EQUINE BOARD REVIEW

Colic highlights:

·         Ý Temp – anterior enteritis, Colitis

·         Ý Pulse – Ischemia, obstruction, displacement

·         Ý reflux – anterior enteritis

·         Rectal palpation

NSAIDS

·         Most commonly used:

a.       Banamine

b.       Phenylbutazone

c.       Dipyrone

d.       Ketoprofen

·         Inhibit cyclooxygenase enzyme-mediated production of eicosanoids form arachidonic acid in the cell membrane

·         Ketoprofen may also reduce inflammation by inhibitng lipoxygenase enzyme mediated synthesis of leukotrienes

·         Toxicity:

Phenylbutazone > Banamine > Ketoprofen

·         Toxicity thought to be result of reduced local sythesis of PGE causing decreased GI and renal blood flow and GI cytoprotection

·         Exacerbated by dehydration

·         Side effects:

a.       GI ulceration

b.       Protein loss

c.       Abdominal pain

d.       Endotoxemia

e.       Ulceration of the right dorsal colon – phenylbutazone

f.         Paplillary necrosis – renal toxicity from phenylbutazone

·         H2 antagonists  and sucralfate

Anti-ulcer meds

·         H2 antagonists (Cimetindine – Tagamet)

·         Proton pump inhibitors (Omeprazole – Prolosec)

·         PGE2 (Misoprostol)

·         Cytoprotective agents - Sucrafalate

H2 blockers – Anti-ulcer medications

·         Hydrophobic histamine analog (contains an imidizole ring)

·         A Reversible competitive antagonist to H2 receptor, It has NO H1 blocking activity, so acts solely on gastric secretion (no effect on allergic rxns)

·         Blocks histamine stimulated gastric acid secretion by 85-100% (usually around 85%)

·         Has no effect on gastric motility, bilary or pancreatic secretion

·         Used chronically in human medicine, but should be used for a 12 week period only.  Ulcers will come back after medication is stopped b/c H. pyloric bacteria.  So Tagamet + antibiotic are ulcer tx.

·         Clinical uses include gastric ulcer tx, chronic gastritis, reflux exophogitis, prophylactically prior to mast cell removal

·         Examples

Ranitidine (Zantac)

Fomotidine (Pepcid)

Nizatidine (Axid)

Cimetidine (Tagamet) – has profound effect on microsomal enzyme inhibitors, so has many drug interactions.

     Physiologic H2 Blocker – Proton Pump Inhibitor

·         Omeprazole (Prilosec)

·         Blocks ALL acid producers b/c blocks protone pump,  blocks 100%, gastric acid is completely inhibited

·         Used in cases that are refractory to competitive H2 blockers

·         Cost twice as much as Cimetdine, so not used much in vet med

·         Recommended for short term use only b/c can  cause gastric hypertrophy, will actually change the morphology of the stomach

Sucralfalate

Sucrose almuminum hydroxide give PO

Action:  Sucrose and aluminum split and sucrose physically binds to the epithelium ulcer and protests it from acid.  Also binds to acid & bile & inactivates it

Advantages – minimal abstorption. Stays in the stomach, cheap

Disadvantages – must give regularly, also binds to orally administered drugs esp Tagamet

Can give 1-2 hours prior to other anti-ulcer medications to allow Sucralfate time to bind to ulcer

Avoid Sucralfate in decreased kidney fxn.

PGE1 (Misoprostel (Cytotec)

·         Prevents NSAID-induced gastric ulcers

·         Arthritic dogs on chronic aspirin tx has ß GI ulceration when given misoprostel

·         This should not be used around pregnant women b/c it may cause abortion

·         Rapidly absorbed through the skin

DMSO

·         Scavenge hydroxyl radicals generated by neutrophils during inflammation and reperfusion

·         Tx endotoxemia and cerebral edema

·         Can cause IV hemolysis, so no greater than a 10 percent solution should be administered at a relatively slow rate

Dental disorders

Cribbing

·         Excessive wear on rostral margin of upper central incisors

Supernumerary teeth

·         Dental bud is split during development, usually with incisors

Parrot mouth – brachygnathia, the upper jaw is longer than the lower jaw

Sow mouth/monkey mouth – prognathia, the lower jaw is longer than the upper jaw

Shear mouth

·           Maxilla is wider than the mandible

·           Sharp edges on buccal of upper and lingual of lower

Other disorders

·         Wolf tooth extraction – First premolar

·         Removal of dental caps – deciduous teeth of premolars that can impede the eruption of underlying permanent tooth

·         Extraction of cheek teeth – severe periodontal dz w/ abscesses w/in the roots; requires general anesthesia and intubation; x-rays

Equine Anesthesia and recovery

Preanesthesia

a.       withold food for 12 hours (not water)

b.       Mineral oil 6 hours before sx

c.       Atropine or Isoproterenol only when anesthesia used will induce bradycardia (atropine will cause ileus)

d.       Sedate with Xylazine or Detomidine

Anesthesia

a.       Induction agents – GG, Thiopental, Ketamine, Telazol, Profofol

b.       Inhalation – Halothane (more potent and more lipid soluble, but more myocardial depression), Isoflurane (peripheral vasodilation), Sevoflurane

Blood pressure during anesthesia – ideal MAP is 60-90

a.       Dobutamine - b agonist

b.       Dopamine - Ý renal fusion

c.       Phenylephrine – only if very low BP, short acting

d.       Ephedrine – vasopressin

Ventilation during anesthesia

a.       Normal ventilation is  PaCO2 is 35-45

b.       However, moderate hypercapnia of PaCO2 > 55-65 will actually improve muscle perfusion and prevent neuropathy post sx

c.       Severe hypercapnia of > 70 mmHg shifts dissociatio curve to the right causing arrhythmias and abnormal breathing patterns

Anesthesia complications

Apnea caused by:

·         Early induction period of anesthetic b/c high plasma protein concentration

·         Too deep anesthesia

·         Doxapram can be used as a respiratory stimulant that also initiates relase of endogenous epinephrine and causes and Ý in HR and BP

Hypoxemia

·         Is when PaO2 is less than 60 (should be > 90)

·         Caused by hypoventilation or ventilation –perfusion mismatch

·         Tx by:

a.       Dobutamie infusion – increases oxygen delivery to tissue

b.       Clenbuterol - b2 agonist

c.       minimizing time in dorsal recumbency

Neuromyopathy

·         Swollen and painful muscle, weakness, profuse sweating, myoglobinuria (port wine urine), Ý CK, SGOT, non-weight bearing

·         Caused by:

a.       improper positioning during anesthesia

b.       malignant hyperthermia

c.       prolonged sx

d.       excessive anesthetic depth

e.       low PaO2, ß BP or acidosis

·         Prevented by:

a.       maintaining light anesthesia and c/v fxns

b.       avoid excessed preanesthetic especially phenothiazines

c.       Adequate padding

d.       Support of upper front and hind legs

e.       Balanced electrolytes and Ca gluconate (maintain muscle contraction)

f.         Dobutamine, dopamine or ephedrine to maintain adequate BP

g.       Don’t put horse under until surgeon is ready

h.       Dantrolene – muscle relaxation

i.         Diazepam – muscle relaxation

j.         Na bicarb – correct metabolic acidosis

Standing sedation

·         Ace + (Xylazine &/or Butorphanol, Meperidine, Pentazocine &/or xylazine)

·         Xylazine + (Butorphanol, Pentazocine)

·         Detomidine + Butorphanol

Intercoccygeal Epidural

·         Lidocaine (5-10 mL) –fast & short

·         Xylazine in saline – slow & long

·         Lidocaine + Xylazine w/ saline – fast and long

Lumbosacral or suarachnoid epidural

·         Detomidine in saline &/or morphine

·         Butorphanol + lidocaine

Injectable anesthetics

·         Thiopental – long, rough recovery

·         GG/Thiopental – better muscle relaxation, poor analgesia

·         Xylazine/Ketamine – (xylazine 5 min before ketamine), smooth induction and recovery, inadequate muscle relaxation

·         Xylazine/Ketamine/Butorphanol – give w/ xylazine, improved analgesia

·         Xylazine/Ketamine/Diazepam – improved muscle relaxation

·         GG/Xylazine/Ketamine – narcosis, analgesia & muscle relaxation, smooth recovery, reverse w/ yohimbine, tolazoline, atipamezole

·         Detomidine/Ketamine – recovery depends on duration of anesthesia

·         GG/Detomidine/Ketamine – same as triple drip above, but recovery slightly longer

·         Xylazine/Telazol – relatively smooth recovery & may require more than one attempt

·         Detomidine/Telazol – same as above

·         Propofol – short term, rapid redistribution and hepatic metabolism

·         Profofol/GG – lasts longer

Viral Respiratory Dzs of horses

Equine influenza

Equine herpesvirus

Equine Viral Arteritis

Equine adenovirus

Equine rhinovirus

Equine Influenza

·         Contagious, aerosol transmission

·         Type A, envelope contains neuroaminase N and hemagglutinin H

·         Exhibits ‘Antigenic Drift’ so vaccines need constant updating

·         More severe in younger horses

·         Spread at shows, sales, racetracks, breeding farms

·         Clinical signs are acute onset, fever, coughing, nasal discharge

·         Can causes damage to resp tract leading to 2° bacteria infection

·         Cardiomyopathy due to viral damage to myocardium is rare sequela

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