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Flashcards in Anesthetics part 2 Deck (78):

only legal Dissociative Anesthetic

Only ketamine is used legally


how is ketamine used

• Used alone or with tranquilizers and opiods to induce anesthesia
– Cats—for minor procedures or to facilitate restraint
• Subanesthetic dose for analgesia


ketamine MOA

Mode of Action
• Disrupts nerve transmission in some brain sections
• Selective stimulation in parts of the brain
• Trancelike state – Critter appears awake – Immobile and unaware of surroundings *”Waxy rigidity”


waxy rigidity

muscles tense and goes back. can twist and will go right back


ketamine peak of action

Peakaction – 1-2 minutes after IV injection – 10 minutes after IM injection


ketamine duration of effect

– 20-30 minutes
– Increased dose prolongs duration but doesn’t increase anesthetic effect


ketamine metabolized?

All dissociatives are either metabolized in the liver or excreted unchanged in the urine
– Avoid use in critters with liver or kidney disease


Cataleptoid (what the heck is this???) state

waxy rigidity


what reflexes are intact with ketamine

Palpebral, corneal, pedal, PLR, laryngeal,


Ocular effects of ketamine

– Eyes remain open (therefore must keep eyes moist)
– Central dilated pupil – MUST use ophthalmic ointment


Dissociative Effects muscle tone

– Normal to muscle rigidity – Counteract with concurrent tranquilizer


Dissociative Effects analgesia

– Somatic analgesia – Visceral analgesia


ketamine still

Sensitivity to sensory stimuli


ketamine sides

vivid halucinations, amnesia


Dissociative Effects on the Cardiovascular System

Increase in heart rate • Increased cardiac output • Increased mean blood pressure • Effects due to stimulation of the SNS


so while ketamine seems safer for patients with heart disease it

increases cardiac workload and increases myO2cardial make sick hearts work harder!


Dissociative Effects on the Respiratory System

Respiratory rate and tidal volume remain stable
• Respiratory depression usually insignificant
• Apneustic (what’s this?) respiration at higher doses hold their breath


Adverse Effects of Dissociatives on the Cardiovascular System

• Decreased inotropy • Cardiac arrhythmias in response to
epinephrine release
• Relatively safer than others...
• Significantly increased salivation and respiratory tract secretions with potential for aspiration.


Other Adverse Effects of Dissociatives

• Increased intracranial and intraocular pressure
• NO reversal agent


Dexmedetomidine (Precedex) what is it? and how it affects heart and respiratory system

(Precedex) Increasingly-used α2-agonist sedative – Minimal respiratory depression – Good analgesia – “Dulls” cardiovascular responses to anesthesia – “Sympatholytic”


Etomidate what is it and what its used for

(Amidate) Noncontrolled, sedative-hypnotic imidazole drug with no analgesic properties
• Used for IV induction (although it hurts!)
• Minimal effects on the cardiovascular and respiratory systems! One of the few injectable anesthetics (>Propofol) to decrease ICP.expensive!!!


Etomidate onset, POA, duration

Short half-life makes for finer anesthetic control: – Onset of action: 30–60 seconds – Peak effect: 1 minute – Duration: 3–5 minutes; terminated by redistribution


etomidate distribution protein binding metabolism and half life

Distribution: Vd: 2-4.5 L/kg
– Protein binding: 76% – Metabolism: Hepatic and plasma esterases – Half-life redistribution: 29 minutes – Half-life elimination: 2.9 to 5.3 hours
Like a much safer, fast-acting barbituate!


benzodiazepine MOA

Tranquilizers-all controlled substances *As with most other anesthetics & sedatives & hypnotics it targets Υ-amino- butyric acid receptors (GABA) since GABA is the major inhibitory CNS neurotransmitter. can synergize with ketamine. gets rid of waxy rigidity


valium half life

diazepam, benzodiazepine 1-4 days (long duration)


Versed half life

midazolam, 2-6 hours (short duration)


ativan half life

loazepam, benzodiazepine 10-20 hours (medium duration)


Effects of Benzodiazepines

 CNS  Calming and antianxiety  Not an effective sedative or analgesic  Anticonvulsant (raises seizure threshold)

Cardiovascular and respiratory systems  Minimal effect with a high margin of safety *Midazolam has a greater hypotensive effect than the others.
Skeletal muscle relaxation
  Potentiate general anesthetics


Diazepam(Valium) how to use

Not water soluble (should only be administered concurrently with opiods, thiopental, & propofol)
–Don’t mix with water- soluble drugs!
– Don’t store in plastic – Light sensitive


Lorazepam(Ativan) how to use

-Water soluble/poorly lipid soluble.
-Decreasing use in open-heart
*D.O.C. for symptomatic treatment of recreational stimulant overdose.
*High addictive potential and antegrade amnesia effects make it popular in the non-licensed pharmaceutical industry.


Midazolam(Versed) how to use

– Water soluble (unlike valium)
– Can be administered IM or SC
– VERY commonly used in combination with Propofol for cardiac surgical anesthetic induction.


side effects of benzodiazepines

Also cause antegrade amnesia (how could this be a problem?)
• Long-term use results in the development of tolerance and dependence. can be used so people dont remember surgery


Benzodiazepine Reversal

Flumazenil (Anexate) effectively reverses the effects of benzodiazepines by competitive inhibition at the GABA receptor sites. but is rarely used in the cardiovascular setting (why?)


Inhaled Anesthetics
Volatile anesthetics

All are liquids at room temperatures and pressures.


Nitrous oxide is

a gas at room temperatures and pressures (but this blue tank ain’t room pressure!


soflurane and sevoflurane are the most common

sed agents in this class
• Liquid at room temperature • Stored in a vaporizer on
an anesthetic machine
• Vaporized in oxygen blend that flows through the vaporizer



• High vapor pressure: needs a precision vaporizer
• Blood:gaspartitioncoefficient: rapid induction and recovery • Good for induction with a mask
or chamber • High controllability of depth
of anesthesia • MAC = 2.34% to 2.58%



future! • Closely related to isoflurane
• Expensive
• Lowestblood:gaspartitioncoefficient: very rapid induction and recovery
• Used with a special precision vaporizer • MAC = 7.2% and 9.8%
– Least potent inhalant agent • Eliminated by the lungs.
one breath aesthesia



Most commonly used inhalant agent in North America
Isoflurane (Cont’d)
• Properties – High vapor pressure: need a precision
– Low blood:gas partition coefficient: rapid induction and recovery Good for induction with mask or chamber – MAC = 1.3% to 1.63%: helps determine
initial vaporizer setting
– Low rubber solubility
– Stable at room temperature; no preservatives needed



The archetypical halogenated volatile anesthetic.
• Relatively rapid induction & recovery. • Not explosive like some of its predecessors
(Notice the door...) Somewhatarrhythmogenic • Somewhat metabolized (a BAD thing!)
producing hepatotoxic byproducts
• Somewhat contributing to malignant hyperthermia (particularly when used in conjunction with succinylcholine)No longer used in the U.S.A...
‘Cause it is the reference standard





Uptake and Distribution of Halogenated Organic Compounds

• Liquid anesthetic is vaporized and mixed with oxygen-blend gas
• Mixture travels to lungs (alveoli) &/or oxygenator and diffuses into the bloodstream.


Uptake and Distribution of
Halogenated Organic Compounds
(Cont’d) diffusion rate

Diffusion rate is dependent on concentration gradient (alveoli/capillary &/or opposite sides of oxygenator membrane/pseudomembrane) and lipid solubility


Concentration gradient is greatest during initial induction whyy?

because no anesthetic during induction. same with coming off


Distribution to tissues is dependent on blood supply  Lipid solubility determines entry into tissues
through cell walls. why?



Depth of anesthesia is dependent

partial pressure
of anesthetic in the brain


 Partial pressure in the brain is dependent on

partial pressure of the anesthetic in blood and


Maintenance of anesthesia is dependent on

sufficient quantities of anesthetic delivered to the lungs &/or oxygenator bundle fibers.


Elimination of Halogenated Organic Compounds

Reducing amount of anesthetic administered reduces amount delivered to the alveoli/oxygenator
• Blood level is initially higher than alveolar/oxygenator level
• Concentration gradient now favors anesthetic diffusion from blood into the alveoli/oxygenator vent
• Blood levels drop quickly as patient breathes out anesthetic from the alveoli/oxygenator bundle
• Brain levels drop as less anesthetic is delivered by blood
• Patient wakes up


Adverse Effects of Halogenated Organic Compounds on cns?

– Increased intracranial pressure in patients with
head trauma or brain tumors – Considered safe for epileptic animals


Adverse Effects of Halogenated Organic Compounds on cardio system?

–Decreases blood pressure and may
decrease renal blood flow


Adverse Effects of Halogenated Organic Compounds on respiratory system?

– Hypoventilation
– Carbon dioxide retention and respiratory acidosis


One of perfusionists’ most effective tools for changing blood pressure/arterial pressure is their anesthetic vaporizer.

Increasing the level (percentage) of volatile anesthetic provides a reliable, dose-dependent vasodilatory response.
• This is caused by a com- bination of direct vaso- dilatory effect and sympatholytic effect.


volatile Anesthetics
• Potential Disadvantages:

– Very significant hemodynamic variability
from patient to patient. – Possibility of “coronary steal syndrome”


Coronary Steal

– Arteriolar dilation of normal vessels diverts blood away from stenotic areas
– Commonly associated with adenosine, dipyridamole, and SNP
– Forane causes steal and new ST-T segment depression
– May not be important since Forane reduces SVR, depresses the myocardium yet maintains CO


Physical and Chemical Properties of Inhalant Anesthetics

• Important properties to consider – Vapor pressure – Partition coefficient – Minimum alveolar concentration (MAC) – Rubber solubility
– Cardiac output dependent


Vapor Pressure

• “The tendency of an inhalation anesthetic to vaporize to its gaseous state”
• Determines how readily an inhalation anesthetic will evaporate in the anesthetic machine vaporizer
• Temperature and anesthetic agent dependent
gas has higher pressure than water.


Volatile agents vapor pressure

– High vapor pressure
– Isoflurane, sevoflurane, desflurane, and halothane
– Delivered from a precision vaporizer to control the delivery concentration
– All precision vaporizers are made to deliver only one specific halogenated agent


Non volatile agents vapor pressure

Nonvolatileagents – Low vapor pressure – Methoxyflurane – Delivered from a nonprecision vaporizer
***NO LONGER USED (but now you understand why they are referred to as “precision vaporizers”


blood gas partition coefficient

The measure of the solubility of an inhalation anesthetic in blood as compared to alveolar/oxygenator gas Indication of the speed of induction and recovery for an inhalation anesthetic agent
• Low blood:gas partition coefficient – Agent is relatively less soluble in blood
than alveolar/oxygenator gas
– Faster expected induction and recovery


Blood: gas partition coefficient determines the

clinical use of the anesthetic agent – Maintenance: How fast will the anesthetic depth change in response to changes in the vaporizer setting?
– Recovery: How long will the patient sleep after anesthesia? early extubation
– How soon do I have to turn down/off my vaporizer so volatile anesthetics won’t depress the heart as we try to wean? have to gauge how fast its coming out of solutuion


Minimum Alveolar Concentration

“The concentration of anesthetic vapor in alveoli that is required to prevent a motor response in 50% of patients subjected to surgical pain stimuli”
*This is confusing because it isn’t really a minimum concentration, it’s really an average concentration. measure of potency


he lower the MAC

the more potent the anesthetic agent and the lower the vaporizer setting (does this make sense?)


MAC may be altered

by age, metabolic activity, body temperature, disease, pregnancy, obesity, and other agents present
• Every patient must be monitored as an individual


A vaporizer setting of

roughly 1-2 X the MAC of an agent is required for surgical anesthesia and completely depends on the individual critter!


Rubber Solubility

LikeBlood:GasPartitionCoefficient except with the rubber/plastic/silicon parts of your ventilation circuit.
• An anesthetic circuit can act like another compartment or reservoir for the distribution of gas.
• What does this mean for YOU!? slows down anesthetics. anesthetic rebound. have to give more


Given what you know... will changes in blood flow or sweep rate effect volatile anesthetic levels?

increasing gas flow will increase amount of anesthetic


Effects of Isoflurane

Maintains cardiac output, heart rate, and rhythm – Fewest adverse cardiovascular effects


adverse effects of isoflurane

Depresses the respiratory system • Maintains cerebral blood flow • Almost completely eliminated through the lungs • Induces adequate to good muscle relaxation • Provides little or no analgesia after anesthesia
• Can produce carbon monoxide when exposed to a desiccated carbon dioxide absorbent


Effects and Adverse Effects of Sevoflurane

Minimal cardiovascular depression
• Depresses respiratory system
• Eliminated by the lungs, minimal hepatic metabolism
• Maintainscerebralbloodflow
• Induces adequate muscle relaxation
• Some thrashing, etc. and excitement during recovery


Nitrous Oxide

Excellent analgesic, poor anesthetic (by itself )
• Doesn’t require a precision vaporizer
• Often mixed with other gas anesthetics to produce better analgesia (NEVER more than 80% N2O!)
• Very poorly soluble in blood and tissues presenting two problems for us:


NO problems

2.) Diffusion Hypoxia ...therefore little used in cardiac surgery


Unlike other gas anesthetics, nitrous oxide is a

compressed liquid, therefore: it is always giving off vapor so gauge will show its full when its really not


halothane MAC and blood/gas partition coefficient

.75% AND 2.4


isoflurane MAC and blood/gas partition coefficient

1.2% AND 1.4


sevoflurane MAC and blood/gas partition coefficient

2% AND.65


nitrous oxide MAC and blood/gas partition coefficient

105% AND .47


desflurane MAC and blood/gas partition coefficient

6% AND .42