Exam 2- Inhalational Agents Flashcards
potent inhaled anesthetics are mostly in what state?
liquid state at normal room temperature
what is vapor?
gaseous phase of a substance at a temperature which the substance can exist in either a liquid or a solid state below a critical temperature for that substance
what is a variable bypass vaproizer?
one in which the total gas glow is divided in two streams by a variable resistance proportioning valve
where does the majority of a volatile agent flow through?
the bypass line
what does the Tech 6 vaporizer do?
contains an electrical filament that heats the desflurane to 39º C
what what does the Tech 6 vaporizer do to the saturated vapor pressure?
raises it
what does a higher pressure do to Desflurane?
removes the need for a pressurized carrier gas
what would make an ideal agent?
non-pungent, non-flammable, fast induction, fast wake-up, no harmful metabolites
3 main phases of anesthesia?
induction, maintenance, emergence
how is an anesthetic state obtained?
combination of amnesia, analgesia, and lack of response to noxious stimuli
what does the myer-overton theory state?
the lipid solubility is directly proportional to the potency of an inhaled anesthetic
the ultimate effect of inhaled anesthetics depends on
reaching a therapeutic level in the CNS/brain/spinal cord
unconsciousness is based on effects of what system?
the reticular activating system
analgesia effect is based on what part of the body?
the spinothalamic tract
amnesia affects what parts of the brain?
the amygdala and hippocampus
immobility affects of anesthesia affect what part of the body?
the ventral horn of the spinal cord
what are ideal characteristics of inhaled gases
pleasant to inhale, smooth induction and emergence
low solubility
easy to administer and analyze
stable in CO2 absorbers, inflammable, not metabolized
specific site of action
No CV or Resp side effects, non toxic, pain control, muscle relaxation
amnesia and loss of conscious occur when?
at lower levels of anesthesia
immobility occurs at what level of anesthesia?
higher levels than amnesia and loss of consciousness
stage I
induction to loss of consciousness
state II
delirium w a period of excitement
pupils during stage II
dilated
gaze during stage II
disconjugate
in which stage will patient have an increase HR and RR
stage II
in which stage is the patient at highest risk for laryngospasm or bronchospasm?
stage II
stage III
surgical plane, fixed gaze, constricted pupils
stage IV
overdose
shallow/irregular RR
hypotension/profound CV collapse
dilated/unresponsive pupils
when is inhalational induction commonly seen?
pediatrics
vital capacity breath
prime entire circuit with the gas, quicker than tidal volume breathing
N2O/O2 induction
70% : 30% until induced
sevoflurane induction
7-8% until induced
can you use desflurane for mask induction?
yes? but it is pungent. patients may cough.
volatile agents effect on airway?
can relax airway smooth muscle and produce bronchodilation
what stages of anesthesia do patients undergoing inhaled induction experience?
stage I, II, and III
what stage of anesthesia do patients undergoing inhalational induction especially experience?
excitatory
which kind of induction bypasses the second stage?
IV induction
what are advantages of inhalation induction?
less trauma, no IV access, short pediatric cases, bronchodilator effect
what are disadvantages to inhalation induction?
smell
excitatory stage
delayed airway
gas bypassing scavenger system
what gas smells the best?
sevo
MAC
the inhalational anesthetic concentration at which 50% of the population will not move to painful or noxious stimuli
MAC is a direct measure of
the potency of the volatile anesthetic
how much does MAC vary among individuals
10-15%
how does MAC relate to brain partial pressure?
MAC mirrors brain pressure
potency is directly related to
solubility
are MAC anesthesia values additive?
yes
MAC-BAR
MAC needed to block autonomic responsiveness to painful stimuli
MAC-BAR values
1.5-2.0 MAC
MAC-awake
alveolar concentration at which patients open their eyes
MAC-awake values
0.4-0.5 to lose consciousness and 0.15 to regain it
awareness and recall are usually thought to be prevented at what MAC?
0..4-0.5 MAC
what MAC will prevent movement in 95% of surgical patients?
1.2-1.3
nitrous oxide MAC and vapor pressure
MAC- 104
vapor pressure- 38,770
halothane MAC and vapor pressure
MAC- 0.75
vapor pressure- 244
isoflurane MAC and vapor pressure
MAC- 1.17
vapor pressure- 240
sevoflurane MAC and vapor pressure
MAC- 1.8
vapor pressure- 157
desflurane MAC and vapor pressure
MAC- 6.6
vapor pressure- 660
does duration of anesthesia change MAC?
no
does anesthetic metabolism change MAC
no
does hyperkalemia change MAC
no
does hyper or hypo carbia change MAC
no
does gender change MAC
no
does thyroid function change MAC
no
does metabolic alkalosis change MAC
no
which population requires a higher MAC requirement?
young, healthy patients
what factors may increase MAC
hyperthermia, drugs, natural red hair, hypernatremia, chronic alcohol abuse
what drugs might increase mac
drugs that increase CNS catecholamine levels
- MAOI
-cocaine
-ephedrine
-levodopa
-amphetamine abuse
what factors may decrease MAC
hypothermia, Benzos, older age, pregnancy, alpha agonists (precedex), acute alcohol ingestion, hyponatremia, hypotension, drugs, severe anemia, low MAP <50mmHg
what is the only true gas?
N2O
inhaled anesthetic properties
nonionized, low molecular weights, rapid diffusion
sevoflurane boiling point
59º C
sevoflurane vapor pressure at 20º C
157 mmHg
sevoflurane blood: gas partition coefficient
0.65
sevoflurane oil: gas partition coefficient
47
sevoflurane MAC
1.8
sevoflurane % metabolized in the body
2-5%
desflurane boiling point
24º C
desflurane vapor pressure
669 mmHg
desflurane blood:gas partition coefficient
0.43
desflurane oil:gas partition coefficient
19
desflurane MAC
6.6
desflurane % metabolized in the body
0.02%
isoflurane boiling point
49º C
isoflurane vapor pressure
238 mmHg
isoflurane blood:gas partition coefficient
1.46
isoflurane oil:gas partition coefficient
91
isoflurane MAC
1.17
isoflurane % metabolized in the body
0.2%
nitrous oxide boiling point
-88ºC
nitrous oxide vapor pressure
38,770 mmHg
nitrous oxide blood:gas partition coefficient
0.46
nitrous oxide oil: gas partition coefficient
1.4
nitrous oxide MAC
104
nitrous oxide % metabolized in the body
0%
can plasma and tissues absorb the anesthetic well?
no.
at equilibrium, CNS partial pressure equals
blood partial pressure which equals alveolar partial pressure
which factors increase the speed of onset of inhaled anesthetics?
high inspired concentration
high alveolar minute ventilation
low blood solubility
high MAC
FGF
fresh gas flow; determined by flowmeter settings and vaporizer
FI
inspired gas concentration, determined by fresh gas flow, breathing circuit volume, and circuit absorption
FA
alveolar gas; determined by uptake, ventilation, the concentration effect and second gas effect
Fa
arterial gas, affected by ventilation perfusion mismatch
Goal of inhalational anesthesia
anesthetic state in the CNS/brain
to achieve optimal and constant partial pressure of anesthetic in the brain
inspired gas concentration depends on
Fresh gas flow and rate
Breathing system volume
Absorption of machine circuit
what determines the speed of onset for inhalation agents?
solubility in the blood
more insoluble inhaled agents
are taken up much slower by the blood SO INDUCTION IS FASTER
how is the solubility of an anesthetic expressed?
partition coefficients
does isoflurane have a high blood : gas coefficient
yes, 1.4
it is soluble; slower induction/wakeup
which inhaled anesthetic has a low blood : gas coefficient
desflurane (0.42)
poor solubility
rapid induction/wake up
what parallels anesthetic requirements
oil:gas partition coefficient
higher MAC level
lower B:G coefficient
decrease in potency
associated with a decrease in the oil:gas partition coefficient
as cardiac output increases what happens to anesthetic uptake?
it increases
what % cardiac output does the vessel rich group recieve?
75%
what % cardiac output does the muscle recieve?
19%
what % cardiac output does fat recieve?
6%
how much blood flow does the vessel poor group recieve?
less than 1%
are inhalational agents lipid soluble?
yes, very
ways to speed up the equilibrium of FA/FI
increase minute ventilation
decrease FRC
for mask inductions: breathe deeply before applying the mask, breathe deeply and quickly after applying the mask
describe the second gas effect
Uptake of a large volume of a first or primary gas (usually Nitrous) from alveoli accelerates the rate of increase of the PA of a co-administered second gas
concentration of inhaled anesthetics in the tissues at the end of anesthetic depends on
solubility of the agent and time of administration
exhaled gases from the patient will be rebreathed uneless
fresh gas flow rates are >5L/min
which anesthetics are non-pungent?
sevoflurane, halothane, and nitrous
which anesthetic agents are pungent?
desflurane and isoflurane
why might PaCO2 increasee?
dose dependent depression of the ventilatory response to hypercarbia
which anesthetic agent might be irritating to smokers?
desflurane
inhalational agent cardiovascular effects
reduce MAP, CO, and Cl in dose dependent ways
myocardial depression
decreased SVR –> hypotension from vasodilation
reduce BP via relaxation of vascular smooth muscle causing a decrease in SVR
which agent activates the sympathetic nervous system and increases SVR?
N2O
which inhalation agent can lead to increases in CVP and arterial pressures?
N2O
which inhalation agents can increase HR and BP due to sympathetic stimulation?
isoflurane and desflurane
which inhalation agent demonstrates initial tachycardia?
desflurane
what do inhalational agents do to the CNS?
dose dependent increases in cerebral blood flow by direct vasodilation
increased ICP
how is increased ICP from inhalational agents attenuated?
hyperventilation
inhalational agent obstetric effects?
dose-dependent decreases in uterine smooth muscle contractility and blood flow
what MAC are obstetric effects seen at?
> 1 MAC
inhalational agent effect on kidneys?
decreased GFR
do inhaled anesthetics undergo liver metabolism?
minimally
how are inhaled anesthetics most commonly biodegraded?
CYP450 oxidation
inhalational anesthetic neuromuscular system effects
dose dependent skeletal muscle relaxation
what can inhalational agents do to recovery from nondepolarizing muscle relaxants?
delay recovery because of synergistic effects
when is post-op cognitive dysfunction an increased concern?
elderly and pediatric patients
what is emergence delirium
acute state of confusion/agitation after anesthesia
when is emergence delirium more commonly seen?
20-80% in pediatrics in both sexed 2-6 yrs old
what inhalational agents more commonly have emergence delirium effects?
sevoflurane and desflurane
how long does emergence delirium last and how does it end?
10-15 mins; terminated spontaneously or after IV dose of propofol, midazolam, clonidine, precedex, ketamine, opioids, etc
when is there a higher probability of Compound A production?
low flow rates
closed circuit breathing systems
warm/dry CO2 absorbers
Sevoflurane use
how much CO2 can soda lime absorb
23 L of CO2 per 100g of absorbent
what are the final products of CO2 neutralization
carbonates, heat, water
what type of capnography would you see in a patient when the CO2 absorbent is exhausted?
rising ETCO2 waveform
isoflurane chemical makeup
5 fluorine atoms and 1 chlorine atom
desflurane chemical makeup
6 fluorine atoms
sevoflurane chemical makeup
7 fluorine atoms
which inhaled agents are chiral?
desflurane and isoflurane
which inhaled agent has no chiral carbon?
sevoflurane
what is a coronary steal
diversion of blood from a myocardial bed with limited or inadequate perfusion to a bed with more perfusion
which inhalation agent is associated with a coronary steal?
isoflurane
which inhalation agent is associated with a dose dependent decrease in mean arterial pressure?
isoflurane
which inhalation agent is associated with a dose dependent increase in cerebral blood flow?
isoflurane
which inhalation agent is associated with a resistance to degradation?
isoflurane
which inhalation agent is non-pungent
sevoflurane
which inhalation agent is associated with minimal sympathetic activation?
sevoflurane
which inhalation agent is insoluble in blood
desfluranew
which inhalation agent is associated with faster to sleep and wake up times
desflurane
which inhalation agent is a potential airway irritant?
desflurane
TEC6 vaporizer
dual-circuit, NOT variable bypass
what temperature is the TEC6 vaporizer heated to?
39º C
can you fill the TEC6 vaporizer during use?
yes
inhalation agents should be avoided in what population?
patients w a high risk of PONV
characteristics of N2O
Colorless, non-pungent, non-explosive, non-flammable
which inhalation agent has minimal CV effects but can increase bp?
nitrous oxide
which inhalation agent can increase RR and decrease TV?
nitrous oxide
does N2O trigger MH?
no
nitrous oxide musculoskeletal effects
no muscle relaxation or uterine relaxation
when is N2O use contraindicated?
bowel cases, pneumothorax/blebs, venous air emboli, middle ear surgery, some eye surgeries
is N2O a good analgesic?
yes
what inactivates methionine synthease?
N2O
what is the best approach to prevent OR pollution with anesthetic gases and reduce waste?
shutting off the fresh gas flows
when does diffusion hypoxia occur?
when nitrous is discontinued abruptly, usually occurs in the first 5 min after stopping nitrous
when should nitrous be discontinued during an anesthesia case
early to filly the lungs with oxygen and decrease the chance of arterial hypoxemia
risk factors for intraoperative awareness?
age, gender, substance use, paralytic use, type of surgery,
what MAC will decrease potential for intra-op awareness?
0.4-0.5 MAC of gas
malignant hyperthermia
profound uncontrolled release of Ca from the sarcoplasmic reticulum
what induces MH?
succinylcholine and inhalational agents
what does MH do to capnography?
unexplained increase in ETCO2
what is a late sign of MH?
increased temp
what kind of gas needs less fresh gas flow?
low solubility anesthetics
what volatile agent is the most destructive to climate change?
desflurane
how long can desflurane last in the atmosphere?
up to 14 years
how long can isoflurane and sevoflurane last in the atmosphere?
3.2 years for isoflurane and 1.1 year for sevoflurane
what gas directly relates to destruction of the O-zone
nitrous oxide
MAC decreases at what rate
approx. 6% per decade
what is a potential risk with high, long-lasting concentrations of secoflurane
can trigger EEG abnormalities …unsure
is N2O associated with POCD and delirium?
yes
is N2o meant to be a complete anesthetic itself?
no, it is a co-anesthetic used to supplement
by what % does O2 consumption decrease during general anesthesia?
10-15%
what happens to FRC during general anesthesia?
it is decreased
what do volatile anesthetics and N2O do to ciliary movement?
they reduce it, and alter the characteristics of mucus
where are inhaled anesthetics primarily excreted?
the lungs
NIOSH exposure limits
25 ppm for N2O and 2 ppm for volatile anesthetics
what can halothane cause
hepatotoxicity
