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176 Cards in this Set
- Front
- Back
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Primary body systems of focus for pre-anesthetic evaluations
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Nervous
Cardiovascular Pulmonary Hepatic Renal |
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First stage of preanesthetic assessment
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Should occur 1-7 days prior to anesthesia, to pursue further diagnostics & treat any abnormalities beforehand
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Second stage of preanesthetic assessment
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An abbreviated evaluation that should occur when the patient is admitted, usually the only part of the assessment that is performed
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Main components of the preanesthetic evaluation
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history & physical exam
blood work & other diagnostics needed only when indicated by abnormalities in the history/physical |
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Major Components of the History
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Signalment
Main Complaint History of present illness Medical history Current health status Systems review |
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Systems Review
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Series of open-ended questions about each system of concern: general health, nervous, cardio, pulmonary, GI, urinary, musculoskeletal, skin
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Fasting for anesthesia
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reduces risk of regurgitation & aspiration, minimum of 6 hours for Ca & Fe
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Concurrent medications with anticipated anesthesia
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Meds should be given regularly, but not between anesthetic premed & induction
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Drugs to consider with anesthetics
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aminoglycosides, barbiturates, B-blockers, Ca channel blockers, carbonic anhydrase inhibitors, chloramphenicol, corticosteroids, digitalis, H2 blockers, NSAIDs
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Usual minimum basic Clin Path tests performed for preanesthesia
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PCV, TP, BUN
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Electrocardiogram in preanesthetic assessment
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Needed for older & traumatized patients, as well as those with known/suspected heart diseases
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ASA Classifications
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Summarizes the patient-related factors ONLY that contribute to the risks of anesthesia
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ASA Category I
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Excellent Risk: normal, healthy animal, for elective surgery
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ASA Category II
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Good Risk: Neonatal or geriatric, patients with mild systemic diseases, mild obesity, simple fractures
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ASA Category III
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Fair Risk:Patients with moderate systemic disease, fever, moderate dehydration/hypovolemia, chronic heart/renal disease
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ASA Category IV
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Poor risk: Severe systemic disease that threatens life, shock, severe dehydration, anemia, diabetes, cardiac/ renal/hepatic/pulmonary disease
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ASA Category V
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Guarded risk: moribund patients: not expected to survive 24 hours, severe shock, DIC
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ASA E designation
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designates an emergency case in which there isn't time for proper evaluation & preparation
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Locations of opioid receptors
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brain, spinal cord
myenteric complexes of the GI tract, kidney, heart, adrenal gland & joint capsules |
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Types of opioid receptors
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Mu
Delta Kappa |
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Effect of opioids
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ANALGESIA
sedation euphoria dysphoria excitement |
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3 Main sites of opioid action
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1. inhibt pain transmission in dorsal horn
2. inhibit somatosensory afferents @ supraspinal level 3 activation of descending inhibitory pathways |
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Full agonist opioids
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MORPHINE
high affinity and activation @ all relavent receptors Profound analgesia & significant side effects higher dose=higher effect, no limit to effect (death) |
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Partial agonist opioids
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Buprenorphine
affinity at only some receptors, with significant activity @ those receptors |
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Agonist-Antagonist opioids
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Butorphanol
agonists @ some opioid receptors, antagonists @ others |
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Full antagonist opioids
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naloxone
have affinity for opioid receptors, but have no activity: used as reversal agents, block agonists |
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Opioid effects on Cardiovascular system
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minimal: some bradycardia
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Opioid effects on respiratory system
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potentially potent depressents
↓resp rate & volume initial tachypnea |
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Opioid effects on CNS
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relieve pain w/o blocking motor activity or consciousness
CNS depressent in dog CNS excitement in cat, horse, cow, sheep Vomitting stimulation Hypothermia in dogs |
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Other opioid effects
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pupillary constriction (miosis) in dog, rabbit, rat
pupillary dilation (mydriasis) in cats, horses intial emptying of GI tract when given |
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Metabolism of opioids
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LIVER
urinary excretion |
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Opioid agonists to know
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Morphine Sulfate
Hydromorphone Oxymorphine Fentanyl |
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Effects of Morphine Sulfate
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Opioid agonist
causes histamine release when given IV excitement in cats vomitting Lasts 4-6 hours |
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Effects of Hydromorphone
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more potent & more expensive than morphine
less nausea, emesis & sedation than morphine but does not cause histamine release lasts 4-6 hours |
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Effects of Oxymorphone
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10 times more potent & more expensive than morphine
more sedation & less histamine release than morphine |
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Effects of Fentanyl
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80-100 times more potent than morphine
highly lipophilic= rapid onset & short duration (30min) rarely see histamine release available as transdermal patch |
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Significance of Opioid potency
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Higher potency=must lower the dose to compensate
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Partial opioid agonist to know
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Buprenorphine
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effects of Buprenorphine
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Partial Mu agonist=high affinity, partial activity
slow onset, long duration (8-12 hrs) used for post-op analgesia available intra-bucal for cats |
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Opioid Agonist-Antagonists to know
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Butorphanol
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Effects of Butorphanol
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3-5 times as potent as morphine, w/ less resp. effect
affinity for Mu & Kappa receptors: agonist @ Kappa, antagonist @ Mu Only lasts .75-1hour, & not really good for invasive procedures |
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Opioid Antagonists to know
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Naloxone
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Effects of Naloxone
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A narcotic antagonist
high affinity for Mu recept. rapid onset, short duration (15-45 min.)=multiple dosing to offset opioid agonists liver metabolism |
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Factors determining amount of chemical restraint needed
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Breed
Temperment Physical condition Procedure (pain, duration) Concurrent meds Familiarity w/ agents |
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When to use chemical restraint
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-Less painful procedures w/ cooperative patients
-Local/Regional anesthetic possible instead of general -No anesthetic machine avail. -Outpatient procedures -Very short procedures -Need lower cost or to avoid inhalant (airway procedures) |
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Advantages of Chemical restraint
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no environmental pollution
no anesthetic machine maybe less cardiopul depress. maybe faster changes in anesthetic depths some reversible |
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Disadvantages of chemical restraint
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-not be adequate for all procedures
-may be excessive for procedure -"all or nothing" -may not be as closely monitored as inhalants |
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Protocol for chemical restraint
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combinations of agents used
-reduces dosages -reduces unwanted side effects -more ideal anesthetic state -requires knowledge of drugs, their interactions and side effects |
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Use Effects of Acepromazine
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Tranquilization excellent when in combination w/ opioids
Antiemetic Potentiates analgesia of other drugs Injection not painful |
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Use Effects of Diazepam
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Minimal cardiopulmonary depression
Muscle relaxation Used in combination with opioids for fragile patient Reversible |
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Use Effects of Midazolam
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Min cardiopulmonary depression
Muscle relaxation Use with opioids for fragile patient, Reversible Water soluble & compatible with other drugs solution |
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Use Effects of Xylazine
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Sedation
Analgesia Muscle relaxation excellent in combination with opioids Reversible More consistant with opioids |
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Use Effects of Medetomidine
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Sedation
Analgesia Muscle relaxation excellent in combination with opioids Reversible More consistant with opioids |
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Use Effects of Morphine
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Analgesia
Some sedation Minimal cardiovascular effects |
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Use Effects of Butorphanol
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Mild analgesia
Some sedation |
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Use Effects of Oxymorphone
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Profound analgesia
Some sedation Reversible |
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Use Effects of Hydromorphone
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Profound analgesia
Some sedation Reversible No histamine release |
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Use Effects of Thiopental
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Rapid Onset & recovery from single dose
Inexpensive Can be added to other sedatives if immobilization needed |
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Use Effects of Propofol
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Titratable to effect
Rapid recovery even with repeated doses Can be used in patients with hepatic or renal insufficiency |
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Use Effects of Ketamine And
Tiletamine |
EXCELLENT IMMOBILIZATION in fractious animals when combined with other agents
Analgesia Bronchodilation IV use of ketamine & Diazepam can be titrated |
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Caution for use Acepromazine
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Hypotension, Does not provide good chemical restraint when used as the sole agent
Lowers seizure threshold Longeronset of action (20-30 min., May cause Prolonged effects in some patients |
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Caution for use Diazepam
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Not useful for sedation in healthy animals when used as sole agent
Diazepam not water soluble Variable absorption when given IM |
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Caution for use Midazolam
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Not useful for sedation in healthy animals when used as sole agent
Diazepam not water soluble Variable absorption when given IM, Costly |
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Caution for use Xylazine
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Cardiopulmonary effects=↓ significant
Avoid in urinary tract obstruction cases Only recommended for "young, healthy, exercise tolerant animals |
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Caution for use Medetomidine
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Cardiopulmonary effects=↓ significant
Avoid in urinary tract obstruction cases Only recommended for "young, healthy, exercise tolerant animals |
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Caution for use Morphine
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Histamine release
Respiratory depression Bradycardia Emesis |
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Caution for use Butorphanol
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Few side effects
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Caution for use Oxymorphone
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Bradycardia
Respiratory depression Emesis |
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Caution for use Hydromorphone
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Bradycardia
Respiratory Depression Emesis |
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Caution for use Thiopental
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Recovery may be rough
Significant cardiopulmonary depression Must be given IV Repeated doses may lead to prolonged recovery |
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Caution for use Propofol
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Must be given IV
Strict aseptic handling Cardiopulmonary depression Heinz bodies in cats after repeated daily doses |
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Caution for use Ketamine and
Tiletamine |
Psychogenic effects
Do not use in patients with seizures May have prolonged rough recoveries especially in dogs |
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Significance of vapor pressure
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The greater the vapor pressure, the greater the
concentration of the drug deliverable to the patient. |
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Significance of Solubility
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Determines uptake and
distribution within body |
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Significance of Partition coefficient
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Concentration ratio of an anesthetic in the solvent and gas phases Blood:Gas partition
coefficient |
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The ultimate goal of inhalant anesthetic
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to achieve an adequate partial pressure(Panes) in the brain to cause the desired level of CNS depression
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Factors that determine Alveolar partial pressure
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Anesthetic input
Anesthetic uptake |
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Factors that determine Anesthetic input
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Ventilation
Inspired concentration Breathing system |
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Factors that determine Anesthetic uptake
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Solubility
Cardiac output Alveolar to venous partial pressure difference |
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Significance of Alveolar partial pressure
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P(Alveolus) --> P(artery) -->
P(brain) |
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MAC definition
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Minimum alveolar concentration
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Significance of MAC
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Min. alveolar concentration of an anesthetic that produces
immobility in 50% of subjects exposed to a noxious stimulus |
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How to measure MAC
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Usually measured in volumes %
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Factors that do not affect
MAC |
Species
Duration of anesthesia Gender |
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Factors that increase MAC
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Hyperthermia
CNS stimulants Hypernatremia Hyperthyroidism |
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Factors that decrease MAC
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Hypothermia
CNS depressants Hyponatremia Hypothyroidism Pregnancy Hypotension Anemia Hypoxia Age |
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Popular inhalant anesthetics
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Isoflurane
Sevoflurane |
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CNS effects of Isoflurane/Sevoflurane
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CNS depression
Decrease in cerebral metabolic oxygen requirements Increase in cerebral blood flow |
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Cardiovascular effects of Isoflurane/Sevoflurane
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Decrease in mean arterial blood pressure
Increase in heart rate Decrease in cardiac output |
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Respiratory effects of Isoflurane/Sevoflurane
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Dose dependant depression
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Other effects of Isoflurane/Sevoflurane
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-Decrease renal blood flow and glomerular filtration rate
-Reduction in liver blood flow and oxygen delivery |
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Isoflurane metabolism
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0.2% undergoes hepatic
metabolism |
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MAC & B:G partition coefficient of Isoflurane
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MAC=1.3%
B:G=1:1.4 |
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Metabolism of Sevoflurane
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3-5% undergoes hepatic metabolism
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MAC & B:G partition coefficient of Sevoflurane
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MAC=2.4%
B:G=1:0.7 |
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Why give Anesthetic Premeds?
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↓anesthetic requirements
Calm/↓ stress, ↑ safety Smooth anesthetic period Sedation, Analgesia Muscle relaxation, ↓ vomitting/regurg |
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Classes of Drugs used for Premed/sedation?
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Anticholinergics
Tranquilizers/sedatives Opiods |
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Anticholinergic drugs for premed/sedation?
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Atropine
Glycopyrrolate |
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Tranquilizers/sedatives for premed/sedation?
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Phenothiazines
Benzodiazepines Alpha-2 agonists |
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Why give anticholinergics as premeds?
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prevent/treat bradycardia
decrease secretions |
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How Anticholinergics work?
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bind to muscarinic cholinergic receptors & prevent ACh from binding
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Physiologic effects of Atropine
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Cardio: ↑ HR, ↔ in BP
Resp: bronchodilation, ↓ secretions CNS: readily crosses BBB Other: Dilates pupils ↓ tears, ↓ GI motility |
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When not to give atropine
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Not good for LA- GI stasis
patients w/ glaucoma, synechia, tachycardia |
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Metabolism of Atropine
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Liver
Cats, rats & rabbits burn through fast b/c atropine esterase |
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Physiolog effects of Glycopyrrolate
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Cardio: ↑ HR, ↔ in BP
Resp: bronchodilation, ↓ secretions Other: ↓ GI motility CNS: DOES NOT CROSS BBB |
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Primary differences between Glycopyrrolate & atropine
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Glyco=no CNS signs, lower doses needed
Longer duration of action Less likely to cause arrhythmias |
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Phenothiazine sedatives
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Acepromazine
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Acepromazine mechanism of action
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Blocks dopamine @ post synapse
Blocks serotonine & Alpha-1 receptors |
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Reasons for giving Acepromazine
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Sedation
Antiemetic antiarrhythmic Antihistaminic Antipuritic |
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CNS effects of Acepromazine
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CNS depression
↓ seizure threshold Depresses thermoregulation potentiates opioid sedatives No analgesia |
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Cardio & Resp effects of Acepromazine
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↓ BP
↓ PCV & TP ↓ Platelets function minimal RESP effects |
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Other effects of Acepromazine
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Muscle relaxation
Delayed gastric emptying penile prolaspe |
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Onset/duration of Acepromazine
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onset: 20-30 minutes
duration: 3-6 hours |
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Reasons for Benzodiazepine administration?
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sedation
muscle relaxation anxiolysis anticonvulsant |
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How Benzodiazepines work?
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GABA agonist-increases action, increases frequency of opening, hyperpolarizes neurons= less excitable
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Benzodiazepines used
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Diazepam
Midazolam Zolazepam |
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Benzodiazapine antagonists
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flumazenil
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Physiologic effects of Diazepam
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Minimal effects on Cardiovascular & Resp
CNS= calming w/o sedation, anti-convulsant, muscle relaxant Paradoxic excitement |
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Pelcularities of Diazepam
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Comes in propylene gylcol vehicle= IM absorption can be unpredictable
Paradoxic excitement in both cats & dogs |
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Effects of midazolam
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Minimal effects on Cardiovascular & slight Resp depression
CNS= calming w/o sedation, anti-convulsant, muscle relaxant |
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Pelcularities of midazolam
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More predictible than diazepam
Shorter duration than diazepam prohibitively expensive for most vet medicine |
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What to know about Zolazepam
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only used with tiletamine
works the same as other benzodiazepines Dogs burn through fast, for faster recovery |
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Flumazenil
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Benzodiazepine antagonist
high affinity for receptors reverses cardiopulmonary & anticonvulsant effects works in 2-4 minutes, only lasts 60 minutes so may need to redose most useful in field work |
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Alpha-2 agonists to know
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Xylazine
Medetomidine Detomidine Romifidine |
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Reasons for administration of Alpha-2 agonists
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Sedation
Analgesia Muscle relaxation Sympatholysis |
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Action of Alpha-2 agonists
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Binds Alpha-2 receptors, reduces sympathetic discharge & reduces norepinephrine release
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Cardiovascular effects of Alpha-2 agonists
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↓HR
arrhythmogenic initial ↑BP, followed by hypotension |
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Respiratory effects of Alpha-2 agonists
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↓rate & depth of breathing
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CNS effects of Alpha-2 agonists
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Sedation
Muscle relaxation Analgesia (personality changes-humans) |
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Other effects of Alpha-2 agonists
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Emesis
Altered GI function Hypothermia Hypoinsulinemia increased uterine tone Mydriasis Increased urine production |
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Xylazine
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Least selective Alpha-2
works in 3-5 minutes IV, but only last an hour causes relaxation of the larynx=risk of aspiration pneumonia |
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Detomidine
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More selective than xylazine
used more in LA, because greater potency (can give less) last ~ 2 hours |
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Medetomidine
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VERY Selective alpha-2 agonist
only used in SA |
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Romifidine
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Recently approved
Very selective alpha-2 agonist |
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Pecularities of Alpha-2 agonists
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don't really work if the patient is excited before giving
reserved for young, healthy exercise-tolerant patients |
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Alpha-2 antagonists
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Tolazoline
Yohimibine Atipamezole Reversal agents |
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Yohimibine
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Alpha-2 antagonist
enhances Norepi release can cause hyperexcitement, tachycardia, hypotension |
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Tolazoline
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Least selective Alpha-2 antagonist
Induces H-2 effects-GI bleeding, diarrhea |
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Atipamezole
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Most selective Alpha-2 antagonist
doesn't really act @ other receptors don't need to redose |
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Characteristics of the Ideal injectable anasthetic
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Water soluble
Long shelf life stable in light small volumes needed wide margin of safety Short duration of action Analgesia Muscle relaxation No life-threatening changes |
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Classes of Injectable Anesthetics
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Barbituates
Propofol Etomidate Dissociatives |
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Types of Barbituate Anesthetics
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Long acting- Phenobarb
Short acting- Pentobarb Ultra short acting- Thiopental |
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CNS effects of Barbituate Anesthetics
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GABA agonist- enhances & mimics GABA action= hyperpolarization of neurons
CNS Depression No analgesia |
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Cardiovascular effects of Barbituate Anesthetics
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↑ HR
↓ SV & contractility ↓ BP may cause ventricular arrhythmias |
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Resp. effects of Barbituate Anesthetics
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Potent depressants
↓ tidal volume & rate Altered sensitivity to CO2 |
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Other effects of Barbituates
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Hypothermia
Tissue Sloughing when not injected into a vein cross placenta No effect on GI, liver or kidneys |
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Factors affecting depth of anesthesia when using barbituates
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Dose-amount, route, & rate
Ionization- Protein binding-less= deeper depth |
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How Ionization of bartituates affects the depth of anesthesia
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more ionized=less active= lighter depth
more alkaline solution=more ionized more acidic solution=more nonionized=deeper plain |
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Factors affecting duration of barbituates
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Redistribution=how long it stays in the brain
Metabolism |
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Redistribution of barbituates
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Vessel rich=brain, liver=most of cardiac outpur
Lean=muscle Fat- Vessel poor=bone highest [brain] w/in a min. of injection, lean 10-15 min. stays in fat, repeated dosing= longer anesthetic time |
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Unique properties of Propofol
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Insoluble in water-comes as an emulsion
used for induction & for maintenance stable @ room temps & in light No preservative=bacteria can grow, & get endotoxins production... throw it away after a few hours of being open |
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CNS effects of Propofol
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↓intracranial pressure
unknown/unclear affect on seizure activity |
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Action of Propofol
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GABA agonist
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Cardiovascular effects of Propofol
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↑ HR
↓ SV & contractility ↓ BP may cause ventricular arrhythmias |
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Resp. effects of Propofol
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Periods of apnea
Mild hypercapnia |
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Other effects of Propofol
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Oxidative RBC injury, with repeated dosing
No perivascular sloughing, as with barbituates |
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Metabolism & excretion of propofol
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Onset w/in 10 min.
Recovery w/in 20-30 hepatic & likely "extra" hepatic metabolism non-cumulative effect, recovery w/in 30 min of last shot, no matter how many you give |
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Etomidate
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A non-barbituate
Imidazole derivative anesthetic insoluble in water= has propylene glycol vehicle |
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CNS Effects of Etomidate
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acts on GABA receptors
↓ cerebral BF & intracranial pressure no analgesia Myoclonic movements |
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Cardiovascular effects of etomidate
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No significant effects on any part of cardio system
Can use in patients w/ heart disease |
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Respiratory effects of etomidate
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Slight depression
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Other noteable effects of etomidate
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pain @ injection site
Adrenal suppresion Nausea & vomiting-during induction & recovery possible |
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Metabolism of etomidate
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Rapid onset
Rapid hepatic metabolism rapid recovery |
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Dissociative anesthetics
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Ketamine
Tiletamine makes patient dissociated/unaware of the environment |
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Ketamine
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A dissociative anesthetic
Trance-like state Immobility Versatile |
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Chemical characteristics of Ketamine
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low molecular weight
high lipid solubility =rapid onset time |
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CNS effects of Ketamine
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Dose related unconsciousness & analgesia
↑ cerebral BF & intracranial pressure don't use in epileptic/ head trauma patients Hallucinations |
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Cardiovascular effects of ketamine
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has indirect effects
↑ HR, BP & CO ↑ myocardial O2 consumption |
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Respiratory effects of ketamine
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Apneustic ventilation
↓ Resp. rate & minute volume does not depress resp. response to hypoxia ↑ trachial secretions (use w/ anticholinergic to ↓) |
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Other noteable effects of ketamine
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↑ intraocular pressure
limb ridigity spontaneous limb movements Eyes stay open (need to protect & keep moist) |
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Admin of Ketamine
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IV or IM
Rapid onset (30-90 seconds-IV) Lasts 3-10 minutes Dogs metabolize, cats excrete unchange |
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Tiletamine
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Only available in combination w/ zolazepam = telazol
Longer duration & more analgesia than ketamine |
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CNS effects of Telazol
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Dose related unconsciousness & analgesia
↑ cerebral BF & intracranial pressure Hallucinations Not enough for deep, visceral procedures |
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Cardiovascular effects of Telazol
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has indirect effects
↑ HR, BP & CO ↑ myocardial O2 consumption |
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Respiratory effects of Telazol
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Apneustic ventilation
↓ Resp. rate & minute volume does not depress resp. response to hypoxia ↑ trachial secretions (use w/ anticholinergic to ↓) |
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Species difference in using Telazole
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Onset times rapid (minutes)
Dogs burn through much fast about an hour, w/ hepatic metabolism Cats last longer, 3+ hours, excreted unchanged |
