Unit 3 Anesthetic Agents Flashcards
Anesthesia
loss of sensation or state without feeling
General anesthesia
Clinical state where there is an induced loss of consciousness or total insensibility (no pain) in a reversible manner
Full body, can cause decreased respiration, decreased blood pressure
Local anesthesia
limited to small area; minimal system disturbances
Commonly not adequate for many different procedures
Triad of anesthesia
Asleep, pain-free, still
Ideal anesthetic agent
Unconsciousness, amnesia, analgesia (no pain), skeletal muscle relaxation, areflexia, good minute-to-minute control
Is there any one drug considered to be an ideal anesthetic?
No
Use adjuvant drugs prior to anesthesia to make more safe & comfortable
Preanesthetic Medication uses
Relieve anxiety (benzodiazepines), Prevent allergic rxn (antihistaminics), prevent nausea/vomiting (antiemetics), analgesia (opiods), prevent bradycardia & secretion (atropine, glycopyrrolate)
4 phases of general anesthesia
Induction, Maintenance, Emergence, & Recovery
Induction phase
Initial administration until desired level is achieved
Maintenance phase
Desired level of anesthesia is maintained
Emergence phase
From sub-optimal concentration of anesthetic until it reaches zero
Recovery phase
From discontinuance of anesthetic agent until full restoration of function
4 Stages of Anesthesia
Analgesia, Excitement, Surgical Anesthesia, Medullary Depression
Analgesia Stage
1st stage
No pain, amnesia, euphoria; start to fall asleep
Excitement Stage
2nd stage Excitement, delirium, combative behavior
More asleep than stage 1
Want to get through this phase as fast as possible
Surgical Anesthesia Stage
Stage 3
Unconsciousness, regular respiration, decreasing eye movement
Want in this stage for surgery
Medullary Depression Stage
Stage 4
Do not want to enter this stage
Respiratory arrest, cardiac depression & arrest, no eye movement
Inhalable general anesthetics
Gasses/vapors
Usually used for maintenance of anesthesia
Can be used for induction in pediatrics
I.V. or fixed anesthetics
Used for induction & short surgical procedures
More common for maintentance
Anesthetic MOA
Depress spontaneous & evoked neuronal activity
Induce hyperpolarization, increase firing threshold (lesser activity), inhibit synaptic transmission & response to NT
Anesthetics may alter ion channels by
Increasing GABAa receptor Cl channel activity (enhance inhibitory NT), activate VG K channels (hyperpolarization & reduce activation), & inhibit glutamate NMDA receptors (decreased excitatory)
Advantages of inhalable anesthetic agents
Easy to control depth
Readily reversible, minute-to-minute control
Disadvantages of inhalable agents
Induction not as fast or smooth as fixed agents
Factors that affect rate of onset & recovery of inhalable agents
Anesthetic concentration in inspired air, pulmonary ventilation rate, solubility in blood & lipid, pulmonary blood flow, arteriovenous concentration gradient, elimination
Higher concentration of anesthetic in inspired air =
Higher partial pressure in lungs & Faster onset of anesthesia
Increase alveolar ventilation =
more gas molecules into blood/time & faster anesthesia onset
Less soluble in blood =
more rapid rise in partial pressure in blood & faster induction
However, also faster elimination from brain
More soluble in lipid =
more potent
high blood flow =
slower onset
Slower rate of uptake in alveolar/arterial =
fast induction
Minimum alveolar concentration (MAC)
concentration of anesthetic in inspired air at equilibrium when there is no response to noxious stimulus in 50% of patients
Lower MAC =
more potent anesthetic
Higher lipid solubility =
more potent anesthetic (lower MAC)
Anesthesia is produced when anesthetic px in brain is _____ MAC value
greater
Nitrous Oxide
Gaseous inhalation (laughing gas) Rapid onset & recovery (low blood/gas coefficient = poor solubility)
Nitrous Oxide advantages
Good analgesia
Relatively safe, nontoxic
Rapid onset/recovery
2nd Gas effect (reduces induction time for primary agent, which reduces required concentration & toxicity)
Nitrous Oxide limitation
Incomplete anesthetic
Low potency (insufficient for surgical anesthesia)
Diffusion hypoxia, increased risk of abortion & decreased conception probability
Nitrous Oxide Uses
Complimentary agent to other more toxic agents
Cannot be SOLE anesthetic
Minor procedures (dentistry) or EMS
Halothane
halogenated agent
Today not used often (poor analgesia & muscle relaxation), slower recovery, caused decreased cardiac output & hypotension, high incidence of post-op hepatitis
Enflurane
Halogenated
Not used often today - CNS stimulation effects (EEG convulsive pattern, jerking, twitching)
Isoflurane
Halogenated Used for maintenance Pungency limits mask induction Very long duration Lower toxicity
Desflurane
Halogenated
Fastest onset & recover, excellent minute-to-minute control
2nd most commonly used inhalable
More irritating to respiratory passages than others - bronchial irritation with cough & laryngeal spasm
Sevoflurane
Halogenated most commonly used
Mask induction, rapid onset & recovery, very potent, controllable (low solubility & high potency)
Low airway irritation
IV drug use
Induction (most commonly) & maintenance
IV drug advantages
Quick induction, rapid & complete recovery
IV drug disadvantages
Can’t reverse effects, slow elimination, CV & respiratory effects
Thiopental
Barbiturate
Commonly used induction agent
Rapidly diffuse out of brain & redistributes to other tissues (longer duration of action)
Highly soluble
Propofol
IV anesthetic
99.9% of all inductions, can be used as continuous IV drip
Good quality of recovery (awake, clear head)
Keatmine
IV anesthetic
Dissociative anesthesia - intense analgesia, catalepsy, & amnesia (can appear to be awake)
Non-competitive glutamate NMDA receptor antagonist
Emergence phenomenon - unpleasant dreams & hallucinations
Good for pts with
compromised cardiac status
Do NOT give to pts with psychiatric hx
Midazolam
Benzo
Good for sedation, amnesia, & anxiolytic properties (potentiate GABAa recepetors)
Local anesthesia
loss of sensation limited to a local area or region of body
Blocks generation & propagation of nerve impulse in a reversible, regional loss of function
Topical (surface) local anesthesia
To skin, wounds, burns, mucous membranes
Skin penetration is critical factor
Perineural Infiltration
injection of agent around specific area where anesthesia is desired
Easy to deliver to specific area
However increases potential for systemic absorption & toxicity
Nerve Block
Injection of agent around specific nerve to block conduction of sensory & motor fibers distal to block
Less drug required to block larger areas distal to injection site
However requires more skill/knowledge
Spinal Block
Injection of agent into CSF in lumbar subarachnoid space to reach roots of spinal nerve that supply specific region
More reliable block, return of CSF ensures correct location of needle
Conscious with minimal disruption of organ function
However no titration or reversibility, time limitations
Epidural Block
Injection of agent into extradural space & block nerve root as it passes through space
No time limitation, may be used 4-7 days post op
Less reliable than spinal block
Local anesthetic MOA
Blockade of VG sodium channels
Decrease in generation & conduction of action potentials
Local anesthetic amides
Metabolized in liver
Longer 1/2 life & longer duration of action than esters
Local anesthetic esters
Metabolized in plasma via BChE
Short plasma 1/2 life & duration of action
Minimum anesthetic concentration (Cm)
minimum concentration of drug for standard block
Relative standard of potency
Bigger fiber size =
greater Cm (more drug required)
Fibers blocked first
Smallest fibers & myelinated fibers
B-fibers first, A-alpha last
Increase in pH =
Decreased Cm (need less of drug)
Increased Ca concentration =
increased Cm
Vasoconstrictor substances
reduce local blood flow & reduce systemic absorption & reduce LA toxicity
Use epinephrine
Factors that affect reversal of local anesthesia
Dilution by ECF (high to low LA concentration), Absorption into circulation (most important factor), Redistribution to other areas, Use of vasoconstrictors
PABA (para-aminobenzoic acid) metabolite
Inactive metabolite from LA ester
Prone to allergic reactions
Hypersensitivity to LA
Esters most likely
Also commonly allergic to methyparaben (preservative)
Systemic toxicity to LA
Esters less likely because rapid metabolism
Bupivicaine adverse effects
systemic toxicity has cardiac selectivity that can lead to complete cardiac collapse & death
Treatment for LAST (local anesthetic toxicity)
IV lipid emulsion or IntraLipid
Absorbs circulating lipophilic toxin & reduces unbound free toxin available to bind to myocardium
Lidocaine
LA standard
Can be given topically & by injection
Most common for epidural going to C-section (2%)
Intermediate-duration procedures
Lidocaine toxicity
CNS excitation, TNS (transient neurologic symptoms) - increased sensitivity or pain to touch
Bupivacaine
Amide LA
Epidural infusion in labor & postoperative pain
Spinal anesthetic
Articaine
Amide LA
Dental anesthetic
Cocaine
ester LA
topical for ear,nose, & throat procedures
Benzocaine
ester LA Topical only (high lipid solubility)
Chloroprocaine
Ester LA
short duration procedures
Epidural agent for labor (especially C section) - lower risk systemic toxicity & fetal exposure
Exparel-Liposome
LA
encased bupivicaine - post op relief
very expensive
EMLA (eutectic mixture of local anesthetics)
LA mixture
Lidocaine + prilocaine
topical
TAC (tetracaine, adrenalin, & cocaine)
topical LA in pediatric ER
