Anesthesia - Drugs used in Phases & the Mind Body Problem (Lectures 7A & 7B) Flashcards
What is consciousness?
- Introspective approach: assumed consciousness
- Behavioral approach: consciousness doesn’t exist, all behavior is reflexive
- Biopsychilogy approach: it is a group of forerbrain activities, is present in waking and absent in sleep, present during instinctive patterns and goal oriented behaviours, isn’t involved in all brain processes
Hypnotic general anesthetic definition
suppress all sense by making you unconscious (most anesthetics)
Dissociative general anesthetic definition
suppresses pain by dissociating you from the environment (doesn’t actually suppress all senses)
Local anesthetic definition
temporarily blocks impulses to primary afferents (usually inhibiting VDSCs)
History of general anesthetics & the drugs used
- People used to use asphyxiation, knocking people out, or some drugs for anesthesia (opium, alcohol, atropine, cannabis)
- 19th century → holding people down during surgery, surgery was primitive, surgeons were fast
- NO2 & ether - first pure anesthetics (1700s and 1800s) → known they killed pain but were not used in medicine and had parties with it instead (judging u)
- First introduced in dentistry by goodman and gilman
- NO2 pain killer effects seen (1840s) but a demonstration at the hospital was not successful, later demonstration of it was
- Chloroform - ether and chloroform induce excitement (stage 2) and nausea (1940s)
- Barbiturates - injectable but hard to reverse (now used in rats) (1911)
- Cyclopropane - 1929
- Halothane - worked for many years but caused liver toxicity (1950s)
- Isoflurane, enflurane, sevoflurane - halothane derivatives used today
Function of hypnosis, analgesia, amnesia, and muscle relaxation in general anesthesia?
Hypnosis - putting you to sleep
Analgesia - pain suppression (NO2)
Amnesia - no recollection of experience
Muscle relaxation - no jerk movements during surgery
Phases of procedure
Preanesthetic medication - anxiolytics so you don’t worry
Induction - put you to sleep
Maintenance - keep you asleep
Emergence
Common drugs of induction
Induction - IV agents, prevents claustrophobia
- Barbiturates (thiopental, methohexital) → rapid induction, short action (REDISTRIBUTION) (used before)
- Propofol, etomidate - rapid induction, short action (REDISTRIBUTION)
Administer low dose of it in IV - Drugs made to have high partition coefficient so it is fat soluble so it crosses the BBB and goes to the brain fast (more drug in brain then body)
- The brain is highly perfused so it equilibrates to the dose and you fall asleep
- Redistribution starts to occur and drug goes to other areas as the concentration of it drops in the vascular areas and leaves the brain
IV given first because patients don’t like the mask because it is claustrophobic and large doses of IV are not reversible so it is not preferred, after the patient falls alseep they are given the mask
- Succinylcholine - muscle relaxant (ventilation)
- Blocks nicotinic receptors to paralyze you - no reflexes
Ketamine
Drugs used in premedication
Benzodiazepines - sedation (ex. midazolam)
Opioids - to minimize pain and lightens anesthetic load
Belladonna alkaloids - decrease secretions so you don’t choke (ex. Atropine, scopolamine)
- Antagonize the muscarinic-cholinergic receptors to cause dry mouth and dry nose because saliva and other secretions can choke you
Drugs used in maintenance
Maintenance - gasses, volatile liquids
- Halothane used to be used
- Sevoflurane, desflurane, isoflurane, enflurane - newer gasses, less risk of liver damage
- Nitrous oxide - adjunct with analgesia → still use because it is a pain killer
Side effects of general anesthetics
Very few with modern drugs like sevoflurane
Side effects related to genetics
- Succinylcholine - long action in patients
- Don’t have much active cholinesterase due a variant allele so it takes them longer to wake up (20 min - 1 hr instead of 5 min) → keep them in hypnotic state
- All anesthetics - malignant hyperthermia
- Skeletal drugs are overactive so temperature skyrockets, need to administer medication (runs in families)
Non hypnotic anesthesia agents
neuroleptanalgesia/neuroleptanesthesia for minor surgery
- Extreme sedative neuroleptic (makes you inactive and calm) + an opioid (to kill pain) → patient is awake and calm and can’t feel pain
- Droperidol and fentanyl
Dissociative anesthesia
- Ketamine derived from PCP (angel dust)
minor surgery, vet surgery and emergencies → outpatient emergency situation like a car crash as there is no risk of OD
- Doesn’t suppress breathing and relaxes you → safe
Split brain
- Result of surgery cutting the corpus callosum to stop epilepsy
- Only occurs if the WHOLE corpus callosum is cut
- Doesn’t occur if the anterior ⅔ portion is cut
- Results in two separate consciousnesses with separate sensations, memories, skills, motivations, and motor controls
- Left cortex: understands and produces speech, moves right side of body
- Right cortex: understands simple speech but can’t produce speech, moves right side of body, good at patterns but not symbols
- Left hand puts down book that the person can’t read (right side) even though the left side is happy to read it
- Man beating wife with one hand and other is protecting her
Pencil and paper maze - one side had the pencil and could not complete the maze and the other side took it
Unilateral neglect
- Damage to right parietal lobe
- Person doesn’t attend to things in their left visual field or what’s on the left side of their body → they no longer enter consciousness
- Visual cortex still recording it but high order brain structures ignoring it
- Only dresses their right side, shaves right side of face, eats right side of pancake
- Can only name things on the right from a remembered location but when they flipped the sides they could name what they skipped over because it was now on their right
- They can still answer if things are the same or different on the sides but not what it actually is on the left
Blind sight
- Damage to occipital lobe - visual cortex
- Person loses visual neocortex function → cortically blind
- They have half their visual field and if you close the good one they can still reach for things and avoid obstacles → can navigate blind spot → can access subcortical info
