Nervous System- Anesthetics by Schriefer Flashcards

Nitrous oxide
Terms Definitions
Nervous System- Anesthetics by Schriefer
Nervous System- Anesthetics by Schriefer
Uptake, Distribution and Elimination of Anesthetic Gases

Partial Pressure
the pressure exerted by a gas in a mixture of gases. For our purposes it is a measure of the CONCENTRATION of a gas.


Blood/Gas partition coefficient (λ) – a measure of the solubility of an anesthetic gas in the blood. lower the lambda, the faster the onset.
Nitrous Oxide
saturate the blood quickly, increasing the amount in the gaseous phase. goes from the blood into the body's tissues (esp. the brain)

this happens quickly because N2O doesn't saturate in the blood well.

faster onset. saturated and transfered more quickly.

lower the lambda, the faster the onset!

The speed of induction and emergent(recovery) is determined by the rate of change of the partial pressure (concentration) of the gas in the brain, which is determined by the partial pressure of the gas in arterial blood.
The best correlation with speed of induction is with blood/gas partition coefficient (inverse correlation).
Uptake, Distribution and Elimination of Anesthetic Gases:
Summary
During administration of an anesthetic, its concentration in blood rises toward that in the inspired gas.

Tissue concentrations rise also, approaching the concentration in the arterial blood. The concentration rises most rapidly in tissues with high blood flow, and lags in tissues with lower flow.

Eimination determined by the above factors operating in the reverse direction. lambda of 1 will go to sleep and wake up quicker than a lambda of 4
What is the therapeutic indices for general anesthetics?
Therapeutic indices for most general anesthetics is low (2-4); accurate control of dosage is necessary for safe use.

don't really kill because if you give too much, just turn it off, and the pt. will exhale the extra for you.
what is MAC?
Potency – for most drugs usually expressed as activity per unit weight administered. This expression not useful for anesthetic gases because no fixed dose is given

-Relative potency of anesthetic gases expressed as MAC
-MAC is defined as the Minimal Alveolar Concentration that will block movement of 50% of patients in response to incision
-MAC correlates with lipid/gas partition coefficient

sounds like the ED50 (effective dose)

if you're giving too much gas, you're not giving enough oxygen, so potency is a concern.

as MAC increases, the lipid solubility decreases. this means that if you give .76 halothane, half the patients will go to sleep. nitrous oxide isnt very potent because it's not very lipid soluble. halothane is very lipid soluble so it's more potent, so less you have to give, so the lower the MAC.
lambda onset

MAC potency
lambda onset

MAC potency
Efficacy... nitrous oxide vs a complete anesthetic
Efficacy – for anesthetic gases, efficacy is related to potency

Since most are extremely potent, they can produce all stages of anesthesia at low concentrations allowing sufficient O2 to the patient. These are known as complete anesthetics.

Nitrous oxide is an incomplete anesthetic because it can’t produce all stages of anesthesia without producing hypoxia (MAC = 105). Therefore N2O has less efficacy than a complete anesthetic.
Characteristics of an ideal general anesthetic (what do we want from our anesthetics?)
-Provide a smooth and rapid induction of unconsciousness
-Produce amnesia
-Block troublesome reflexes
-Produce skeletal muscle relaxation
-Produce analgesia
-Provide a smooth and rapid emergence and recovery without long lasting adverse effects


use combo of drugs to achieve these goals.
Preanesthetic Medications
Preanesthetic medications – drugs given generally prior to anesthesia (may be given during or after, as well) in order to:
-Decrease anxiety without producing excessive drowsiness
-Facilitate a rapid, smooth induction without prolonging emergence
-Provide amnesia for the perioperative period
-Relieve pre-and post-operative pain
-Minimize undesirable side effects of anesthetics
Conscious sedation”
used for colonoscopy. give a benzo. dont need an anesthesiologist.
Theories of Anesthetic Action
No single theory adequately explains how anesthetics exert their pharmacological effects.
Physical theories
Based on physico-chemical properties of anesthetics, e.g., lipid solubility. Are obsolete, but do explain how anesthetics reach site of action.
Receptor theories
State that anesthetics exert their effects by direct interactions with proteins (membrane receptors or in ion channels).
Most anesthetics directly and indirectly increase GABAA and glycine activity.
Anesthetics also generally inhibit the activity of excitatory transmitters acetylcholine (Nicotinic) and serotonin. Ketamine and nitrous oxide inhibit glutamate activity.
Thus neurons are hyperpolarized.
General pharmacological effects

CNS, ANS, CV, Respiration, Hypothermia
CNS – dose dependent depression of all portions of CNS. Order of sensitivity (most to least) is RAS and cortex → hippocampus → basal ganglia → cerebellum → spinal cord → medulla (irregularly descending anesthesia)

Autonomic nervous system: Inhibition of sympathetics; Stimulation of parasympathetics; Nausea and vomiting

Cardiovascular: Dose related negative inotropic effect; ↓ BP; Arrhythmias
Sensitization to circulating catecholamines (epinephrine); Increased cerebral blood flow and CSF pressure

Respiration: Dose dependent depression of medullary respiratory center

Hypothermia: Altered thermoregulatory control and reduced metabolic rate
Miscellaneous effects
Decrease lower esophageal sphincter tone
*Halothane hepatitis – free radical metabolites (immune phenomenon)
*Malignant hyperthermia – genetic susceptibility
Post-operative cognitive dysfunction
Anesthesia awareness (muscle relaxant w/o anesthetic)
what is the only anesthetic gas?
nitrous oxide

lambda 0.5
lipid solubility 1.4
MAC: 100 (incomplete anesthetic)

fast onset and recovery because of the low lambda
Name 5 volatile liquids

(inhalation = "-ane")
Halothane (Fluothane) ; MAC 0.8, lambda 2.4

Isoflurane (Forane) – commonly used anesthetic for adults; MAC 1.2 will put people to sleep

Enflurane (Ethrane) – like isoflurane, except increased risk of *seizures. Rarely used

Desflurane (Suprane) – similar to isoflurane except for more rapid emergence, and more irritating to airway. Commonly used.

Sevoflurane (Ultane) – similar to desflurane except not irritating to airway. Commonly used.

Methoxyflurane- renal nephrotoxicity
Intravenous agents

Thiopental
Thiopental- rapid acting barbiturate and used as an induction agent (put people to sleep); short duration of action not because it's metabolized quickly, but because of REDISTRIBUTION right to the brain, stored in the fat.

with repeated use, you get accumulation, giving slow recovery and a hangover.
General pharmacological effects

CNS, ANS, CV, Respiration, Hypothermia
CNS – dose dependent depression of all portions of CNS. Order of sensitivity (most to least) is RAS and cortex → hippocampus → basal ganglia → cerebellum → spinal cord → medulla (irregularly descending anesthesia)

Autonomic nervous system: Inhibition of sympathetics; Stimulation of parasympathetics; Nausea and vomiting

Cardiovascular: Dose related negative inotropic effect; ↓ BP; Arrhythmias
Sensitization to circulating catecholamines (epinephrine); Increased cerebral blood flow and CSF pressure

Respiration: Dose dependent depression of medullary respiratory center

Hypothermia: Altered thermoregulatory control and reduced metabolic rate
the most common induction agent nowadays is.... heeee heeeee heeeeeeeee oW!
Propofol. replacing thiopental. you can continue to give propofol for a long duration of time and you don't get that slow recovery. you can use it as a sole anesthetic agent if you wish.

fast onset, fast recovery. some CV and resp. depression. pain at the injection site.

milk of amnesia!
Miscellaneous effects
Decrease lower esophageal sphincter tone
*Halothane hepatitis – free radical metabolites (immune phenomenon)
*Malignant hyperthermia – genetic susceptibility
Post-operative cognitive dysfunction
Anesthesia awareness (muscle relaxant w/o anesthetic)
ketamine
Dissociative

causes psychomemeto effects.
doesnt put you to sleep, but to a dissociative state. if you throw nitrous oxide with it, you will go to sleep.

you get weird dreams, so you have to be quiet in the OR when the patient is waking up.

not used all that much.
Benzodiazepines:

diazepam, diazolam
not used much, need to use a good amount.

advantage is little CV and resp. depression

slow onset, slow recovery.
diazapam- action terminated by redistribution.
what is the only anesthetic gas?
nitrous oxide

lambda 0.5
lipid solubility 1.4
MAC: 100 (incomplete anesthetic)

fast onset and recovery because of the low lambda
when do you use etomidate?
used for short procedures (putting in chest tubes, etc) or intubation.

Fast onset, fairly fast recovery
Excitatory effects during induction and recovery, Adrenocortical suppression (when used for a long time)
Less cardiovascular and respiratory depression than with other iv drugs; Causes pain at injection site
Name 5 volatile liquids

(inhalation = "-ane")
Halothane (Fluothane) ; MAC 0.8, lambda 2.4

Isoflurane (Forane) – commonly used anesthetic for adults; MAC 1.2 will put people to sleep

Enflurane (Ethrane) – like isoflurane, except increased risk of *seizures. Rarely used

Desflurane (Suprane) – similar to isoflurane except for more rapid emergence, and more irritating to airway. Commonly used.

Sevoflurane (Ultane) – similar to desflurane except not irritating to airway. Commonly used.

Methoxyflurane- renal nephrotoxicity
Dexmedetomidine (Precedex) is what receptor type interaction?
α2 agonist

used in the ICU to keep intubated patients sedated.
Intravenous agents

Thiopental
Thiopental- rapid acting barbiturate and used as an induction agent (put people to sleep); short duration of action not because it's metabolized quickly, but because of REDISTRIBUTION right to the brain, stored in the fat.

with repeated use, you get accumulation, giving slow recovery and a hangover.
the most common induction agent nowadays is.... heeee heeeee heeeeeeeee oW!
Propofol. replacing thiopental. you can continue to give propofol for a long duration of time and you don't get that slow recovery. you can use it as a sole anesthetic agent if you wish.

fast onset, fast recovery. some CV and resp. depression. pain at the injection site.

milk of amnesia!
ketamine
Dissociative

causes psychomemeto effects.
doesnt put you to sleep, but to a dissociative state. if you throw nitrous oxide with it, you will go to sleep.

you get weird dreams, so you have to be quiet in the OR when the patient is waking up.

not used all that much.
Benzodiazepines:

diazepam, diazolam
not used much, need to use a good amount.

advantage is little CV and resp. depression

slow onset, slow recovery.
diazapam- action terminated by redistribution.
when do you use etomidate?
used for short procedures (putting in chest tubes, etc) or intubation.

Fast onset, fairly fast recovery
Excitatory effects during induction and recovery, Adrenocortical suppression (when used for a long time)
Less cardiovascular and respiratory depression than with other iv drugs; Causes pain at injection site
Dexmedetomidine (Precedex) is what receptor type interaction?
α2 agonist

used in the ICU to keep intubated patients sedated.
General pharmacological effects

CNS, ANS, CV, Respiration, Hypothermia
CNS – dose dependent depression of all portions of CNS. Order of sensitivity (most to least) is RAS and cortex → hippocampus → basal ganglia → cerebellum → spinal cord → medulla (irregularly descending anesthesia)

Autonomic nervous system: Inhibition of sympathetics; Stimulation of parasympathetics; Nausea and vomiting

Cardiovascular: Dose related negative inotropic effect; ↓ BP; Arrhythmias
Sensitization to circulating catecholamines (epinephrine); Increased cerebral blood flow and CSF pressure

Respiration: Dose dependent depression of medullary respiratory center

Hypothermia: Altered thermoregulatory control and reduced metabolic rate
Miscellaneous effects
Decrease lower esophageal sphincter tone
*Halothane hepatitis – free radical metabolites (immune phenomenon)
*Malignant hyperthermia – genetic susceptibility
Post-operative cognitive dysfunction
Anesthesia awareness (muscle relaxant w/o anesthetic)
what is the only anesthetic gas?
nitrous oxide

lambda 0.5
lipid solubility 1.4
MAC: 100 (incomplete anesthetic)

fast onset and recovery because of the low lambda
Name 5 volatile liquids

(inhalation = "-ane")
Halothane (Fluothane) ; MAC 0.8, lambda 2.4

Isoflurane (Forane) – commonly used anesthetic for adults; MAC 1.2 will put people to sleep

Enflurane (Ethrane) – like isoflurane, except increased risk of *seizures. Rarely used

Desflurane (Suprane) – similar to isoflurane except for more rapid emergence, and more irritating to airway. Commonly used.

Sevoflurane (Ultane) – similar to desflurane except not irritating to airway. Commonly used.

Methoxyflurane- renal nephrotoxicity
Intravenous agents

Thiopental
Thiopental- rapid acting barbiturate and used as an induction agent (put people to sleep); short duration of action not because it's metabolized quickly, but because of REDISTRIBUTION right to the brain, stored in the fat.

with repeated use, you get accumulation, giving slow recovery and a hangover.
the most common induction agent nowadays is.... heeee heeeee heeeeeeeee oW!
Propofol. replacing thiopental. you can continue to give propofol for a long duration of time and you don't get that slow recovery. you can use it as a sole anesthetic agent if you wish.

fast onset, fast recovery. some CV and resp. depression. pain at the injection site.

milk of amnesia!
ketamine
Dissociative

causes psychomemeto effects.
doesnt put you to sleep, but to a dissociative state. if you throw nitrous oxide with it, you will go to sleep.

you get weird dreams, so you have to be quiet in the OR when the patient is waking up.

not used all that much.
Benzodiazepines:

diazepam, diazolam
not used much, need to use a good amount.

advantage is little CV and resp. depression

slow onset, slow recovery.
diazapam- action terminated by redistribution.
when do you use etomidate?
used for short procedures (putting in chest tubes, etc) or intubation.

Fast onset, fairly fast recovery
Excitatory effects during induction and recovery, Adrenocortical suppression (when used for a long time)
Less cardiovascular and respiratory depression than with other iv drugs; Causes pain at injection site
Dexmedetomidine (Precedex) is what receptor type interaction?
α2 agonist

used in the ICU to keep intubated patients sedated.
Anesthetic Antagonists:

Naloxone (Narcan) and nalmefene (Revex) reverses
opioids
Flumazenil (Romazicon) reverses
benzodiazepines
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Term:
Definition:
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