23

• 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

Question 24

Outline management of urinary tract obstruction

Answer 24

• 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

Question 25

Describe retrograde hydropulsion

Answer 25

- 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

Question 26

Outline urinary diversion - CYSTOSTOMY

Answer 26

= 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)

Question 27

What methods can be used to remove calculi/some other obstructing lesion?

Answer 27

- cystotomy | - urethrotomy (avoid, better to flush stone into bladder then do a cystotomy)

Question 28

Outline urethrotomy

Answer 28

- 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

Question 29

What are the 2 neurogenic causes of urine retention?

Answer 29

- LMN bladder | - UMN bladder

Question 30

Outline urinary diversion - URETHROSTOMY

Answer 30

- 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)

Question 31

What are the sx options for managing upper urinary tract obstructio?

Answer 31

- KIDNEY: nephrotomy or pyelolithotomy | - Other rarely used methods: urethral resection and anastomosis, vagino-urethroplasty

Question 32

Outline causes of urinary tract obstruction

Answer 32

- 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.

Question 33

Describe urinary tract obstruction

Answer 33

- UPPER UT: kidneys, ureters | - LOWER UT: bladder, urethra

Question 34

Examples of intra-urethral causes of obstruction

Answer 34

- calculi - tumours - inflammatory dz - FBs (rare)

Question 35

Examples: extra-urethral causes of obstruction

Answer 35

- bladder masses - pelvic masses - prostatic dz - trauma (penile, pelvic, iatrogenic = perineal rupture repair or TPO = triple pelvic osteotomy) - others

Question 36

Causes: bladder displacement

Answer 36

- retroflexion: perineal rupture - Displacement: abdominal wall ruptures/ pelvic fractures - bladder torsion

Question 37

What is functional urethral obstruction?

Answer 37

= 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

Question 38

List sx options for management of urethral obstruction

Answer 38

- 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)

Question 39

List some cutting edge techniques and their indications

Answer 39

- urethral stenting (strictures, tumours) - balloon dilations (strictures) - endoluminal lithotripsy (calculi) - endoluminal resection/ ablation (tumours, polyps)

Question 40

List different ureteral surgeries

Answer 40

- ureteronephrectomy - ureterotomy - ureteral anastomosis - ureteroneocystostomy (+/- psoas cystopexy, +/- renal descensus) - implants (SC ureteral bypass system = SUB, ureteral stent, nephrostomy tube)