EXAM #3: GENERAL ANESTHESIA Flashcards
What are the advantages of general anesthesia?
Body wide anesthesia
What are the disadvantages of general anesthesia?
Disturbance of all organ systems
What are the advantages of local anesthesia?
Minimal system disturbance
What is the disadvantage of local anesthesia?
Anesthesia may not be adequate
What are the six characteristics of an ideal anesthetic agent?
1) Unconsciousness
2) Amnesia
3) Analgesia
4) Skeletal muscle relaxation
5) Areflexia
6) Good minute-to-minute control
What is the “Triad of Anesthesia?’
1) Asleep
2) Pain-free
3) Still
What is the pharmacologic synonym of unconsciousness?
Hypnosis
What are the four major things that you want to know about a patient as an anesthesiologist?
Patient history and/or blood relative history of:
1) Malignant hyperthermia
2) Cardiovascular disease
3) Respirator disease
4) Allergies
What is “balanced anesthesia?”
Use of a combination of drugs to produce all the effects of ideal anesthesia
No anesthetic is ideal
What are the PHASES of anesthesia?
1) Induction
2) Maintenance
3) Emergence
4) Recovery
What are the STAGES of anesthesia?
1) Analgesia
2) Excitement
- Body is “fighting” the anesthetic drug and patient can become combative
3) Surgical anesthesia
4) Medullary depression
What is the main purpose for inhalable anesthetics?
Maintenance of anesthesia
What is the main purpose of IV anesthetics?
Induction of anesthesia
What are the three general mechanisms of action of the general anesthetic agents?
1) Increased GABA-A channel activity
2) Activation of K+ channels
3) Inhibit glutamate NMDA receptors
What are the advantages of gaseous general anesthesia?
1) Easy to control depth of anesthesia
2) Minute-to-minute control
What is the disadvantage of gaseous anesthesia?
Anesthesia induction is not as fast or smooth as IV
Which “direction” do gas molecules move?
Down their partial pressure gradient
What factor results in a faster achievement of anesthetic concentration in the blood?
Higher initial concentration in air
–>leads to higher partial pressure in the lungs–>bloodd
What is the effect of alveolar ventilation on anesthesia onset?
Higher alveolar ventilation leads to more gas molecules/time and a faster rate of onset
What is the Otswald Coefficient?
Blood: gas partition coefficient i.e. the solubility of the anesthetic in the blood
What does a low Otswald Coefficient mean?
Low solubility
Otswald Coefficient is preferable for a fast rate of anesthesia onset, high or low? Why?
Low solubility i.e. low Otwald Coefficient, which translates to a faster buildup of the agent in the blood
What does the blood: brain partition coefficient translate into?
Solubility of the agent in lipid
What does a high lipid solubility of an anesthetic agent translate into?
More potent
What does a high pulmonary blood flow translate into in general anesthesia?
Slower onset
What does a low pulmonary blood flow translate into in general anesthesia?
Faster onset
How does the Otswald Coefficient effect elimination?
Low solubility equals faster elimination
What is the MAC value?
Minimum alveolar concentration i.e. the concentration of anesthetic in alveolar air at which there is no response to noxious stimuli in 50% of patients
What does a low MAC value translate into?
More potent anesthetic
What does a high MAC value translate into?
Less potent anesthetic
How are the MAC values of combinations of inhaled anesthetic described?
Additive
What important clinical factor will decrease the MAC value?
Presence of CNS depressants
What is the hallmark gaseous general anesthetic?
Nitrous Oxide
Why is NO described as almost an ideal anesthetic agent?
1) Good analgesia
2) Relatively nontoxic
3) Rapid onset and recovery
What is the major limitation of NO?
Incomplete anesthetic b/c MAC value is 110%
I.e. in 50% of patients, NO cannot be given in sufficient quantities to eliminate response to noxious stimuli
What is the common use for NO?
Carrier agent for another anesthetic gas
What is the second gas effect?
Utilizing the additive MAC of gaseous agents by combining two gases to reduce induction time
What are the advantages of the 2nd gas effect?
1) Reduced induction time
2) Reduced concentration of primary agent
3) Reduced toxicity of primary agent
What are the major disadvantages of NO?
1) Lack of potency
2) Diffusion hypoxia
3) Increased risk of spontaneous abortion and decreased probability of concenptoin
What is diffusion hypoxia?
- When d/c NO rapidly diffuses from the body into the alveoli
- Diffusion into the alveoli dilutes the gases in the alveoli i.e. oxygen
- PAO2 decreases leading to hypoxia
Note that this is combated by progressive d/c of NO and administration of 100% oxygen*
Clinically, what do you need to remember about NO?
Cannot be used as sole anesthetic agent for surgical anesthesia
List the halogenated anesthetic agents.
Halothane
Enfulrane
Isoflurane
Desflurane
Why are anesthetic agents halogenated?
1) Reduces flammability
2) Increased potency
What is the drawback to halogenation?
Increased toxicity and side effects
What are halogenated agents primarily used for in anesthesia?
Maintenance of anesthesia
What is the prototypical halogenated agent?
Halothane
What toxicity is associated with Halothane?
Hepatitis
What are the side effects associated with Enflurane?
CNS stimulant effects
What is the clinical utility of Isoflurane?
Primary anesthetic agent used for maintenance of anesthesia
With lower toxicity compared to other halogenated agents
What is Desflurane?
Second most common agent used for maintenance of anesthesia
What side effect is associated with Desflurane?
Respiratory irritant producing bronchioconstriction, cough, and laryngeal spasm
What is Sevoflurane?
Newest and most popular halogenated anesthetic agent
What is the advantage of Sevoflurane?
Low airway irritation vs. Desoflurane
What is malignant hyperthermia?
- Hypermetabolic crisis when an MH-susceptible (MHS) individual is exposed to a volatile anesthetic
- Exposure leads to elevated intracellular Ca++ in skeletal muscle, causing sustained contraction
- Sustained muscle contraction generates more body heat than can be dissipated
–>Result is marked hyperthermia (life-threatening)
What is Thiopental?
Barbiturate general anesthetic used for induction of anesthesia
What is Propofol?
- “Milk of Amnesia”
- Newer drug and most frequently used anesthesia induction agent
How does Propofol differ from Thiopental in terms of maintenance?
Propofol can be given as a continuous IV drip
What is the major advantage of Propofol clinically?
Excellent recovery from anesthesia
What type of anesthesia does Ketamine result in?
Dissociative anesthesia
What is the mechanism of action of Ketamine?
NMDA receptor antagonist i.e. glutamate antagonist
What is the side effect of Ketamine?
Emergence pheomenon
What is the mechanism of action of Midazolam?
Benzodiazepine that increases the frequency of GABA-A receptor opening
What are the role of Midazolam in general anesthesia?
Adjuvant agent
What are the indications for Midazolam?
1) Sedation for painful procedures
2) Induction agent in high risk patients
