Urethral Obstruction Flashcards
compare the male urethra to the female urethra; compare cats to dogs
-male urethra is longer and narrower than female so is more likely to obstruct
-cats have a longer internal urethral sphincter compared to dogs, so spasm can cause obstruction
describe the muscular construct of the urethra
proximal 1/4 to 1/3 is smooth muscle and the remainder is striated
describe the consequences/pathophysiology of urethral obstruction
- leads to accumulation of urine and pressure within urethra and bladder
- once bladder can no longer distend, pressure necrosis and mucosal cell death occurs
- if necrosis is severe enough, bladder can rupture, leading to uroabdomen
- increased pressure in lower urinary tract is eventually transmitted up ureters to kidneys
- post-renal pressure exceeds glomerular filtration pressure
- marked reduction of GFR causes decreased urine production
-elevated BUN, creatinine, phosphorous
-metabolic acidosis
-marked hyperkalemia
-postrenal azotemia, can be profound but degree of azotemia does not correlate to prognosis
describe etiology of urethral obstruction in dogs versus cats
dogs: urolithiasis and neoplasia most common
-terriers, cocker spaniels, pugs predisposed to stone formation
cats:
-feline idiopathic cystitis by far most common (usually young to middle aged)
-uncommon for cats to have stones or neoplasia but possible
describe pathogensis of feline idiopathic cystitis
- stress activates sympathetic nervous system, reaulting in alterations in bladder wall
-degradation of GAG layer of bladder urothelium
-exposure to urine activates nociceptors - pain causes stress and potentiates SNS response resulting in even more pain and stress
- mucosal inflammatory debris, mucus, cells, crystalluria organize into urethral plugs, resulting in pain and stress which causes urethral spasming
- progression from non-obstructive (just painful) commonly to obstructive uropathy
describe feline lower urinary tract disease (FLUTD) etiology
- very common
-feline idiopathic cystitis is most common cause - less common is urethral calculi or uroliths
- even rarer are UTIs, urethral strictures, or neoplasia
describe lifestyle triggers for urethral obstruction for cats idiopathic cystitis/FLUTD
- indoor only cats
- nervous/fearful cats
- dry food only
- obesity, inactivity
- multi-cat households
- infrequent water intake
- not enough litter boxes
- life event: moving, new family member (human or animal), holidays (parties)
describe lower urinary signs
- stranguria: straining to urinate
-can be confused for constipation by owners - dysuria: abnormal/difficult urination
- hematuria: grossly bloody appearance to urine
-must differentiate from pigmenturia! - pollakuria: frequent small urinations
-common in inflammatory processes - periuria: inappropriate urination
-outside of box - other clinical signs can be very vague
-owners may not observe straining
-multi-cat households can be difficult to ID if someone isn’t peeing - spectrum from lethargy to shock
-systemic compromise - vomiting is frequent concurrent clinical signs
-increased intra-abdominal pressure and straining, also secondary to azotemia.uremia
EVERY SICK MALE CAT SHOULD HAVE HIS BLADDER PALPATED
describe physical exam for urethral obstruction
- assess cardiovascular stability FIRST
-hyperkalemia can cause ventricular arrhythmias and bradycardia
-may be in hypovolemic shock if vomiting - gentle palpation of bladder
-obstructed: large and firm, painful, unable to express (be careful!!), overfull water balloon
-non-obstructed: small, often empty (due to pollakuria), uncomfortable, soft, expressible (if not empty) - rectal exam (dogs);
-may be able to feel stones in urethra
-prostatic enlargement can cause urethral obstruction
describe initial ER diagnostics for urethral obstruction
- PCV/TS/lactate
- electrolytes/blood gas: mainly looking at potassium and renal markers
- AFAST scan:
-abdominal free fluid? tap it!
–diagnose uroabdomen via paired K and creatinine
-identify urinary bladder: may see debris or stones
describe urinalysis of a urethral obstruction
- usually lots of blood and protein
2 crystalluria does not confirm presence of stones but does suggest risk
- pH:
- <7.0: calcium oxalate, purines, and cystine
- >7.0 struvite - urine culture and susceptibility:
-indicated because UTIs may occur secondary to stones or may induce stone formation
-FLUTD uncommonly associated with infections though
describe radiographs of urethral obstruction
be sure to get ENTIRE urethra in image!!
- radiopaque stones: size, shape, how many, where they are
- not usually helpful for masses unless using contrast
- if placing indwelling urinary catheter, take radiographs AFTER to also confirm placement of catheter in urinary bladder
describe full abdominal ultrasound for urethral obstruction
- not usually needed for blocked toms
-mostly for dogs - most helpful if suspect tumor of bladder or urethra (such a TCC)
- can help identify radiolucent stones
what is the first treatment goal for urethral obstruction?
treat hyperkalemia!!!
- potassium can become extremely elevated due to decreased excretion
- clinical consequences:
-ECG changes:
-variable arrhythmias: predominantly bradycardia - life threatening!!
-should be first priority of initial assessment and stabilization - unblocking and fluids are ultimate treatment
-this takes time, so treat in other ways to buy time from definitive intervention
describe hyperkalemia ECG in order of what is seen (earliest to latest)
- suppression of P wave amplitude
-treat even with this most mild change!! - widened QRS complex
- tented T waves
- bradycardia
- atrial standstill
- ventricular tachycardia/fibrillation
describe the drugs used to treat hyperkalemia
- calcium gluconate:
-MOA: reduced cardiac excitability by increasing RMP
-dose: give SLOW (over 10 min)
-does not decrease K+, is just cardioprotective while waiting for other interventions to work - dextrose:
-MOA: stimulates endogenous insulin release, driving K+ into cells
-well tolerated, least aggressive - insulin:
-MOA: drives K+ into cells
-FOLLOW WITH DEXTROSE or will make hypoglycemia - terbutaline:
-stimulates Na-K-ATPase pump to drive K+ into cells
-may induce tachycardia - sodium bicarbonate:
-indirectly activates Na-K-ATPase pump to drive K+ into cells
-reserved for refractory/severe cases
what is next for treating urethral obstruction after treating hyperkalemia?
urinary catheterization; but NEED SEDATION (heavy and/or general anesthesia)
- use pure-mu such as methadone or fentanyl optimal for analesia
- other sedation titrated to effect and based on hemodynamic stability and comorbidities
-dexmedetomidine if no CV instability
-midazolam +/- ketamine or alfaxolone if heart disease or CV unstable
-intubation and inhalant GA if necessary - adjust based on patient
-consider local blocks
-very sick may need little to no drugs
describe decompressive cystocentesis
- alleviates discomfort, gives you more time to prepare to unblock
-pros: easier to unblock without backpressure, especially if trying to retropulse stones
-risk: uroabdomen, infection, hemoabdomen - likely safe IF bladder is drained
-unhealthy bladders at risk regardless
describe urinary catheter placement
- position in dorsal, stretch legs cranially
- clip around prepuce/scrotum, scrub (iodine)
- use sterile technique
- extrude penis: apply downward pressure above and below prepuce
- once catheter is seated. pull penis dorsally and caudally to straighten urethra
- advance catheter while flushing to retropulse intaluminal sludge, crystals, etc,
-the flushing is what relieves the obstruction, NOT the catheter
-DO NOT apply heavy pressure to obstruction with catheter, you WILL tear the urethra - if using separate unblocking catheter, remove, place indwelling, and secure to prepuce
- empty +/- lavage bladder
- recover with an e collar ON!!
describe the 4 types of urinary catheters
- tom cat: rigid and can cause tissue trauma, not intended for indwelling use
- red rubber: flexible, can be left as indwelling, cheap, requires butterfly, tape, and suture to secure
- slippery sam: can be used to unblock and left indwelling
- mila urinary catheter: can be used to unblock or left indwelling
describe retrograde hydropulsion
- heavy sedation and decompressive cystocentesis first
- flush urethra with a 1:1 mixture of saline and lubricant
- assistant places gloved finger into rectum and occludes pelvic urethra by placing firm pressure against the ischium
- a urinary catheter is attached to a 20-35ml syringe filled with saline is inserted into urethra and advaced to site of stones
- saline injected until pelvic urethra expands
- assistant quickly removes pressure on pelvic urethra while you continue to quickly flush saline through catheter
- goal is to propel saline and stones back into bladder
what if you cannot de-obstruct the urethra or tear it?
- percutaneous antegrade urethral catheterization
-feed guidewire from bladder down urethra (wuth US or fluoro guidance) and feed u cath over wire back into bladder - percutaneous pigtail cystotomy tube:
-bypass urethra
-indwelling catheter placed through body wall into bladder
both above take skill and special equipment (specialty)
when in doubt: decompressive cysto overnight, try to unblock again next day or refer
what if the owner cannot afford hospitalization?
- successful outpatient therapy
-decompressive cysto
-acepromazine and analgesia
-low-stress environment or discharge - not for cats with elevated creatinine
describe in hospital management of a blocked cat
- IV fluids
-correct dehydration
-post-obstructive diuresis: match ins with outs - monitor urine output and appearance closely:
-once urine appears mostly normal and underlying cause of obstruction fixed, can remove catheter - usually need some degree of analgesia
-don’t usually recommend NSAIDs due to kidnye injury during obstruction - do not recommend antibiotics unless have proof of active UTI contributing to obstructive process
what if it happens again?
perineal urethrostomy: amputates distal penile urethra, prevents obstruction
-does not prevent FIC or non-obstructive FLUTD signs
risks: ascending bacterial cystitis, urethrostomy or urethral stricture
-owners report good long term QOL
describe prognosis of urethral obstruction
- 90-95% survival to discharge with optimal care
- recurrence is common:
-33% of cats have recurrent UO; reobstruction is significant cause for euthanasia bc costly - factors associated with increased RUO
-older, indoor only, larger, catheter, use of phenoxybenzamine and prazosin
