Anesthesia

Question 1

Definition of general anesthesia:

Answer 1

State of CNS depression

• patient has complete absence of sensations and is unconscious
• controlled AND reversible

Question 2

Five goals of general anesthesia:

Answer 2

1. loss of awareness or consciousness
2. amnesia
3. analgesia
4. blunting of the autonomic nervous system (BANS)
5. skeletal muscle relaxation

Question 3

Two types of anesthetics:

Answer 3

Inhalation-gaseous

Injection

Question 4

Dalton’s law as it applies to inhaled anesthetics:

Answer 4

P(total)=P(anesthetic) + P(oxygen)

**need oxygen pressure of 20.9% to survive so most you can have for the other gases is ~79% (usually need waaayyy less)

Question 5

Henry’s Law as it applies to inhaled anesthetics:

Answer 5

Drug dissolved in fluid (blood) does NOT raise the partial pressure of the drug in that fluid

**clinical effect of drug is related to the amount of UNDISSOLVED drug in the blood

***analogous to the relationship between free and protein bound drugs in the blood

Question 6

More anesthetic dissolved in blood means….

Answer 6

**takes longer to attain equilibrium (when undissolved drug can begin to have desired clinical effect)

**greater concentration of anesthetic at equilibrium

Question 7

Compare drug partial pressure in delivered gas, inspired air, alveoli, arteries, and brain during:

Induction

At anesthesia

Recovery

Answer 7

Induction:
delivered gas > inspired air > alveoli > arteries > brain

At anesthesia:
inspired air = alveolar = arterial = brain

Recovery:
delivered gas < EXpired air < alveoli < VENOUS < brain

Question 8

Describe drug solubility with respect to speed of onset for nitrous oxide, desflurane, sevoflurane, isoflurane, halothane:

Answer 8

Lease soluble Fastest onset
Nitrous oxide

                        desflurane

                          sevoflurane

                            isoflurane

                             halothane most soluble                                             slowest onset

Question 9

Where in the body does anesthesia take place?

Answer 9

brain

Question 10

All inhaled anesthetics share which characteristic (could be called only known mechanism of action)?

Answer 10

they all cause changes in membrane fluidity

**no know specific site of action

Question 11

What is the dose of anesthetic (vol %) that produces surgical anesthesia in 50% of patients?

Answer 11

Minimum Alveolar Concentration (MAC)

**surgical anesthesia usually achieved around 1.3-1.5 MACs

deep anesthesia ensues around 2 MACs

Question 12

Lowest MAC = ?

Answer 12

most potent

Question 13

4 factors affecting MACs:

Answer 13

age

pre-existing disease

effects of other CNS depressants

ambient temp (ORs are COLD)

Question 14

Amount of drug necessary to produce effect of specified intensity:

Answer 14

Potency

Question 15

What does lipid solubility have to do with potency?

Answer 15

more lipid soluble = greater potency

**expressed as oil:gas partition coefficient

***don’t confuse with water (blood) solubility which deals with speed of onset (blood:gas partition coefficient)

Question 16

Most potent inhaled anesthetic?

Answer 16

Halothane (oil:gas partition coefficient = 224)

Question 17

Fastest onset inhaled anesthetic?

Answer 17

Nitrous oxide (blood:gas partition coefficient = 0.5)

Question 18

Type of anesthetics that leave body most slowly?

Answer 18

fat soluble

Question 19

Three routes of elimination (inhaled anesthetics):

Answer 19

Lungs (primary)

skin and mucous membranes

can enter atmosphere (OR needs good ventilation!!)

Question 20

Only toxicologically important aspect of clearing inhaled anesthetics:

Answer 20

liberation of chemically reactive halides (bromide, chloride, and fluoride) can harm kidneys, liver, and reproductive organs

Question 21

CNS side effects of inhaled anesthetics:

Answer 21

decreased brain metabolic rate

increased cerebral blood flow

increased intracranial pressure

Question 22

CV side effects of inhaled anesthetics:

Answer 22

decreased myocardial contractility and stroke volume –> lower arterial pressure

sensitizes myocardium to catecholamines–>increased automaticity (adding epi could cause fatal arrhythmia!!)

Question 23

NON CNS or CV side effects of inhaled anesthetics?

Answer 23

respiratory depression (isoflurane, desflurane, sevoflurane > halothane > nitrous oxide)

muscle relaxation at high doses

Malignant hyperthermia (except nitrous), most common with halothane

Question 24

how do you treat malignant hyperthermia

pharmacologically?

physically?

Answer 24

dantrolene to block Ca+ release from sarcoplasmic reticulum

cool patient with ice bags/cold water

Question 25

Most potent inhaled anesthetic (MAC 0.7-0.9) least expensive no laryngeal irritation higher risk for malignant hyperthermia inadequate analgesia and muscle relaxation

Answer 25

Halothane

Question 26

Potent inhaled anesthetic DOES not sensitize myocardium to catecholamines Less hepatotoxicity rare arrhythmias pungent odor potential for malignant hyperthermia

Answer 26

Isoflurane

Question 27

New inhaled anesthetic approved in 1996 high potency low blood solubility (rapid onset, rapid recovery, almost perfect anesthetic)

Answer 27

Sevoflurane

Question 28

Only inhaled anesthetic that is actually a gas low blood solubility--> rapid onset little effect on CV function mild to moderate analgesia MAC = 104%, can't use alone!!!! no muscle relaxing effect diffusion hypoxia if rapidly discontinued

Answer 28

Nitrous oxide

Question 29

Three advantages of injectable anesthetics:

Answer 29

act faster best suited for INDUCTION of anesthesia useful for short operations

Question 30

disadvantage of injectable anesthetics

Answer 30

muscle relaxation after IV is poor | -unsuitable as a single drug anesthetic

Question 31

5 injectable anesthetics:

Answer 31

barbiturates benzodiazepines propofol ketamine opiods

Question 32

Facilitates GABA induced Cl- entry into neurons leading to hyperpolerization and CNS depression rapid onset (very lipid soluble) short action (quick recovery) Danger: toxicity, anesthetic dose is between 50-70% of LD50

Answer 32

Barbiturates Thiopental and Methohexital

Question 33

Facilitates GABA induced Cl- entry into neurons leading to CNS depression less CV suppression than barbiturates most important for AMNESTIC action insufficient for anesthesia when given alone used as induction agent prior to anesthesia

Answer 33

benzodiazepines Midazolam (Versed) and Diazepam (Valium)

Question 34

Rapid induction and recovery from anesthesia May be given alone to maintain anesthesia or used for induction as part of balanced anesthesia technique Must be given as emulsion patients generally awaken from anesthesia feeling more “clear headed” and are not nauseous (anti-emetic action) Most significant respiratory effect is apnea (22-45%) May result in injection site pain

Answer 34

Propofol (Diprivan) **abused among providers "cat nap" deaths

Question 35

related to PCP has dissociative effect anesthetic, analgesic, amnestic, and sedative airway reflexes and respiration maintained may actually stimulate CV sys drawback: may induce hallucination abused at raves possible depression tx

Answer 35

ketamine

Question 36

high potency, short acting analgesia anesthesia hemodynamic stability- good for pts w compromised myocardial function respiration must be maintained artificially usually supplemented with inhaled anesthetic, benzos, or propofol

Answer 36

opiods - fentanyl - sufentanyl - alfentanil