Anesthetic Inhalants

Question 1

what is the maineneance phase of anesthesia

Answer 1

• to keep the patient in an unconsious state as long as required
• usually switch from IV to an inhaled general anesthetic

Question 2

how to achieve “balanced anesthesia”

Answer 2

sedatives, analgesics and general anesthetics are each administered at a low to moderate dose - safer than high dose single-drug protocols

Question 3

what are the goals during maintenence anesthesia

Answer 3

• keep patient in stage 3 sugical anesthesia
• adequate analgesia during surgical procedures
• physiologic homeostasis (monitor vitals)

Question 4

true or false: inhalent anesthetics are cleared much faster than IV general anesthetics

Answer 4

true

Question 5

what determines the safety of a general anesthetic

Answer 5

the extent to CV and respiratory functions are impaired at concentrations required to maintain unconsciousness

Question 6

Characteristics of an ideal inhalent anesthetic

Answer 6

• produces unconsciousness while maintaining brainstem function
• negligible visceral toxicity
• non-flammable
• non-pungent odour
• compatible with anesthetic machinery
• does not react woth soda lime
• chemically stable
• potent

Question 7

why have we switched from using Ether as an inhaland anesthetic to using halogenated hydrocarbons

Answer 7

• ether is flammable
• substituting halogens for hydrogens reduces flammability and improves safety

Question 8

Halothane as an inhaled anesthetic

Answer 8

• safer than ether but still unstable because it contains Br
• must be combines with stabilizing molecule: thymol
• problem is thymol accumulates on machine valves, causing malfunction
• halothane breaks down in the presence of soda lime and releases a toxic compound
• sensitizes the myocardium to epinephrine - promotes arrhythmia

Question 9

what is soda lime

Answer 9

a CO2 absorbant used in most inhalent machines - removes CO2

Question 10

hepatic and renal toxicity of inhalants (halothane)

Answer 10

• halothane undergoes extensive hepatic biotransformation into toxic metabolites
• metabolites are at highest concentration in the liver and kidney
• toxicity is directly related to the extent which an nhalent is metabolized
• Halothane = 40% metabolized, Isofluorane = 0.2% metabolized (no organ toxicity)

Question 11

Evolution of halogenated hydrocarbons from Halothane

Answer 11

• switch to those that have an ether linkage
• switch bromine for more fluorines
• ether + fluorine = safer inhalent
• e.g. isoflurane and sevoflurane

Question 12

what are the main inhalents we use today

Answer 12

isoflurane
sevoflurane
- theraputic index = 2 to 4 (narrow)

Question 13

most likely Mechanism of action for inhalant anesthetics

Answer 13

• facilitate the interaction of GABA with the GABAa receptor in the brain

Question 14

why are inhalent anesthetics a volatile liquid before administration

Answer 14

• they are poured into a vapour chamber that is connected to the oxygen floe system of the anestheric machine
• vapor chamber turns this liquid to gas

Question 15

Anesthetic machine as a rebreather recycling machine

Answer 15

• anesthetic is breathed in by patient
• ## patient breathes out

Question 16

which part of the anesthetic machine enters the patient

Answer 16

• endotracheal tube: delivers the anesthetic
• inflatable cuff: creates a seal in the trachea to prevent vapor from escaping into the room and prevent inhalation og saliva or stomach contents

Question 17

Pathway of anesthetic vapor in the body

Answer 17

anesthetic vapor is delivered in pure oxygen - absorbed from lungs into systemic circulation - districuted to tissues

Question 18

how is anesthetic removed from the body

Answer 18

• mainly though exhalation
• small amount may be metabolized by liver

Question 19

how can we remove inhalants rapidly from the body in an emergency

Answer 19

• reduce the anesthetic concentration
• apply artificial respiration
• drug concentration in the body falls as drug is exhaled

Question 20

what determines the speed at which anesthetics enter and leave the brain and cause their effects?

Answer 20

solubility and concentration

Question 21

solubility of halothane vs isoflurane

Answer 21

halothane = highly soluble in tissues
isoflurane = less soluble in tissues

Question 22

solubility vs. concentration of an inhalent

Answer 22

if a drug is poorly soluble in tissues, we must administer a high concentration of it in the inspired air to achiece the same concentration in the brain as a more soluble drug

Question 23

what is the depth of anesthesia proportional to

Answer 23

the partial pressure created by the anesthetic

Question 24

high solubility volatile anesthetic (halothane) =

Answer 24

• low partial pressure within tissues
• don’t need high concentration to cross from alveolar air to blood
• slow diffusion
• slower onset and recovery

Question 25

poorly soluble volatile anesthetic (isoflurane) =

Answer 25

- high partial pressure within tissues - need higher concentration to cross from alveolar air to blood - fast diffusion - faster onset and recovery

Question 26

why is partial pressure more critical than concentration for inhalant anesthetics

Answer 26

- creates an equilibrium across tissues to produce the anesthetic effect - uptake and distribution driven by pressure gradients - correlates with clinical effects pg hypnosis, amnesia and immobility

Question 27

conventration vs. partial pessure

Answer 27

concentration - the rate at which the partial pressure rises partial pressure - determines the effectoveness of an anesthetic

Question 28

what factors influence the delivery of inhalants from the lungs to the brain

Answer 28

1. ratio of the concentration of volatile anesthetic in blood compared to alveolar gas once PP has been equilibrated (BGPC) 2. Concentration of anesthetic in the inspired gas mixture (MAC) 3. Ventilation rate of patient

Question 29

what is the blood:gas partition coefficient (BGPC)

Answer 29

- a value that indicates the relative solubility of the drug in blood vs alveolar gas - highere BGPC = highly soluble

Question 30

if an anesthetic has a high BGPC...

Answer 30

a large amount of it will have to be taken up in the body's blood before being passed on to the tissues of the brain

Question 31

isoflurane has a BGPC of 1.4, what does this mean?

Answer 31

at partial pressure equilibrium, the concentration will be 1.4x higher in tissues than in the alveolar air

Question 32

a low BCPG means...

Answer 32

- anesthetic is poorly soluble in blood - has a high partial pressure - fast onset/recovery

Question 33

why do we prefer to use anesthetics with low tissue solubility

Answer 33

- we want to be able to adjust anesthetic depth rapidly

Question 34

what is the minimum alveolar concentration (MAC)

Answer 34

- measure of potency at the level of the lungs - the concentration in the inspired gas that will prevent 50% of petients from being awakened in response to mild pain - expressed as a percent vapour in the inspired gas

Question 35

MAC is inversly realted to potency and solubility...

Answer 35

low MAC = high potency low MAC = high solubility - therefore would need a higher concentration of isoflurane to achieve the same level of unconsciousness as halothane

Question 36

how can we control the inspired anesthetic concentration

Answer 36

- using a precision vapour - MAC tells us what to set the vapourizer dial to

Question 37

in situations where it is not ideal to premedicate patients what happens to the MAC?

Answer 37

- we start woth the vapour setting at 1.3 so it is the concentration at which 95% of non-premedicated patients will not respond to pain, then reduce to 50% for maintenence

Question 38

what influence the elimination of inhalents from the body

Answer 38

- solubility in tissues (MAINLY) - respiration rate - pulmonary blood flow

Question 39

adverse effects of inhalants on thermoregulation

Answer 39

- depress thermoregulation and cause hypothermia

Question 40

adverse effects of inhalants on metabolism

Answer 40

- extent of metabolizm related to toxicity - can lead to hepatotocicity and renal toxicity - only a problem in long procedures with halothane or very long procedures with sevoflurane

Question 41

Rare adverse effect of inhalant - malignant hyperthermia

Answer 41

- an inherited susceptibility caused by mutations in a gene that codes for skeletal muscle calcium release channels - when exposed to a halogenated hydrocarbon it triggers uncontrolled muscle contraction - body temp rises and brain damage may occur - can be treated by administering a skeletal muscle relaxant

Question 42

Characteristics of Isoflurane

Answer 42

- most commonly used inhaled anesthetic - no hepatic or renal toxicity - low solubility in tissues - rapid chamges in depth are possible - low depression of CO, but causes vasodilation which causes dose-dependent drop in BP - highly stable - wont react with soda lime

Question 43

what is the only real drawback of isoflurane

Answer 43

has a pungent odour - can cause gagging in non premedicated patients

Question 44

safety of isoflurane compared to halothane

Answer 44

- isoflurane has a much larger safety margin at the lungs - the lethal effects of both drugs begon at the same brain drug concentration - isoflurane still produces its desired effect at lower brain concentrations

Question 45

Characteristics of Sevoflurane

Answer 45

- similar to isoflurane - even less soluble in tissues so faster onset and recovery - minimal metabolism = low toxicity - less potent than isoflurane = higher MAC - main advantage = non-pungent odour

Question 46

drawbacks of sevoflurane

Answer 46

- humans can metabolize up to 5%, but fluoride ions appear to damage renal tubules whem hey accumulate during long procedures - breaks down in the presence of soda lime to form toxic compound during long procedures

Question 47

Characteristics of nitrous oxide

Answer 47

- aka laughing gas - inhibits the NMDA receptor in the brain - a weak CNS depressant - cannot produce anasthesia - used to reduce the amount of hydrocarbon inhalant needed to produce unconciousness - provides excellent analgesia and alleviates anxiety - very safe