Ch 25: General Anesthetics Flashcards
General Anesthetics
useful for rendering patients that are unable to experience pain during procedures: surgical obstetric therapeutic diagnostic
General Anesthetic produce an unconscious state
- Depress the CNS
- Depress CV system
- Depress Respiratory System
Depress the CNS
- Loss regulatory mechanisms
a. thermoregulation
b. baroreceptor reactivity - respiratory
- Lose protective mechanisms
a. glottic reflexes
b. position injuries - corneal abrasions
Depress CV system
- Decreased contractility
- Peripheral vasodilation
- Reduced organ perfusion
Depress Respiratory system
- Induced Hypoxemia
2. Cause retention of secretions (pneumonia)
Why do we use general anesthesia?
Patients want to be sleep patients are uncooperative can't use a regional anesthesia produce amnesia produce analgesia promote muscle relaxation
4 stages of general anesthesia
analgesia excitement
surgical anesthesia
medullary paralysis
analgesia
somewhat conscious
excitement
unconscious & amnesic, but agitated & restless
surgical anesthesia
slow, deep breathing, muscle relaxation
medullary paralysis
breathing stops, CV collapse…. need support for life
Inhaled agents
potent rapid induction & recovery muscle relaxant non-irritating to airway no excess CV depression suppresses excessive sympathetic activity
Types of inhaled agents
gases
volatile liquids
gases
traditionally ether & chloroform, now only nitrous oxide (N2O)
volatile liquids
halothane
isoflurane
desflurane
sevoflurane (newest)
Inhaled agent pharmacokinetics
- must reach a therapeutic tissue concentration in the brain
- highly lipophilic
(will get widely distributed throughout body) - Induction & recovery time increased in obese patients (adipose “sink”)
- recovery is based on respiratory, CV. and metabolic rates
pharmacokinetics
drugs moves from machine to lungs, to blood, to CNS circulation, to local sites
Induction time based on:
- conc. of drub, pressure of system, response rate
- solubility of gas, CO, pressure gradient
- solubility into brain tissue, blood flow into tissue, artery to vein pressure difference
reversal of anesthesia
- turn vaporizer to “0” & hyperventilate
- most leaves unmetabolized through lungs
- if needs to be metabolized, liver function is important in recovery time
- circulation effects speed of drug movement
General Perturbation Theory
- works by disrupting membranes
- potency correlated w/ lipid solubility
- similar effects for a variety of chemical structures
- presumable “squeeze” membranes to slow ion flux
- general phenomena throughout brain
Specific Receptor Theory
- bind to receptor sites or ion channels to slow Na+ influx
- related to lipophilicity
- variety of ion channels & receptors (GABA-a & NMDA)
reduced neurotransmission
- may cause strengthened inhibition/ reduced excitation
- a greater effect on excitatory transmission than inhibitory
inhaled agent side effects
- cv depression
- decreased B.P & H.R.
- depressed airway reflexes (cough)
- bronchodilator (good for asthma & emphysema)
- decreased ciliary action (retain secretions)
- reduced ability to speed up respiration following hypoxia & hypercarbia
- may enhance potency
- likely to reduce side effects of either
intravenous agents
used for induction of anesthesia
from stage 1 to 3 quickly
IV agents used
thiopental midazolam propofol ketamine etomidate
sodium pentathol (thiopental)
- depress RAS
- ultra short acting Barb (30 sec hypnosis)
- last 5-10 mins (mostly for induction)
side effects of sodium pentathol (thiopental)
cv depression (prob. w/ heart disease patients) respiratory depression (significant) risk stage 2 if adequate dose
Propofol
- presumed GABA-a action
- quick induction
- rapid recovery (even w/ sustained infusions)
- hypnotic but not analgesic
side effects of propofol
similar to Pentothal
fast or slow heart rate high or low blood pressure injection site reactions (burning, stinging, or pain) apnea rash itching
Ketamine
- binds NMDA receptor, inhibits glutamate action
- dissociates thalamus from limbic system
- patient appears conscious, but unable to respond to stimulus (dissociative anesthesia)
side effects of ketamine
- Cardiovascular
** increased B.P & C.O
(avoid in patients w/ arterial disease, hypertension, aneurisms) - Respiratory
- minimally affected (good for asthmatics)
- CNS
- analgesic = good for short procedures
- strong hallucinogen (kids like, but not adults)
Etomidate
- depress RAS
- simian to pentothal in kinetics
- reduce respiration
- minimal CV effects (hypnotic, not analgesic)
- disinhibits extrapyramidal motor centers (myoclonic movements)
adjuvants
- to sedate/ calm
- pentobarbital (barbs)
- morphine/ meperidine (opioids)
- diazepam/ lorazepam (Benzos)
- diphenhydramine/ promethazine (anti-hist)
- Neuromuscular junction blockers
- ——–gallamine, pancuronium, succinylcholine
