Exam 10: General Anesthetics Flashcards
purpose of atropine pre-op
Prevent bradyarrhythmias that can be caused by general anesthesia
Fast acting IV agent used to induce anesthesia
Propofol
Inhaled anesthetics used to maintain anesthesia after propofol
N2O plus another inhaled general anesthetic (-flurane)
emergence excitement
5-30% of patients experience restlessness, crying, moaning, thrashing when they come out of anesthesia
Drug that can be used to combat shivering due to hypothermia post-up
Merperidine
What property of inhaled anesthetics greatly affects how fast they work?
Water (blood) solubility
High solubility = slow induction
Low solubility = fast induction
Measurement of water solubility
Blood/gas partition coefficient
(concentration in blood)/(concentration in lung) when gas is in equilibrium
how quickly does N2O work? Why?
Fast
poorly soluble in blood (low blood/gas partition coefficient
How do we measure potency of inhaled general anesthetics?
MAC
Minimum Alveolar Concentration
Inhaled concentration for 50% of patients to not respond to pinprick pain
How does MAC relate to lipid solubility?
More lipid soluble = more potent
Less lipid soluble = less potent
What’s weird regarding lipid/water solubility of anesthetics?
Poorly water-soluble agents aren’t necessarily highly lipid soluble
Ex. N2O has low lipid and water solubility (fast induction, but low potency)
What’s a really good way to find out how conscious a sleeping patient is?
BIS
Bispectral Index
real time computer analysis of patient EEG
Give you a 0-100 scale from deep coma to awake
N2O side effects (3)
- air pockets (middle ear)
- Blood pressure change
- Depresses ventillary response to hypoxia
What is one side effect that N2O does NOT have compared to the other inhaled GAs/
Malignant hyperthermia
Inhaled anesthetic still used in 3rd world. Side effects?
Diethyl ether
Cheap, effective but irritates airway and is flammable
Problem with cyclopropane
Spontaneous combustion
Side effect of halothane
decreased BP at 1 MAC Vasodilation Decreased cardiac output bradycardia Decreased GFR Decreased ventilation rate Halothane hepatitis
Pharmacokinetics of halothane
Blood:Gas partition = 2.3
Slowest induction, recovery
Rare, 50% fatal side effect of halothane
Halothane Hepatitis
Enflurane odor
Sweet
Halothane metabolism
liver
Enflurane side effects
Produces electrical seizure activity, though no
evidence, contraindicated for epileptics
Isoflurane odor
Pungent
Where is isoflurane excreted?
99% unchanged excreted from lungs
Preferred inhaled GA for neurosurgery? Why?
Isoflurane
Modest vasodilation in cerebral vasculature, but metabolic rate of brain is decreased
Desflurane disadvantage
Irritating- causes coughing, secretions
you have to induce with IV before giving them this
Where is desflurane excreted?
99% unchanged excreted from lungs
Sevoflurane excretion
99% unchanged excreted from lungs
Potential danger of sevoflurane
Causes CO2 absorber to heat up, could potentially cause a fire
Advantage of sevoflurane over desflurane?
Non-irritating to airway, so you can use it to induce
Preferred inhaled GA for patients prone to myocardial ischemia? why?
sevoflurane
does not change cardiac output
2 characteristics of IV general anesthetics
- Act fast (
Sodium thiopental mechanism
Barbiturate
Enhances effects of GABA at GABAA receptors
Sodium thiopental metabolism
Liver
Sodium thiopental side effects
Decreases brain metabolic rate, ICP, and cerebral blood flow
Decreases heart contractility and causes vasodilation
Decreases ventilation
Interesting use of Sodium thiopental
Lethal injection
Propofol constitution
Super fatty (white)
Careful with patients with high triglyceride levels
Not water soluble
Most common agent of induction of anesthesia in the USA
Propofol
Advantage of propofol over Sodium thiopental
no hangover (faster discharge, better outcomes)
propofol mechanism
Enhances effects of GABA at GABAA receptors
Side effects of propofol
- Decreased ventilation (even more than Sodium Thiopental)
- Major decrease in BP (vasodilation and less heart contractility)
- May hurt on injection
Advantages of propofol
Safe in pregnant women
Anti-emetic properties
Who might be good patients with whom to use Etomidate?
Those prone to hypotension
Mechanism of Etomidate
Enhances effects go GABA at GABAA receptors
Also activates GABAA receptors without GABA being present
Side effects of etomidate
Pain on injection
Myoclonic movements
Nausea/vomiting
Inhibit adrenal gland synthetic enzymes
Advantage of Etomidate over propofil
It doesnt decrease BP or cardiac output
Ketamine advantage
Produces profound analgesia
Ketamine mechanism
NDMA antagonist
Inhibits voltage sensitive Na, K channels
Side effects of ketamine
Increased cerebral blood flow Emergence delerium (1 hr post emergence, hallucinations, vivid dreams)
Ketamine effects of ventilation
Modest decrease in ventilation
Bronchodilation
Ketamine effects of CV system
Increases BP, CO and HR
useful for patients at risk of hypotension
Ketamine effects of urogenital system
Caron abuse leads to severe deterioration of the urinary bladder
What is the point of GA adjuncts
Decrease the dose of GA needed to reach desired anesthesia
“Balanced anesthesia”
Best benzo pre-op sedation (amnesia)
Midazolam (versed)
it is water soluble, the others aren’t
also doesn’t irritate blood vessels
Role of opioids in anesthesia
Minimize vascular reflex to noxious, painful stimuli
Potent analgesics, since only ketamine of the anesthetics has effective analgesic properties
Side effects of opioids
Nausea, vomiting
Decreased ventilation, HR, BP
What opioid has the shortest duration of action?
Remifentanil
Dexmedetomidine use in anesthesia
Alpha 2 agonist
Used for sedation (off label)
Does not decrease ventilation, so it is useful in non-intubated patients
How does anesthesia contribute to hypothermia?
Vasodilation is a side effect of most of the anesthetics we talked about (convective heat loss)
Mechanism of malignant hyperthermia
Ryanodine calcium channels do not close, leading to uncontrolled muscle contraction and heat generation
How can malignant hyperthermia kill you fast
Myocytes eventually lyse, releasing potassium which can cause fatal cardiac effects
Treatment for malignant hyperthermia
Dantrolene
Dantrolene mechanism
Ryanodine receptor inhibitor