General anesthesia-injectable anesthetic agents Flashcards by Jessica Ernst

ideal anesthetic

does not depend on metabolism for termination

enables rapid induction, quick alteration in depth, rapid recovery

no cardiopulmonary changes

no tissue irritation

no special equipment

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selection of anesthesia depends on

signalment

patient personality

physical status (ASA)

time required for surgical procedure

familiarity with technique

equipment and personnel available

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why injectable?

simplicity

availability

cost-drugs and equipment

rapid, controllable onset

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examples of when to use injectable anesthetics

short general anesthesia-dx, minor procedures

induction-intubation, follow with inhalant

longer periods of anesthesia-MRI, bronchoscopy, where inhalants are unavailable/CI

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why not just injectables?

most procedures take > 20 minutes

difficult to achieve triad for long periods

recovery based on redistribution and metabolism

recovery may be unpredictable, prolonged, rough

depth is difficult to control

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general pharmacology

blood is the delivary medium

drugs are bound to proteins

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what affects a drug ability to cross the blood brain barrier?

lipid solubility

low MW

non-ionized

non-protein bound

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thiopental

barbiturates

reconstitute with sterile water/saline (2.5, 5%)

alkaline must get intravascular

precipitates with most other drugs-flush catheter between drugs

onset: 20 to 30 s

short duration, cumulative

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thiopental MOA

GABA-mimetic effect decreasing the rate of dissociation

can also directly activate Cl channels–>hyperpolarization (inactive neurons for short period of time)

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thiopental metabolism

hepatic

sight hounds prolonged duration

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thiopental cardiovascular effects

increased HR and SVR

ventricular bigeminy common plus other arrhythmias

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thiopental respiratory effects

marked depression of both rates and tidal volume

apnea

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thiopental other effects

decrease cerebral metabolic rate of oxygen consumption–>cerebroprotective

anticonvulsant

no analgesia

hyperglycemia, leukopenia, anemia-transient

splenomegaly

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Ketamine characteristics

dissociatve anesthetic-depression of corticothalamic axis, thalamus, stimulation of limbic, hippocampus

NMDA antagonist-blocks action of glutamate in CNS

soluble in water

10% solution (100 mg/ml)

IV, IM

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ketamine pharmacology

typically given with benzo (diazepam, midazolam)

onset :60 to 90 seconds (IV)

duration (5 to 20 minutes)

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metabolism of ketamine

hepatic most species

cats-prolonged effect

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ketamine cardiovascular effects

indirect CV stimulation-increased HR, MAP, CO

directly negative inotrope

sympathomimetic effects

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ketamine respiratory effects

decreases rate and minute ventilation

bronchodilation

apneustic pattern seen in high doses, CRI

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Ketamine CNS effects

increase CBF, ICP

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ketamine other effects

increased IOP

muscle rigidity

laryngeal reflexes intact

somatic analgesia

+/- salivation

somatic analgesia at subanesthetic doses

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telazol

Tiletamine & Zolazepam

dissociatve + Benzo

lyophilized power

reconstituted with sterile water (50 mg/ml of each drug)

potency higher and longer duration than ketammine

absoprtion with IM administration

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propofol

phenol

prepared in lipid emulsion-soybean oil, glycerol, egg lecithin

supports bacterial growth-handle aseptically

no preservative-short shelf life-24 hours

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propofol onset and duration

onset 30-60 sec

duration: 5 to 10 minutes

propofol metabolism

hepatic and extrahepatic

significant pulmonary uptake

propofol MOA

GABA receptor decreased dissociation--\>increased Cl--\>hyperpolarization

propofol CV effects

decreased HR, systemic vascular resistance--\>decrease MAP increase HR negative inotrope

propofol respiratory effects

dose dependent depression apnea enhanced with opioids decreases RR, and tidal volume

propofol other effects

decrease CMRO2 decreases IOP painful injections in small vessels proconvulsant propofol infusion syndrome (lactic acidosis) splenomegaly no analgesia

propofol shakes

proconvulsant activity rare not cortical epileptic activity spontaneous excitatory movements of subcortical origin no need to avoid in patients with seizure hx

cats and propofol

slower recoveries oxidative RBC damage heinz body anemia because it is a phenol not symptomatic

propofol 28

shelf life 28 days labeled for dogs only preservative-2% benzyl alcohol-toxic to cats in high doses safe in cats at clinical doses

Etomidate characteristics

imidazole derivative 35% propylene glycol new lipid emulsion? pH: 6.0 high osmolality--\>hemolysis, pain

etomidate onset and duration

30 to 60 seconds duration: 3 to 10 minutes ,dose related

etomidate metabolism

hydrolysis via hepatic enzymes and Plasma esterases

etomidate MOA

GABA decreased dissociation--\>increaesd Cl--\>hyperpolarizationE

Etomidate CV effects

minimal changes in HR, SV, CO +/- decrease in systemic vascular resistance MAP may decrease up to 15%

etomidate respiratory effects

depression caused by decreased in tidal volume occasionally increase RR

etomidate other effects

decrease CMRO2 may activate seizure foci (may have anticonvulsant properties) depresses adrenocorticla function myoclonus-usually give benzo retching/vomiting no analgesia expensive

alphaxalone

neurosteroid clear, aqueous solution, iso-osmolar pH: 6.5 to 7.0 sturcture similar to progestterone IM and IV Schedule III

alphaxalone onset and duration

onset: 30 to 60 seconds duration: 3 to 8 minutes

alphaxalone metabolism

hepatic

alphaxalone MOA

GABA decreased dissociation--\>increased Cl--\>hyperpolarization involvement of centrally located glycine receptors

alphaxalone CV effects

decreased HR, MAP negative inotrope increased HR with low MAP

alphaxalone respiratory effects

dose dependent depression hypoventilation and apnea-side effects

alphaxalone other effects

similar to propofol painful on IM injections hyperaesthetic recoveries-reduced with sedatives decreased CMRO2 no analgesia

therapeutic index

LD50/ED50 Larger TI are safer drugs

indution qualities of thiopental

alkaline must go IV smooth reliable not available currently

etomidate induction qualities

hyperosmolar--\>pain myoclonus, retching physiologically nice expensive

propofol induction qualities

lipid emulsion, must be aseptic smooth, reliable

alphaxalone induction qualities

IM, IV smooth reliable

ketamine/diazepam induction qualities

IM or IV widest safety margin

thiopental recovery qualities

smooth prolonged in sight hounds

etomidate recovery qualities

usually smooth but can be rough premeds important

propofol recovery qualities

smooth reliable

ketamine/diazepam recovery qualities

acceptable increased motor activity Telazol have prolonged recovery

alphaxalone

anedcotally can be rough

titrate to effect

calculate expected dose-premeds, sedative effects give a portion of expected dose assess effect repeat... continue until desired effect reached