general anesthesia Flashcards
name the three stages for general anesthesia
induction, maintenance, recovery
name the three routes of administration
endotracheal/inhalation
intravenous
oral
endotracheal/inhalation route of administration
Blood volume completely passes through the lungs
• Re-breathing is facilitated by the carbon dioxide absorber
intravenous route of administration
Continuous and bolus dosing
• Route for supportive medications
oral route of administration
Pre-operative for pediatric patients
• To sedate the patient before placing intravenous lines
therapeutic monitoring
End tidal anesthetic concentration • Bispectral index • Level of sedation • Richmond agitation and sedation scale • Ramsey’s scale • Level of paralysis • Train of four
toxic monitoring
Vital signs • Blood pressure, heart rate and rhythm, temperature, oxygen saturation • Laboratory • Blood gas arterial • Blood gas venous • Electrolytes
mechanism of action for inhaled anesthetics
Block excitatory responses
• N-methyl D-aspartate (NMDA) receptors antagonist
decrease binding and action of glutamate, the main
excitatory neurotransmitter
• Blocking nicotinic acetylcholine receptors to reduce the
response to noxious stimuli
Potentiate inhibitory transmitters
• Activating glycine channels
• Activate GABAa
Two-pore-domain K+ channels in the neuronal cell membrane are activated leading to hyperpolarizing and delayed transmission
what does the uptake of inhaled anesthetics depend on?
Depends on:
• Solubility in body tissue (partition coefficients)
• The potential reservoir for soluble gases is
large and will be filled more slowly
• More soluble–>more likely to stay in the blood (high blood:gas partition
coefficient) = Slower onset
• Less soluble (low blood:gas partition
coefficient) = Faster onset
- Cardiac output
- Alveolar-venous partial pressure difference
nitrous oxide
Produces sedation and analgesia
• NMDA receptor antagonism and activation of two-poredomain K+ channels
• Concentrations between 20-50%
• Poor solubility in blood and other tissues leads to
quick equilibration
• Rapid induction and rapid emergence
• Low potency leads to little utility as a sole anesthetic
• Can be combined with other gases to quicken induction
• MAC of 105%
dont really give it in the hopsital. more in the abulatory setting
halogenated gases
Share similar mechanisms of action
• All can be combined with nitrous oxide to facilitate quicker
induction
• Advantages over earlier drugs such as diethylether
◼ Well tolerated
◼ Lower blood:gas solubility coefficient
◼ Non explosive
• Dose dependent decrease in cardiac output and blood
pressure
• Not analgesic
comparison of inhalation anesthetics
The more soluble an anesthetic is in blood, the more of it must be dissolved in blood to raise its partial pressure in the blood
Halothane
Slow induction and slow recovery
• Lowest cost of halogenated gases
• Cardiac effects
Direct myocardial depressant
Predictable decrease in arterial blood pressure of 20-
25 mmHg
Sensitizes the myocardium to epinephrine and
circulating catecholamines –>Ventricular arrhythmias
Decreases auto-regulation in end organs, decreased
perfusion to gut, liver, and kidneys
• Bronchodilator: May be used in resistant status asthmaticus
• Some metabolism by the liver, may cause oxidative stress
and potential hepatic necrosis
more about halothane
Due to side effect profile compared to other agents:
• Little utility as a general anesthetic in the U.S.
• May be used globally in low resource areas
• Some utility as a treatment for asthma
Desflurane
Very low blood:gas, rapid induction and recovery
• Irritating to airway so not often used for induction
• Cardiac effects
Decreased blood pressure due to decreased systemic
vascular resistance
Does not subside with duration of anesthesia
Increased heart rate due to sympathetic stimulation
• Respiratory effects
Decreased ventilation, increased carbon dioxide retention, potential laryngospasm
Sevoflurane
Rapid induction and rapid recovery from anesthesia
• Some metabolism by the liver
• Some interaction with carbon dioxide absorber soda lime
Produces compound A which is speculated to increase
nephrotoxicity
• Cardiac effects
Decreased blood pressure due to decreased systemic
vascular resistance
Does NOT increase heart rate
• Respiratory effects
Decreased ventilation
Bronchodilation (most potent of all halogenated gases)
and not irritating so suitable for induction
Isoflurane
Low blood:gas, quick induction and quick reversal of
anesthesia
Due to pungent odor rarely used for induction but can be used for maintenance
• Cardiac effects
Decreased systemic vascular resistance leading to
decreased blood pressure
Dilation of coronary and cerebral vessels Increased heart rate due to sympathetic stimulation
• Respiratory
Decreases ventilation, concentration-dependant
• May be preferred in cardiac or neurosurgery
Malignant Hyperthermia
Can be induced by all halogenated gases
• Due to genetic predisposition
• Can also be induced by depolarizing neuromuscular
blockers
• A condition of severe muscle contraction that is
fatal if left untreated
• Hyper-metabolic state that depletes adenosine
triphosphate (ATP)
• Discontinuation of the anesthetic and
administration of dantrolene are the life-saving
treatments
Intravenous Anesthetics
Can be given with or without inhalation agents
• Also used for moderate sedation
• Endotracheal intubation not necessary
• Used to facilitate one or more desired outcomes of
anesthesia
• Analgesia, amnesia, sedation, or immobility
• May be given in place of inhalation anesthetics in
high risk patients or for induction
Barbiturates (WONT BE TESTED ON)
thiopental
methohexital
thiopental
Anesthetic effect in 30s, lasting 5-8 minutes • Duration of action increases with prolonged use • Half-life about 11 hours • Use limited to induction • May cause transient hypotension and tachycardia • Should be avoided in patients with abnormalities in porphyrin metabolism`
METHOHEXITAL
Similar onset and duration to thiopental • Shorter half-life of 4 hours • Injection site pain • Potential for excitatory reactions • Hiccoughs, movements, seizures • Limits utility
opioids
fentanyl
sufentanil
remifentanil
propofol
The most commonly used • Rapid onset and short duration • Potentiates GABA, NMDA antagonist • Formulated in a lipid emulsion ◼ Contains soy and egg
advantages of propofol
Quick onset and short duration • Predictable patient response and pharmacokinetics • Decreases intracranial pressure • Desired for neurosurgery • Little to no post-operative nausea and vomiting • Generally well tolerated
disadvantages of propofol
Hypotension • Direct myocardial depressant • Decreased peripheral vascular resistance • Apnea • No analgesic properties • Allergies • Lipid formulation • Hypertriglyceridemia • Infusion syndrome
ketamine
NMDA receptor antagonist
• Causes amnesia, analgesia,
and catalepsy
• Disassociative anesthesia
Sympathetic stimulation
Increased peripheral and pulmonary vascular resistance Increased heart rate Can produce hallucinations (pre-medicate with benzodiazepine)
• No respiratory depression
• Onset within 1 minute
• Duration 10-15 minutes
• Half-life about 2 hours
• Most utility in children
Less susceptible to
hallucinogenic and
emergence effects
Etomidate
Modulation of GABA
• Quick onset and short duration
• Adrenal insufficiency through prolonged infusion
May be observed after a single dose
• Well tolerated and a preferred agent for induction
or intubation
Little respiratory depression
Favorable cardiac effects
Dexmedetomidine
Central alpha 2 receptor agonist
Specific for the alpha 2a receptor producing more
sedation than cardiovascular effects
Decreased norepinephrine release from central
nervous system
• Sedation with ease of wakening with stimulation
Not intended for deep sedation
• No respiratory depression
• Bradycardia and hypotension are most common side
effects
Adjunctive Agents
Anti-emetics
• Given peri-operatively to prevent post-operative nausea and vomiting
-Anti-inflammatory agents
NSAIDS such as ketorolac
Acetaminophen
• Peripheral vasoconstrictors
To mitigate the peripheral vasodilation from anesthetics
• Anti-histamines
Decrease histamine release from anesthetic agents
Augment sedation Decrease anxiety
Anti-muscarinic agents
Decrease respiratory secretions
Mitigate cardiovascular effects
• Neuromuscular blocking agents
To immobilize the patient Adequate sedation and analgesia are necessary BEFORE administration
Higher risk of malignant hyperthermia if depolarizing agents used with halogenated gases
