General Anesthetics - Lichtblau Flashcards
1
Q
What are the four stages of anesthesia?
A
- Analgesia and amnesia (good)
- Delirium (bad)
- Surgical anesthesia (good)
- Medullary depression (bad)
2
Q
Why is it difficult to uncover the precise cellular mechanism of anesthetic action?
A
- Diverse chemical structures that do not interact with pharmacologically defined receptors, but the anesthetics impact all physiological systems (even though there is no specific site of action).
- Known to cause physical changes in cell membrane fluidity
3
Q
What is “balanced” anesthesia?
A
Combined use of multiple drugs
- General anesthetic = loss of awareness or consciousness
- Benzodiazepine = amnesia
- Opioid = analgesia, blunting of the ANS
- Neuromuscular blocker = skeletal muscle relaxation
4
Q
What are some general pharmacological characteristics of inhalation anesthetics?
A
- Gaseous
- Administration through vaporizer/flowmeter
- Diverse chemical structures
- Do not interact with pharmacologically-defined receptors (compared to IV)
- Impact all physiological systems (no specific site of action)
- Known to cause physical changes in cell membrane fluidity
5
Q
Why is the partial pressure of an inhalation anesthetic a more important variable in producing anesthesia than blood concentrations of the agent?
A
- It’s not the total concentration of anesthetic in the blood that counts, only that which doesn’t dissolve.
- Amount of undissolved drug in the blood is related to the clinical effect
- That is what raises partial pressure.
- Kind of like concentration of free drug as compared to total concentration which includes protein-bound drug. Only free drug has pharmacological effects.
6
Q
What is the MAC value?
A
- Minimum Alveolar Concentration (MAC)
- Dose of anesthetic (in a percent volume) producing a surgical anesthesia in 50% of patient population = ED50
7
Q
Why is MAC value a useful index in anesthesiology?
A
- Anesthetics with the lowest MAC are the most potent
- Surgical anesthesia uses 1.3-1.5 MACs
- Deep anesthesia uses about 2 MACs
8
Q
Why can’t you produce surgical anesthesia with nitrous oxide?
A
- Need 104 MACs in order to achieve total anesthesia of the patient.
- Also need to have at least 21% oxygen in the mixture for the patient to live.
- This is not possible, which is why nitrous oxide is not a very potent anesthetic.
9
Q
What does the blood:gas ratio tell you about the characteristics of an anesthetic agent?
A
- solubility in the blood –> must be dissolved in blood to raise its partial pressure
- The more soluble a drug is in blood, the longer it takes to raise its partial pressure in blood (Pblood)
- smaller blood:gas partition coefficient –> faster onset/rate of induction
- Nitrous oxide = 0.5
- Halothane = 2.5
10
Q
What happens in Stage I of anesthesia?
A
- Analgesia & Amnesia
- Point of induction to the loss of consciousness
- Patient can still respond to commands, reflexes present
- May include voluntary signs of resistance to procedure
11
Q
What happens in Stage II of anesthesia?
A
- Delirium
- begins with loss of consciousness
- patient may be agitated or combative and may thrash about and struggle
- blood pressure and respiratory rate fluctuate
- non-purposeful rapid eye movements
- breath-holding, vomiting, and laryngospasm may occur
- ***PATIENT SHOULD MOVE THROUGH THIS STAGE AS FAST AS POSSIBLE***
- ideally no memory
12
Q
What happens in Stage III of anesthesia?
A
- Surgical anesthesia
- respiration becomes regular
- with increasing concentrations of anesthetic –> autonomic reflexes may become depressed
- four planes of anesthesia (I - light surgical, II - moderate surgical, III - deep surgical, IV - excessive surgical)
13
Q
What happens during Stage IV of anesthesia?
A
- Medullary depression
- stage of relative overdose
- maintenance of this stage may result in cardiovascular collapse and severe respiratory depression
- BAD NEWS
14
Q
What does the oil:gas partition coefficient tell you about the characteristics of an anesthetic agent?
A
Larger oil:gas partition coefficient –> higher anesthetic potency
Nitrous oxide = 1
Halothane = 224
15
Q
Why is the rate of anesthesia induction slower when you use agents that are more soluble in the blood?
A
- Amount of undissolved drug in blood is related to the clinical effect
- smaller clinical effect if anesthetic is soluvle in the blood (dissolved)
- drugs dissolved in fluid DO NOT raise the Panesthetic in that fluid
- longer it takes to attain equilibrium
- greater concentration of anesthetic at equilibrium
16
Q
What variables influence anesthetic recovery and anesthetic elimination from the body?
A
- Fat-soluble anesthetics leave body fat slowest
- Route of elimiation
- Primary: Lungs
- Skin & mucous membranes
- Biotransformation
- toxicologically important –> liberation of chemically-reactive halide ions which can acutely or chronically harm kidneys, liver, and reproductive organs
- Metabolism of inhalation anesthetics
- Methoxyflurane > halothane > sevoflurane > isoflurane >> nitrous oxide
17
Q
What properties make some anesthetics more useful than others?
A
- stable shelf life
- compatibility with existing delivery equipment
- inexpensive
- non-explosive/nonflammable
- easily vaporized under ambient conditions
- low blood solubility
- potent
- no cardiopulmonary depression
- not irritating to airways
- no interaction with catecholamines
- good muscle relaxation
- minimal metabolism
- not toxic to kidneys, liver, or gut
18
Q
What are common aspects of all halogenated anesthetics?
A
- CNS effects
- decrease brain metabolic rate
- increase cerebral blood flow
- increase intracranial pressure
- CV effects
- decreased myocardial contractility and stroke volume leading to lower arterial blood pressure
- sensitizes myocardium to catecholamines (if you add EPI after BP drops –> fatal arrhythmias)
- Respiratory depression
- Muscle relaxation at high doses
- Malignant hyperthermia may occur
19
Q
What are advantages & disadvantages of using Halothane to produce general anesthesia?
A
- Advantages
- Low blood solubility (rapid onset)
- little effect on overall cardiovascular fxn
- Second gas effect: lowers MAC of other inhalation anesthetics
- Mild-moderate analgesic activity
- Disadvantages
- MAC = 104% (can’t use as sole anesthetic agent)
- No muscle relaxing effect
- Diffusion hypoxia if rapidly discontinued
- rapid transfer from blood to alveoli –> displaces air –> lack of oxygen uptake = hypoxia
20
Q
Why/Why isn’t sevoflurane an almost perfect inhalation anesthetic?
A
It is almost perfect inhalation anesthetic!
- rapid onset (5-10) minutes
- rapid recovery - same day surgery
- high potency (low % of inspired gas)
- low blood solubility
21
Q
How does nitrous oxide compare to other inhalation anesthetics?
A
Only inhalation anesthetic that is a gas.
22
Q
Why are injectable anesthetics often used for anesthesia induction as well as for short-duration anesthesia?
A
- They act faster
- Unsuitable as a single drug anesthetic for many surgical procedures
- musle relaxation after IV anesthetics is poor
23
Q
How do pharmological principles of drug distribution, redistribution, and drug accumulation influence the administration and use of injectable anesthetics?
A
***
24
Q
What is a “dissociative anesthetic”?
A
- Dissociatives are a class of hallucinogen, which distort perceptions of sight and sound and produce feelings of detachment - dissociation - from the environment and self
- patient appears to be awake (eyes open)
- do not feel pain
- Anesthetic, analgesic, amnestic, & sedative
25
What is the MOA of dissociative anesthetics like Ketamine (Ketalar)?
NMDA Glutamate Receptor Antagonist
* Rapid onset of action when given IM/IV (1-2min)
* Relatively short duration of action (~20 min)
* Relatively high therapeutic index
* Drawback: delirium & hallucinations
26
When might it be best to use a "dissociative anesthetic" for anesthesia purposes?
* Children
* Quick procedures
* Patient's with unstable cardiovascular function
27
Why would you use an opioid as an anesthetic?
* High dose opioids good for:
* analgesia
* anesthesia
* Hemodynamic stability
* good for patient with compromised myocaridial function
* Respiration must be maintained artificially and may be depressed into the postoperative period
* Usually supplemented with inhalation anesthetic, benzodiazepine, or propofol
28
What injectable anesthetic facilitates GABA induced Cl- entry into neurons leading to CNS depression, has a rapid onset (seconds)/short action (minutes), anesthetic dose between 50-75% of the LD50, and includes Thiopental (Pentothal) & Methohexital (Brevital)?
Barbiturates
29
What injectable anesthetic faccilitates GABA induced Cl- entry into neurons leading to CNS depression, has less cardiovascular/respiratory depression that barbituates, is significant for it's amnestic action, is used as an induction agent prior to anesthesia because it is insufficient for anesthesia when given alone, and includes drugs like Midazolam (Versed) and Diazepam (Valium)?
Benzodiazepines
30
What injectable anesthetic has a rapid induction (50 seconds) & recovery (4-8 minutes) from anesthesia, may be given alone to maintain anesthesia or used for induction as part of balanced anesthesia technique, must be given as emulsion, results in apnea (22-45%), may result in injection site pain, and includes drugs like Diprivan?
Propofol
31
What is GABA? How does it work? What effect do barbituates and benzodiazepines have on GABA?
* GABA is the primary inhibitory neuro-transmitter in the brain.
* works by opening Cl- channels causing the cell to become hyper-polarized
* Benzodiazepines/barbituates enhance the binding of GABA to its receptor and enhance its ability to open Cl- channels allowing more Cl- to enter the cell
* benzos = increase **frequency** of channel openings
* barbs = increase **duration** of channel openings
