Anesthetics part 2 Flashcards
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,
swallowing
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
sevoflurane
• 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%
suprane/desflurane
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
isoflurane
Most commonly used inhalant agent in North America
Isoflurane (Cont’d)
• Properties – High vapor pressure: need a precision
vaporizer
– 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
halothane
The archetypical halogenated volatile anesthetic.
Halothane
• 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
enflurane
1
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?
1
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
alveoli
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.
(Why?)
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…
…how 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
