22 General Anesthesia I Flashcards
What is general anesthesia?
A pharmacologically-induced state of unconsciousness, amnesia, relaxation of skeletal muscles (immobility), and reduction in autonomic responses
What is amnesia?
Lack of recall
What is unconsciousness (hypnosis)?
Impaired perception and response to stimuli
What is analgesia?
The absence of pain sensation without loss of consciousness
What is premedication?
Sedation/anxiolysis before induction
What is induction?
Initiation of unconsciousness
What is maintenance?
The period during surgery
What is emergence?
Regaining consciousness
What is recovery?
Stabilization
What are the uses of volatile anesthetics?
Used for maintenance of anesthesia and for induction in some cases
What effects do volatile anesthetics produce (analgesia/amnesia/etc)?
Are they safe?
Amnesia
muscle relaxation
suppression of hemodynamic responses to surgical stimulus
Yes, safe
What are the 6 necessary characteristics of volatile anesthetics?
Absence of flammability vaporized at ambient temperature potent (low inspired percentage required) low solubility in blood minimal tissue metabolism produce skeletal muscle relaxation
In what drug class will some drugs have these additional good characteristics? suppress activation of sympathetic NS non irritating to airway low level of myocardial depression absence of hepatic and renal toxicity
volatile anesthetics
What is partial pressure?
What is the significance for a volatile anesthetic?
PP of a gas is expressed as a percent of all gases in a given volume
It is used to measure dosage
Where is partial pressure of a volatile anesthetic measured? What is that measurement estimating
It is measured in the alveoli, which is estimating the level in the brain
What does MAC stand for?
What is its significance?
MAC = minimum alveolar concentration
1 MAC = concentration of inhaled anesthetic that prevents skeletal muscle movements in response to a noxious stimulus in 50% of patients
It is a relative measure of depth of anesthesia and can be used to compare inhaled anesthetics
Useful index of potency
What is the significance of ~1.3MAC?
It prevents skeletal muscle movement in nearly all patients during surgery
How does the potency of NO compare to other inhaled anesthetics (-fluranes)?
Approximately what is its MAC?
Nitrous oxide is drastically less potent.
Its MAC is ~100 (105-110)
Which -flurane has the lowest MAC?
Desflurane
Isoflurane
Sevoflurane
Isoflurane - MAC=1.15
Which -flurane has the highest MAC?
Desflurane
Isoflurane
Sevoflurane
Desflurane - MAC=7.25
How does the solubility of volatile anesthetics change its affects?
Which is more preferable for a short surgery? High or low solubility?
Solubility is critical for the onset and elimination
High solubility = slow onset and offset
Low solubility = fast onset and offset
Low solubility more preferable for short surgery
How does solubility affect the partial pressure of an anesthetic gas in the blood? Why is this significant?
Anesthetic gases dissolved into the blood result in a decreased partial pressure in the blood. The partial pressure of the anesthetic gas in the brain produces general anesthesia
Anesthetic solubility = blood:gas partition coefficient
T/F
A high solubility means a greater blood gas partition coefficient
True
Anesthetic solubility = blood:gas partition coefficient
T/F
A high blood:gas partition coefficient means a greater effect on the brain than a low blood:gas partition coefficient.
False
High blood:gas partition coefficient -> high solubility -> lower concentration of gas having effect in brain
Which -flurane has the highest blood-gas partition coefficient?
Desflurane
Isoflurane
Sevoflurane
Isoflurane - 1.4
Which -flurane has the lowest blood-gas partition coefficient?
Desflurane
Isoflurane
Sevoflurane
Desflurane - 0.42
Which -flurane does NO have the closest blood-gas partition coefficient to?
Desflurane - 0.42
NO - 0.46
How is nitrous oxide often used because of its very high MAC?
as an adjunct to the potent volatile anesthetic agents
What receptors do volatile anesthetics affect? Do they primarily affect CNS or PNS?
Facilitate inhibitory neurotransmission at GABA and glycine receptors. Reduce excitatory glutamate transmission
CNS
How can the EEG be used with anesthesia?
It approximates anesthetic depth
Drugs strongly affecting what CNS receptors are used for anesthesia?
GABA and glutamate receptors
Drugs affecting what receptors have an effect on the properties of the administered anesthesia?
NE, ACh, and Hist
MAC sparing
What are general side effects/complications of volatile anesthetics?
Side effects: Respiratory depressants Decrease arterial blood pressure (decrease HR, CO, and systemic vascular resistance) - good for tachycardia during surgery but problem with hemorrhage hypotension) Complications: Malignant hyperthermia
What is malignant hyperthermia?
In susceptible individuals, anesthetics trigger increases in skeletal muscle metabolism, which overwhelms the body’s capacity to supply O2, remove CO2, and regulate body temp
What drugs can cause malignant hyperthermia?
Volatile anesthetics and succinylcholine
What drug treats malignant hyperthermia?
Dantrolene
