Anesthesia for Animals with GI and Hepatic Disease

Question 1

what disturbances SHOULD be corrected before surgery in GI patients?

Answer 1

fluid, electrolyte, and acid-base disturbances

Question 2

how can GI cases present? (5)

Answer 2

1. nausea and vomiting
2. abdominal distension/colic
   -very painful!!! give sedation/analgesia!
3. obstruction or perforation of the GI tract
   -esophageal/GI masses and FB
   -intussusception, volvulus, impaction
4. loss of vascular and mucosal integrity
5. susceptible to bacteremia, endotoxemia, sepsis, hypotension, and ararhythmias

Question 3

describe pre-anesthetic preparation of GI patients

Answer 3

1. rehydration
2. relief of abdominal distension and pain
   -sedation, pain management
   -deflate if you can:
   –SA = orogastric tube, or use trochar or catheter under sedation over area of most distension/ping
3. antimicrobials
4. pre-anesthetic medication
5. ECG monitoring:
   -VPC= most common seen in GI patients!
   -if frequent, weak pulse, multifocal, and high HR, treat!
   -VPCs due to: pain, electrolyte abnormalities (K+), myocardial ischemia, acid-base imbalance, altered sympathetic activity, drugs, intra-abdominal masses (spleen)
   -use lidocaine to treat and consider fentanyl CRI
6. pre-oxygenation
7. anti-emetic drugs
   -don’t want them vomiting when sedated/intubated and can’t protect airway!! these patients are at high risk of aspiration pneumonia

Question 4

what are the consequences of abdominal distension?

Answer 4

1. compression of diaphragm and lung field
   -atelectasis (alveoli start to collapse)
   -decrease in pulmonary compliance
   -decrease in gas exchange (hypoxemia)
2. compression of vena cava
   -decrease in venous return (preload)
   -decrease in cardiac output
   -decrease in tissue perfusion

address as soon as you can!!!

Question 5

describe drug considerations for GI patients

Answer 5

1. opioids and benzodiazepines:
   -good analgesia and sedation with minimal cardiovascular depression
   -can induce anesthesia
   -GOOD to use
2. acepromazine:
   -hypotension, long duration, no analgesia, not reversible
   -AVOID
   -if end up having to do CPR and using epi, will not be able to achieve vasoconstriction as effectively with acepromazine on board! (works on alpha and beta receptors)
3. alpha-2 agonists:
   -hypertension, vomiting, bradyarrhythmias, sedatives, analgesic
   -pros and cons, use really depends on situation; low doses may be appropriate and is reversible! if really sick and recumbent, probs avoid
4. etomidate:
   -no cardiovascular depression, good for induction
   -GOOD for use! esp if very sick and recumbent
5. ketamine:
   -used with benzodiazepines
   -can stimulate the sympathetic nervous system
   -could help SNS increase CO
   -GOOD to use (in lower doses)
   -but if animal has been sick for a while (horse colicking 12-24hr or several hours) may be catecholamine depleted so stimulation of SNS may no longer yield any results
6. propofol and alfaxolone:
   -hypotension, short duration, not analgesic, respiratory depression
   -pros and cons: resp depression counteracted if intubate and ventilate; may just avoid a big bolus because will cause more hypotension then you want
7. isoflurane and sevoflurane:
   -inhalants of choice, rapid onset and quick recovery, will cause the MOST CV depression
   -pros and cons depending on how sick the animal is
   -maybe better to combo inhalant plus injectable (CRIs to use lower dose of inhalant)

Question 6

describe analgesia of SA GI patients

Answer 6

1. systemic drugs: boluses and/or CRIs
   -opioids, alpha-2 agonists, ketamine, lidocaine, etc.
2. local blocks:
   -transversus abdominus plane (TAP) block
   -rectus sheath block

Question 7

describe analgesia of LA GI patients

Answer 7

1. systemic drugs: boluses and/or CRIs
   -opioids, alpha-2 agonists, ketamine, etc.
2. local blocks:
   -ruminants: inverted L, distal paravertebral and proximal paravertebral
   -allows for lots of standing surgical options

Question 8

describe monitoring and support of GI patients

Answer 8

1. MM color and CRT: perfusion
2. invasive blood pressure: common for acute abdomen
3. PCV/TP, blood gases, electrolytes
4. fluid therapy: crystalloids and colloids
5. analgesics
6. oxgen on recovery
7. maintain normal body temp

Question 9

describe intra-op monitoring and support of GI patients

Answer 9

1. mechanical ventilation: pros and cons
   -inspiratory phase during normal breathing is CV friendly and promotes preload
   -mechanical ventilators are the opposite! creating positive instead of negative pressure in the thorax = decrease preload
2. minimize inhalant concentration to avoid hypotension
   -supplement CRIs: opioids, ketamine, lidocaine
3. blood pressure and ECG
   -better invasive BP
   -maintain adequate perfusion
4. positive inotropes and vasopressors
   -help to maintain perfusion
   -review table!!

Question 10

describe clinical presentation of chronic GI patients

Answer 10

1. chronic V/D
2. weight loss and muscle waste
3. change in appetite
4. abdominal discomfort or pain
5. changes in stool consistency/appearance
6. edema or ascites due to hypoproteinemia

Question 11

why do we anesthetize chronic GI patients?

Answer 11

1. diagnostic procedures:
   -endoscopy +/- biopsies
   -exploratory laparotomy
   -image-assisted procedures
   -swallowing studies
2. therapeutic procedures:
   -feeding tube placement
   -surgical correction of stensosi
   -mass removals

Question 12

what are anesthetic concerns of chronic GI patients?

Answer 12

1. hypoproteinemia
   -TP <3.5-4g/dL or
   -albumin <1.5 g/dL
   -give colloids!!
2. regurgitation/aspiration:
   -due to decreased motility
3. electrolyte imbalances
4. acid-base disturbances
5. anemia

Question 13

describe drug considerations for chronic GI patients

Answer 13

1. anesthetic drugs are protein bound
   -the lower protein in these chronic patients results in more unbound drug available
2. protein is necessary for oncotic pressure
   -increased risk of hypotension
   -risk of edema

Question 14

what drugs may be considered to prevent regurgitation and aspiration in chronic GI patients

Answer 14

1. pre/peri anesthetic promotiliy agents
   -cisapride
   -mnetaclopramine
2. other pre-anesthesia GI meds
   -famotidine
   -omeprazole: MUST be oral (give a few days prior)
   -pantoprazole: IV, can switch to day of procedure
   -maropitant
   -ondansetron

Question 15

describe anesthetic concerns for hepatic disease

Answer 15

1. hypoglycemia
2. hypoproteinemia
3. decreased clotting factors
4. decreased drug metabolism

remember!
-hepatic enzyme activity is NOT indicative of hepatic function; use
1. chemistry: albumin, BUN, bilirubin, glucose, cholesterol
2. specific tests: pre and post prandial bile acids, ammonia levels, coagulation tests

Question 16

what are precautions for patients with liver disease?

Answer 16

1. avoid agents requiring excessive hepatic metabolism
2. maintain adequate cardiac output and BP to prevent poor hepatic flow
   -liver receives about 20% of CO
3. avoid hypoxemia, can lead to hepatic hypoxia
4. know coagulation status and be prepared to treat abnormalities
   -factors V, VII, IX, XI, XII, XIII, fibrinogen, prothrombin, plasminogen, antithrombin, etc, made in liver
5. investigate and treat if present:
   -hypoproteinemia
   -hypoglycemia

Question 17

describe drug considerations for hepatic patients

Answer 17

1. avoid drugs that are:
   -long acting
   -non-reversible
   -highly metabolized by liver
   -can cause severe CV depression

-ex. acepromazine, medetomidine, dexmedetomidine

2. use drugs that are:
   -short acting
   -reversible
   -have high hepatic extraction ratio (ER)
   –hepatic clearance = cardiac output x ER
   -are CV friendly

-ex. benzodiazepines, opioid (except methadone), propofol, isoflurance, sevoflurane

Question 18

describe anesthetic management of hepatic patients (4)

Answer 18

1. may need inotropic support of blood pressure
2. maintain adequate fluid and oncotic support
3. keep normothermic
4. maintain urine output
   -using a catheter because if kidneys are perfused, so is the liver
   -not used very often due to concerns for contamination