Anesthetic Agents and Adjuncts (Veterinary)

What is an anesthetic agents or adjunct? Anesthetic agent: any drug used to induce a loss of sensation with or without unconsciousness Adjunct: a drug that is not a true anesthetic, but that is used during anesthesia to produce other desired effects such as sedation, mu...

What is an anesthetic agents or adjunct? Anesthetic agent: any drug used to induce a loss of sensation with or without unconsciousness Adjunct: a drug that is not a true anesthetic, but that is used during anesthesia to produce other desired effects such as sedation, muscle relaxation, analgesia, reversal, neuromuscular blockade, or parasympathetic blockade Anesthesia Agents & Adjuncts: Pharmacology Terminology (review). Anesthesia Textbook p53  Intrinsic Activity: ability of a drug to produce a biological response, a measure of a drug efficacy or potency  Drug efficacy: is the ability of a drug (after binding with receptors) to initiate change which leads to certain effects  Potency: is a comparative measure of different doses of two drugs that are needed to produce the same pharmacological effect  Agonists: bind to & stimulate target tissue (most anesthetic agents & adjuncts are agonists)  Antagonists: bind to target tissues & do not stimulate. reversal agents  Pharmacokinetics: the effect the body has on a drug, think ADME (absorption, distribution, metabolism, excretion)  Pharmacodynamics: the effects a drug has on the body (mechanism of action – MOA, side effects/adverse effects)  Agents & Adjuncts Various classifications of Drugs. They can be based on:  Route of Administration: SQ, IM, IV, PO,...  Time of Administration: Pre-medication, Induction, Maintenance, Recovery – how we will review drugs used in anesthesia today  Principle Effect: Local vs. general, sedatives/tranquilizers vs. analgesics, neuromuscular blockers, anticholinergic agents, reversal agents  Drug chemistry & pharmacology  4 Drug Combinations  Don’t mix drugs in a single syringe unless they are compatible – look this up  Don’t administer a drug combination if a precipitate develops when the drugs are mixed  Most anesthetic agents and adjuncts are water soluble  Diazepam is not water soluble – highly imcompatible  NOT ALL drug with obviously precipitate, some will only produce heat or worse a physiological reaction.  Post compatibility charts in your clinic for easy reference  Or have on hand a compatibility pharmacy textbook, or app  Pre-anesthesia Medications “Pre-meds” Why we pre-medicate:  Calm or sedate the patient (reduce excitement, increase handleability)  Reduce stress, anxiety & catecholamine release  Provide analgesia & muscle relaxation  Anesthetic-sparing (reduces amount required of induction & maintenance drugs)  Reduction/elimination adverse effects of other drugs  Improves vital systems stability during operative period  Improved quality of recovery from anesthesia: less excitement, smoother anesthetic  Adjuncts to local anesthesia  Anesthesia Textbook p59 Pre-medications Routes Rankings of Routes  SQ  IM Onset of Action: IV (fastest) >> IM >  IV SC (slowest)  Oral Duration of action: SC (longest) > IM >> IV (shortest)  Administration of pain medication before the pain occurs Commonly involves adding Preemptiv analgesic to premedication e Analgesia prior to anesthesia Reduces overall requirement for analgesia and duration of administration – MAC sparing Prevents windup Copyright © 2017 by Elsevier, Inc. All rights reserved. 7 Perioperative Pain Management  Preemptive analgesia  Begins in preoperative period with premedication  May be administered as part of anesthetic premedication  Transdermal fentanyl patch  NSAIDs primarily in large animals  Multimodal therapy throughout  The use of more than one drug to control pain  Cover multiple receptors and mechanisms of action  Reduce dose of individual drugs and anesthetic agent Copyright © 2017 by Elsevier, Inc. All rights reserved. 8  Pre-Med: Phenothiazines: Acepromazine dopaminergic receptor inhibitor Advantages Disadvantages Mild sedation, anxiolytic, less CV: Vasodilation – hypotension, interest in surroundings hypothermia, increased HR Anesthetic sparing Non reservable Antiemetic effects Avoid in MDRI Gene Dogs (herding) May lower seizure threshold Smoother induction No analgesic Prevents histamine release Less effective in cats Can treat opioid dysphoria Worsens respiratory depressive effect of other drugs  Pre-Med: Acepromazine  If I could say a few things about Acepromazine I would say (TECH TIPS):  There are various concentrations – WATCH OUT  Produces mild to moderate sedation  Cause vasodilation = hypotension & hypothermia!  Non reversible!  :. Not good in compromised patients  Anesthesia Textbook p63 Pre-Med: Dexmedetomidine αlpha 2 Adrenergic Agonists Advantages Disadvantages Profound sedation (most Profound peripheral profound group of sedatives) vasoconstriction Reversable (atipamezole) - reflex bradycardia Moderate muscle relaxation Possible arrythmias (1st 2nd AV Block) Mild Analgesia Mild bradypnea, reduces GI motility Anesthetic sparing (50-80%) Not to be used in ill/compromised Reduces stress - lessens Severe reduction of CO possible sympathetic outflow :. Only use in normal healthy  Pre-Med: Dexmedetomidine  If I could say a few things about Dexmedetomidine I would say (TECH TIP):  Potent concentrations – WATCH OUT *dilute often  doses are extremely*** small volumes  Concentration usually in mcg/mL ! (no need to convert if dosage also in mcg/kg  Profound sedation!  Biphasic CV effect!  First profound vasoconstriction which causes hypertension (we don’t often catch this on our monitors)  See paler mucous membranes, or IV more difficult  Second the heart has to slow down to compensate!  Bradycardia expected, don’t be afraid, only treat if hypotensive too.  Reversible!  Anesthesia Textbook p65/67-68, reversal on p68- 69 Pre-Med: Opioids: Hydromorphone Pure Mu Agonist! (we love mu) Advantages Disadvantages Profound Analgesia CV & Respiratory Depression (strongest) Mild to moderate sedation Vomiting, Nausea, hypersalivation Reversable (Naloxone) Dysphoria (any), excitement (cats) Anesthetic sparing Excitement or Dysphoria Minimal direct CV effects Ileus (colic in horses), reduce GI motility - Suitable in Histamine release compromised/ill Less nausea & histamine Abuse Potential Class II Narcotic release compared to Highly addictive (not good for chronic morphine but more than pain)  Pre-Med: Hydromorphone  If I could say a few things about Hydromorphone I would say (TECH TP):  There are various concentrations  Never leave unattended, heavily controlled (log!)  Potent analgesic  Causes respiratory depression  Hypoventilation, hypercapnea, +/- hypoxia  Reversible!  IM? Pant & Vomit! :. Not a good choice Pre-Med: Butorphanol partial mu antagonist (, & kappa agonist :. aka mixed agonist/antagonist = because it attaches to multiple opioid receptors Advantages Disadvantages Mild - Moderate Analgesia Weaker analgesic if stronger needed Mild to moderate sedation Analgesia Plateau at high (stimulates Kappa receptors causing doses sedation) Partially Reversable (Naloxone Blocks Mu receptors and will reserve only the mu effects) therefore a pure mu drug should not work well Antitussive Effects! Abuse potential Class IV Good in GI compromised  Butorphanol mixed (& partial)  If I could say a few things about But-or-phan-ol I would say (TECH TIP):  Great in compromised patients with mild or no pain  Great for dyspnea (less respiratory depressive effects)  More sedative in the dog than the cat  KAPPA agonist – up to 2 hours for both  Mild analgesic effects  Mu antagonist – 45 min duration only Sometimes is called “Torb” in clinics from its trade name “Torbugesic” 16 Pre-Med: Opioids: Buprenorphine partial mu agonist, kappa antagonist (& partial delta agonist) :. mixed agonist/antagonist opioid Advantages Disadvantages Mild – Moderately strong analgesia Analgesia plateau (ceiling (partial mu agonist) :. Less effect) at high doses analgesia than a mu agonist Mild to moderate sedation Slow onset 30min regardless of route (can be an advantage Reversable or partially (Naloxone) too) oral option! Anesthetic sparing Long duration (can be an advantage too) Good in GI compromised Can not be given with pure mu Higher doses may increase duration, & Abuse potential, Class III 72hr form available (Simbadol)  Buprenorphine partial mu agonist, kappa antagonist  If I could say a few things about Bup-ren-or-phine I would say:  Longer/delayed onset >30min even if injected  Longer duration  Various forms  Injectable – 6-8 hours, up to 12 hours  Injectable Slow release “SR” – 72 hours!  Good for moderate to severe pain  dose dependant, good for mild pain too  Partial agonists avidly bind & partially activate mu receptors.  Transmucosal administration in cats  Great TGH medication trade name example “Vetergesic” 18  Opioids Overall:  Vary in potency, duration, and adverse effects  Opioid Receptors/Pain control = Mu, Kappa, Delta  Mu is the strongest and best pain control  Kappa is the sedation effects  Delta is ??? Mild pain?  Used for premedication or intra or post operative analgesia  Diminish windup pain too!  Induce state of potent sedation  Neuroleptanalgesia  Respiratory Depressant  Reduce rate, and tidal volume = hypoventilation Hypoventilation leads to hypercapnia!  Anesthesia Textbook If you hypoventilate on room air you p69-72 can go hypoxemia, which can lead to 19 Bonus Content: How Opioids Work Video (does review Hydromorph Naloxone concepts one (Reversal) discussed!): https://yo utu.be/z0 BybzuhjQ Q?si=6aI ehWBIOP xpzKCO Pre-Med: Benzodiazepines: Diazepam/Midazolam GABA receptor agonist Advantages Disadvantages Sedative, hypnosis (species diff) Paradoxical excitation *esp. cat Reversible (Flumazenil) with midazolam Muscle relaxation No analgesia Anti-convulsant Diazepam can’t be given IM (burns) Minimal CV effect Diazepam sensitive to plastics & light Minimal Resp effects Abuse potential Class IV Reduces amt of inductions  *few disadvantages Anesthesia Textbook p64-65  22 Ampule Medications:  Common medications include Diazepam, Epinephrine, https://youtu.be/vas3WHm Atropine WtAI?si=advp79oBibwBpfQ 3 Process of breaking ampules: https://youtu.be/mFKj3_Wk8  Hand hygiene, 5 R’s, view ID lines, or dots, flick liquid down m8?si=RI4GqFV_H8z7Z-TF  The dot indicates the position of the scored glass https://youtu.be/zmxAL1ZN 964?si=B2qoVAQHvR6Qo6V  Wrap gauze with alcohol, face dot away from you, & snap L away from you over or near a sharps container.  See notes below for details.