Exam 3 - Congenital Portosystemic Shunts Flashcards
the portal vein collects blood from what major organs?
pancreas, spleen, & gi tract - filtered through the liver prior to entering systemic circulation
T/F: 75-80% of the afferent blood supply & 50% of the oxygen supply to the liver is taken care of through the portal vein
true
what is the general definition of a liver shunt?
abnormal connection between the portal vasculature & systemic circulation
what are the 3 main types of congenital PSS?
- extrahepatic
- intrahepatic
- microvascular dysplasia
when do we see acquired PSS?
occurs secondary to portal hypertension - usually multiple, near the left kidney/root of the mesentery
liver failure
T/F: extrahepatic shunts make up 65-75% of congenital shunts in dogs & cats
true
how do extrahepatic shunts happen?
originate from any part of the portal vein & connect to the caudal vena cava in the abdomen or the azygous vein in the thoracic cavity
how does microvascular dysplasia/portal vein hypoplasia occur?
small intrahepatic portal vessels/portal endothelial hypoplasia
abnormal flow of blood between portal & systemic circulation
very similar presentation to extrahepatic PSS - may happen concurrently
what is an intrahepatic shunt?
the shunt is occurring within the liver - 35% of single congenital PSS in dogs & 10% in cats
what is the common presentation of companion animals with extrahepatic shunts?
small & toy breeds - yorkies, havanese, maltese, pugs, & mini schnauzers
usually presents <1 year of age with the exception of mini schnauzers (7 years old +)
may be combined with microvascular dysplasia
what dogs are commonly affected by microvascular dysplasia alone?
cairn terriers & yorkies
what signalment is commonly seen with intrahepatic shunts?
large breed dogs - irish wolfhounds, goldens, labs, GSD, cattle dogs
why may we see more severe signs at a younger age in dogs with an intrahepatic shunts?
they have large shunt volumes, so affected faster
what are the 3 main categories of clinical signs seen in animals with PSS?
- neurologic
- gastrointestinal
- urinary
what is the most important toxin involved in hepatic encephalopathy?
ammonia!!! it crosses the blood brain barrier
why is it so bad that ammonia crosses the blood brain barrier?
leads to hepatic encephalopathy because the brain doesn’t have a urea cycle
NH3+ glutamine leads to osmotic stress of astrocytes -> cell swelling -> edema in the brain
what is the underlying cause of the majority of clinical signs in animals with PSS?
hepatic encephalopathy - hyperammonia
what may exacerbate signs of hepatic encephalopathy?
high protein meal
concurrent disease - infection
what are the main sources of ammonia in the body?
small intestinal enterocyte catabolism of glutamine!!!!
endogenous protein metabolism
bacterial breakdown of AA in colon
bacterial & intestinal urease action on urea
T/F: signs related to hepatic encephalopathy worsen after eating in 30-50% of cases
true
what general signs are associated with hepatic encephalopathy? what are some more severe signs?
general - anorexia, depression, weight loss, nausea, ptyalism (especially in cats), & intermittent vomiting
severe - ataxia, aggression, circling, head pressing, cortical blindness, coma
what animals with PSS are at risk for urethral obstruction?
small male dogs
what urinary tract signs are seen in relation to PSS?
ammonium biurate crystals collect in the bladder & form urate cystoliths (not visible on rads)
stranguria, pollakiuria, & hematuria
what is a unique clinical sign seen in cats with PSS/hepatic encephalopathy?
copper irises
what is seen on a chemistry panel that is supportive of PSS?
low BUN, cholesterol, albumin, glucose
mild to moderate AlkP and/or ALT elevation
what is seen on a CBC that is supportive of PSS?
microcytosis, normochromic non-regenerative anemia, & possible leukocytosis
what is seen on a urinalysis that is supportive of PSS?
decreased USG & ammonium biurate crystalluria
when should you do a coag panel for PSS animals?
in very sick animals - prolonged PT in about 53% of PSS patients
how are bile acids used for diagnosing an animal with PSS?
pull blood after the patient has fasted for 12 hours
feed a small amount of food with a normal fat content - fat is the primary stimulus for CCK secretion
pull blood 2 hours later
with PSS, post-prandial bile acids are typically in the 100s (10-20x pre-prandial)
normal range for pre-prandial: <13
normal range for post-prandial: <25
what is the normal physiology of bile acids? what is the abnormalities seen in this sequence in animals with PSS?
bile acids are released by the liver/gall bladder into the duodenum & are normally absorbed via the portal vein & returned to the liver for reabsorption
with a PSS, post-prandial bile acids are not effectively returned to the liver, so post-prandial bile acid levels are markedly elevated
how is ammonia testing used to diagnose PSS in dogs/cats?
blood ammonia levels will be elevated in animals with liver failure or PSS
doesn’t remain stable once drawn - must transport on ice & run immediately (normal range is 0-50)
T/F: abnormal hepatic function testing doesn’t confirm PSS, but it does confirm that hepatic function is reduced
true
what imaging is used for diagnosing PSS?
CT angiography - look for anomalous vessels between the portal vein & vena cava, decreased number of hepatic & portal veins, small liver size, & portal vein:aorta ratio <0.7
what is the gold standard of diagnosing PSS in humans?
CT angiography - helpful for surgical planning, & less reliant on user experience than ultrasound
how is an abdominal ultrasound used to diagnose PSS?
very operator dependent, & has a better sensitivity for intrahepatic shunts vs extrahepatic shunts
how is nuclear scintigraphy used to diagnose PSS in small animals?
injection of Tech-99m & look for activity to appear in the heart compared to the liver
what are the goals of medical management for PSS?
manage clinical signs
decrease absorption of ammonia
decrease interaction between enteric bacteria & nitrogenous substances in the gi tract
in severe cases, reduce cerebral edema
think of as palliation & not a cure
how is diet management used for treating PSS?
highly digestible, moderately protein restricted diet (14-18% in dogs & 24-31% in cats)
small frequent meals to reduce work by the liver
what are the benefits of using lactulose for patients with PSS?
decreases colonic pH through the trapping of ammonium ions within the colon to decrease absorption
inhibition of ammonia production by colonic bacteria
movement of water into the colon via osmosis decreases the transit time through the gi tract which leads to decreased bacterial ammonia release
how is lactulose used for patients with PSS?
synthetic disaccaride
given orally or via enema in emergency situations - titrate dose to achieve 2-3 soft stools per day, but not diarrhea
what are some common antibiotics used for treating PSS?
metronidazole, amoxicillin
given orally if patient is stable - IV if not
what is the purpose of using antibiotics for animals with PSS?
reduce gi flora to reduce ammonia production
when are anticonvulsants indicated for use in animals with PSS?
always indicated if patient is actively seizing - acutely stop seizure (midazolam) & start keppra
what medicine should be used if you think your patient has an intrahepatic PSS?
proton pump inhibitor!!!! omeprazole - need to prevent gastric ulcers
what is the goal of using surgery for treating patients with PSS? how are these patients managed prior to & after surgery?
gradually occlude the anomalous vessel to restore normal blood flow through the portal vein
stabilized with medical management first & then continued at least 8 weeks post op
why is there a high anesthetic risk for animals with PSS?
these animals have a poor drug metabolism
if small, risk of hypothermia
higher risk for hypotension
are you going to pursue surgical correction for acquired PSS? why?
nope - contraindicated
will make portal hypertension worse
are you going to pursue surgical correction for microvascular dysplasia? why?
no - no surgical cure
medical management only
what surgical options do you have for extrahepatic PSS correction?
ameroid constrictor
thin film banding
partial or complete suture ligation
what surgical options do you have for intrahepatic PSS correction?
endovascular coiling
ameroid constrictor
thin film banding
partial or complete suture ligation
why is complete ligation not well tolerated in patients with PSS?
overloads the liver leading to portal hypertension & severe complications and may require a second surgery later on
how is suture ligation done for correcting PSS?
dissect around the shunt & occlude with silk suture
can measure intra-operative portal pressure to guide degree of ligation
generally not a recommended procedure
what is an ameroid constrictor? how is it used for correcting PSS?
inner ring of casein surrounded by stainless steel ring, so casein swells as it absorbs body fluids which decreases the inner diameter & causes a fibrotic reaction
causes gradual attenuation of the shunt - majority within 3-10 days but continued occlusion over 2-5 weeks
what is thin film banding? how is it used to correct PSS?
strip of cellophane cut & folded that is passed around the shunt & secured with metal hemoclips
gradual occlusion due to fibrosis & inflammation - closure times are variable, & complete closure may be less predictable especially in cats
how is endovascular coiling used to correct intrahepatic PSS?
vascular stent is placed in the vena cava & thrombogenic coils are placed in the shunt which causes acute partial occlusion & gradual complete occlusion
what other things should be done during surgical correction of a PSS?
liver biopsy - especially in patients where a shunt was suspected but not identified, if biopsy is consistent with a shunt, likely have microvascular dysplasia
address any uroliths
spay/neuter - hereditary component of the disease
what are some post-op considerations of your PSS patients?
close ICU monitoring - shunt isn’t occluded right away, so still must treat as if they have a PSS
continue medical management for at least 8 weeks after rechecking bile acids or ammonia every 4 weeks & gradually discontinuing medical management if tolerated by the patient
what are mortality rates seen post-op in extrahepatic & intrahepatic PSS?
extrahepatic - 32% with suture ligation, 7% with ameroid, & 6-9% with thin film banding
intrahepatic - acute mortality up to 28% but improving with endovascular techniques
what are some post-op complications seen in PSS patients?
hypoglycemia
seizures - often refractory/fatal
portal hypertension - rare with ameroid, but when acute, life threatening
bleeding
development of additional single or multiple acquired shunts - secondary to chronic portal hypertension or the shunt vessel closed too quickly for portal system to adjust
what is the prognosis of a patient with an extrahepatic PSS using medical management?
can have long term survival but doesn’t reverse underlying disorder - within 5 years, 90% of medically managed dogs die
what is the prognosis of a patient with an extrahepatic PSS using surgical correction?
comparable short & long term outcomes between ameroid & thin film banding
best if complete ligation achieved - more likely with ameroid
80-94% in dogs & 75-80% in cats
why is medical management for intrahepatic PSS not successful alone?
these animals are progressively neurologic & urinary signs are common
what is the prognosis for intrahepatic shunts treated surgically?
fair to excellent in 80% of dogs with a MST >6 years
