Anaesthesia Flashcards
what do general anesthetics do?
depress the CNS to produce loss of consciousness, loss of responsiveness to sensory stimuli, including pain and relaxation of muscles
how are general anesthetics administered?
either volatile liquids or gases vaporized in oxygen and administered by inhalation or non-volatile liquids applied by injection
general anesthesia involves:
1-analgesia (opioids)
2- amnesia (barbiturates)
3- inhibition of reflexes (a variety of drugs)
4- skeletal muscle relaxation (NMJ blocking agents)
5- rapid hypnosis (barbiturates and other drugs)
***no drug can currently produce all 5 responses thus combinations of drugs are used to produce a balanced anesthesia
combination of drugs can:
reduce the requirement for inhaled anesthetics
minimize their side effects
increase their safety
in addition, the doses of barbiturates, opioids, NMJ blocking agents, etc can be reduced, also increasing safety
what are barbiturates?
depress the CNS
what are the stages of general anesthesia?
stage I: analgesia
stage II: excitement
stage III: surgical anesthesia
stage IV: imminent death
stage I of general anesthesia:
analgesia: inability to feel pain
normal respiration voluntary control of ocular movement normal pupil size normal eye reflexes normal muscle tone normal reps response to skin incision
stage II of general anesthesia:
excitement and hyperactivity
dilated pupils
eyelid reflexes
tense muscle tone
stage III of general anesthesia:
surgical anesthesia
4 planes
respiration gradually decreases
eye motion decreases
pupils constrict in planes 1& 2 then dilate
eye reflexes decrease
muscle tone decreases
in plane 3 no respiratory response to skin incision
stage IV of general anesthesia:
imminent death; paralysis of the medulla
apnea
dilated pupils
flaccid muscle tone
no reps response
what are the 2 types of inhaled general anesthetics?
1- gas
-nitrous oxide
2- volatile liquid
general adverse effects of gas inhaled general anesthetics:
COMMON dizziness drowsiness nausea euphoria vomiting
SERIOUS
malignant hyperthermia
apnea
cyanosis
general adverse effects of volatile liquid general anesthetics:
COMMON
drowsiness
nausea
vomiting
SERIOUS myocardial depression marked hypotension pulmonary vasocontriction heptotoxicity
dosages of gas inhaled general anesthetics are expressed as:
alveolar concentrations such as the minimum alveolar concentration (MAC)
what is MAC?
Minimum Alveolar Concentration=
concentration at which 50% of the patients do not move during surgery. This is the percent of the gas mixture or percent of 760 mm Hg pressure
MAC is an index of the potency of an inhaled anesthetic
MAC has a very steep dose-response curve and is inversely proportional to anesthetic potency
how does age affect MAC?
lower in the elderly
- not affected by sex, height or weight
the higher the % of MAC required, the ______the drug
less potent
what is lipophilicity?
the ability of a chemical compound to dissolve in fats, lipid, oils, etc
what is lipophilicity mechanism of action?
extremely lipophilic, therefore, their solubility disrupts the membrane lipid bilayer of cells, thus increasing the threshold to fire
the more lipid soluble an agent is, the more potent anesthetic it becomes = Myer-Overton Principle
what is MAC influenced by?
1- PULMONARY VENTILATION
2- PULMONARY BLOOD FLOW
3- WATER SOLUBILITY
how does pulmonary ventilation affect MAC?
can affect speed of induction- thus the more rapidly air is exchanged, the more rapidly anesthesia will be achieved
how does pulmonary blood flow affect MAC?
affects how quickly an anesthetic leaves the alveolus and enters the blood. the faster blood flows by the alveolus, the longer it takes to increase blood concentration of anesthetic.
Conversely, the more slowly blood passes the alveolus (due to decreased BP or decreased blood volume), the more rapidly anesthesia is induced
how does water solubility affect MAC?
anesthetics which are not very water soluble (lipid soluble) build up rapidly in the alveolus and approach the concentration required to produce unconscious.
A more water soluble drug will first mix in the large watery blood reservoir before sufficient concentrations are achieved in the alveolus to induce unconsciousness
what are the pharmacological effects of anesthesia?
1- block flow of sodium into neurons
2- enhance the inhibitory action of GABA
3- delays impulses and reduces neural activity
4- produces unconsciousness
5- produces lack of responsiveness to painful stimuli
when and why are intravenous anesthetics used?
used in situations that require short duration anesthesia (outpatient surgery)
used to supplement inhalation anesthetics
primarily used as adjuncts to inhalation agents
administered first
rapidly induce unconsciousness
what are some types of IV anesthetics?
Barbiturate
Benzodiazepines
Opioids
Propofol
Ketamine
Barbiturates:
Thiopental
Methohexital
*rapid onset and potent, but no analgesia
benzodiazepines:
Diazepam
Lorazepam
Midazolam
*produce sedation but not analgesia; produce amnesia
Opioids:
Fentanyl
*good analgesia; for intro-operative pain
Propofol:
commonly used for sedation during procedures or in the ICU
Ketamine:
rarely used in adults, good analgesia, produces delusions
adjuncts to anesthesia:
barbiturates
opioids
anticholinergic
dopamine blocker
phenothiazine
neuromuscular blocker
what are the 5 techniques for applying local anesthesia?
topical nerve block infiltration spinal epidural
what are local anesthetics?
amides and esters
stop axonal conduction
block sodium channels
causes rapid loss of sensation in limited part of body
local anesthetics reversibly block:
impulse conduction along nerve axons that utilize sodium channels to generate an AP
cocaine was the first such agent used but then abandoned due to its addictive properties
local anesthetics may be contraindicated in patients with:
cardiovascular conditions because they have anti arrhythmic properties
types of local anesthetics:
short acting procaine (1 hour)
intermediate acting lidocaine (1-2.5 hours)
long acting tetracaine (3-9 hours)
why are vasoconstrictor substances (such as NE) co-administered with local anesthetics?
to limit absorption and concentrate them at the site of injection
how are topical anesthetics applied?
directly to the skin or mucous membranes
what is the major topical anesthetic?
Benzocaine
Lidocaine and tetracaine can also be used topically
topical anesthetics are used to:
relieve or prevent pain from minor burns, irritation, itching
also used to numb an area before an injection is given
what are expected adverse effects of topical anesthetics?
skin irritation
hypersensitivity reactions
what are muscle relaxants?
drugs that affect skeletal muscle function
what are the 2 groups of muscle relaxants?
Neuromuscular blockers (NMJ)
Spasmolytics
what are NMJ blockers used for?
used in intensive care units to cause paralysis and as an adjunctive to anesthesia
indicated to relax skeletal muscles during surgery
to reduce the intensity of muscle spasms in electrically-induced convulsions
to manage patients who are fighting mechanical ventilation
nondepolarizing vs. depolarizing agents
what are spasmolytics used for?
used to reduce spasticity in a variety of neurologic disorders
what are non depolarizing agents?
curare alkaloids such as tubocurarine, pancuronium bromide, pipecuronium and vecuronium.
they block neurotransmitter action of ACh. NMJ agents do not cross the BBB and have no action on the CNS. For this reason, anesthesia is induced before neuromuscular blockade is started.
The neuromuscular blocking actions of tubocurarine may be revered with anticholinesterases such as neostigmine, pyridostigmine and edrophonium
what are depolarizing agents ?
(succinylcholine) cause excessive depolarization which desensitizes muscles and renders them UNREPSONSIVE
(depolarization– increased permeability to Na+ and K+)???
what is spasticity?
increase in tonic stretch reflexes
increased flexor muscle spasm
muscle weakness
reflex arc involvement
higher center involvement (“UMND”) affects descending pathways leading to alpha motor neurons hyper-excitability
what are spasmolytics?
skeletal muscle relaxing agents that relieve acute musculoskeletal pain, spasm or spasticity
types of spasmolytics (central)?
Carisoprodol
Baclofen
Diazepam
Tizanidine
carisoprodol is primarily used to:
used to treat acute, painful musculoskeletal conditions due to trauma, inflammation, and anxiety.
other drugs used for acute spasticity include: Chlorphenesin Chlorzoxazone Cyclobenzaprine Metaxalone Methocarbamol Orphenadrine
Baclofen is a:
GABA analog acting at GABAb receptors which depresses neuronal activity, decreasing the frequency and degree of muscle spasms and reduces muscle tone.
It is the drug of choice bc it produces less sedation than diazepam and less peripheral muscle weakness that dantrolene.
used for paraplegic or quadriplegic patients with SC lesions caused by either MS or trauma
Intrathecal Baclofen used for management of severe spasticity/pain when non responsive to medication by other routes of administration
diazepam is effective for:
both acute spasms and chronic spasticity.
indicated for patients with SC lesions or those with Cerebral palsy
anti-spasmolytic effect in part due to action in the SC (effective in patients with cord transection)
Tizanidine is related to:
clonidine
enhances both pre and postsynaptic inhibition in the SC. also inhibits nociceptive transmission (dorsal horn)
what are spasmolytics (peripheral)?
Dantrolene
what is dantrolene?
has similar effects to other central drugs but it works directly on the muscle by inhibiting calcium release necessary for muscle relaxation.
it is most effective for spasticity with cerebral origin (MS, Cerebral palsy)
