Pathways to Foreign Veterinary Qualification : Clinical Anesthesia

Opioids

Opioids are categorized into full opioid agonists, partial opioid agonists, and synthetic opioids.
Full opioid agonists (acting on mu, kappa, and delta receptors) include morphine, oxymorphone, hydrocodone, codeine, and oxycodone.
Partial opioid agonists include buprenorphine and butorphanol.
Tramadol is a synthetic opioid.
The antidote for opioids is naloxone.

Barbiturates are categorized by their duration of action: short-acting, intermediate-acting, and long-acting.
Short-acting barbiturates are thiopental and methohexital.
Intermediate-acting barbiturates include pentobarbital.
Long-acting barbiturates include phenobarbital.
The antidote for barbiturates is nikethamide.

This category includes propofol, etomidate, alfaxalone, chloral hydrate, magnesium sulfate, and chloralose.
Chloral hydrate, magnesium sulfate, and chloralose are now used rarely compared to previous common use.

Adrenergics target alpha (Alpha 1, Alpha 2) and beta (Beta 1, Beta 2, Beta 3) receptors, with some drugs being non-selective.
Alpha 1 agonists include phenylephrine.
Alpha 2 agonists include xylazine, detomidine, medetomidine, and dexmedetomidine.
Beta 1 agonists include dobutamine.
Beta 2 agonists include clenbuterol, albuterol (salbutamol), and terbutaline.
Non-selective beta agonists include isoproterenol (isoprenaline).
Non-selective adrenergics (catecholamines) include epinephrine, norepinephrine, dopamine, and dobutamine.
Epinephrine, norepinephrine, and dopamine are natural, while dobutamine is synthetic.
Epinephrine acts on Alpha 1, Beta 1, and Beta 2 receptors, showing very little Alpha 1 activity.
Norepinephrine primarily acts on Alpha 1 and Beta 1, with minimal Beta 2 activity.
Dopamine mainly acts on dopaminergic receptors (D1 and D2), but higher doses also affect Beta 1, Beta 2, and Alpha 2.
Dobutamine mainly acts on Beta 1, with higher doses affecting Beta 2 and Alpha 1.

Alpha 1 receptors are located on arteries of all organs, causing vasoconstriction, which increases blood flow and total peripheral resistance.
Alpha 2 receptors are present on veins, causing venodilation, which can lead to decreased heart rate, cardiac output, respiratory rate, and generalized hypotension.
Beta 1 receptors, known as cardiac receptors, are found on the heart and kidneys, increasing heart rate, stroke volume, and cardiac output.
Beta 2 receptors are located on arteries, causing vasodilation and decreasing blood flow.
Beta 3 receptors are found on adipose tissue and currently have no significant clinical role.

Important: A positive inotrope increases heart rate and contractility, while vasoconstriction (VC) refers to the narrowing of blood vessels.

Epinephrine is both a positive inotrope and a vasoconstrictor.
Norepinephrine is primarily a vasoconstrictor and a less effective positive inotrope compared to epinephrine.
Dopamine and dobutamine are positive inotropes.

These drugs block the action of alpha and beta receptors, serving as antidotes to adrenergic agonists.
Alpha 1 blockers include prazosin.
Alpha 2 blockers include yohimbine (antidote for xylazine), atipamezole, and tolazoline (antidotes for detomidine or medetomidine).
Non-selective alpha blockers (blocking Alpha 1 and Alpha 2) include phentolamine and phenoxybenzamine.
Beta 1 blockers include atenolol and metoprolol.
Beta 2 blockers currently have no clinical use.
Non-selective beta blockers include pindolol, sotalol, and propranolol.

Cholinergic drugs include parasympathomimetics (cholinergics/cholinomimetics) and parasympatholytics (antidotes for parasympathomimetics).
Direct-acting parasympathomimetics include acetylcholine (endogenous but not clinically used), methacholine, carbachol, bethanechol, and pilocarpine.
Indirect-acting parasympathomimetics are divided into carbamates and organophosphates.
- Carbamates (e.g., physostigmine, neostigmine, edrophonium) are reversible.
- Organophosphates are generally irreversible.
Parasympatholytics include atropine, glycopyrrolate, and scopolamine.
Nicotinic antagonists include hexamethonium and trimethaphan.
Levels of Consciousness and Awareness
- Anesthesia is a state where an animal is completely unconscious and exhibits no response to painful stimuli.
- Sedation involves an animal being nearly unconscious but still capable of a purposeful response to painful stimuli.
  Both anesthesia and sedation involve Central Nervous System (CNS) depression.
- Tranquilization is a behavioral change that relieves anxiety, making the animal relaxed but still aware of its surroundings. Unlike sedation or anesthesia, tranquilization does not cause CNS depression.
  
  Drugs causing tranquilization are known as anxiolytics, anti-anxiety drugs, or tranquilizers.

Here is a comparison of these states:

Term	Consciousness Level	Pain Response	CNS Depression	Awareness of Surroundings
Anesthesia	Completely unconscious	No response	Yes	No
Sedation	Nearly unconscious	Purposeful response	Yes	No
Tranquilization	Aware	(Implied aware)	No	Yes

Narcosis refers to a state of deep sleep from which a patient cannot be easily aroused, similar to the effect of strong sleeping pills where the patient remains asleep until the drug's action subsides.
Hypnosis is an artificially induced sleep or a trance-like state resulting from moderate CNS depression, from which the patient can be readily aroused.

Balanced anesthesia is achieved by administering multiple drugs to produce three primary properties: unconsciousness, analgesia (pain relief), and no reflex response to any stimuli.
Dissociative anesthesia involves drugs that uniquely dissociate the thalamocortical and limbic systems.
Unlike general anesthetics that induce complete unconsciousness through CNS depression, dissociative drugs cause a cataleptoid state where the animal's eyes remain open, swallowing reflexes are intact, and skeletal muscles are contracted, yet the animal is unaware of painful stimuli.