Inhaled Anesthetics: Part 1 Flashcards
What three groups do we categorize inhaled anesthetics?
Ethers, alkanes, and gases
What are examples of ethers? For inhalers anesthetics
Desflurane
Isoflurane
Sevoflurane
Enflurane
Ether
What are examples of Alkanes? For inhaled anesthetics
Halothane
Chloroform
What are examples of gases? For inhaled anesthetics
Xenon
Nitrous oxide
Cyclopropane
How many fluorine atoms does Isoflurane?
5 fluorine atoms and
1 chlorine atom
How many fluorine atoms are in desflurane?
6 fluorine atoms
How many fluorine atoms does Sevo have?
7 fluorine atoms
Which inhaled anesthetic has a bromine atom?
Halothane
What is vapor pressure?
The pressure exerted by a vapor in equilibrium with its liquid or solid phase inside of a closed container
What is vapor pressure directly proportional to?
Temperature
^ temperature = ^ vapor pressure
What is evaporation?
Process where a compound transitions from its liquid state to its gaseous state at a temperature below its boiling point
Vapor pressure is < atmospheric pressure
What is boiling?
Boiling occurs when vapor pressure = atmospheric pressure
What is the equation for partial pressure of a gas?
Vol% x total gas pressure = partial pressure of that particular gas
What can Isoflurane and desflurane produce in desiccated soda lime?
Carbon monoxide
What can Sevo produce? (even in hydrated soda lime)
Compound A
What is the vapor pressure and boiling point of Sevo?
VP: 157
BP: 59 degrees Celsius
What is the vapor pressure and boiling point of Des?
VP: 669
BP: 22 degrees Celsius
What is the vapor pressure and boiling point if Isoflurane?
VP: 238
BP: 49 degrees Celsius
What is the vapor pressure and boiling point of nitrous oxide?
VP: 38,770
BP: -88 degrees Celsius
What is the blood:gas coefficient and oil:gas coefficient of Sevo?
B:G ~ 0.65
O:G ~ 47
What is the blood:gas coefficient and Oil:gas coefficient for Desflurane?
B:G ~ 0.42
O:G ~ 19
What is the blood:gas coefficient and oil:gas coefficient for Isoflurane?
B:G ~ 1.46
O:G ~ 91
What is the blood:gas and oil:gas coefficients for Nitrous oxide?
B:G ~ 0.46
O:G ~ 1.4
What are some factors that will increase the FA/FI (wash in of anesthetic gases)
Increased fresh gas flows
High alveolar ventilation
Low FRC
Low time constant
low anatomical dead space
What are some factors that will decrease uptake? Aka cause a faster onset
Low solubility
Low CO
Low Pa-Pv difference
What is the vessel rich group? What does it contain and how much cardiac output does it receive? how much body mass is it?
Contains: heart, brain, kidneys, liver, endocrine
Body mass: 10%
CO: 75%
What are some factors that would cause a slower onset? Think decreased wash in
Low fresh gas flows
Low alveolar ventilation
High FRC
High time constant
High anatomical dead space
What are some factors that would cause a slower onset? Think an increase in uptake
High CO
High solubility
High Pa-Pv difference
What is the muscle group? What is it’s % mass and how much CO does it receive?
Contains: muscle and skin
% mass: 50
CO: 20
What is the Fat group? How much body mass does it contain? What % of CO does it receive?
Contains: fat
Body mass: 20%
CO: 5%
What is the hepatic biotransformation of Nitrous oxide?
0.004
What is the hepatic biotransformation of Des?
0.02
What is the hepatic biotransformation of iso?
0.2
What is the hepatic biotransformation of Sevo?
2-5
What is the hepatic biotransformation of halothane?
20
What is the FDA recommendation for Sevo and fresh gas flows?
FGF of 1L/min for up to 2 MAC hours and 2 L/min for > 2 MAC hrs
What byproduct of halothane s has been implicated in causing halothane hepatitis?
Trifluoroacetic acid (TFA)
What is the concentration effect?
The higher the concentration of inhalation anesthetic delivered to the alveolus (FA), the faster it’s onset of action.
This is also called overpressuring
Explain concentrating with Nitrous oxide.
Nitrous is more soluble than nitrogen (which is the primary gas in the lung)
When nitrous is introduced, volume of nitrous going from alveolus to blood is higher than nitrogen. This causes the alveolus to shrink ~ reducing alveolar volume and causing a relative increase in FA
What is the difference if the second gas effect and the concentration effect?
The concentration effect deals with a single gas, the second gas effect describes the consequences of the concentration effect when a second gas is co-administered.
The second gas effect produces a more meaningful benefit with what agents?
More soluble agents
ISO > Sevo > Des
What is diffusion hypoxia?
It’s when the nitrous that has accumulated in the body transfer back to the alveoli for elimination. This temporarily dilutes alveolar O2 and CO2 ~ leading to hypoxia and hypocarbia
How do you mitigate diffusion hypoxia?
Administration of oxygen 3-5 minutes after nitrous has been discontinued
What type of agents are affected the most in a right-left cardiac shunt?
Agents with low solubility (desflurane)
Because agents like ISO are more soluble, they are more dissolved in the blood, which offsets the dilution
How does a right-to-left shunt affect IV inductions?
Faster induction. Blood bypasses the lungs and travels to the brain faster
How does a left-to-right shunt affect volatile agents?
Does not have a meaningful effect on anesthetic uptake
How does a left-to-right shunt affect IV induction agents?
Slower IV induction
Agent is recirculating in lungs
If SF6 is placed for a retinal detachment, when should nitrous oxide be discontinued and when can it be restarted?
Discontinued: 15 mins before placement
Restarted: 7-10 days after
When should we avoid N2O after other types of bubbles?
Air: 5 days
Perfluoropropane: 30 days
Silicone oil: no contractindication
What is the most realizable way to check the internal pressure of an ETT or LMA?
Manometer
What vitamin does nitrous oxide irreversibly inhibit?
Vitamin B12, which then inhibits methionine synthase (which is required for folate metabolism and myelin production)
Risk of complications regarding nitrous oxide and B12 is increased by what pre-existing B12 deficiencies?
Pernicious anemia, alcoholism, strict vegan diet, recreational use of N2O
What is the potency of the volatile anesthetics from lowest to highest
Nitrous< Des< Sevo<ISO
MAC is a measure of what?
Potency
What is the MAC of all the anesthetics?
ISO: 1.2
Sevo: 2
Des: 6.6
Nitrous: 104
What is MAC-awake?
Alveolar concentration where a patient opens his or her eyes.
0.5 during induction
As low as 0.15 during recovery
What is MAC-bar?
The alveolar concentration required to block autonomic response following a painful stimulus
1.5 MAC
When are awareness and recall generally assumed to be prevented?
0.4-0.5 MAC
What are some things that increase MAC requirements?
Chronic alcohol consumption
Amphetamine intoxication
Cocaine
MAOIs
Ephedrine
Levodopa
Hypernatremia
Age (infants ^)
Hyperthermia
Red hair
What are some things that decrease MAC requirements?
Acute alcohol
IV anesthetics
N2O
Opioids
Alpha 2 agonists
Lithium
Lidocaine
Hyponatremia
Prematurity
Old age
Hypothermia
Hypotension
Anemia
CPB
Metabolic acidosis
Hypo-osmolarity
Postpartum period
PaCO2 > 95 mmHg
What are some things that have no effect on MAC?
Hypokalemia
Hypothyroid
Hypomagnesemia
Gender
Hypertension
What is the Meyer-Overton Rule?
Lipid solubility is directly proportional to potency of an inhaled anesthetic
What is the unitary hypothesis?
All anesthetics share a similar MOA, but each may work at a different site.
Generally speaking, volatile anesthetics have what effects on their target receptors?
They stimulate inhibitory receptors
They inhibit stimulatory receptors
What are some inhibitory pathways that volatile anesthetics stimulate?
GABA
glycine
Potassium channels
What are some stimulatory pathways that volatile anesthetics inhibit?
NMDA
Nicotinic
Sodium channels
Dendritic spine function and mobility
In the spinal cord, where so volatile anesthetics produce immobility?
Ventral horn
Which anesthetics do NOT stimulate the GABA receptor?
Xenon
Nitrous
(They have NMDA antagonism)
What are the pharmacological effects of volatile anesthetics? Think parts of the brain and spinal cord
Unconsciousness: RAS
Amnesia: hippocampus
Analgesia: spinothalamic tract
Immobility: ventral horn
What so volatile anesthetics do to hemodynamics?
HR: increase (iso/Des/nitrous) or maintain (sevo)
BP: decrease (except Des and xenon)
CO: decrease (except xenon)
SVR: decrease (except nitrous and xenon)
What aspect of the EKG do volatile anesthetics affect?
QT interval
What is the potency of coronary artery vasodilation?
ISO>Des>Sevo
How do halogenated anesthetics affect the respiratory pattern?
Reduce tidal volume
Increase RR
Impair response to carbon dioxide
Impair motor neuron output and muscle tone to the upper airway
(This increases dead space)
What does a decreased response to carbon dioxide do to the CO2 response curve? What are some causes?
Down and to the right
Causes: volatile anesthetics
Opioids
Metabolic alkalosis
Denervation if peripheral chemoreceptors
What happens when you increase the apneic threshold?
You increase the PaCO2 at which a patient is stimulated to breathe
What are some causes of a left shift in the CO2 response curve?
Anxiety
Surgical stimulation
Metabolic acidosis
Increased ICP
Salicylates
Doxapram
Which agents inhibit the hypoxic drive the most? Remember that it’s the reactive oxygen species that affect the glomus cells ~ there species occur after metabolism
Halothane > Sevo > ISO > Des
It goes in order of hepatic biotransformation
What is the best agent for a patient who relies on the hypoxic drive to breathe?
Desflurane
Where are the carotid baroreceptors located?
carotid sinus
Where are the carotid chemoreceptors located?
Carotid body
What do volatile anesthetics do to the cerebral metabolic rate?
Reduce it, but only to an isoelectric state
This is a 1.5-2.0 sevo MAC
What do volatile anesthetic do to cerebral blood flow?
Increase it.
They uncouple CMRO2 and CBF
This can be problematic with patients with increased ICP
How do volatile agents affect Cerebrospinal fluid volume?
Iso: increases absorption
Desflurane: increases production
Sevo: decreases production
What is the best way to preserve evoked potentials
TIVA
What so volatile anesthetics do to evoked potentials
Decrease amplitude
Increase latency
What is the max MAC you should use when monitoring evoked potentials?
0.5 MAC
Match each peripheral nerve with its function?
A Alpha: motor
A Delta: fast pain
B: preganglionic SNS
C: slow pain
What is the order of blockade in neural fibers
1st: B fibers (ANS fibers)
2nd: C fibers (slow pain, temp, touch)
3rd: A-delta fibers (fast pain, touch, temp)
4th: A-alpha (motor, proprioception)
Fibers that are more easily blocked have a _______ ____
Fibers that are more resistant to local anesthetics have a ________ ____
Lower cm
Higher cm
Where and when do local anesthetics bind?
Local anesthetics bind to the alpha sub-unit of the sodium channel when it is in the ACTIVE or INACTIVE states
What is a use-dependent or physic block?
The more frequently a nerve is depolarized and voltage-gated sodium channels open, the more time available for local anesthetic binding to occur and the faster the nerve will be blocked.
