Inhalational Agents Part 1 Flashcards
What are the three A’s of anesthesia?
Amnesia- loss of memory
Analgesia- loss of sensation and pain control
Areflexia- lack of movement (minimizes sympathetic and parasympathetic changes in vital signs)
What is a benefit to using gas over other agents?
Gas has the three properties of amnesia, analgesia, and areflexia versus other drugs would need to be combined to get all of these effects
Gases affect what areas of the body?
cerebral cortex, brain stem arousal centers, central thalamus, and spinal cord
Gases crosses
the blood brain barrier quickly because it is lipophilic, carbon based, and diffuses quickly
List the stages of anesthesia in order:
Stage 1: amnesia and anesthesia
Stage 2: delirium and excitation
Stage 3: surgical anesthesia
Stage 4: anesthetic overdose
What occurs in stage 1 of anesthesia?
light plain of anesthesia; initiation of anesthesia to the loss of consciousness; patient able to follow simple commands, protective reflexes remain intact, eyelid reflex intact
What occurs in stage 2 of anesthesia?
loss of consciousness and lid reflex, irregular breathing pattern, dilated pupils; neurons that inhibit excitation are not functional and can lead to vomiting, laryngospasm, cardiac arrest, and emergence delirium
Would not want to manipulate anything in this stage due to hyper-reactivity
What occurs in stage 3 of anesthesia?
cessation of spontaneous respirations; absence of eyelash response and swallowing reflexes
risk for aspiration because there’s no airway reflexes
What is stage 4 of anesthesia?
cardiovascular collapse requiring provider intervention
too much of a good thing
What does the respiratory pattern look like under gas?
smaller, more frequent breaths
What patient population tends to be exaggerated for their stages of anesthesia?
children
When we discuss the stages of anesthesia, we are typically discussing
emergence because we give them induction agents as well so we skip some stages
When we give a combination of agents,
we bypass stages such as stage 2 using sedation (benzodiazepines, alpha 2 agonists) and induction/maintenance (barbiturates, propofol, etomidate, ketamine, TIVA
What drugs are synergistic with gases?
analgesics: opioids, non-opioids
Paralytics: non-depolarizing & depolarizing
Adjuncts: regional anesthetics
Would need to give less gas in this situation
Choice of anesthesia is based on:
proposed surgery
patient comorbidities
provider experience
surgeon
Perioperative considerations include:
preoperative- anesthetic based upon assessment, proposed surgery, patient comorbidities, provider experience, and surgeon
intraoperative- married to our plan, need to have back up plan if surgeon is taking longer
postoperative: responsibility to follow up and make sure anesthesia worked
Absorption of inhalational agents are related to:
ventilation, blood uptake, cardiac output, blood solubility, alveolar to blood partial-pressure difference
Where do we measure the concentration of inhalational agents?
at the lungs because we make the assumption that what’s in the lungs is what’s in the brain
Administration of an inhalation agent involves
taking a liquid, vaporizing it, and delivering it to the brain
The main factors in anesthetizing a patient are
technical and machine related, drug specific, and patient factors such as respiratory, circulatory and tissue
What is MAC?
the minimum alveolar concentration (%) required to produce anesthesia (lack of movement) in 50% of the population
What conditions require increased MAC?
hyperthermia, drug-induced increases in CNS activity, hypernatremia, chronic alcohol abuse
assuming that we are using gas only
The dose of gas is expressed as
minimal alveolar concentration or MAC
MAC is
age dependent; peaks at 6 months and decreases with age
The faster the lung concentration rises
the faster anesthesia is achieved
MAC awake means
patients are not getting full anesthetic gas
Factors that decrease MAC include
hypothermia, increasing age, alpha-2 agonists, acute alcohol ingestion, pregnancy, hyponatremia
What are machine-related factors that impact our gas anesthesia?
Rubber and plastic machine pieces and CO2 absorbent can retain gas delaying initial uptake
-can retain small quantities of anesthetic gases so must be flushed
All inhalational agents can trigger
malignant hyperthermia (except nitrous oxide); a thorough flush at 10 L/min for 20 minutes, replacement of all breathing circuits and CO2 absorbent and removal of vaporizers
LIter flow of carrier gas is related to
air, oxygen, and nitrous oxide (less soluble so is able to bring gas along with it)