General anesthetics - sather Flashcards
What is the fundamental method of action of general anesthetics?
What else do they do?
GAs potentiate GABAAergic transmission (potentiate IPSP).
Also POTENTIATE glycine receptors (inhibitory)
ALso potentiate K+ TASK channels (decrease excitability by altering resting membrane potential)
[Volatile GAs (i) partition into the membrane, and (ii) enter hydrophobic pockets in various membrane proteins such as GABAA receptors, other ion channels and perhaps proteins involved in neurotransmitter release.]
What are the ideal characteristics of a general anesthetic?
Short half-life
Low blood solubility
Describe the stages of anesthesia.
Stage I: analgesia
Stage II: excitement, delirium
Stage III: Surgical anesthesia. 4 subcategories
1) regular respirations
2) fixed pupils, muscular relaxation
3) depressed intercostal function
4) diaphragmatic breathing only, fixed pupils
Stage IV - Medullary paralysis (respiratory failure, cardiovascular collapse and death within minutes)
When inducing someone (general anesthesia), in which order will the following occur: loss of temperature regulation, analgesia, loss of muscle tone, loss of consciousness, loss of pupillary light reflex (fixed pupils), respiratory failure, loss of fine motor control
1) loss of fine motor
2) analgesia
3) loss of temperature regulation
4) loss of consciousness
5) loss of pupillary light reflex
6) loss of muscle tone
7) respiratory failure
Describe the differing rates of uptake from different types of blood:tissue in terms of a solubility coefficient.
Tissue:blood coefficients are approximately 1 for “lean tissues”
Brain, heart, muscle, skin –> same solubility as blood
Tissue:blood coefficient for fatty tissues is»_space;greater than 1
[This simply means that anesthetic is ~equally soluble in blood and lean tissues, but that anesthetic is substantially more soluble in fatty tissue than in blood or lean tissues]
What three factors are important in determining anesthetic uptake from blood–> tissues?
1) solubility coefficient
2) perfusion
3) concentration gradient (partial pressures blood vs tissue)
1/MAC = ?
1/Minimum Alveolar Concentration = potency
MAC = concentration at which 50% of people are anesthetized against a small skin incision.
Depth of anesthesia depends upon _____.
the concentration of anesthetic in the brain.
The rate at which an effective concentration of anesthetic is reached in the brain depends upon 5 factors:
(1) concentration of the anesthetic in inspired air,
(2) alveolar ventilation rate,
(3) pulmonary blood flow (cardiac output),
(4) blood:gas partition coefficient, and
(5) potency (oil:gas partition coefficient).
Does increasing the ventilation rate increase the depth of anesthesia?
no. only the rate at which steady state is reached.
Gases which have a higher solubility in blood will induce anesthesia (faster or slower)?
Slower.
INcreased pulmonary blood flow will (increase or decrease) general anesthetic uptake?
Decrease. Less time to diffuse.
What tissues will uptake general anesthetic within (a) minutes (b) 2-4 hours (c) longer?
(a) vascular tissues (brain, kidney, heart, liver, endocrine glands)
(b) muscular tissues, skin
(c) fatty tissues
The oil:gas partition coefficient is an index of GA (potency OR rate of uptake)?
potency.
The blood:gas partition coefficient is related to (kinetics of GA uptake and elimination OR potency)?
Kinetics of uptake/elimination
INcreasing the concentration of GA will increase the ____ of anesthesia.
rate
**I would assume the depth of anesthesia would also change…but this is not explicitly mentioned.
INduction of anesthesia is faster with a (low blood solubility OR a high blood solubility)?
low.
How are volatile anesthetics cleared from the body?
Exhalation. So the respiratory rate and cardiac output will determine the rate of clearance.
Can N2O be used as a sole anesthetic agent?
NO. produces pretty good analgesia, but the concentration cannot get high enough to produce anesthesia.
Why is the uptake rate of N2O faster than expected?
the Concentration Effect. Essentially, more N2O gets taken up due to rapid absorption across the alveoli.
What are two really good reasons Halothane is no longer used as an anesthetic agent?
1) Hepatotoxic. For ∼1/10,000, 2-5 days after anesthesia, fever, anorexia and nausea/vomiting Death occurs in 50% of these patients
2) Malignant hyperthermia. Dantrolene, ice bath. Signs are muscle rigidity, temp spike.
What is the most widely used inhalational anesthetic?
Flurothane.
Why is flurothane so great?
Rapid induction (avoid stage II)
Less organ toxicity
Good muscle relaxant
Minimal myocardial depression
What is one problem with flurothane?
What is the workaround?
Pungent odor causes cough.
So you induce with propofol, then use flurothane.
Sevoflurane doesn’t cause cough. Why isn’t it used instead of flurothane?
Kidney toxicity
Mostly used for induction
circulatory failure occurs at ____ the effective concentration for surgical anesthesia
only 2-4x
In practice, what factor of MAC is used for general anesthesia?
0.8-1.3 MAC
**99% of ppl have no response to pain at 1.3 MAC
What 6 categories of drug might be used during a typical surgical procedure?
Name the category and a specific drug
1) Anti-anxiety agent: (BDZ, diazepam)
2) Induction agent: (Thiopental)
3) Analgesic: (Fentanyl)
4) Neuromuscular blocker (vecuronium)
5) Anticholinergic drugs (glycopyrrolate, atropine, scopolamine)
6) Anti-emetic (ondansetron)
Why is an anticholinergic administered during surgery?
reduce GA-induced hypotension, bradycardia, and excess salivary secretions that can choke patient during anesthesia (–> glycopyrrolate, atropine, scopolamine)
Why are anesthetic agents combined?
Addition of MAC (eg .5 + .5 = 1) allows an additive effect of anesthesia without additive effects of side effects.
So this is commonly done.
