General Anesthetics Flashcards
(45 cards)
1
Q
- inhaled gaseous agent
- least soluble (fast)
A
Nitrous Oxide
2
Q
- inhaled volatile agent
- most soluble (slow)
A
Isoflurane
3
Q
- inhaled volatile agent
- second most soluble (more slow)
A
Sevoflurane
4
Q
- inhaled volatile agent
- second least soluble (more fast)
A
Desflurane
5
Q
-IV agent
A
Propofol
6
Q
-IV agent
A
Etomidate
7
Q
-IV agent
A
Ketamine
8
Q
-IV agent
A
Dexmedetomidine
9
Q
Chloroform
A
- 19th century anesthetic
- fell out of use secondary to side effects (hepatitis and arrhythmias)
10
Q
5 Major Effects of General Anesthetics (GA)
A
- unconsciousness
- amnesia
- analgesia
- attentuation of autonomic reflexes (for the benefit of your body)
- skeletal muscle relaxation (for the benefit of the surgeon)
11
Q
Ideal GA
A
- rapid, smooth loss of consciousness
- rapidly reversible on discontinuation
- wide margin of safety
12
Q
Balanced Anesthesia
A
- to minimize side effects and maximize efficacy
- instead of giving large amt of one agent and experiencing all its side effects, you use small amts of many agents to reduce side effects
- can use both inhaled and IV agents
- customize agent combination to type of care
- also includes opioids (maintain anesthetic), BZs (give before due to amnesia effect, helps maintain BP), and neuromuscular blocking drugs (allows you to use less inhaled agents)
13
Q
Conscious Sedation
A
- minimal amts of amnesic and opioid
- pt still able to converse, respond to stimuli and commands
- able to protect airway and maintain ventilation (so if pt vomits during procedure, they are able to protect their airway and prevent aspiration pneumonia
- similar to being pretty drunk and not remembering much
- if you don’t want pt to move or talk then you want GA and not “conscious sedation”
14
Q
Continuum through GA
A
- decreases in responsiveness to painful stimuli and commands
- decrease in ability to protect airway and maintain normal ventilation
- once pt has los tthe ability to protect the airway, it is considered GA
- most operators desire such high degree of immobility and unresponsiveness for their pts that their request for “sedation” is actually GA
15
Q
GA Induction
A
Take Off!
16
Q
GA Maintenance
A
Mid Flight
Hemodynamically Stable and Perfused
17
Q
GA Emergence
A
Landing!
18
Q
Gaseous Inhaled Anesthetic
A
- gas at room temperature
- currently only agent is Nitrous Oxide (relatively low potency, used in addition to other agents)
- good amnesic and analgesic actions
- xenon is experimental
- really quick on and off
- good saving agent
19
Q
Volatile Inhaled Anesthetic
A
- liquid at room temperature
- halogenated ethers (mostly fluorinated)
- isoflurane, sevoflurane, desflurane are most commonly used
- used primarily for maintenance, except in pediatrics where it is used for induction (b/c children would rather have this than a big fat needle)
- not flammable
- not used for induction because horrible smell, feels like you are being smothered and takes about 10 min to work
20
Q
Pharmacokinetics of Inhaled Anesthetic
A
-ideal agent is fast on/fast off with adequate potency
21
Q
Onset of Inhaled Anesthetic
A
- driving force for uptake of inhaled anesthetics to its target organ (CNS) is alveolar partial pressure (or alveolar fraction) of anesthetic
- Fa = alveolar fraction
- Pa = partial pressure
22
Q
Increased Fi (inspired fraction or partial pressure)
A
the higher the fraction or the higher the flow of anesthetic through the top of the airway, the faster your anesthetic onset
23
Q
Increased Alveolar Ventilation
A
the more you increase alveolar ventilation, the faster the onset
24
Q
Inhaled Agent Parameters on Onset
A
- solubility of inhaled agent (blood:gas partition coefficient)
- more insoluble agents have faster onset
- more insoluble agents “fill the well” faster
- nitric oxide is least soluble
- isofluorine most soluble, so takes the longest
- halothane is very soluble, so very slow
25
Pharmacokinetics of Inhaled Agents (Emergence)
- onset in reverse, except Fi is zero (inspired fraction is zero because you put them on 100% oxygen)
- alveolar ventilation is most important factor in emergence (you're blowing it off faster)
- metabolism is a minor factor in emergence
- degree of metabolism (SEVO>ISO>DES>N2O)
26
Pharmacodynamics of Inhaled Anesthetics (MAC)
- MAC: Minimal Alveolar Concentration (measure of potency)
- partial pressure of inhalation anesthetic in the alveoli at which 50% of a population of non-relaxed pts remain immobile at skin incision
- if you give a muscle paralytic, then you will need less of inhaled agent to get to the same point
27
Inhalation Anesthetic Effect on Cardiovascular System
- decrease in BP (as a result of decreased systemic vascular resistance and negative inotropy)
- agent specific SVR/inotropy effects
28
Inhalation Anesthetic Effect on Respiratory System
- increased RR
- decrease Vt
- for an overall decrease in minute volume
- increased RR with decreased tidal volume... so you are pretty much panting
29
Inhalation Anesthetic Effect on Hepatic System
- decrease in portal vein flow
- increase in liver enzymes are rarely seen
- can cause hypoperfusion in pts with liver disease, but the actual agent will not cause a hepatitis
30
Inhalation Anesthetic Effect on Uterine Smooth Muscle
- decrease in uterine tone (helpful during delivery but may lead to increase in uterine bleeding)
- helpful during Cesarian sections
31
Adverse Effects and Toxicity of Inhalation Anesthetics
- organ toxicity, mutagenicity and carcinogenicity with inhalation agents have been in animal studies with little if any human correlation
- nitrous oxide can potentially cause a decrease in methionine synthase activity causing megaloblastic anemia
- studies of miscarriages in OR personnel cannot be linked to anesthetic gas exposure
32
Malignant Hyperthermia
- potential side effect of inhaled anesthetics
- hypermetabolic syndrome in genetically susceptible patient after exposure to triggering agents (halogenated inhalationals and succinylcholine)
- incidence is rare
- caused by a decreased in reuptake of Ca++ from the sacroplasmic reticulum
- calcium sitting there jsut causing unstoppable muscle contraction
- hyperthermia b/c muscles keep contracting
- potential for myoglobinuria
- you have hypercapnia (increased CO2) b/c of increased metabolism
- prolonged muscle contraction leading to hyperthermia, hypercapnia, hypoxia, hyperkalemia
- hyperkalemia b/c excreting the intracellular contents
- important to ask about family hx of reaction to GA
33
Dantrolene
- txt of malignant hyperthermia
| - given as antidote by inhibiting release of Ca++ from the sacroplasmic reticulum
34
IV Anesthetics
- preferred method of induction (very quick)
| - help pt go to sleep during induction
35
Pharmacokinetics of IV Anesthetics (Propofol/Etomidate/Ketamine)
- all 3 are lipophilic
- preferential partitioning into highly perfused lipophilic tissues (brain and SC)
- rapid onset of action
36
Elimination of IV Anesthetics
- rapid redistribution from highly perfused tissues into lean tissues for quick offset of action
- liver metabolism is rapid as well, but occurs later
- good context sensitive 1/2 time: this describes the elimination 1/2 time after a continuous infusion (this is an important factor in the drug's suitability for maintenance sedation)
- the longer you use a drug, the longer it is going to take to wear off
- propofol is nice flat curve and good for long-term sedation
37
Thiopental
- IV anesthetic
- can't use for long term b/c take forever to come off
- half-time quickly increases as infusion duration increases
38
- IV anesthetic
- used for induction and short sedation
- minimal hemodynamic effects (i.e. HR, BP, inotropy)
- non-analgesic
Etomidate
39
- IV anesthetic
- "Milk of Amnesia"
- used for induction and maintenance of GA as well as Sedation
- important to use w/i 8 hrs of dispensing to prevent bacterial contamination
- GABA agonist
- non-analgesic (can't use as pure anesthetic)
- amnesic
- antiemetic (in small doses)
Propofol
40
Propofol Adverse Effects
- CV: vasodilatory and negatively inotropic (BP drops)
- Respiratory: Decrease in Vt, RR, and minute volume
- Decrease in upper airway reflexes (so if vomiting, you can get stuff going down the cords)
41
Etomidate Adverse Effects
- adrenal suppressive effects, so don't use it long-term
- endocrine effects: dose dependent inhibition of 11B-hydroxylase (cholesterol to cortisol pathway) which limits its use for prolonged sedation
- respiratory depressant (like propofol)
- burns on injection (propofol burns a little on injection, but etomidate is much worse)
- associated with increased nausea and vomiting
42
- IV anesthetic
- disconnects your pain center and reticular activating system
- phencylidine derivative
- dissociative anesthesia w/ nystagmus (cataleptic state)
- NMDA receptor antagonist
- ANALGESIC!!!
Ketamine
43
Adverse Effects of Ketamine
- increases in HR, BP, and CO
- minimal if any respiratory depression
- bad dreams and nightmares, especially in adolescents
- airway reflexes are preserved in most situations
- hallucinations and unpleasant emergence may occur, so co-administration of a BZ is recommended
- lacrimation and secretions are increased (very inc. salivation during surgery)
44
Ketamine and Opioid Tolerance
-subanalgesic doses may help in limiting or reversing opioid tolerance
45
- IV anesthetic
- used for sedation or adjunct to GA
- alpha-2 agonist
- both sedative and analgesic
- receptors are in the locus ceruleus and spinal cord
- preserves respiratory drive
- significant decreases in BP and HR can be seen (HR sometimes in 30s)
- context sensitive 1/2 time is significantly increased after 8 hours of infusion
Dexmedetomidine
