Anesthhetic Pharmacology (Mod 2) Flashcards
Pharmacodynamics vs Pharmacokinetics?
- Deals with what the drug does to the drug (anticholingerics/mimetic and that crap)
- What does the body do to the drug (i.e metabolism)
Define Induction
Transition from an awake state to an anesthetize state
Define Recovery
State of consciousness of an individual when hey are awake or easily arousable and aware of surroundings following the elimination of an anesthetic
What is the purpose of inhaled anesthetic agents?
Inhaled anesthetic are primarily used to maintain the anesthetic state AFTER induction by some other agent (like propofol)
What is the ciruclation/distribution pathway of inhaled anesthetic?
Distributes well to all parts, but becomes most concentrated in the fatty tissue
- this occurs because this area is not as well vascularized
- it gets held because it takes longer to get there and exit (its more like a storage place where it gets saturated as a uptake area)
What is Minimum Alveolar Concentratino (MAC)
- Important
Dose that we’re going to providing, but it is not dose specific. It’s the minimum we need.
- Levels associated with partial pressures to deliver the desired range by varying the inspired partial pressure (Pi)…we set this. measure is not precise
- Controls the depth of anesthesia, anesthesiologist have precise control of the level of anesthetic in the CNS
How is level of anesthetic in the CNS (Pcns) determined?
The CNS partial pressure (Pcns) is monitored via alveolar partial pressure (Palv) because it cannot be directly monitored.
- its a substitute method for Pcns because Pcns tracks palv with only a small lag time
How is alveolar partial pressure (Palv) measured?
Palv is measured directly as the partial pressure of anesthetic in the end tidal exhaled gas, when dead space no longer contributes to the exhaled gas
Why is the potency of anesthetic is related inversely to its Minimum Alveolar Concentration (MAC)
- what doe sit mean?
- edit this is a important point
MAC is alveolar partial pressure that abolishes a movement response to a surgical incision in 50%, so you need to give MORE than you need bc they may not be affected by it
- If the MAC is small, the potency is high and relatively low partial pressure of anesthetic will be sufficient to cause anesthesia
- MAC is associated with how much drug they are getting, partial pressure deals with how it is being delivered??? —> Partial pressure is associated how much more gas is needed to deliver the drug itself, lower MAC needs less partial pressure
What is the alveolar partial pressure that results in the lightest possible anethesia called?
Minimum alveolar concentration (MAC)
What could be indicators of movement response if a paralytic is applied?
Vitals such as HR.
- so the patient may not necessarily grimace or flinch in response to surgical incisions
What MAC concentration do you typically want to aim for?
edit
1.1-1.3
- as you increase the dose, more people will not response to surgical incision
- standard deviation is approx 10% (MAC + 1SD)
- Example: Refer to slide 7. to achieve 68% anesthetic state, you want to multiply the partial pressure MAC (slide 8) of a drug by 1.1
How are separate douses of anesthetic gasses admined overtime over affect?
Effects of anesthetic are additive (they stack)
- 0.5 of 1 in combo w/another 0.5 drug will increase potency to 1 MAC of a single agent
What conditions would require a patient to need a higher MAC (increased MAC) of anesthetic gas?
- aka more mac needed to induce them
- Pt with Hyperthermia
- Chronic alcohol abuse
- Pt with that drug use or amphetamines, and CNS stimulants (they have higher tolerances)
What conditions would require a patient to need a lower MAC (decreased MAC) of anesthetic gas?
- aka less mac needed less to induce them
The following will need less anesthetic drug use:
- Advanced age
- Hypothermia
- Severe hypotension
- Otehr agents; opiates, valium
- Acute drugs or ETOH into
- Pregnancy
- High PCO2 or Low PO2
What is the Meyer Overton Rule?
Oil/gas partition coefficient that helps us understand the potency of the anesthetic gas
- As the oil/gas partition increases, MAC decreases
- The potency of an anesthetic increases as its solubility in oil increases
- The gases do not bind to receptors, they disrupt the nervous system in the body enters the lipid bilayers in the CNS
What are the benefits of using a mixture of inhaled anesthetic gasses? (3)
Allows for:
- Anesthetic potency
- Recovery
- Inhaled agents and IV agent combinations allows for the above goals to be achieved
What are pharmacokinetics characteristics of an ideal inhaled anesthetic? (2)
- Provides a rapid and pleasant induction of surgical anesthesia
- Provides a smooth and rapid recovery to a fully functional and concisions state
what factor limits the transfer of anesthetic in both lungs and the tissue in terms of capillary beds and blood?
Perfusion rates rather than difffusion rates
- The transfer of anesthetic is limited by perfusion rather than diffusion
- increasing the rate of diffusion will not increase the rate of induction of anesthesia
In the realm of the pharmkinentics of anesnethic gasses; what does the concept of compartments refer to?
The different spaces agents need access to, to achieve their desired effect
What pathway does anesthetic gas generally diffuse within the body?
- Pt breathes in gas (spontaneous or via vent)
- Anesthetic reaches the alveoli; must diffuse across the AC membrane into the pulmonary capillaries
- Gas should diffuse into the blood
- Blood brain barrier (site of action) aka CNS
Why is partial pressure of alveolar and systemic arterial pressure nearly the same in healthy adults?
edit
- add more to this card aka be more specific
The lungs optimize gas diffusion and Inspired Partial pressure
- The capillary beds in tissues delivery oxygen rapidly to all cells in the body through a series.
- The end goal will be D, but gas will still pass through ABC eventually filling the capacities in this areas
- All compartments will equilibrate to equal Pi
What does a compartments equilibrium depend on?
The volume capacity and flow rate of blood (and subsequent diffusion) -> which is perfusion limited.
- Blood flow refers to level of blood flow delivering anesthetic
- Equilibrium of partial pressure of the compartment with he incoming flow takes place more quickly when the inflow is larger or compartment capacity is smaller
What is the primary determinant of diffusion?
Partial pressure of gas
What are the compartment groups for distribution of blood to tissues? (4)
slide 19
- adjust later
- Vessel Rich Group (VRG)
- Muscle Group (MRG)
- Fat Group (FG)
- Vessel Poor Group (VPG)
When does Movement of agents stop?
when pressure equilibrium is achieved because no pressure gradient exists
Which tissue group receives
How do you speed up induction of anesthetic gas?
Increases MV (via rr and vt)
- Its all about the partial pressure of gas; you have to increase the partial pressure of the inhalant anesthetic
- If Vt increases but partial pressure remains the same, the speed of induction won’t increase
What is the first step of equal ration of partial pressure of VRG (Pvrg)?
Managing Pi (inspired partial pressure)
- Palv results from the balance between delivery by ventilation and removal by uptake into the blood stream (Part); dynamic process.
- Think about the concentration gradient like a cup with a hole. 1 drop for every 3 drops leaving will leave in total water levels dropping
- The Palv is constantly dropping basically
What methods can increase the delivery of anesthetic? (2)
- Increased ventilation
- Increased Pi to raise Palv
What factors could lower anesthetic uptake/affect aka lowers the Palv?
- Increased uptake into the bloodstream caused by a large blood/gas coefficient (Increased solubility of a anesthetic into the blood) —> ask about this point later think about it as peeing in a pool vs a river stream => the pee leaves faster out of the river than the pool
- Increased cardiac output (CO)
Equilibrium of Palv with Pi is faster with what factors? (3)
- Lower blood solubility (Small B/G coefficient)
- Lower CO
- Smaller arterial to venous partial pressure difference
oil gas partition vs partial pressure alveolar equilbrium?
- look into it
- Deals with potency/concentration
- Deals with solubility
What does a small b/g coefficient imply?
- aka what does a low solubility mean?
A low solubility means it doesn’t bind well with the components in the blood (like albumin for example)
What does a large b/g coefficient mean
The anesthetic is soluble in blood
- It takes longer for the blood to become saturated with a large b/g coefficient agent: Palv = Part take longer
- This means that blood can hold more anesthetic agents with a large B/G compared to an agent with a low b/g. it will require more to acquire the anesthetic state
What is equilbrium of tissue with alveolar partial pressures fast?
Changes to Palv are transmitted rapidly to systemic arterioles bc equilibrium across the pulmonary capillaries is fast
- The circulation time from pulmonary veins to issue capillaries is generally less than 10 seconds
What are the implications of a high rate of uptake of anesthetic ino the blood stream?
Prevents Palv from rising rapidly meaning there will be
- Slow induction
- Slow recovery
What must occur for induction to occur?
Palv must equilbrium with Pi
- Palv can only equilbrium with Pi when Pvrg is in equilbrium w/Palv
- Recall: Large blood/gas (b/g) coefficient limits the rate of alveolar uptake (highly soluble in blood) -> if gasses dissolve into the blood, they leave and disrupt equilibrium
- slide 26
Can anesthetic displace oxygen in the blood?
Yes; you need to mix the gasses with oxygen.
- potent is kept and maintained at a certain rate to maintain the anesthetic state
What are ventilation factors that limit anaesthetics?
- slide 26
b/g coefficent: Partial alveolar pressure must equilibrate with partial inspired pressure for induction to occur.
- Partial alveolar pressure can only equilibrate with Pi when pressure in the VRG is in equilibrium with partial alveolar pressure
Does a combination of a tissue low capacity and high blood flow result in?
Short equilibration time
what exerts a partial pressure and in turn increases induction in the realm of the blood/gas (b/g) model?
- hint think solubility
Lower capacity; less gasses bind to less proteins which means more gas moves into the plasma. You want a small b/g coefficient.
- Equilibrium occurs faster with more pressure and hence faster induction
- if binded to a protein, it won’t exhibit a pressure; you want a pressure to create the induction affect