premeds, induction agents, Inhalation Anesthetics Flashcards
Anesthetic agent
any drug used to induce a loss of sensation w/ or w/out unconsciousness
Adjunct
not true anesthetic but used during anesthesia to produce other desired effects- sedation, muscle relax, analgesia, reversal, neuromuscular block
Pharmacokinetics
effect body has on a drug incl movement of drug within the body
Pharmacodynamics
effect a drug has on the body; drug action
Agonists
drug that binds to and stimulates tissue receptors
Antagonists
drug that binds to but doesn’t stimulate tissue receptors
Partial agonists
drug that binds to but only partly stimulates tissue receptors
Agonist-antagonist
drug that binds to >1 receptor site, simultaneously stimulating at least one and blocking at least 1
Why dispense Premedication
○ To calm or sedate
○ To minimize adverse effects of other drugs
○ To reduce dose of other drugs
○ To produce smoother inductions
○ To decrease pain
○ To produce muscle relaxation
Classes of Premedication
● Anticholinergics
● Phenothiazines
● Benzodiazepines
● Alpha 2 adrenergic agonists
● Opioids
what are Anticholinergics
● Block the binding of acetylcholine at the muscarinic receptor (parasympathetic system)
○ Allow ‘fight or flight’ to predominate
anticholinergics effects
○ Prevents bradycardia
○ Reduces salivation and secretions of lacrimal, GI, and respiratory
tract
○ Mydriasis
○ Bronchodilation
anticholinergics adverse effects
○ May induce first or second degree AV block resulting in
sinus tachycardia
○ Atropine may induce temporary bradycardia if given at
low doses
○ Increased viscosity of salivary and respiratory
secretions
common anticholinergics
atropine, glycopyrolate
Atropine characteristics
○ Onset is 5 min. IM, and 1 min. IV
○ Peak effect in 10-20 min IM and 3-4 min IV
○ Duration of 60-90 min
○ Choice for CPCR (Cardiopulmonary cerebral resuscitation, CPR)
glycopyrolate characteristics
○ Peak effect in 30-45 min
○ Duration of 2-3 hrs
○ Less likely to induce arrhythmias
○ Suppresses salivation more effectively
○ Minimally crosses placental barrier
common phenothiazines
● Acepromazine maleate (‘ace’ or ‘acepromazine’)
routes for ACE
IV, IM, SQ, oral
is there reversal for ACE
no
ACE onset of action, duration
● Onset of action
○ 15 min if given IM in dogs or IV in horses
○ Peak effect in 30-60 min
● Duration
○ 4-8 hrs in small animals
○ 1-3 hrs in horses
○ Longer in sick, old, or debilitated animals
ACE effects
● Major effects:
○ Sedation
○ Peripheral vasodilation
■ Hypotension
■ Increased HR
■ Increased heat loss
○ Antiarrhythmic
○ Antiemetic
● Mild effects
○ No respiratory depression, but worsens resp depression of other agents
○ Antihistamine
○ No analgesia
Adverse effects
○ Reduction of seizure threshold
○ Hypotension
○ Penile prolapse
○ Reduced PCV
■ Caused by increased uptake of RBC by spleen
ACE use
or who not to use it on
● Remember! - Effects are dose dependent, higher doses
causes increased hypotension without increased sedation
● Increased potency is noted in geriatrics, neonates, liver
and cardiac patients
● Collies, Aussies, sighthounds, boxers and giant breeds
can be more sensitive to effects
Benzodiazepines examples
○ Diazepam
○ Midazolam
○ Zolazepam
○ Lorazepam
○ Alprozolam
routes for benzodiazepines
IV, IM (not diazepam), oral
Reversal available for benzodiazepines?
Yes- flumazenil
○ Not used commonly due to expense and infrequency of need
benzodiazepines onset/ duration
● Onset of action
○ 15 min given IM
● Duration
○ 1-4 hrs
which benzodiazepine is not water soluable
diazapam
what should diazapam only be mixed with
.ketamine
Benzodiazepines effects
● Major effects
○ Antianxiety and calming effect
○ Anticonvulsant
○ Muscle relaxation
○ Appetite stimulant in cats and ruminants
● Minor effects
○ No analgesia
○ Minimal effects on respiratory or cardiovascular systems
■ Good use for anesthetic of high-risk and geriatric patients
● Adverse effects
○ Produce unreliable sedation in young healthy animals (dysphoria, excitement, ataxia)
○ Large animals may become ataxic or recumbent, horses may have muscle tremors/twitching
○ Can cross placental barrier, therefore may see CNS depression in neonates
○ Diazepam given rapidly IV can cause pain, bradycardia, hypotension, and apnea
○ Cats receiving oral diazepam can develop hepatic failure
what is diazapam soluble in
plastic
Diazepam and midazolam sensitive to what
light
why are Benzodiazepines used with other agents
to help achieve safe,
smooth induction to anesthesia
Midazolam used for what
commonly in protocols for pocket pets
and birds
what is diazepam used for
used for behavior modification
are benzodiazepines controlled substances
yes
Alpha 2 Adrenoceptor
Agonists (A-2 agonists) examples
Drugs
○ Xylazine
○ Medetomidine
○ Dexmedetomidine
○ Detomidine
○ Romifidine
how to administer A2 agonists
IV, IM, (SQ - not as reliable)
are reversals available for A2’s
yes
onset/ durations for A2’s
● Onset of action
○ 5-15 min if given IV
○ 15-30 min if given IM
● Duration
○ Approx 1-2 hrs
effects of A2’s
● Major effects
○ Cause dose-dependent sedation that is profound
■ Horses often lower their head and droop their lower lip
○ Have analgesic properties (lasts ~ 20 min in xylazine)
○ Major cardiovascular effects
■ After injection patient experiences vasoconstriction, hypertension and bradycardia (pale mm)
■ May have arrhythmias during this time
■ This phase followed by phase of hypotension and further bradycardia (not seen in medetomidine/dexmedetomidine)
■ Effects more severe if given IV
○ Depression of respiratory system (dose-dependent effect) that is most notable in ruminants
○ Muscle relaxation
○ Vomiting in cats (some dogs) that is most common with xylazine
● Minor effects
○ Hyperglycemia due to reduced secretion of insulin by pancreas
○ Hypothermia occurs due to loss of thermoregulation
○ Markedly reduces amounts of other agents required
Adverse effects (most profound if given IV)
○ May become hyper responsive or aggressive
(especially if excited prior to injection)
○ Horses may become more likely to kick
○ Cattle may lie down (very sensitive to a2s)
○ Dramatic decrease in HR, BP, & CO
○ Brachycephalics or animals with upper airway obstruction may suffer dyspnea
○ Diuresis
○ GI effects: bloat, increased salivation, regurgitation
○ Late stage abortion in ruminants
○ Sweating in horses
○ Intra-arterial injection can cause seizures or collapse
are A2’s absorbed by the skin
Absorbed through open skin or mucous
membranes
who should use A2’s
For young, healthy patients!
can you use A2’s with anticholinergics
Co-administration with an anticholinergic will increase the workload of the heart and myocardial oxygen consumption
○ You will not be allowed to use anticholinergics with A-2s
Xylazine characteristics
○ Available in two concentrations
○ Very out of flavor in small animal medicine
○ Used in combinations with horses
Dexmedetomidine/Medetomidine characteristics
○ Used in small animals
○ Dexdomitor vs domitor
○ Greater potency and adverse effects are less
pronounced than xylazine
○ Recommend dosing based on body surface area
○ Often mixed with other agents
○ Can be used alone for minor procedures
■ Rads, ultrasound (can be aroused with stimuli)
Detomidine characterisitcs
Used for equine
○ Has twice the duration of xylazine
○ Used in horses for sedation, analgesia, and muscle relaxation
○ Often combined with other agents
○ Most potent of the a-2s
Romifidine characteristics
○ Used for equine
○ Has longest duration of action
○ Produces least ataxia and head droop
Alpha 2 Antagonists drugs
○ Tolazoline
○ Yohimbine
○ Atipamezole
how are A2 antagonist drugs administered
○ IM (IV, SQ)
A2 antagonist onset timing
5-10 min
Alpha 2 Antagonists effects
● Adverse effects
○ Amount given should be based on amount of agonist
given
○ If >30 min since injection of agonist, amount of
antagonist should be recalculated
○ Overdose can cause excitement, muscle tremors,
hypotension, tachycardia, salivation and diarrhea
Use of A2 antagonists
○ Tolazoline most used to reverse xylazine in ruminants
○ Yohimbine most used to reverse xylazine in cats, dogs, horses, and exotics
○ Atipamezole used to reverse dexmedetomidine
○ Will reverse sedation and analgesia
IV atipamezole recommended?
no
opioid agonists
○ Morphine
○ Hydromorphone
○ Oxymorphone
○ Fentanyl
○ Meperidine
opioid Partial agonists
Buprenorphine
opioid Agonist-antagonists
Butorphanol
opioid Antagonists
Naloxone
opioid routes
IV, IM, SQ, oral, rectal, transdermal, epidural
opioid reversal
Naloxone
opioid duration
○ In general ½ - 3 hrs
○ Buprenorphine = 6-8 hrs
○ Morphine = 6-8 hrs
opioid effects
● Major effects
○ Can cause sedation or excitement
○ Analgesia
○ Bradycardia
○ Minimal decrease in resp rate and tidal volume
○ May cause panting
○ May be hyper responsive
● Minor effects
○ Dogs may become hypothermic
○ Cats become hyperthermic
○ Sweating in horses
○ Decreased urine production with urine retention
● Adverse effects
○ Anxiety, dysphoria
○ Bradycardia - from increased vagal tone
○ Decreased resp rate and tidal volume - this is dose dependent and worsens if given with other respiratory depressant drugs
○ Salivation and vomiting
○ Initial increased peristalsis then ileus
○ Addiction
○ Caution in use with head traumas or CNS disorders
opioid uses
○ Analgesic
○ Premed
○ Neuroleptanalgesia
optioids controlled substances?
yes, except naloxone
Neuroleptanalgesia
A state of profound sedation and analgesia induced by the simultaneous administration of an opioid and
tranquilizer
○ Can be used for sedation for minor procedures or to induce anesthesia
○ Do not give rapidly IV
Opioid Antagonists
Naloxone
Opioid Antagonists route
IM.IV
opioid antagonist onset, duration
● Onset of action
○ 2 min IV
○ 5 min IM
● Duration
○ 30-60 min
Opioid Antagonists effects
○ Reverses desirable and undesirable effects of opioids
Opioid Antagonists uses
○ In cases of overdoses
○ Emergencies
○ Reversal of neuroleptanalgesia
○ Neonates delivered by c-section
Induction Agents loss of consciousness
○ Unconsciousness is achieved once sufficient brain
levels obtained
○ Movement of agent from blood to brain occurs via concentration gradients
○ Speed of induction and recovery determined by the lipid solubility of agent
○ Drugs that are highly lipid soluble cross cell
membranes faster (faster onset and recovery)
how do induction agents work
Upon injection of agent
○ High levels of drug in blood
○ These drugs rapidly are taken up by brain
○ Low level in muscle, fat, and organs
Once injection is completed
○ Levels in blood drop
○ Agent leaves brain because of concentration gradient
○ Agent leaves blood and enters tissues
Recovery occurs
○ Once levels in brain become low enough, the animal recovers consciousness
○ The drug however is still in the fat, muscle, and tissues
○ Different drugs excreted differently but patient not fully recovered until all agent has left body (may take >24 hrs)
Propofol characteristics
● Ultra-short acting
● Nonbarbiturate
● Used for induction and maintenance of anesthesia
● Also used for treatment of status epilepticus
● Pharmacology
○ Minimal water solubility
○ Milky, but can be given IV
is profol controlled
● Non Controlled - but many practices will still record in drug log as a precaution.
onset and duration
● Onset of action
○ 30-60 sec
● Duration
○ 5-10 min
Propofol effects
● Major effects
○ Dose dependent CNS depression
○ Cardiac depression - bradycardia, decreased CO, hypotension
○ Respiratory depressant - APNEA
○ Twitching during induction
○ Muscle relaxation
● Minor effects
○ Relatively safe for animals with liver and kidney dysfunction
○ Appetite stimulant at low doses
○ Antiemetic
○ Decreases intracranial and intraocular pressure
● Adverse effects
○ Excitement during induction if injection is too slow
○ Hypotension - may be prolonged if patient previously
hypotensive
○ Induction apnea
○ Irritating when given SQ
○ Heinz body formation in repeated dosing to cats
propofol uses
○ Give does slowly to effect (bolus first half, then give to effect)
○ Can also be used as CRI to maintain GA
○ Manufacturer recommends discarding product after 6 hrs of opening
○ Cost is 4X that of ket/val
Alfaxalone characteristics
● Ultrashort-acting injectable anesthetic
● Wide margin of safety
● Relatively new in Canada
● Can be given IV or IM
● Works similar to propofol
Alfaxalone effects
● Effects
○ Dose-dependent CNS depression & resp depression
■ Apnea
○ Hypotension (especially when used with inhalant)
○ Muscle relaxation
○ No analgesia
○ Cardio system depression minimal
○ Smooth induction, no excitement
○ Not irritating in inadvertently given perivascular
Alfaxalone use
○ Given similar to propofol - bolus ~ half, then to effect
○ Duration 5-10 min
○ Repeated dose does not prolong recovery, therefore CRIs are possible
○ Better shelf life
what Dissociative Anesthetics are used
○ Ketamine
○ Ketamine-Diazepam combo
ketamine onset, duration
● Onset of action
○ 1-2 min IV
○ 10 min IM
● Duration
○ 20-30 min
○ Higher dose increases duration, not depth
ketamine effects
● Effects
○ Cataleptic state - patient does not respond to stimulus and maintains muscle rigidity
○ Intact reflexes - difficult to assess depth
○ Central eye that has mydriatic pupils and open lids
○ Normal or increased muscle tone
○ Analgesia to skin and limbs, limited to viscera
○ Amnesia - humans
○ Increased sensory stimuli
○ Do not become bradycardic
● Adverse effects
○ Stimulation to sound, light, etc
○ Abnormal behaviors in recovery
○ Nystagmus
○ Decrease contractility - patient with heart disease can not compensate
○ Predispose to development of arrhythmias
○ Increase salivation and resp secretions
○ Tissue irritation if given perivascular
○ Increased intracranial and intraocular pressure
ketamine dosing
Can be given IM or IV
ketamine use
○ IM use is limited to fractious cats
○ Can be given orally to fractious cats
○ If given repeated doses can increase risk of seizure activity and prolong recovery
○ Undergoes hepatic metabolism and renal excretion - use caution if renal or hepatic disease
Ketamine-Diazepam use
○ IV induction for cats and dogs
○ Equal volumes of each mixed in same syringe (watch for precip)
○ Give to effect
○ Duration: 5-10 min
○ Minimal cardiac depression
○ Good muscle relaxation
○ Superior recovery
○ Some analgesia
Guaifenesin (GGE) characteristics
● Not an anesthetic on its own - given in combination with other agents
● Needs to be reconstituted
Guaifenesin (GGE) effects
● Effects
○ Muscle relaxation
○ Minimal cardiopulmonary effects
● Adverse effects
○ Can cause thrombophlebitis or tissue reaction if given perivascular
Guaifenesin (GGE) use
○ Used in combination with other agents for induction and maintenance of anesthesia
○ Given rapidly IV after premed until signs of knuckling noticed, then induction agent given
why Inhalation Anesthetic Agents used
○ Easier to control depth
○ Elimination through lungs
■ Less dependent on liver and kidneys
○ Less expensive than injectables
inhalation agents cons
○ Expensive equipment required
○ Waste gas pose risk to patient and staff
Inhalation Anesthetic Agents characteristics
● Liquids at room temperature
● Stored in vaporizer
○ Evaporate in the oxygen that
flows through
● Eliminated through the body via the
lungs
○ Provided the animal continues to
breathe!
● Minimal liver metabolism
inhalation anesthetic agents CNS effects
Dose related, reversible depression (to a point)
○ Hypothermia
○ No analgesia
○ Increased intracranial pressure, especially if poor
ventilation and CO2 levels increase
○ Paddling, excitement and muscle tremors on recovery (counteract with premed)
Isoflurane characteristics
○ Most commonly used agent
○ Fewest cardiovascular effects of halogenated
compounds
○ Depressed respiratory system
○ Eliminated through lungs
○ Adequate muscle relaxation
○ No analgesia
○ Rapid induction/recovery
○ Pungent aroma
Sevoflurane characteristics
○ Very rapid induction and recovery
○ Minimal cardiovascular depression
○ Eliminated by lungs
○ Adequate muscle relaxation
○ Some paddling on recovery
