Ch 117 urethra Flashcards
(73 cards)
List the layers of the urethra
Mucosa (transitional > squamous epithelium)
Submucosa
Muscularis
Describe the urethra muscularis in the male and female dogs and cat
Male dog:
- Inner longitudinal smooth surrounded by outer circumferential striated
- Striated muscle is 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
- striated muscle fibers in the distal third > 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
striated muscle > innervated by pudendal n.
Anatomy
Male
- divided anatomically into pelvic and penile components
- subdivided into preprostatic and prostatic
- penile component begins at the ischial arch and is surrounded by the corpus spongiosum
- Gonadectomy or age at time of gonadectomy does not affect urethral diameter in mature male cats
female
- urethra of female dogs contains significantly more collagen and less muscle than male dogs
- increase in the proportion of collagen and reduction in muscle in the urethra of gonadectomized female dogs, compared with intact dogs
- findings suggest that steroidal hormones may influence the morphology of the canine urethra
What is the urethral diameter of male cats at the level of the bulbourethral glands compared to the penile urethra
Bulbourethral gland 1.3mm
Penile urethra 0.7mm
Initial management of patients with suspected urethral obstruction should include:
- evaluation of hemodynamic status,
- correction of metabolic derangements,
- urinary diversion
- postobstructive diuresis (once unblocked)
What is the theorised mechanism of hypothermia in cats with urethral obstruction?
Reduction in the thermoregulatory set point in the hypothalamus secondary to uraemia
Or secondary to volume depletion and shock
What is the time frame for renal decompensation and death in aminals with complete urethral obstruction?
Renal decompensation within 24hr
Death 3-6d
What fluid is most efficient for correcting electrolyte derangement with urethral obstruction?
LRS
alkalinizing effect helps to drive potassium ions intracellularly
List options and mode of action of each option for the treatment of hyperkalaemia
10% Ca Gluconate
- Increases threshold for cardiac myocyte depolarisation. 0.5-1.5ml/kg IV over 5-10 min, last 30-60min
IV dextrose +/- regular insulin
- Drived K intracellularly by cotransport. Lasts 2-4hr
Na Bicarb
- Enables H ions to move extracellularly in exchange for K. Only used if severe acidosis
ECG changes
- spiked T-waves
- depressed R-waves,
- prolonged QRS and PR intervals and ST segment depression,
- smaller and wider P-waves with a prolonged QT interval,
- atrial standstill,
- eventually wide QRS complexes and ventricular arrhythmias
unblock
catheter are unsuccessful:
- retrograde urohydropulsion under general anesthesia
- improved by lubricating agents, topical anesthesia, or coccygeal epidural
- bladder decompression can be maintained by intermittent cystocentesis
- placement of a cystostomy tube (minimally invasive inguinal approach)
- a guide wire can be passed through the body wall and antegrade out the urethra
diagnosis
RADS
- radiopaque urinary calculi,
- Positive-contrast retrograde urethrography (best for suspected tear)
- retrograde vaginourethrocystography in females
- Negative (air)-contrast radiography is contraindicated with suspected lower urinary tract trauma
- Ideally, fluoroscopy should be performed
- gradual withdrawal of the catheter or use of a voiding cystogram
- cannot be catheterized, a normograde urethrocystogram
ultrasound limited, CT/MRI not well described
Cystoscope
- evaluation and treatment of a variety of lower urinary tract diseases
List 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
exposure of submucosal tissue to urine may promote formation of scar tissue, reducing the elastic qualities
Urethral Healing
partial
- Conservative therapy is indicated
- mucosal continuity and the flow of urine is diverted
complete
- Primary surgical repair or permanent urinary diversion is indicated
- urethral mucosa may retract, and fibrotic tissue may ultimately bridge the gap and obstruct
- ventral midline celiotomy/pubic osteotomy followed by antegrade (through the bladder) or retrograde urethral catheterization may be required to identify the distal end of the proximal urethral segment
- Diversion (cystostomy tube or indwelling urethral catheter) is recommended for 3 to 5 days to minimize the risk for urethral stricture
- size 4-0 or 5-0 USP
- tensile strength of poliglecaprone 25 (Monocryl; Ethicon) is lost at a relatively rapid rate when immersed in a container of urine
- presence of an indwelling catheter can promote inflammation and ascending infection
- Some reduction in urethral luminal diameter at the site of surgical repair is anticipated, regardless of whether or not a catheter is left in place after surgery.
How much narrowing of the urethral lumen occurs before clinical signs occur?
60%
Urethrotomy
- commonly indicated for removal of calculi
- if can be dislodged and flushed back into the bladder, cystotomy is preferable to urethrotomy
- DOGS prescrotal region, because calculi most often lodge at the base of the os penis
- optimal location for urethrotomy because of the superficial position of the urethra and paucity of surrounding cavernous tissue
- Perineal and prepubic urethrotomy can be performed
- minimally invasive perineal urethrotomy can be performed under simultaneous ultrasonographic and fluoroscopic guidance > for insertion of a scope
- Hemorrhage, especially associated with urination, is the most common complication
- Urethral stricture is an uncommon
Prescrotal Urethrotomy
- prepuce should be irrigated with dilute antiseptic
- Retrograde urethral catheterization is used to facilitate identification of the urethra and determine the level of the obstruction
- 2-cm incision is made on the ventral midline immediately caudal to the os penis
- paired retractor penis muscles are retracted laterally.
- The urethra and surrounding corpus spongiosum is identified as a purple
- Profuse hemorrhage is expected > cotton tip or ellulose surgical spears
- Calculi are removed, and the urethral catheter is advanced proximally into the bladder.
- A cystotomy can be performed
- The urethra is flushed antegrade and retrograde
alternative
- modification of this technique is urethrotomy through the glans penis
closure?
- second intention healing, urination will occur from the urethral incision for 10 to 14 days until the wound heals (petroleum-based jelly may reduce urine scalding and scrotal dermatitis)
- if haemorrhage profuse may need closure
- primary closure 4/0
List the options for a urethrostomy
Scrotal
Perineal
Transpelvic
Subpubic
Prepubic
How long should the incision in the urethra be for a urethrostomy?
How much contraction is expected during healing?
2.5-4cm long (approx 5-8x urethral diameter)
Will contract by 1/3-1/2 during healing
stoma will contract by one-third to one-half of its original length
Hows does a continuous suture in a scrotal urethrostomy effect post-op haemorrhage?
Decreases time of active haemorrhage from 4.2d to 0.2d
Scrotal Urethrostomy in Male Dogs
- preferred over perineal urethrostomy because the urethra is relatively superficial and wide at the level of the scrotum, and less hemorrhage occurs
- urethral mucosa is incredibly thin and somewhat fragile, and tissue handling must be gentle and precise
- Apposition can often be improved by using a two-step process during suture placement
- A urinary catheter is placed
- sutures are placed from the tunica albuginea to the subcutaneous tissue on either side of the intended urethrostomy site to maintain the penis and urethra in a superficial position
- incision is centered on the urethral midline
- Use of magnification may be beneficial,
- Elizabethan collar should be maintained for 2 to 3 week
- Bleeding associated with urination occurs for an average of 3 to 5 days after urethrostomy and is usually self-limiting.
complications
- haemorrhage
- Intermittent urine scald,
- recurrent urinary tract infections,
- recurrent obstruction from calculi
- stricture (uncommon)
each occurred in 10% of dogs
What is the name of the standard cat PU technique?
Wilson and Harrison technique
What ventral structures need to be transected during a cat PU?
Ventral penile ligament
Attachment of ischiocavernosus muscles