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Injectable Anesthetic Agents - Coggle Diagram
Injectable Anesthetic Agents
General Anesthesia Triad
Muscle relaxation (immobility)
Analgesia
Unconsciousness
=your very basic goals
General Pharmacology
Blood = delivery medium
Bound to proteins
[drug]
Plasma pH
[protein]
Blood brain barrier
Lipid solubility (lipophilic)
Molecular weight (small)
Ionized vs non-ionized
Protein bound vs non-protein bound
Ketamine
Dissociative anesthetic (phenylcyclidine derivative)
Depression of corticothalamic axis, thalamus
Stimulation of limbic, hippocampus
“Cataleptoid”
NMDA antagonist
Blocks action of glutamate in CNS
Soluble in water
10% solution (100mg/mL)
IV, also IM
Controlled substance
Typically given with benzodiazepine or propofol
Diazepam, midazolam
Onset as solo agent 60-90 seconds (IV)
Duration
5-20 minutes (IV)
Route, dose
Metabolism
Hepatic most species
Cats, urinary excretion
Cardiovascular effects
Indirect CV stimulation
Central & peripheral sympathomimetic effects
Increased HR, MAP, CO
SVR unchanged
Directly NEGATIVE inotrope
Respiratory effects
Decreases rate and minute ventilation
Bronchodilation
Apneustic pattern (high doses, CRI)
Other effects
Increased IOP
Muscle rigidity
Laryngeal reflexes intact
Analgesia at subanesthetic doses!
+/-Salivation
Doses
2 mg/kg (with propofol)
5-8 mg/kg (with benzodiazepine)
1-3 mg/kg/hr for PIVA
2-10 mcg/kg/min for analgesia (0.12-.6 mg/kg/hr)
induction qualities
IM or IV
Widest safety margin
cardiopulmonary effects
Sympathomimetic effects
Bronchodilation
recovery qualities
Acceptable
Increased motor activity
Telazol
Tiletamine & Zolazepam
Dissociative + Benzodiazepine 1:1 ratio
Lyophilized powder
Reconstituted with sterile water (5mL)
100 mg/mL total
50 mg/mL of each drug
Potency higher (1mg/kg each)
Duration longer
Absorption with IM administration
prolonged recovery qualities
Propofol
Phenol
Insoluble (slightly) in water
Prepared in lipid emulsion
Soybean oil
glycerol
egg lecithin
Supports bacterial growth
Handle aseptically
No preservative
Short shelf life: 6 - 24 hours
Onset 15-30 seconds
Duration 5 -10 minutes
Metabolism
Hepatic AND extra-hepatic
Significant pulmonary uptake
Mechanism of Action
GABA
Decreased dissociation -> Increased Cl- -> hyperpolarization
Cardiovascular effects
Decreased HR, SVR -> MAP
Increased HR
Negative inotrope
Respiratory effects
Dose-dependent depression
Apnea 25-35% human patients
Enhanced with opioids and ketamine
Decreases RR, TV
Other effects
Decreases IOP
Painful injections in small vessels
Proconvulsant activity “Propofol shakes”
Rare
NOT cortical epileptic activity
Spontaneous excitatory movements of subcortical origin
NO need to avoid in patients with seizure history
Splenomegaly
No analgesia
Cats
Slower recoveries
Oxidative RBC damage
Heinz-body anemia
Dose (IV only)
Induction dose based on level of sedation in patient
2-6 mg/kg typical
Propofol>Alfaxalone for cardiopulmonary effects
Decrease HR (usually)
Negative inotrope
VASODILATION
Apnea
recovery qualities smooth, reliable
Propofol 28
Shelf life = 28 days
Labeled for DOGS ONLY
Preservative
2% Benzyl Alcohol
Safe in cats at clinical doses
Metabolism of BA requires glucuronic acid conjugation
Toxic -> Acidosis, neurologic signs (salivation, excitation, hyperaesthesia, ataxia, seizures, death within 1-5 days)
induction qualities
Lipid emulsion -> aseptic
Smooth, reliable
Etomidate
Imidazole derivative
35% propylene glycol
New lipid emulsion
pH = 6.0
High osmolality
4640 mOsm/L (plasma ~ 300)
Hemolysis
Pain
Onset 30-60 seconds
Duration
3-10 minutes
Dose related
Metabolism is hydrolysis via hepatic enzymes AND plasma esterases
Mechanism of Action
GABA
Decreased dissociation -> Increased Cl- -> hyperpolarization
Cardiovascular effects
Minimal change in HR, SV, CO
+/- Decrease in SVR
MAP MAY decrease up to 15%
Respiratory effects
Depression caused by decrease in TV
Occasionally increase RR
Other effects
Depresses adrenocortical function
Myoclonus
Spontaneous movement occur in absence of premeds!
Usually give with benzodiazepine
Retching/Vomiting
NO analgesia
$$$
induction qualities
Hyperosmolar -> Pain,hemolysis
Myoclonus, retching
Physiologically ‘nice’
cardiopulmonary effects
NO CHANGE in HR
NO CHANGE in RR
recovery qualities
Usually smooth, can be rough
Premeds important
Alfaxalone
Neurosteroid
A clear, aqueous solution
1% (10 mg/mL)
Iso-osmolar
pH 6.5-7.0
Structure similar to progesterone
NO sex hormone, glucocorticoid or mineralocorticoid effects
Intramuscular administration in addition to IV!
Controlled substance
Onset 30-60 seconds
Duration 3-8 minutes
Metabolism Hepatic
Mechanism of Action
GABA
Decreased dissociation -> Increased Cl- -> hyperpolarization
Involvement of centrally located glycine receptors?
Cardiovascular effects
Decreased HR, MAP
Negative inotrope
Increased HR with low MAP
Respiratory effects
Dose-dependent depression
Hypoventilation and apnea were most common side effects
Other effects
At clinically relevant doses = physiologically superior to propofol
Possible pain on IM injection*
Hyperaesthetic recoveries
Reduced with sedatives
NO analgesia
$$$
Doses
IM premedicant 1-3 mg/kg
IV induction 1-2 mg/kg
induction qualities
IM (pain?) or IV
Smooth, reliable
recovery qualities can be rough when used a sole agent
DEA Controlled Substances Act
Propofol
Etomidate
Ketamine C-III
Tiletamine (Telazol®) C-III
Opioid-benzo combos C-II
Alphaxalone C-IV
“Titrate to effect”
Calculate expected dose
Premedications
Sedative effects
Give a portion of expected dose
Assess effect
Repeat….
Continue until desired effect reached
Art!