Chapter 117: Urethra Flashcards
Urethra is innervated by which nerves?
hypogastric and pelvic
Urethralis is innervated by which nerve exclusively ?
Pudendal nerve
Blood supply by which artery?
Internal pudendal artery (prostatic, urethral and penile branches)
Average diameter of male cat urethra?
0.7mm
Average diameter of female dogs?
0.5cm
MOA of calcium gluconate?
- Increases the threshold for cardiac myocyte depolarization, soley cardioprotective agent, does not alter serum K+ level
- DOA: 30-60mins
most common site of male urethral obstructions
cd os penis
how to improve success of urohydropulsion?
LA, lube, coccygeal epidural LA, different sizes of urethral catheter used
animals only show clinical signs when urethral diameter is narrowed over what %?
> 60%
urethral mucosa can regenerate in X days
7 days
Which urethrostomy is most useful for revision of failed perineal urethrostomies?
TPU
Most common complication from scrotal PU in a dog?
Persistent haemorrhage, haematuria 3-5 days postop and usually self-limiting
common 2 complications from PU in cats?
Stricture and urine extravasation
TPU - how much in mm length and mm in width to remove from cd ischium to expose urethra?
12mm in length and 10mm in width
MST is prolonged if what happens prior to SEMS placement (self-expanding metallic stent)?
NSAID and chemo
Most significant complication with SEMS?
Urinary incontinence 26%
stranguria is 2nd most common
( other complications bladder atony, recurrent obstruction and stent migration)
Tx options for a urethral stricture?
- Urethrostomy proximal to site
- R and A
- Balloon dilatation
- Stent placement
- experimentally - Urethral replacement
What is the most common complication post urethropexy/R and A?
Post op haemorrhage 39%
List the layers of the urethra:
- Mucosa (transitional epithelium proximally, squamous distally)
- Submucosa (vascular)
- Muscularis
Describe the muscularis layer of the urethra in the male and female dog and cat:
Male dog:
- Inner longitudinal smooth surrounded by outer circumferential striated
- Smooth muscle is in the distal 2/3rds of the urethra
- Striated mostly Type II fast twitch, some Type I slow twitch
Male cats:
- 3 layers of smooth muscle - inner longitudinal, middle circumferential, outer longitudinal
Female dog:
- Three smooth muscle layers as male cats
- Smooth muscle essentially absent in terminal urethra
- Prominent sphincter of striated muscle at external urethral orifice
Female cat:
- Significantly more smooth muscle and significantly less striated urethral sphincter than female dog
What is the urethral diameter of male cats at the level of the pre/post prostatic, bulbourethral glands and at the penile urethra?
-Pre/Post prostatic both 2mm
- Bulbourethral gland 1.3mm
- Penile urethra 0.7mm
How long is the urethra in a male cat?
8.5 to 10.5 cm
How long is the urethra in a male dog?
~25cm in a 25lb dog
Urethral length in female dogs and cats?
7-10 cm
Width of urethral lumen in female dogs?
0.5cm
What is the theorized mechanism of hypothermia in cats with urethral obstruction?
- Reduction in the thermoregulatory set point in the hypothalamus secondary to uremia
- Or secondary to volume depletion and shock.
What is the time frame for renal decompensation and death in animals with complete urethral obstruction?
- Renal decompensation within 24hr
- Death 3-6 days
What fluid is most efficient for correcting electrolyte derangement with urethral obstruction?
Lactated ringer’s solution (LRS) - give at least 15 min of fluids before anesthesia.
List options and mode of action of each option for the treatment of hyperkalemia:
10% Calcium Gluconate
- Increases threshold for cardiac myocyte depolarization. 0.5-1.5ml/kg IV over 5-10 min, last 30-60min
IV dextrose +/- regular insulin
- Drives K intracellularly by cotransport. Lasts 2-4hr
Sodium Bicarbonate
- Enables H ions to move extracellularly in exchange for K. Only used if severe acidosis
What are the critical factors which effect urethral healing?
- Mucosal continuity
- Urine extravasation
If a strip of mucosa is left intact and urine is diverted, the urethral mucosa can regenerate within 7 days
How much narrowing of the urethral lumen can occur before clinical signs appear?
60%
What can plain abdominal radiographs tell you for urethral lesions? What are they not good at?
Abnormal location of bladder, radiopaque calculi
Not good for trauma (need contrast)
What is the imaging modality of choice for urethral lesions?
Positive-contrast retrograde urethrography
Use fluoro, balloon catheter in distal urethra
Negative-contrast (air) urethrography is contraindicated in trauma for what reasons?
Rarely shows location of tears
Can cause fatal air embolism
Ultrasound of the urethra is limited to the extrapelvic portions, but can add information about what?
Wall thickness and mucosal surface contour.
What is an emerging method of evaluating the urethra and treating lesions?
Cystoscopy/urethroscopy.
-Stricture dilation, laser lithotripsy, laser ablations, submucosal collagen injections
What type of suture should you use for the urethra?
4-0 or 5-0 Monocryl or PDS if concerned it will take time. Taper needle.
What is the prognosis after urethral anastomosis?
Guarded - Some degree of stenosis is expected
Male dogs most commonly obstruct where?
At os penis
What type of analgesia can be used to help unobstruct a dog?
Coccygeal epidural
