Anesthetic and Analgesic Agents

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Anesthetic and Analgesic Agents

• Tessa Bowers, LVT

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What do you really know about the drugs you use?

• Name
• Strength
• Dosage ranges (species specific)
• Common uses
• Systemic effects
• Reversibility
• Routes

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Drug Categories

• Inhalant
• Benzodiazepine
• Pure Opioid and partial agonist/antagonist
• Dissociative
• Tranquilizer/Alpha-2 Agonist
• Hypnotic
• Non-barbiturate
• Anticholinergic
• Local
• Non-steroidal Anti-inflammatories (NSAID)
• Agonists

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Cookie cutter drug protocols

• It is imperative to limit the use of cookie
  cutter dosage protocols.
• Every patient is different.
• Drugs along with their dosages should be adjusted
  base on their species, age, PE, blood work, past
  anesthetic experiences, and procedure.

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Inhalants

• Isoflurane
• Allows for rapid changes in induction, depth
  transition, and recovery
• Causes respiratory depression, depression of
  cardiac contractility, vasodilatation, increases
  ICP
• Contraindicated for pets in shock or history of
  malignant hyperthermia
• MAC 1.3 in dogs and 1.6 in cats, surgical plane
  1 1.5x MAC

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Sevoflurane

• Allows for very rapid changes in induction, depth
  transition, and recovery
• Causes respiratory depression, depression of
  cardiac contractility, vasodilation, increase ICP
• Contraindicated in animals in shock or history of
  malignant hyperthermia
• MAC 2.4 in dogs and 2.6 in cats, surgical plane
  1 1.5x MAC
• Does not cause larynospasm

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Benzodiazepines

• Diazepam
• Anticonvulsant
• Excellent muscle relaxant
• Minimal CV depression
• Minimal respiratory depression
• Reduces ICP
• When used in conjunction with other medications,
  reduces required doses necessary

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Diazepam Causes

• Delayed recovery in pets with hepatic dysfunction
• Excitation in young, health patients
• Potentates respiratory depression of opioids
• Occasional PVC after IV dose (due to propylene
  glycol solvent)
• Significant thrombophelbitis with rapid IV
• False urine glucose

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Diazepam Uses

• IM administration is accompanied by poor and
  erratic absorption
• Non water soluble, will sting if given IM
• Crosses the blood brain barrier
• Metabolized in the liver, eliminated primarily in
  the urine.
• Reversible by Flumazenil (0.1 mg/kg IV)
• Dosage 0.1 0.2 mg/kg IV
• May be used as a CRI but binds to plastic and
  should be protected by light

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Midazolam

• Delayed recovery in pets with hepatic dysfunction
• Highly protein bound
• Excitation in young, health patients
• Potentates respiratory depression of opioids
• Nearly 3x times as potent as diazepam
• Crosses the blood brain barrier

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Midazolam Uses

• Well absorbed after SC and IM injections
• Water soluble, does not sting after IM injections
• Shorter duration than Diazepam
• Metabolized in the liver
• Reversible by Flumazenil (0.1 mg/kg IV)
• Dosage 0.1 0.3 mg/kg IV, IM, SC
• CRI 0.3 mg/kg/hr, protect from light

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Butorphanol

• Synthetic partial agonist/antagonist opioid
• Minimal organ toxicity
• More rapid onset then morphine
• Does not cause histamine release
• Does not induce vomiting
• Minimal respiratory depression then other opioid
  agonists
• Antitussive
• Antiemetic

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Butorphanol Undesirable Effects

• At high doses will cause dysphoria, nystagmus,
  salivation, hyperthermia, and decrease GI
  motility
• Ceiling effect to analgesic action
• Analgesic and sedation effects are short lived
  due to drug duration
• Unless frequent dosing, does not provide aid in
  inhalant reduction needs

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Butorphanol Uses

• Parenteral analgesia for mild pain in dogs and
  cats
• Opioid partial antagonist or reversal agent
• Onset of action approximately 5 minutes
• Peak analgesic and sedation effects 15 30
  minutes
• Reversible by Naloxone (0.04 0.1 mg/kg IV/IM)
• Dosage 0.1 0.5 mg/kg IV, IM, SC (alone)
• Sedation effects prolonged when combined with
  other drugs

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Morphine

• Agonist at mu opiate receptor
• Minimal organ toxicity
• Histamine release with IV injection, sometimes
  causing pronounced vasodilation/hypotension
• Induces vomiting with IM or SC injection
• Antitussive

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Undesirable effects from Morphine

• Slow onset of action
• Induces bradycardia (or tachycardia due to
  coronary vasoconstriction)
• Miosis in dogs
• Decreased GI motility (may have immediate
  defecation, then GI slows)
• Respiratory depression
• Dysphoria at high doses in cats
• Constipation
• Bronchoconstriction
• Hyperthermia in cats and hypothermia in dogs

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Wait theres more....

• Morphine causes a decrease in sympathetic nervous
  tone, which can lead to decreased venous tone,
  decreased CO, pooling of blood, decreased
  arterial pressure secondary to decrease return
• GI side effects include nausea, vomiting,
  decreased intestinal peristalis

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Morphine Uses

• Parenteral analgesia for moderate pain
• Epidural analgesia for abdominal and hind body
  surgical procedures (exploratory, PU, orthopedic
  are some examples)
• Contraindicated in head trauma, respiratory
  disease or acute respiratory dysfunction
• Crosses the placenta
• Provides better sedation THEN analgesia

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Sedation does not pain control

• Morphine needs to be protected from light
• Incompatible with heparin
• Increase Amylase and Lipase upto 24 hours
  following administration
• Reversed by naloxone
• Dogs 0.1 1 mg/kg IM, SC (IV 10 of this)
• Cats 0.05 0.2 mg/kg IM, SC
• Epidural 0.1 mg/kg, duration 12 to 24 hours

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Hydromorphone

• Agonist at mu opiate receptor
• Minimal organ toxicity
• 5x more potent then morphine
• Mild histamine release with IV injection
• More rapid onset then morphine
• Induces vomiting with IM or SC injection
• Antitussive

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Undesirable effects of Hydro

• Dose dependant respiratory depression
• Dysphoria at high doses, use a tranquilzer with
• Side effects include sedation, bradycardia,
  slight decrease in cardiac contractility and
  blood pressure, panting
• Do not use with patients that have head trauma,
  increased ICP, acute abdomen, respiratory disease
• Do not use with patients that are bradycardic
• Be careful with GDV and other obstructive disease

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Hydromorphone Uses

• Use for analgesia for moderate to severe pain in
  dogs and cats
• Epidural analgesia for abdominal and hindlimb
  body surgical procedures
• Increase Amylase and lipase up to 24 hours

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Hydromorphone Dosage

• Sedation onset (route dependant) 5 10 minutes
• Analgesic onset (route dependant) 15 30 minutes
• Metabolized in the liver, excreted by the kidneys
• Reversible by naloxone
• Dogs 0.05 mg 0.4 mg/kg IV, IM, SC q 2 -4
• Cats 0.02 mg 0.2 mg/kg IV, IM, SC q 2 6
• CRI

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Fentanyl

• Pure mu opioid agonist
• Extremely rapid onset with extremely short
  duration
• Neuroleptanalgesia in dogs when combined with a
  benzodiazepine or acepromazine
• Reversible by naloxone, but normally not
  necessary due to its short duration

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Fentanyl effects

• Excitatory at high doses or alone in
  young/healthy dogs or cats
• Respiratory depression
• Dose related bradycardia
• Urine retention, possible constipation, possible
  ileus
• Increase Amylase/Lipase up to 24 hours
• Dosage 2 10 mcg/kg IV as bolus, then CRI
• Recent studies with patches show 18 hours till
  effect

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Buprenorphine

• A partial opiate agonist
• Because of the above may not provide appropriate
  analgesia for moderate to severe pain.
  (thoracotomy and orthopedic procedures)
• Slower onset of action (30 min 1 hour)
• Do not give SC, poor erratic absorption
• IV, IM, SL every 4 to 8 hours, BUT does have a
  ceiling effect.

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Buprenorphine Effects

• Incompatible with diazepam
• Side effects include decrease blood pressure, HR,
  and rarely respiratory rate
• Highly plasma protein bound (not albumin)
• Crosses the placenta
• Dogs 0.005 0.02 mg/kg
• Cats 0.005 0.01 mg/kg

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Dissociative

• Ketamine can be used SC, IM, IV for
  anesthesia/chemical restraint
• Inhibits NMDA receptors for adjunct use to
  control pain
• Inhibits GABA and may block serotonin,
  norepiniephrine, and dopamine
• Superficial analgesia
• Rapid onset of effects, no matter the route
• Sympathetic stimulation

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Ketamine effects

• Muscle rigidity if given alone
• Seizures in 20 of cats
• Increase ICP, IOP, BP, salivation, temperature
• Increase CO increase in HR, increase in MAP and
  in CVP
• Eyes remain open, mild jaw tone once induced
• Pain with IM injections
• Sensitive to noise during induction/recovery

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Ketamine Use

• Do not use in patients with shock, renal/liver
  impairment, alone, hypertension, ICP,
  hyperthyroidism
• Decreases airway resistance. Do not use for
  airway procedures
• Good for patients in wind up. Low dose CRI.
• Dogs and Cats 10 mg/kg IV
• CRI 0.1 0.6 mg/kg/min

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Tranquilizer

• Acepromazine
• antiarrhythmic, antiemetic, antihistamine
• slow onset, even in IV (up to 15 minutes)
• duration (12 24 hours)
• Occasional bradycardia (or reflex tachycardia)
• Lower dosage in giant breeds and greyhounds
• Incompatible with diazepam and glycopyrrolate
• dogs and cats 0.025 0.5 mg/kg IV
• 0.025 0.1 mg/kg IM/SC

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Alpha 2

• Domitor (medetomidine)
• Primary use for restraint and quick procedures at
  regular veterinarians
• Beneficial for wind up patients
• At bottle dosage causes cardiac depression,
  decrease BP (or hypertension caused by
  vasoconstriction)
• At much lower dosage plus and opiod, decreases
  these side effects
• Reversible with atipamazole (IM only)

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Hypnotic

• Propofol
• Rapid and short acting
• Reduces ICP, IOP
• Transient apnea (worsened by other drugs)
• Hypotension and bradycardia
• Repeated doses in cats may cause increase Heinz
  body production, slow recoveries, anorexia,
  lethargy, diarrhea
• Repeated doses in dogs may cause autoimmune
  problems

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Propofol uses

• Do not use with patients that are anemic,
  dehydrated, hypovolemic, shock, hypoproteinemia
• Onset within 1 minute, duration 2-5 minutes
• Dosage 4 6 mg/kg IV, give over 60 90 seconds.
  
• CRI intra-op 0.4 mg/kg IV
• Side effects may be less if given while
  administering crystalloid therapy

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Non-Barbiturate Etomidate

• IV anesthetic agent useful in patients with
  pre-existing cardiac dysfunction or the
  critically ill
• Little effect on CV system, RR, decreases
  cerebral blood flow and O2 consumption
• Do not use with hypoproteinemic patients
• Pain at IV site, retching, transient hemolysis
• Pre-treating with diazepam and/or opioid reduces
  the above effects along with dosage

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Etomidate

• Give via rapid IV injection, via an IV line to
  reduce pain and chance of hemolysis
• Protect from light at room temperature
• Duration of hypnosis 3 -5 minutes
• Recovery slower then propofol
• Onset 15 to 30 seconds
• Duration 5 to 15 minutes
• Etomidate alone 1 -3 mg/kg IV
• Etomidate 1 mg/kg IV diazepam 0.5 mg/kg IV

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Anticholinergic

• Atropine
• Protects the heart from bradycardia of reflex
  vagal stimulation and bradycardia induced by the
  effects of drugs
• Glycopyrrolate
• Anticholinergic of choice for patients with
  hyperthryoidism and HCM
• Incompatible with dex sp and diazepam ( others)

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Glycopyrrolate and Atropine

• Glycopyrrolate
• Will not cross blood brain barrier
• Marginally crosses
• Tachycardia (some)
• IV peak 1 5 minutes
• IM, SC peak 30-40 min
• Vagalytic effects 2 -3 hr
• 0.005-0.01mg/kg IV
• 0.01-0.02 mg/kg IM, SC

• Atropine
• Crosses the blood brain barrier
• Crosses the placenta
• Tachycardia (raging)
• IV peak 3-4 minutes
• Antihistamines may enhance effects
• 0.01-0.02 mg/kg IV
• 0.020.04 mg/kg IM, SC

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Local anesthetics

• Lidocaine
• Rapid onset
• Duration 60 120 min
• Quickly absorbed
• Given IV to fast may cause rapid pressure drop
• Decrease general anesthetic needs
• Local and systemic use

• Bupivacaine
• 4x more potent then lidocaine
• Used for regional epidural nerve blocks
• Onset slow to intermediate
• Duration 3-10 hours
• Cardiac toxicity higher

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NSAIDs

• These drugs as a class share common therapeutic
  actions
• anti-inflammatory
• analgesic effects
• antipyretic effects
• Are effective to both acute and chronic pain with
  minimal side effects
• COX-1 inhibitors are more commonly known for
  their side effects. (ie piroxacam)
• COX-2 inhibitors oral longer acting, less SE.
• Do not alter the patients CNS, respiratory, CV
  system

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General Info

• The use of NSAIDs predisposes animals to gastric
  erosions and ulceration, especially those the GI
  disease.
• On the ER side of things we see worst case
  scenario......
• PO SID Rimadyl, Etogesic, Metacam, Deramaxx,
  Previcox
• IV SID Rimadyl, Metacam
• Do not change from one to another w/out waiting a
  minimum of 48 to 72 hours.

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Antagonists

• Flumazenil
• Benzodiazepine antagonist
• Antagonizes the sedative and amnestic qualities
• May benefit treating encephalopathy with severe
  hepatic failure
• May cause vomiting, cutaneous vasodilation,
  vertigo, ataxia, blurred vision
• Discard once in syringe after 24 hours
• Antagonist 0.01 mg/kg IV

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Naloxone

• Pure opioid antagonist, reverse apomorphone
• Reversal of CNS and respiratory depressant
• Being investigated to treat septic, hypovolemic,
  or cardiogenic shock
• At high doses increases dopamine levels and
  seizures may be seen
• Sudden reversal can cause a catecholamine surge,
  resulting in tachycardia, hypertension,
  dysrhythmias, and pulmonary edema

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Use of Naloxone

• Crosses the placenta
• IV onset is 1-2 minutes, duration 20-40min
• IM onset w/in 5 min, duration 40-70 min
• Duration of reversal is normally shorter then the
  drug you are reversing
• IV 0.01 mg/kg and IM 0.04 mg/kg
• Protect from light

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Questions?