Inhaled Anesthetics Flashcards
Function of the Respiratory System
- Gas exchange
- Acid-base balance
- Phonation
- Pulmonary defense
- Metabolism
• Upper Airway Function
Humidification and filtration of inspired air.
Tracheobronchial tree function
conduct gas flow to and from the alveoli
alveoli generations present secondary to dichotomous division
23
How many alveoli are present for gas exchange?
300 million
Gas exchange begins at generations
17-19
Largest alveoli are found where?
Apex
Function of the THIN side of alvoli?
gas exchange
Function of the thick side of alveoli?
Structural support
Supplies circulation to the tracheobronchial tree to the level of the respiratory bronchioles
Bronchial circulation
bronchial circulation arrives from the aorta via which vessels
2 left arteries & 1 right artery
receives output from the right heart and pulmonary arteries
pulmonary circulation
takes part in perfusion tissues taking part in gas exchange
Pulmonary circulation
perfusion of tissues that TAKE PART in pulmonary exchange
Pulmonary circulation
passes through pulmonary capillaries, O2 is taken up, and CO2 eliminated
Deoxygenated
blood returned to the left side of the heart via the pulmonary veins is said to be
oxygenated
Combination of what elements decreased flammability?
Carbon together with fluorine
Halothane produced what negative side effects when introduced in the 1950’s?
Hepatitis and dysthymias
Halothane is a dysrhymogenic worsened by which drug?
Epinephrine
Halothane brand name
Fluothane
Enflurane brand namE
Ethrane
Isoflurane brand name
Forane
Desflurane brand name
Suprane
Sevoflurane brand name
Ultane
all agents are volatile anesthetics except
Nitrous oxide
Most beneficial features of IA
speed of onset, gaseous state, route of administration.
Features of IA contributing to rapid diffusion.
unionization & low molecular weight
How drugs affect the body
pharmacodynamics
how the body affects drugs
pharmacokinetics
Pharmacokinetic features unique to IA
uptake, redistribution, biotransformation, excretion
absorption equates to what for IA
uptake
metabolism equates to what for IA
biotransformation
distribution equates to what for IA
redistribution
elimination equates to what for IA
excretion
propels IA across barriers to action sites in the CNS
partial pressure gradients
tissue group first reach by blood/anesthetic
VRG
VRG includes which organs
brain, kidney, heart, liver
second tissue group reached by anesthetic/blood mixture
muscle, skin
last tissue group reached by anesthetic/blood mixture
fat, connective tissue
VRG AKA tissue of ____ effect
desired
muscle and skin AKA the tissue of ____ effect
undesired
fat and connective tissue is known as the site of ___.
accumulation
At what point does the saturation of fat tissue play a role in emergence?
> 4 hour anesthetic time
VRG % body mass
10%
Muscle % body mass
50%
fat % body mass
20%
VRG % cardiac output
75%
Muscle % cardiac output
19%
Fat % cardiac output
6%
VRG perfusion
55-500 (ml/min/100g)
muscle perfusion
3 (ml/min/100g)
fat perfusion
1 (ml/min/100g)
goal of anesthesia
establish specific concentrations of anesthetics in the CNS.
Partial pressure in the CNS equates to what other compartments?
blood and alveoli
Sevo Vapor pressure
157
Des vapor pressure
669
Iso vapor pressure
238
Enflurane vapor pressure
172
Halothane vapor pressure
243
Sevo B/G coefficient
0.65
Des BG coefficient
0.42
Iso BG coefficient
1.46
Enflurane BG coefficient
1.9
Halothane BG coefficient
2.5
Nitrous oxide BG coefficient
0.46
Nitrous oxide vapor pressure
38,770
Nitrous oxide vapor pressure
38,770
Sevo MAC
1.8%
Des MAC
6.6%
Iso MAC
1.17%
Enflurane MAC
1.63%
Halothane MAC
0.75%
Nitrous oxide MAC
104%
IA that are unstable in MOIST CO2 absorber?
Sevo & Halothane
vapor pressure
pressure exerted by a vapor in a closed container when at equilibrium with its liquid and gas phase.
vapor pressure increases as ____ increases.
temperature
boiling point
temp at which a liquid’s vapor exceeds atmospheric pressure in an open container.
1 atmosphere = _____ mmHg
760
Partial pressure
fractional amount of pressure a single gas exerts within a gas mixture.
Dalton’s law of partial pressures
the total gas pressure in a container is equal to the sum of the partial pressures exerted by each individual gas.
solubility
the tendency of a gas to equilibrate with a solution, determines concentration.
Gases are more soluble in liquid when temperature ____.
decreases
uptake looks at the concentration of
alvolar / inspired
Fi (fraction inspired) represents
concentration of anesthetic leaving the circuit
factors increasing Fi
increased FGF, increased Fd (delivered) from FGO, decrease volume of breathing system (dead space)
factors that decreasing Fi
decreased FGF, increased volume of breathing system (dead space), absorption by anesthesia machine parts, CO2 absorbent decomposition.
Faster Fa relative to Fi results in
faster induction
Factors that speed induction of insoluble agents
increased MV, decreased FRC
What happens to anesthetic uptake as CO increases
minimal effect on insoluble agents. soluble agents however will take longer to achieve adequate alveolar concentration, thus slowing induction.
What happens to anesthetics with deceased CO
decreased CO results in an increased concentration of anesthetic in the alveoli which could lead to overdose and subsequent lower CO/myocardial depression.
What determines clinical effect of anesthetics?
concentration of anesthetics in the CNS and brain tissue.
Factors affecting anesthetic uptake
blood solubility, alveolar blood flow, partial pressure gradient between alveolar and venous blood
agents are taken by blood less readily, results in higher alveolar concentration
insoluble
relative solubilities of anesthetics
partition coefficients
higher partition coefficients results in _____ uptake.
greater
which factors have a greater impact on changing concentrations of soluble agents
MV and CO
How much of a role does metabolism play in delaying induction
little
overpressurization
delivering a higher partial pressure of anesthetic than the desired alveolar concentration of that agent to achieve a quicker desired effect.
Concentration effect
Increasing the inspired concentration of an IA
N2O has the greatest concentrating effect at what concentration?
50%-70%
Augmented gas inflow
high partial pressure of N2O causes the quick influx of N2O into the blood, this causes an increase in the concentration of agent within the alveoli.
second gas effect
N2O augments the effects of a VA due to its higher partial pressure
Concentration/second gas effect is less augmented with ____ agents.
soluble
increasing MV for insoluble agents has what effect
minimal changes
What is the rate limiting step during hyperventilation and increased alveolar concentration.
Spontaneous ventilation. This will eventually provide a negative feedback loop, decreasing alveolar concentration and effects.
right to left VQ mismatch leads to
dilution and slowed induction
Left to right VQ mismatch lead to
may (but likely wont) speed induction
washout
alveolar concentration v. expired concentration at time zero.
all IA have the same rate of elimination until __%
50%
emergence doesnt occur until ____% of anesthetics have been eliminated.
80%-90%
Factors slowing elimination
high tissue solubility, longer anesthetic times (>4 hours), low FGF
diffusion hypoxia
rapid elimination of O2 and CO2 when N2O is discontinued.
treatment for diffusion hypoxia
100% oxygen for 5-10min after discontinuation of N20.
characteristics of an ideal anesthetic
quick onset/recovery, easy to administer, clear indication of anesthetic depth, inexpensive, wide safety margin, minimal effects on organs
Most metabolized IA
Halothane, second is Sevo
Most physically stable VA
Iso
VA not used for mask induction
Des & Iso
VA with risk of coronary steal
Iso
VA with lowest BF solubility, quick recovery
Des
MOST pungent VA
Des
requires a heated/pressurized vaporizer
Des
may see an increase in BP and HR if opioids not provided with this VA
Des
high or rapid increases in concentration of this VA may cause myocardial ischemia.
Des
VA with least airway irritation and most bronchodilation
Sevo
Agents producing carbon monoxide (most to least)
Des, Iso, Sevo
risk of fire due to exothermic reaction
Sevo
Compound A
nephrotoxic in rats
Produces compound A
Sevo
May explode
N2O
analgesic effects
Nitrous oxide, Xenon
IA not metabolized by the body
N2o
not a trigger for MH
N2O & Xenon
risk of PONV
N2o
inactivates b12
N2O
absorbs into gas containing spaces
N2O
May cause myocardial ischemia in hypovolemic patients or those with CAD.
N2O
Sympathetic stimulation. Depresses the myocardium but stimulates catecholamine release
N2O
chemically inert
Xenon
Xenon MAC
71%
disadvantage of Xenon
high cost & scarcity
MAC
Concentration of IA at 1atm preventing skeletal muscle movement with surgical stimulation in 50% of patients.
how do MAC and potency correlate
Increased MAC = low potency
Immobility with MAC occurs primarily in the
spinal cord
MAC Bar
MAC X 1.5
MAC Awake
Follows commands
MAC X 0.5
MAC Memory
Associated with amnesia in 50% of patients
MAC is _____ but the effects may not be the same
additive
MAC was established with what age group
33-55 year olds
MAC decreases by ____% after ___ years of age.
6% after 40 years of age
MAC is highest at what age?
6 months
Factors that reduce MAC
hypothermia, sedatives, other anesthetics, hypoxemia, hyponatremia, anemia, hypotension, pregnancy, lithium, alpha2 agonist, opioids.
Factors increase MAC
Young age, hyperthermia, hypernatremia, CNS stimulants, red hair in females, chronic alcohol abuse, hyperthyroidism
factors that do not affect MAC
duration of anesthesia, gender, hypo/hypercapnia, metabolic alkalosis, hypertension, hyper/hypokalemia
VA cause isoelectric EEG at clinical doses
des, iso, sevo
VA isoelectric EEG changes may revert to continuous despite no changes do dose.
Des
Sevo at MAC __to ___ combined with ________ can decrease CBF and trigger EEG abnormalities and increase ______.
1.5-2, hyperventilation, heart rate
Iso, Des, Sevo have minimal changes to CBF at ___ MAC.
Less than 1
All VA increase CBF , which VA increases CBF the most
Halothane
Uncoupling
increase in CBF despite decrease in CMRO2
Sevo preserves autoregulation up to ____ MAC.
1
which agent preserves autoregulation best at 1.5 MAC
Sevo
Physiological process can diminish/prevent elevated ICP
hyperventilation/hypocapnia
At ____MAC will des, iso, and sevo increase CBF.
1
Which agent increases ICP the most
Des
Which VA may lessen the risk of increased ICP, why?
Sevo. Decreased pungency/airway irritation lessens coughing/bucking.
VA increases PO2 and maintain PO2 better than thiopental during cerebral artery occlusion surgery.
Des
postoperative cognitive dysfunction
impairment to the mental processes of perception, memory, and information processing.
POCD is associated with increased _____ & _____ in the first year following surgery.
Morbidity and Mortality
all IA are associated with POCD, which the most
Iso
N2O is associated with POCD and _____ and high doses interfere with many _________ functions.
delirium , cognitive
all agents at _____ MAC and N20 at ______% can increase EEG frequencies.
> 1MAC, 30%-70%
VA MAC of 1-2 ____frequencies and ______ amplitude of EEG.
decrease, increase
MAC >2 leads to _______ _______
burst suppression
What may be some other causes of EEG changes during administration of anesthesia?
hypoxia, hypercarbia, hypothermia
EVP monitoring results in an _____ in amplitude and ______ in latency.
decrease, increase
_____ EPs are sensitive while _____ EPs are more resistent
visual, brainstem
VA should be avoided in which evoked potential monitoring
MEPs
Sudden MAC increase of ____ can result in sudden EP monitoring changes.
> 0.5 MAC
N2O has what effect on CBF and CMRO2
increases
Addition of N2O to 1MAC of Iso has what effect on CMRO2 and CBF.
No change in CMRO2 but increases CBF
N2O _______ ICP, this can be decreased by ______.
increases, hypocapnia
Avoidance of which IA in cases with likelihood of elevated ICP.
N2O
What intervention can negate the increase in CMRO2 and CBF seen with N2O?
Barbs and narcotics
VA ____ blood pressure.
decrease
VA _______SVR.
Decrease
VA _____CO.
minimal to none
Sevo MAC of ___ does not change HR.
1
VA result in 5-10% increase in baseline HR.
des and iso
transient increase in HR during rapid increase in concentration of which VAs? Which the most?
des and iso . Des the most.
transient increases in HR seen with des and iso can be minimized by administering which agents?
alpha 2 agonists and opioids
N2O increases _____ _____ ______ activity and _____ ______ in concentrations of 40% and higher.
sympathetic nervous system, vascular resistance
N2O + VA = ____ SVR and BP than VA alone.
higher
CO is _________ to brain, muscle, skin with IA administration.
increased.
CO is ______ to the liver, kidney, and gut with IA admin.
decreased
VA decrease HR by
decrease SA node discharge, decrease conduction in His-Purkinje/vascular conduction pathways.
VA _______ QT intervals. Which agent the most?
prolong, des the most
preconditioning protection of myocardium occurs at Sevo MAC dose of ___ and full efficacy at MAC of ___.
1 , 1.5
drugs that can abolish preconditioning of myocardium
Sulfonylureas (Glipizide)
all IA _____ TV and _____ RR
decrease , increase
which agent no longer increases RR above 1 MAC
ISO
IA cause ____ in FRC
Decrease
IA cause what changes in the diaphragm
none
IA cause _______ in intercostal muscle strength.
decrease
all IA cause ______ response to increased CO2
decreased
______ drives ventilation
PaCO2
Apneic threshold
CO2 threshold where respiratory drive stops. 4-5mmHg below resting Pa CO2 in a SV patient.
IA ______ ventilatory response to hypoxia.
decrease
IA best for chronic respiratory pt
Des and Sevo
all VA relax airway smooth muscle, which is best?
Sevo
IA _____ ciliary movement and _____mucus
impair, change
mechanical vent ____ ciliary movement, _____ airways, and _____ mucus.
impairs, dries, thickens
VA effect on PVR
none
N2O can _____ PVR.
increase
VA metabolized to Trifluroacetatic acid (TFA)
Des & Iso
VA _______ effects of NMBs.
Increase
Neuromuscular relaxation with VA is the most at ____MAC.
> 1 MAC.
IA does not affect skeletal muscle relaxation
N2O
