Licht: General Anesthetics I Flashcards
Describe the 4 stages of Anesthesia.
Stage 1: Analgesia and amnesia–Good
Start to lose sens of pain and sense of what is going on
Stage 2: Delerium–Get through quickely
Loss of consciousness, pt agitated/combatitive, breath-holding, vomitting
Stage 3: Surgical anesthesia–Start of surgery!
Respiration regular, autonomic reflexes depressed
Stage 4: Medullary depression–OVERDOSE
Cardiovascular collapse and severe respiratory depression
What is meant by “blanced” anesthesia?
What 4 drugs are used to produce the “combined” effect?
“Balanced” anesthesia requires the combined use of multiple drugs.
- General anesthetic- loss of awareness/consciousness
- Benzodiazepine- amnesia
- Opioid- Analgesia, BANS (blunts autonomic NS)
- Neuromuscular blocker- skeletal muscle relaxation (nicotinic blockers)
Why is it difficult to uncover the precise cellular mechanisms of anesthetic action?
There are NO knowon receptors that the inhaled anesthetics interact with.
The only thing we know is that they are LIPID soluble and change the lipid fluidity of membranes. (When you change the fluidity the receptors that are bound change and cannot be activated properly.)
IA Characteristics:
Diverse chemical structures, don’t interact with pharmacologically definied receptors, impact all physiological symptoms and affect the fluidity of membranes
What theories have been set forth to describe the cellular mechanisms of anesthetic action?
Second Gas Effect!
Rapid uptake of a FIRST anesthetic from alveoli into the blood creates a NEGATIVE pressure in the alveoli and draws MORE of the SECOND inhaled anesthetic agent whoe alveolar uptake might otherwise be slow.
This is how NO works. NO (which is quickly taken up but is NOT a good anesthetic when given alone) is used in combination with drugs that are often more slowly taken up.
This increases time for induction and recovery–> less time in stage II.
What are some pharmacological characteristics of inhalation anesthetics?
Dose Effect: Anesthesia is a dose (concentration)- related phenomenon
Because of the nature of gases, drug concentrations are expressed in terms of partial pressures.
Why is partial pressue of an inhalantion anesthetic more important in producing anesthesia than blood concentrations of an agent?
Drugs DISSOLVED in a fluid (blood concentration) do not raise the Panesthetic in that fluid. The higher the concentration that dissolves in blood the longer it takes to reach equilibrium and a greater concentration of anesthetic is required at equilibrium.
Partial Pressure is related to the amount of UNDISSOLVED drug in the blood.
(Henry’s Law)
What is the MAC value?
Why is it a useful index in anesthesiology?
Dose of anesthetic (%vol) producing surgical anesthesia in 50% of patient population.
Surgical anesthesia is usually attained at 1.3-1.5 MACS to have 100% of patients anesthetized.
Deep anesthesia is at 2 MACs.
Even if you double the concentration you still have room for 02.
How does potency relate to the MAC value?
What is the MOST potent drug?
What is the LEAST potent drug?
Anesthetics with the LOWEST MAC are the MOST potent.
Halothane
Nitrous Oxicde
Why can’t you produce surgical anesthesia with nitrous oxide?
Because you need 104% of anesthetic to be potent and this would still only produce anesthesia in 50% of pts. If you used 104% there would also be no room for O2.
What are the differences between blood: gas and blood: oil coefficients?
Blood/ gas Solubility function of water solubility
The more soluble a drug in the blood, the longer it takes to raise its partial pressure in the blood. (The more water soluble the SLOWER the onset)
Blood/oil Potency function of lipid solubility
The more lipid soluble an anesthetic the greater it’s potency (how fast it wil get to the brain)
Which drug is the most potent?
Which drug has the fastest onset?
Halothane is the most POTENT (need least amt of anesthetic to get anesthesia)
NO has the fastest onset (5x more soluble in the blood)
What variables influence anesthetic recovery and anesthetic elimination from the body?
What are the three routes of elimination?
The time course for elimination is the mirror image of inducion:
P delivered gas < P inspired gas < P alveolar gas < P arterial gas < P brain
Routes of elimination
Lungs, skin, can enter atmosphere
What happens during the metabolism of inhalant anesthetics?
Possible toxicity:
chemically reactive halide ions can acutely or chronically harm kidneys, liver and reproductive organs
Metabolism of inhalation anesthetics
Methoxyflurane (animals) > halothane (most liver/kidney toxicity) >> sevoflurane > isoflurane >> nitrous oxide
What makes some anesthetics more useful than othesr?
Potency- halothane (needs the leaset amt to get anesthesia)
Fast onset- NO
General anesthesia
State of CNS depression
Pt has a complete absence of sensations is and unconscious.
Conrolled and reversible
BANS
Blunting of the autonomic nervous system
One of the goals of general anesthesia
Induced by opioids
Balanced anesthesia
The use of mutiple drugs that leads to the desired effects of anesthesia
- General anesthetic - LOC
- Benzodiazepine - Amnesia
- Opioid- analgesia, BANS
- Neuromuscular blocker - skeletal muscle releaxation
Partial Pressure
Total P = sum of the Partial Ps of each gas in the mixture
Related to the amount of inhaled anesthetic you need to administer.
- You need 21% O2 to survive. The rest can be drugs.
- The less of the drug that dissolves in the blood the more effective/greater it’s partial pressure
Gases and volatile liquids
NO is the ONLY GAS.
All the other inhalation anesthetics are LIQUIDS.
Pts. inhale VAPORS coming off the LIQUIDS.
For each gas used, there is a constant percentatge that exists as vapor. This is what pts breath.
Oil: gas coefficient
The more lipid soluble the anesthetic the greater the potency.
(how fast it will get to the brain)
Blood: Gas Coefficient
The more soluble the drug is in the blood the longer it takes to raise the partial pressure and the slower it wil take effect.
Second Gas Effect
Rapid uptake of first anesthetic from alveoli into blood creeates a negative parial pressure in the alveoli and pulls in the second anesthetic
- First give NO- Not good alone, but allows for faster uptake of second drug, can decrease induction and recovery time
- Can lead to diffuse hypoxia during recovery–NO rappidly moves into alveoli from the blood and can leave no room for O2 in the blood
What is MAC?
Minimum alveolar concentration
- Dose of anesthetic producing surgical anesthesia in 50% of patient population
- Lower MAC value leads to a higher potency
- For surgical anesthesia use 1.3-1.5 MAC’s. Deep anesthesia at about 2 MAC’s
What are the characteristics of an ideal inhalation anesthetic?
- stable shelf life,
- compatible w/ existing equipment, i
- nexpensive, non-explosive,
- LOW blood solubility,
- POTENT,
- no caridopulmonary depression,
- no interaction w/ catecholamines,
- no irritating airways,
- good muscle relaxation,
- minimal metabolism,
- not toxic to kidneys
What are the common halogenated asthetics?
Halothane
isoflurane
methoxyflurane
sevoflurane
What are the common aspects of all halogenated anesthetics?
CNS effects
- decrease brain metabolic rate
- Increase cerebral blood flow
- increase intracranial pressure
CV effects
- Decreased myocardial contractility and stroke volume leading to lower aterial blood pressure
- Sensitizes myocardium to chatecholamines
Respiratory depression
Malignant hypothermia
What are two important side effects to remember related to halogenated anesthetics?
HA’s can lead to decreased myocardial contractility and stroke volume leading to LOWER arterial pressure. This is often treated with epiniephrine, but this can also trigger an arrythmia.
Inhaled anesthetics can also cause malignant hypothermia ( most commonly seen with halothane).
tx: Dantrolene to conteraact the CA being released causing muscle contraction and heat.
What are the advantages and disadvantages of using halothane to produce general anesthesia?
Advantages
- Potent (MAC .7-.9)
- Rapid induction and recovery
- least expensive and volatile
- doesn’t irritate larynx–no laryngospasm
Disadvantages
- Inadequate analgesia and muscle relaxation
- Depresses myocardium and baroreceptor reflexes ( decreased CO and PB)
- Sensitizes myocardium to catecholamines
- Potential for acute/chronic hepatic toxicity
- Malignant hyperthermia
Compare and contrast the effects of halothane, isoflurane, methoxyflurane and desflurane.
Halothane:
Potent, depreses myocardium, hepatic toxicity, malignant hyperthermia
Isoflurane:
Potent and rapid induction, doesn’t sensitize myocardium to E, less hepatotoxic, smells bad, malignant hypothermia
Methyoxyflurane:
Only used by vets- strongly metabolized
Desflurane:
Similar to isoflurane
Rank the inhalation of anesthetics from most metabolized to least metabolized
and
most likely to sensitize myocardium to catecholamines to least likely.
Methoxyflurane > halothane >> sevoflurane > isoflurane >> NO
Halothane > isoflurane, deflurane, sevoflurane > NO
Is sevoflurane an almost perfect inhalation anesthetic?
Yes!
Good potency and fast onset of action.
- High potency (low % of inspired gas)
- Low blood solubility: rapid onset, rapid recovery
- No liver/kidney toxicity
How does NO compare to other inhalation anesthetics?
- ONLY anesthetic that is a gas
- Advantage- low blood solubility (rapid onset)
- Disadvantage- MAC 104% so yo ucan’t use as sole anestehetic agent, no muscle relaxing effect, can cause diffusion hypoxia
Why are injectable anesthetics often used for anesthesia induction as well as for short-duration anesthesia?
- Very fast acting–basically no Stage II, used to get them up to stage II then add anesthetic gas
- Can be used for short operative procedures
Compare and contrast the use of barbituates and propofol for induction of anesthesia
Barbituates
- Rapid onset and short action, allow for quick recovery (used commonly for pulling teeth)
- GABA indcued CL entry into neurons
- Small window for error w/ dosing
Propofol
- **Rapid induction and recovery **
- Can be given to maintain anethesia or used for induction as part of balanced technicque
- Respiratory apnea and injection site pain in some patients
What is meant by the term dissociative anesthetic? What is an example? What is it best used for?
Disociative anesthetic- patietnt appears to be awake (eye open) but they’re unaware of their environment and can’t feel pain so you can do surgery on them. Patient is able to spontaneously breath throughout surgery.
Ketamine
Rapid onset and short duration of action.
Primarily used for induction and maintenance of anesthesia
What is the rational and use of opioids as anesthetics?
They have HIGH potency and they’re SHORT acting.
- Analgesia and anesthesia
- hemodynamic stability–good for patients with compromised myocardial function
- Respiration must be maintained artificially
- Usually supplemented with inahlation anesthetic, benzodizepine or propofol
