With younger patients, you must be concerned about hypoglycemia and hypotension. Until oxygen pressures reach < 60mmHg, there is little change in oxygen saturation.
o Oxygen pressure of 60 mmHg means there is 90% oxygen saturation. Below 60 mmHg, oxygen saturation declines rapidly.
Adrenergic receptors are stimulated by epinephrine and norepinephrine.
o Alpha-1 & Alpha-2 adrenergic receptors are sympathetic receptors located on the arteries. They increase blood pressure by constricting arteries, which causes bradycardia.
o Beta-1 adrenergic receptors are in the heart and increase heart rate & contractility. o Beta-2 adrenergic receptors are in the lungs and smooth muscle. They dilate
bronchioles (let more air in lungs) and dilate skeletal muscles (to get more muscle blood flow).
Blood pressure is the force of the blood pushing against the arteries. o Vasodilators decrease blood pressure.
Vasoconstrictors increase blood pressure.
o Hypotension is systolic pressure less than 80mmHg & mean pressure less than 60 mmHg.
Treat hypotension by decreasing anesthetic gas, fluid boluses, and atropine / glycopyrrolate.
Can use dopamine (an alpha agonist) or norepinephrine CRIs to raise blood pressure.
Normal end-tidal CO2 is 35 – 40 cmH20.
o Best way to decrease CO2 is to increase ventilation. Can manually do this or
decrease anesthetic gas. Cardiopulmonary arrest:
o Under anesthesia, you have ~50% chance of return of spontaneous circulation (complete survival rate).
Under other circumstances, you have ~5% chance.
o The purpose of chest compressions and giving breaths is to maintain blood flow until you can get epinephrine into the body.
Chest compressions by themselves are unlikely to return spontaneous circulation.
o Signs of cardiopulmonary arrest include:
Lack of cardiac activity (no heart rate or blood pressure) Apnea (lack of breathing)
Centrally fixed eye with mydriasis o What to do with cardiopulmonary arrest:
Turn off anesthetic gas and any other depressants (opioid CRIs, etc.) Give shock dose bolus of fluids.
Ensure that airway is maintained by endotracheal tube (palpate larynx or use laryngoscopre).
Give 10 breaths per minute.
Give cardiac compressions (120 compressions per minute).
Purpose of external cardiac massage is to deliver oxygen and epinephrine to the heart and periphery.
Give 1 – 2 doses of low dose of epinephrine (0.01 mg/kg). Give a high dose of epinephrine (0.1 mg/kg) after that.
Epinephrine has alpha and beta adrenergic effects. It directly increases heart rate, heart contractility, and blood pressure. It decreases total peripheral resistance.
Can give atropine if you suspect the arrest is due to vagal stimulation. Open the chest at 4th intercostal space after five minutes of unsuccessful
compressions for intra-thoracic cardiac compressions. Compress apex to base (reverse milking). All anesthetic drugs diminish thermoregulation.
o Never use electric blankets because they burn animals.
o Cold temperature decreases coagulation, decrease leukocyte function, and causes peripheral vasoconstriction (hyperperfusion).
o Low temperatures lower the MAC of anesthetic gases, thus decreasing the required amount of gas.
Small, young, cachectic patients are at risk for hypoglycemia during surgery. o Can cause sympathetic hyperactivity.
Guaifenesin is a centrally-acting muscle relaxant with an unknown mechanism. o Succinylcholine is a depolarizing neuromuscular blocking agent.
o Atracurium is a non-depolarizing neuromuscular blocking agent. Premedication:
o Premedication is administration of drugs prior to anesthetic induction.
o Reduces apprehension, facilitates handling, enhancing peri-operative analgesia, and minimizing adverse effects of anesthetic drugs.
o Acepromazine
This is a phenothiazine.
Tranquilizer that is a dopamine antagonist.
Commonly given with an opioid for neuroleptanalgesia (a state of minimal responsiveness).
Major side effect is hypotension by being an alpha-1 antagonist. This is offset by benefits in healthy animals, but don’t use in hypovolemic patients.
Also decreases seizure threshold and platelet function. o Only decreases seizure threshold IV at higher doses. Causes splenic dilation, decreased hemoglobin concentration, and
decreased hematocrit.
o Don’t use acepromazine with splenic masses.
This can be reversed with the alpha-agonist phenylephrine, which has no cardiac effects.
Not reversible and not an analgesic.
Protects from arrhythmias, is an antiemetic, causes penile protrusion in horses, & is an antihistamine.
Decreases anesthetic requirements up to 40% (lowers MAC) o Opioids can be used as premedications.
o Alpha-2 agonists: (Xylazine, Medetomidine, & Dexmedetomidine) Ruminants are more susceptible.
Analgesics, sedatives, and muscle relaxants Reversed by yohimbine & atipamezole.
Can cause bradycardia, AV block, and decrease GI motility. Causes hypertension then hypotension.
Don’t use in pregnant females because it increases uterine tone. Inhibit insulin and cause hyperglycemia.
Inhibits anti-diuretic hormone (ADH), which means they increase diuresis
Xylazine can be given to cats to vomit.
Avoid in critically ill and heart failure patients because of cardiovascular effects.
o Benzodiazepines: (Diazepam, Midazolam, & Zolazepam) Muscle relaxants and anxiolytics
Are not analgesics Reverse with Flumazenil
o Anticholinergics: (Glycopyrrolate & Atropine)
Inhibit parasympathetic innervation; they increase heart rate and cause bronchodilation
Decrease GI motility, salivation, and bronchial secretions Cause mydriasis
Opioids:
o Analgesics that are parasympathomimetics (activate parasympathetic system). Major side effects dysphoria, respiratory depression, sedation, vomiting,
constipation, and bradycardia.
Decrease the anesthetic requirement (decrease MAC) of isoflurane. Subcutaneous administration causes more vomiting than other
administrations.
When combined with acepromazine emesis is inhibited. o Mu-agonists have greater analgesia than kappa-agonists. o Reversed with Naloxone.
o Hydromorphone Pure agonist o Methadone Pure agonist o Buprenorphine Mixed agonist-antagonits o Fentanyl Pure agonist
Shortest half-life; normally given as a CRI o Butorphanol Mixed agonist-antagonists o Morphine Pure agonist
Induces histamine release, so don’t use with mast cell tumor patients. Epidural morphine provides analgesia for at least 12 hours.
o
Tramodol
Longest acting opoid Induction Agents:
o Propofol:
An induction anesthetic unrelated to other general anesthetics. Causes poor analgesia.
Mechanism of action is unknown.
Causes respiratory depression, increased intraocular pressure, and bradycardia.
With repeated doses, propofol can cause Heinz body anemia in cats.
Short duration of action (2 – 5 minutes) Cleared by the liver.
Cats usually recover from propofol rapidly and smoothly. Not a controlled substance.
No antagonist. o Alfaxalone:
Neuroactive steroid molecule that binds to GABA receptors (inhibitory neurotransmitter).
Can cause respiratory depression, but to a lesser degree than propofol. Provides poor analgesia.
o Benzodiazepines o Ketamine
Ketamine causes an increase in muscle tone, increased intraocular pressure, and increased sympathetic tone.
Causes tachycardia and should be avoided in cats. That’s because up to 20% of cats have undiagnosed hypertrophic cardiomyopathy, where you want to lower heart rate to improve diastolic filling. Preserves blood pressure and breathing well. Also provides some
analgesia.
Combined with diazepam, ketamine is a very good induction agent in healthy patients.
Don’t use in head trauma patients because it will increase intracranial pressure.
Also don’t use in hyperthyroid patients because it can cause thyroid levels to increase.
Don’t use with pheochromocytomas or heart disease because ketamine causes an increase in catecholamines.
Cleared by kidneys in cats and liver in dogs. o
Thiopental is a barbiturate that can cause cardiac arrhythmias.
Thiopental is the barbiturate with the shortest onset of action and duration. Ventricular bigeminy is the most common arrhythmia.
Thiopental, like acepromazine, causes splenic engorgement.
Is a strong irritant if it goes perivascular. Treat by diluting the area with saline.
Not gold standard but can be used effectively and cheaply in healthy patients.
Don’t use in sighthounds (including Greyhounds) because they don’t metabolize it well.
Protein-bound, so will get a disproportionately large effect in hyperproteinemic animals.
Inhalant Anesthetics:
o Advantages over injectable anesthetics are minimal metabolism, rapid adjustment, and the ability to give with oxygen.
o Inhalant anesthetics are the most cardiodepressive drugs.
o Inhalant anesthetics are vasodilators, which decrease blood pressure.
o Can cause malignant hyperthermia due to a hypermetabolic state, especially in swine.
Treat with Dantrolene.
o Less potent & higher MAC = slower induction and recovery.
o Lower mean alveolar concentration (MAC) means increased potency. Desflurane has the highest MAC & Isoflurane has the lowest MAC. o
Sevoflurane
Smoother induction.
Medium potency (less than isoflurane & more than desoflurane)
Produces breakdown product called Compound A which may cause renal damage. o Desflurane Least potent o Isoflurane Most potent o Halothane
Highly metabolized by the liver
Makes myocardium more susceptible to catecholamine-induced arrhythmias.
Can cause malignant hyperthermia. o
Nitrous Oxide
Cannot be used by itself for clinical anesthesia because of its high MAC.
Azathioprine is an immune-suppressive drug not normally used in cats because of bone marrow suppression.
Prednisone should not be used with infection because it will suppress the immune system. o Cats and horses get prednisolone.
o Steroids also have anti-insulin effects (can cause diabetes), joint problems, skin disorders, and renal disorders.
Cyclophosphamide is an immune-suppressive drug.
Ketoconazole can cause hepatotoxicity, anorexia, vomiting, diarrhea, and adrenal insufficiency.
Ivermectin stimulates GABA, an inhibitory neurotransmitter. o Ivermectin is active against mites, nematodes, and ticks.
Not active against trematodes (flukes).
Praziquantel only treats tapeworms.
Penicillins (Penicillin, Ampicillin, Amoxacillin) work by inhibiting formation of peptidoglycan cross-links in bacterial cell walls.
o Effective against gram + and anaerobic bacteria.
o Can combine with beta-lactamase inhibitors such as clavulanic acid to extend spectrum of activity.
o NEVER give procaine penicillin intravenously; it causes CNS toxicity. Cephalosporins (Cephalexin, Cefazolin, Ceftiofur) work by inhibiting formation of
peptidoglycan cross-links in bacterial cell walls.
o Later generations effective against gram +, gram -, & anaerobic bacteria. Vancomycin works by interfering with cell wall synthesis.
o Effective against gram + bacteria. o Use against resistant bacteria only.
Aminoglycosides (Gentamycin, Neomycin, Amikacin) work by binding to the 30s ribosomal subunit, which interferes with protein synthesis.
o Effective against gram - bacteria. o Nephrotoxic & ototoxic
o Poorly absorbed by feline intestinal tract.
Tetracyclines (Tetracycline and Doxycycline) work by binding to the 30s ribosomal subunit, which interferes with protein synthesis.
o Effective against gram +, gram -, & anaerobic bacteria. Also effective against Ehrlichial, Anaplasmal, and Rickettsial bacteria.
o Nephrotoxic and will discolor teeth in puppies.
Chloramphenicol works by binding to the 50s ribosomal subunit, which interferes with protein synthesis.
o Effective against gram -, gram +, & anaerobic bacteria. o Causes bone marrow depression in humans.
o Forbidden in food animals.
Lincosamides (Lincomycin, Clindamycin) work by binding to the 50s ribosomal subunit, which interferes with protein synthesis.
o Effective against gram + & anerobic bacteria. o Do not use in horses.
Macrolides (Erythromycin, Azithromycin, Clarithromycin) work by binding to the 50s ribosomal subunit, which interferes with protein synthesis.
o Effective against gram + & anaerobic bacteria. Metronidazole works be breaking apart DNA.
o Effective against anaerobic bacteria & protozoa. o Can have neurologic side effects.
Rifampin works by inhibiting RNA polymerase. o Effective against gram + bacteria.
o Mainly used against Rhodococcus equi in foals.
Fluoroquinolones (Enrofloxacin, Ciprofloxacin) work by inhibiting DNA gyrase. o Effective against gram - bacteria.
Trimethoprim-sulfamethoxazole (also known as TMS) works by interfering with folate metabolism.
o Effective against gram +, gram -, & anaerobic bacteria.
Bacteria
On bacterial culture & sensitivity reports, oxacillin indicates methicillin resistance. Streptococcus & Staphylococcus are gram + cocci.
Clostridium are anaerobes.
Nocardia & Actinomyces are gram-positive filamentous rods.
o Actinomyces is a normal flora of the mouth and orpharynx. Klebsiella is a gram-negative encapsulated facultative anaerobic rod.