General Anesthesia I Flashcards Preview

Surgery & Anaesthesia - NSULA Vet Tech Program Spring 2016 > General Anesthesia I > Flashcards

Flashcards in General Anesthesia I Deck (42):

Define general anesthesia.

controlled and reversible lack of consciousness, lack of pain sensation, lack of memory, depressed reflexes


What are the four anesthetic procedure phases?

pre-anesthesia, induction, maintenance, recovery


Define induction.

animal leaves normal state of consciousness and enters the anesthetized state


What are two routes of anesthetic induction?

injectable - often followed by gas for maintenance
inhalation - face mask, induction chambers, intubation


Define maintenance.

stable level of anesthetic depth, stage during which the surgical procedure is performed


Define recovery.

when concentration of anesthetic in the brain begins to decrease


How are injectable anesthetics excreted by the body?

most metabolized by the liver and excreted by the kidneys, but there are exceptions


How are inhalent anesthetics excreted by the body?

most commonly used agents are eliminated by the respiratory tract, some older agents have variable amounts of liver metabolism


What is the most important factor in anesthetic safety?

there is no substitute for using your senses


What are the classic stages and planes of anesthesia?

Stage I - beginning of induction
Stage II - excitement phase
Stage III -
Plane 1 - can intubate at this point
Plane 2 - heart rate, breathing rate steady
Plane 3 - 8 breaths per minute or less,
Plane 4 - dying
Stage IV


Define endotracheal intubation.

placement of breathing tube in airway, which minimizes dead space, decreases risk of aspiration, allows direct delivery of oxygen o assist respiration, more efficient delivery with less waste gas


What patients are most at risk for aspiration?

oral surgery/dentistry, unfasted patients


What are the risks of endotracheal intubation?

- stimulates parasympathetic nervous system
- brachycephalic breeds
- laryngospasm, especially cats
- species problems -> blind intubation
- tube too far in, past tracheal bifurcation
- increased dead space - trim length of tube
- cuff inflation - too much -> pressure necrosis/occlusion of tube lumen
- tube obstruction
- loss of tube into airway during recovery
- infection transfer -> disinfect between patients


What brachycephalic traits cause anesthetic risks?

stenotic nares
elongated soft palate
everted pharyngeal ventricles


Which dog breed has the highest anesthetic risk?

English bulldog


What is the inhalation anesthesia mechanism of action?

gas anesthesia within the brain is poorly understood


What is the distribution/elimination route of inhalation anesthesia?

liquid anesthesia -> vaporized into oxygen -> air passages -> alveoli -> bloodstream -> brain


What is the distribution/elimination of inhalation anesthesia control mechanism?

concentration gradient from alveoli -> bloodstream
lipid solubility -> agents leave bloodstream -> brain


What does inhalation anesthetic maintainance require?

requires that enough gas be delivered to alveoli to maintain concentrations in blood and brain


inhalation anesthetic recovery

reduce flow to alveoli -> concentration gradient now favors flow to alveoli from bloodstream and then from brain to bloodstream

running 100% oxygen during recovery will speed process


inhalation anesthetic agent vapor pressure

measure of the amount of liquid that will evaporate at 20 C


high vapor pressure

volatile - vaporizes easily
need precision vaporizers wth a maximum delivery of 5-8% depending on the agent used

examples - sevoflurane, isoflurane, halothane > 30%


blood to gas solubility coefficient

also known as partition coefficient - measure of distribution of age between blood and gas phases of the body


low solubility coefficent

tends to remain in gas phase in lungs rather then dissolving into tissues and blood, steep concentration gradient, rapid induction/recovery

ex. isoflurane, sevoflurane


high solubility coefficient

"sponge effect" - slow induction and recovery


endotracheal intubation materials

3 tubes in size range with cuffs checked for leaks
- stylet for small tubes
- lubricant (water soluable)
- lidocane/cotton tipped applicators
- oral speculum
- laryngoscope
- 2-3 gauze sponges
- roll gauze cut to length appropriate to tie in place
- syringe to inflate cuff
- eye ointment
- gas machine checked and ready to attach to trach tube


Minimum Alveolar Concentration (MAC)

Lowest concentration that produces no response in 50% of patients exposed to a painful stimulus.
A measure of strength or potency of an agent
Low MAC value = more potent than a high MAC value


Factors Influencing Absorption & Elimination

concentration, ventilation, diffusion, pulmonary blood flow, tissue absorption, lipid content of tissues



Greater the concentration, the greater the pressure gradient -> more rapidly anesthetic will diffuse across alveoli



Increased rate/depth will aid in moving more anesthetic vapor across the alveoli



Is a physical process determined by:
The agent’s solubility coefficient
The molecular weight of the gas
The pressure gradient from the alveoli and plasma


pulmonary blood flow

The more blood exposed to the anesthetic gas, the more molecules will move into the blood


tissue absorption

Highly perfused tissues receive and absorb most of the gas taken up by the alveoli (brain, heart, lungs, liver, kidneys, intestine, endocrine glands)


lipid content of tissues

Lipid-rich cells take up more of an anesthetic than lipid-poor cells
Brain highly lipid-rich


halogenated organic compounds

Modern common inhalation agents
Isoflurane – most common
Sevoflurane - common
Halothane – not used today
Methoxyflurane – not used today
Enflurane – little use vet med
Desflurane – little use vet med



Good margin of safety
High vapor pressure
Low solubility coefficient
Rapid induction/recovery
High MAC value (low potency)
Stable at room temp with no preservative
Fewest adverse effects on heart, lungs, etc.
Eliminated by lungs
No post-operative analgesia provided



Rapid induction/recovery (faster than isoflurane)
Best agent for mask/chamber inductions (use 6-8%)
Also good agent for C-sections
Rapid/quiet recovery in horses
Some myocardial depression and vasodilation
Sensitizes myocardium to catecholemine-induced arrhythmias
Causes some respiratory depression
Depresses temperature regulation
Avoid in patients susceptible to malignant hyperthermia
No analgesic effect in recovery period



Introduced in 1956, use dwindling today
Up to 20% eliminated by liver metabolism
Mixed with preservative thymol
Sensitizes heart to catecholemines (i.e. epinephrine)
Some myocardial depression/vasodilation
Increases intracranial pressure
Avoid in head trauma patients
Associated with malignant hyperthermia
Increased temp, muscle rigidity, cardiac arrhythmias, may die



Introduced in 1959, not available today
Low vapor pressure (use in non-precision vaporizer)
Slow induction/recovery
Low MAC (most potent of class)
Considerable solubility in rubber/plastics



Used in human medicine
Rapid induction/recovery
Profound respiratory depression, with mechanical ventilation generally required
In dog, may produce seizure-like muscle spasms



Little use in veterinary medicine
Lowest solubility coefficient
Therefore, most rapid induction/recovery
Extremely volatile (high vapor pressure)
Requires special high-cost vaporizer


Nitrous Oxide

Little used in vet med today
Stored in blue cylinders as compressed gas
Administered via flowmeter, like oxygen
Mixed with oxygen at concentrations of 33-67%
Was used to speed induction and recovery, and provide additional analgesia
Because newer agents have rapid induction/recovery, not used much today except in human dentistry