Pharm Quiz 3 Flashcards
What is the blood gas partition of Isoflurane?
1.46
What is the blood gas partition of nitrous oxide?
0.46
What is the blood gas partition of desflurane?
0.42
What is the blood gas partition of sevoflurane?
0.69
What is the mac % of isoflurane?
1.17 %
What is the mac % of desflurane?
6.6 %
What is the mac % of sevoflurane?
1.8 %
What is the mac % of nitrous oxide?
104 %
What 5 things increases the % of MAC delivered?
- hyperthermia
- red hair
- drug increased CNS catecholamine levels
- cyclosporine
- hypernatremia
What 14 things decreases % of MAC delivered?
- hypothermia
- increasing age
- drug decreased CNS catecholamine levels
- benzos, opioids
- hyponatremia
- alpha-2 agonists
- alcohol intoxication
- pregnancy
- lithium
- lidocaine
- hypoxemia
- hypotension
- CPB
- Neuroaxial opioids
What are 11 things that do nothing to the % of MAC delivered?
- anesthetic metabolism
- alcoholism
- gender
- duration of anesthetic
- PaCO2 15-95 mmHg
- PaO2 >38 mmHg
- BP > 40 mmHg
- hyperkalemia
- hypokalemia
- hyperthyroidism
- hypothyroidism
In pharmacokinetics related to inhaled anesthetics, how is the agent absorbed by the body?(Absorption)
uptake from alveoli to pulmonary blood
In pharmacokinetics related to inhaled anesthetics, how is the agent distributed by the body?(Distribution)
to CNS, VRG, Skeletal muscle, fat
In pharmacokinetics related to inhaled anesthetics, how is the agent metabolized by the body?(Metabolism)
variable % metabolism of the volatile agents, associated with how long each specific volatile agent stays in the body
In pharmacokinetics related to inhaled anesthetics, how is the agent eliminate by the body?(Elimination)
Lung primary site for elimination, metabolism plays a very small role in drug elimination
What are 6 factors that will alter the pharmacokinetics of volatile agents?
- low lean body mass
- high % body fat
- volume distribution
- low hepatic function
- low pulmonary gas exchange(lung disease)
- low cardiac output(cardiac disease)
What is the pathway that volatile follows as it enters the body, and what propels this motion?
- anesthesia machine—>alveoli—>capillaries—>cell membranes—>
- partial pressure gradients
- Brain, blood, and all other tissues equilibrate with partial pressures of inhaled anesthetics
What is meant by the phrase volatile agent equilibration?
the same partial pressure exist in both places for example, iDes%=eDes% or Pa=PA(arterial partial pressure=alveolar partial pressure) alveolar {} = end tidal {} = brain {}
Why might you more likely to equilibrate with desflurane as opposed to isoflurane?
because the difference in their BGP
What is the equilibration between alveoli, arterial blood and brain?
PA(alveolar partial pressure) = Pa(arterial partial pressure) = Pbr(brain partial pressures)
PA and Pbr is determined by two factors
- Input
2. Uptake
What are four factors associated with input of anesthetic agents as related to deliver of VA?
- PI-inhaled partial pressures
- alveolar ventilation
- delivery system
- FRC-lung function
What are the three factors associated with uptake of anesthetic agents as related to delivery of VA?
- anesthetic solubility in tissue-BGPC(blood gas partition coefficient, the lower the BGPC the quicker asleep, the quicker awake)
- cardiac output and cerebral blood flow(lower CO the quicker you go to sleep because of slower blood flow, the amount of VA/alveolar concentration goes up due to slower blood flow, lower CO
- alveolar to venous partial pressure differences(A-vD)
alveolar {} = brain {}
Why do inhaled partial pressures of VA need to be high during the initial phase of anesthesia?
- high initial partial pressures offset impact of uptake
- accelerates induction by increasing rate of rise of PA
- as uptake rate decreases, PI may be decreased
turning flows and VA {} at the start of the case to get the patient anesthetized
What is meant by the concentration effect?
- The higher the PI, the more rapidly PA approaches PI(equilibration)
- Increased PI offsets anesthetic uptake
- the greater the {} of VA, the more rapidly you will equilibrate
- may also provide augmentation of tracheal gas flow
What is meant by the second gas effect?
- ALWAYS INVOLVES N2O*
- reflects ability of a high volume uptake of one gas(nitrous) to accelerate the rate of increase of the PA of a concurrently administered second gas(volatile agent)
- increased tracheal gas flow
How is alveolar ventilation involved in equilibration and VA uptake?
- higher rates of alveolar ventilation promotes the uptake of anesthetic gas
- greater alveolar ventilation = greater rate of increase in equilibration
- neonatal alveolar ventilation to FRC ratio 5:1
- adult alveolar ventilation to FRC ratio 1.5:1
- neonates induce faster*
How does spontaneous ventilation affect volatile agents?
volatile agents—>ventilation depressants
spontaneous ventilation has a negative feedback protective mechanism—>delivery of anesthesia reduced when ventilation reduced
What is the main factor impacting equilibration of anesthetics in the blood as related to alveolar ventilation?
it depends on the solubility of the anesthetic in the blood
- changes in alveolar ventilation influences rate of increase of equilibration more with soluble anesthetics than insoluble anesthetics
- more soluble = harder to get to sleep quickly
What are three machine characteristics that influence rate of equilibration?
- volume of breathing system(for instance a smaller circuit)
- solubility of agent in circuit
- fresh gas flow rates(have gas flows 5 ppm or more to negate effects of volume of anesthetic breathing system)
How are inhaled agents solubilities quantified?
by blood gas partition coefficients
So what does BGP mean in reference to anesthetic solubility?
- rate of increase of equilibration(PA towards PI) is inversely proportional to solubility of anesthetic in blood
- size of blood reservoir depends on solubility of anesthetic in blood
What does having a high BGP mean?
large amount of anesthetic must dissolve in blood for Pa to equilibrate with PA(slower on slower off)
What does having a lower BGP mean?
small amount of anesthetic must dissolve in blood for Pa to equilibrate with PA(quicker on quicker off)
What can be done to overcome blood solubility of anesthetics during induction?
Over pressuring….sustained delivery of high PI…can result in anesthetic overdose with controlled ventilation!
over-pressuring comparable to concentration effect
In insoluble anesthetics what is a description of their equilibration characteristics.
minimal amounts of agent are dissolved before PA=PI(equilibration)
minimal time required before onset of anesthesia
What are two clinical factors influencing BGPC?
- anemia-lower solubility due to less RBC binding sites
- age-less solubility with neonates., elderly IF agent has significant solubility(isoflurane), not true with sevoflurane and desflurane
What is the significance of tissue blood partition coefficients
- determines uptake of anesthetics into tissues
- determines time necessary for tissue partial pressures to = Pa
- volatile agents require 5-15 minutes for Pa=Pbr
- volatile agents require 25-36 hours Pa=Pfat
What is the significance of oil:gas partition and how is it determined?
- its the parallel anesthetic potency(MAC)
- MAC can be estimated by dividing 150 by the oil:gas partition coefficient
- for example Theoretical MAC with an OGP coefficient of 300 would be 0.5%(150/300)
Nitrous is how much more soluble than Nitrogen?
34x, it diffused in faster than nitrogen can leave
In what cases is N2O administration contraindicated in?
- any surgery that could result in a pneumothorax(75% nitrous doubles pneumothorax volume in 10 minutes)
- bowel obstructions
- middle ear-air filled cavity nitrous may rupture tyrannic membranes, negative middle ear pressures occurs after nitrous discontinuation, lead to PONV
How does cardiac output affect the delivery of anesthetic agents?
- cardiac output influences pulmonary blood flow
- increased CO=more rapid anesthetic uptake
- increased CO acts like higher blood solubility(increased CO allows greater blood storage capacity of inhaled agent)
- sick people go to sleep faster(less uptake of agent means PA rises quicker
- the more soluble the inhalation agent the more cardiac output alterations impact uptake
In absence of cardiac shunt, PA and Pa are?
=
How does a R > L shunt affect anesthesia?
- slows induction of anesthesia
- shunted blood dilutes partial pressure of anesthetic in blood coming from alveoli
- slows rate of Pa increase more with insoluble anesthetics(des for example)
- overall effect of R > L shunt on speed of induction is minimal
How does a L>R shunt affect anesthesia?
- minimal effect on anesthetic induction
- best noticeable if R>L shunt also present
- L>R shunts seen with AV fistulas, Atrial septal defects, VSDs and PDAs
What is meant by the alveolar to venous partial pressure difference(A-vD)?
reflects tissue uptake of inhaled anesthetic , VRG is the fastest to equilibrate returning venous blood to PA, continued uptake of anesthetic after VRG equilibration reflects skeletal and fat uptake
infants equilibrate A-vD quicker due to less muscle mass
How do anesthetist measure recovery from anesthesia?
its show by the rate of decrease in the Pbr, which we measure by PA(anesthetic washout from brain is rapid, brain receives large portion of CO, anesthetics are minimally soluble in brain)
Is the the rate of decrease of PA more rapid or less rapid than rate of increase during induction?
the decrease in PA is more rapid than the increase during induction
What is context sensitive 1/2 times?
For volatile agents, its the time needed for 50% reduction in anesthetic concentration. The longer the case the more bank for your buck you would get with a VA like desflurane.
What is the definition of MAC?
- its the minimum alveolar concentration of anesthetic required to prevent skeletal muscle movement in response to a supra maximal painful stimulus in 50% patients
- ED50
- immobility mediated by spinal cord
- *movement does not correlate well with awareness
MAC values are additive(0.5 MAC nitrous oxide + 0.5 MAC sevoflurane = 1 MAC anesthetic
How are red head affected by MAC?
it takes more anesthesia for someone with red hair, MAC is increased
What does anesthesia have with the mechanism of immobility?
Movement has nothing to do with awareness
spinal chord medicated, not brain
spinal cord activity does not correlate with EEG
What neurotransmitters are believed to be involved with inhaled anesthetics?
glycine receptors
Inotropic receptors play an incompletely understood role in anesthesia
How does anesthesia affect unconsciousness?
loss of consciousness involves a different mechanism than immobility, the two actions of VA on brain and VA on spinal cord likely occur at separate anatomical and molecular sites
