Page 637 - Small Animal Internal Medicine, 6th Edition

CHAPTER 36 Hepatobiliary Diseases in the Dog 609

BOX 36.7
VetBooks.ir Treatment of Acute Encephalopathic Crisis

• Remove or treat any identified precipitating cause.
• Give nothing by mouth for 24–48 hours and IV fluids.
• Avoid fluid overload; measure central venous pressure
or monitor carefully clinically.
• Avoid or treat hypokalemia (triggers hepatic
encephalopathy).
• Avoid or treat hypoglycemia (monitor blood glucose
level every 1–2 hours, particularly in small breeds, in
which hypoglycemia is common and can cause
permanent cerebral damage).
• Monitor body temperature, and warm gently or cool
as necessary if hyperthermic after seizures. FIG 36.14
• Administer enemas to remove ammonia from colon— Miniature Schnauzer with a congenital portosystemic shunt
warm water, lactulose, or dilute vinegar. that had postligation seizures and was stabilized with a
• Instill a neomycin retention enema after the colon is propofol infusion.
clear and administer IV ampicillin.
• Treat any seizures: enough to start eating. Propofol infusions can result in Heinz
• Carefully rule out treatable causes (e.g., electrolyte body hemolytic anemia in dogs and cats. Levetiracetam has
imbalances, hypoglycemia, hypertension, been reported to be effective at reducing the risk of post-
idiopathic epilepsy).
• Maintain other intensive care measures (as earlier). operative seizures and death in dogs undergoing surgical
• Treat with anticonvulsant—exact protocol attenuation of extrahepatic PSS with ameroid constrictors
controversial. Options are: when the dogs were pretreated with 20 mg/kg PO q8h, for
• Levetiracetam 20 mg/kg bolus. Repeat as a minimum of 24 hours before surgery (Fryer et al., 2011).
necessary every 20 minutes to maximum However, a recent large multicenter study did not support
60 mg/kg followed by 20 mg/kg tid. Unlikely the use of preoperative levetiracetam as protective against
to work for postligation seizures if dog already seizures, leaving clinicians unclear as to whether to use it
on levetiracetam. or not (Mullins et al., 2019). There are no studies describing
• Propofol bolus (3.5 mg/kg dogs; 1 mg/kg cats) the use of levetiracetam IV in dogs with PSS that are already
followed by infusions (0.1–0.25 mg/kg/min) seizuring, but there are anecdotal reports of its efficacy in
often effective. this situation.
• Phenobarbitol, ketamine, or dexmedetomidine
may also be used. In spite of some early promising reports, there is still no
• Diazepam of very limited efficacy. convincing evidence in support of other pharmacologic
treatments for HE, apart from antibiotics and lactulose, so
other drugs cannot currently be recommended for use in
dogs. Trials of the benzodiazepine receptor antagonist flu-
choice, with potassium added according to its serum con- mazenil in human patients with refractory acute HE have
centration. Serum electrolyte concentrations in dogs with had mixed results. Although flumazenil has been studied in
HE are extremely variable; until the results become available, animals for its ability to reverse the action of benzodiazepine
20 mEq KCl/L in the fluids administered is a safe amount tranquilizers, there have been no clinical studies on its use
to add. Seizuring dogs can be stabilized with a loading dose in acute HE in animals.
of levetiracetam intravenously (see Box 36.7) or low-dose
propofol infusions (Fig. 36.14). The dose of propofol is calcu- DISORDERS ASSOCIATED WITH HIGH
lated by giving an initial bolus to effect, usually about 1 mg/ PORTAL PRESSURE
kg, timing how long it takes for the animal to show mild There are a number of less common congenital vascular dis-
signs of seizures, such as mild limb paddling again, and then orders of the liver in dogs that present with normal or high
dividing the dose by the time required to calculate an infu- portal pressure, rather than the low portal pressure seen in
sion rate. For example, if after a bolus of 1 mg/kg of propofol association with a congenital PSS. Because of the portal
the dog shows signs of seizure activity again after 10 minutes, hypertension, the affected dog may present with the constel-
the infusion rate would be 1/10 = 0.1 mg/kg/min. In practice, lation of typical clinical signs (see Chapter 33), including
the dose of propofol to be given by constant rate infusion is ascites, and the potential for GI ulceration in addition to
usually about 0.1 to 0.2 mg/kg/min. Dogs sometimes need multiple acquired PSSs and HE. With the exception of
to remain on the infusion for hours or days, but the rate can arteriovenous fistulae, none of these conditions can be
be gradually reduced to control seizures while still allow- treated surgically, but some of them have a good long-term
ing the dog to regain consciousness—in some cases, even prognosis with medical management.