Week 5: Inhalational Agents Flashcards
Until middle of the ______ century surgery was done without anesthesia
19th
1840’s - _________, ________, and ________ were the first accepted general anesthetics.
Nitrous oxide
Diethyl ether
Chloroform
October 16, 1846 - ___________ demonstrated Ether for anesthesia at Massachusetts General Hospital
William Morton
When did the specialty of anesthesia start?
1940’s
gaseous phase of a substance at a temperature which the substance can exist in either a liquid or a solid state below a critical temperature for that substance.
Vapor
Potent inhaled anesthetics are mostly in the _____ state at normal room temperature (20 C) and atmospheric pressure (760 mm Hg)
Liquid
** Desflurane kept in special bottle so it remains liquid.
Anesthesia vaporizers facilitate the change of a liquid into a vapor (T/F)
True
Heat of vaporization
is the number of calories required to change 1 gram of liquid into vapor without changing temperature
temperature at which vapor pressure equals atmospheric pressure (760 mmHg)
Boiling point
one in which the total gas flow is divided in two streams by a variable resistance proportioning valve. Usually a small percentage enters a vaporizing chamber, picking up molecules of volatile agent, while the majority travels through a bypass line.
Variable bypass vaporizer
*** Agent specific and concentration calibrated
READ ALL THIS IS REVIEW!!
Contains an electrical filament that heats the desflurane to 39 degrees C.
Raises the Saturated Vapor Pressure
The high pressure removes the need for a pressurized carrier gas
The fresh/diluted gas is separate from the vaporizing pressure
Desflurane is added directly to the fresh gas
The delivered concentration is adjusted by the vaporizer dial.
Tech 6 Vaporizer (Desflurane)
What would make an inhalational agent ideal?
- non-purgent
- non-flammable
- fast induction
- Fast-wake up
- No harmful metabolites
*** no perfect one exists.
General anesthesia is characterized by:
Altered state
Analgesia
Muscle relaxation
Amnesia
Reversible loss of consciousness.
Phases of General Anesthesia
Induction, maintenance, and emergence.
*All of these phases are affected by the pharmacodynamics and pharmacokinetics of the inhalational anesthetics
An Anesthetic state is obtained with a combination of 3 things:
Amnesia,
Analgesia, &
Lack of response to noxious stimuli
States the lipid solubility is directly proportional to the potency of an inhaled anesthetic.
The greater the solubility the lower the MAC value
Myer-Overton Theory
The greater the solubility the_____ the MAC value
lower
The depth of anesthesia is determined by the number of anesthetic molecules that are :
dissolved in the brain
All inhalational anesthetics work via a similar mechanism of action but not all the same sites
What theory?
Unitary Hypothesis
Inhaled anesthetics do what to these:
GABA/ Glycine
Glutamine
Calcium Channels
Potassium
Enhance inhibitory sites/receptors (GABA, Glycine).
Inhibits excitatory channels (Glutamine).
Inhibits calcium channels (Ca2+).
Inhibition of potassium (K+).
Immobility is mediated principally by effects of inhalationals on the
spinal cord
The ultimate effect of inhalational anesthetics depends on reaching a therapeutic level in the
CNS/Brain/Spinal Cord
Sites of Anesthetic Action for unconciousness
Reticular activating system - (Cortex, thalamus, brainstem).
Sites of Anesthetic Action for Analgesia
Spinothalamic tract
Sites of Anesthetic Action for Amnesia
Amygdala, hippocampus.
Sites of Anesthetic Action for immobility
ventral horn.
Ideal Characteristics of Inhaled Gases
Pleasant to inhale, smooth induction and emergence.
Rapid induction and emergence (low solubility).
Easy to administer and analyze, cheap.
Stable in carbon dioxide absorbers, inflammable, not metabolized.
Have a specific site of action.
No CV or respiratory side effects, nontoxic and provides pain control, muscle relaxation and no side effects.
Low solubility of inhaled anesthetics allows for:
Rapid induction and emergence
Anesthesia depth can be assessed by:
Lack of movement in non-paralyzed patient.
Respiratory rate and pattern.
Eye signs?
BP and Pulse values
BIS monitoring?
Effects of anesthetics are dose dependent. _____ & ____occur at lower levels while ________ occurs at much higher levels.
Amnesia & LOC;
Immobility
Conceptualized by Dr. Arthur Guedel during World War I
Guedel Chart
**originally divided into 4 stages.
Guedel Chart was First published in ______. and Depicted the signs and symptoms of ______ anesthesia.
1937;
Ether
Guedel’s Stages of Anesthesia
Stage I
induction to loss of consciousness
Guedel’s Stages of Anesthesia
Delirium with period of excitement, pupils dilated, disconjugate gaze, increased RR/HR, High risk of laryngospasm/bronchospasm
Stage II
Guedel’s Stages of Anesthesia
Surgical plane, fixed gaze, constricted pupils
Stage III
** desired maintenance stage.
Guedel’s Stages of Anesthesia
Overdose, absent or shallow/irregular RR, hypotension/profound CV collapse, dilated/unresponsive pupils
Stage IV
What is an Inhalational Induction?
who is it most common in?
Use of inhalational agents to induce a state of surgical anesthesia from a state of full consciousness
*Most common technique for inducing anesthesia in children undergoing elective surgery.
______ can help speed inhalational induction through the second gas effect.
Nitrous oxide.
*ask patient to take vital capacity breaths or tidal volume breathing.
Inhalational induction of anesthesia with patient breathing normal tidal volumes is _________ than IV and a __________ of a high concentration.
Slower;
gradual increase.
Inhalational induction with vital capacity breaths:
They are _________ than tidal volume breaths but not as __________ as IV inductions.
Quicker; quick
**prime bag with high concentration of gas.
A kid crying is more likely to go to sleep than a calm one with inhalation induction (T/F)
True-
Kid is doing vital capacity breaths.
Two main inhaled Agents for Inhalational Induction
Nitrous oxide (N2O) and Sevoflurane.
*** because it is less irritating, faster, and N2O will help speed it through second gas effects.
N2O and Sevoflurane are used in inhalational induction because they have low incidence of:
&
It is not recommended to use which agent?
-Breath holding
- Coughing
-Secretions
-Laryngospam
*Desflurane.
T/F - Volatile agents can relax airway smooth muscle and produce bronchodilation
True
** sevoflurane and N2O are good at this!!
Patients undergoing inhalational induction exhibit the stages of anesthesia (Especially ________ phase).
Excitement
Phase II
IV induction does not bypass the second phase of anesthesia (T/F)
False - it bypasses second phase.
Pt. pretty much right to sleep.
What are the advantages of inhalational induction?
- Less traumatic
- If no IV access (* specially kids).
- Short pediatric case.
- Bronchodilator effect.
Disadvantages of inhalational induction:
- Smell/irritant
- Excitatory stage (phase II).
- Delayed airway.
- Gas bypassing scavenger system.
MAC is defined as the inhalational anesthetic concentration/alveolar concentration at which 50% of the population will not :
MOVE to painful or noxious stimulus (e.g., surgical incision).
MAC values are sometimes expressed as anesthetic _________.
That is the lower the MAC value the more ______ the agent.
Potency.
Potent.
MAC varies _____ % to _______% among individuals
10 - 15%
MAC mirrors _______ partial pressure
Brain
Potency is directly related to ________. (_________ coefficient)
solubility;
Oil:gas
MAC values are ________: 0.5 MAC of N2O used with 0.5 MAC of Sevoflurane will give an effect of 1.0 MAC anesthetic
additive.
Desflurane has a ______ MAC = _______ potency = _______ solubility.
High MAC;
Low potency,
Low solubility.
Isoflurane has a ______ MAC = _______ potency = _______ solubility.
Low MAC value;
High potency;
High solubility.
MAC-BAR
Range:
MAC needed to Block Autonomic Response to painful stimuli.
or
“Blunt Adrenergic Response.”
Range: 1.5-2.0 MAC
2 MAC- awake:
Range:
alveolar concentration at which patient opens their eyes.
0.15 - 0.5 MAC
*** 0.4-0.5 to lose consciousness and 0.15 to regain it
Awareness MAC
Range:
Important for which patients?
Awareness and recall usually thought to be prevented.
0.4- 0.5 MAC
Trauma patients.
Movement MAC :
Range:
will prevent movement in 95% of surgical patients
1.2- 1.3 MAC
Nitrous Oxide MAC / VP
104 MAC
38,770 VP.
Isoflurane MAC/VP
1.17 MAC
244 VP
Sevoflurane MAC/VP
1.8 MAC
157 VP
Desflurane MAC/VP
6.6 MAC
669 VP
From most potent to least potent:
Des, Iso, Sevo, N2O.
Isoflurane> Sevoflurane> Desflurane> N2O
Factors that DO NOT alter MAC.
- Thyroid function (not directly.
- Anesthetic metabolism: since is <5%.
- Hyperkalemia.
- Hyper/Hypocabia
- Gender
- Duration of anesthesia.
- Metabolic alkalosis.
Factors that increase MAC:
-Hyperthermia
-Hypernatremia
-Drugs that increase CNS catecholamine levels (MAO inhibitors, cocaine, ephedrine, levodopa).
-Excess pheomelanin production (women with natural red hair)
-Chronic ethanol abuse
Factors that decrease MAC:
- Hypothermia
- Preoperative medications.
- Older age
- Pregnancy
- Alpha agonists
- Acute alcohol ingestion
- Hyponatremia
- Induced hypotension - - MAP<50mm Hg.
- Lots of drugs (Lidocaine, Lithium, Ketamine, opioids, benzos).
- Severe anemia
Older age decreases MAC by 6% per decade after age _____.
40
Hyporthermia decreases MAC by ______% per Celcius drop.
2-5%
Pregnancy decreases MAC by ____%
30
Inhaled anesthetics are slow acting, they slowly increase and decrease the anesthetic level.
(T/F)
False:
Rapid acting
Quickly increase and decrease the anesthetic level
Which is a true gas?
Nitrous oxide (N2O)
** that’s why it is on cylinder.
Which are the so-called “potent inhaled anesthetics” ?
They are the vapors of volatile liquids.
** but all are refer to as gases because thats how they are administered to patient.
All ________ with ______ molecular weights so they diffuse rapidly.
nonionized; low
Major advantage of inhaled anesthetics?
They can be delivered to the bloodstream via the lungs
Sevoflurane
Boiling point:
Blood:gas partition coefficient:
Oil:gas partition coefficient:
B.P= 59C
B:G = 0.65
O:G = 47
Desflurane:
Boiling point:
Blood:gas partition coefficient:
Oil:gas partition coefficient:
B.P= 24C
B:G = 0.42
O:G = 19
Isoflurane:
Boiling point:
Blood:gas partition coefficient:
Oil:gas partition coefficient:
B.P= 49C
B:G = 1.46
O:G = 91
Nitrous Oxide:
Boiling point:
Blood:gas partition coefficient:
Oil:gas partition coefficient:
B.P= - 88
B:G = 0.46
O:G = 1.4
At equilibrium, CNS partial pressure equals _____ partial pressure, which in turn equals ______ partial pressure.
blood;
alveolar
3 factors that result in equilibrium:
Inhaled are gases that quickly transfer BIDIRECTIONALLY via the lungs to and from the ________, then to and from the ________.
Plasma and tissues have a _____ capacity to absorb the anesthetic.
Metabolism, excretion, and redistribution are ________ relative to the rate they are delivered and removed from the _______.
Bloodstream ; CNS
Low
Minimal; Lungs.
What is the goal of inhalational anesthetics?
How is this goal achieved?
Establish a specific concentration of anesthetic molecules in the central nervous system
This is done by establishing the specific partial pressure of the agent in the lungs that equilibrates with the brain and spinal cord
Which factors increase the speed of onset of inhaled anesthetics? (4)
- High inspired concentration (dialing more).
- High alveolar minute ventilation : asking patient to take fast breaths.
- Low blood solubility
- High MAC
determined by flowmeter settings and vaporizer
fresh gas flow (FGF).
The fractional concentration of anesthetic leaving the circuit. Determined by FGF, breathing circuit volume and circuit absorption.
Fraction Inspired (FI) gas concentration.
The fractional concentration of anesthetic present in the alveoli. Determined by uptake, ventilation, the concentration effect and second gas effect.
Fraction Alveolar (FA): alveolar gas.
affected by ventilation perfusion mismatch
Fraction Arterial (Fa): arterial gas.
Goal is anesthetic state in the CNS/Brain.
This creates a gradient that leads to equilibrium between the _______ partial pressure of the anesthetic and the partial pressure of the anesthetic in _____.
alveolar (PA);
arterial blood (Pa)
** Anesthetic must travel from the anesthesia machine to the tissue (brain).
The Goal of Inhalational Anesthesia
P_ = P_ = P __
PA = Pa = Pbr
Inspired Gas Concentration (FI) Depends on
- Fresh gas flow and rate
- Breathing system volume
- Absorption of machine circuit.
Ways to speed the increase in Inspired Gas Concentration (FI)
- High fresh gas flow (>4L/min)
- Small breathing circuit
- Less absorption (by CO2 absorbant).
** also rebreathing bag can be collapsed prior to starting the FGF.
For inhaled anesthetics:
Organ of uptake is the ____. and Target’s: ______.
LUNGS;
Target’s: Brain and spinal cord
= [(λ) x (Q) x (PA-Pv)]/Barometric Pressure
Uptake
λ = Solubility
Q = Cardiac Output
PA-Pv = alveolar- venous partial pressure difference
Solubility in the blood: determines speed of _____.
onset
The more soluble the AA is in the blood the _________ the patient becomes anesthetized
slower
Insoluble agents are taken up much slower by the blood so ______ induction (equilibrium).
faster
Solubility of an anesthetic is expressed as ___________.
Partition Coefficients
Partition Coefficients: ratio of the concentration of the anesthetic in the _____ phase to the_______ phase when at equilibrium between the two phases.
blood; gas
All potent agents are highly lipid soluble (T/F)
True
High Blood: Gas Coefficient:
_____ induction/wakeup.
Slow
Technique to speed induction with High blood:partition coefficient agent
Overpressure technique.
Low Blood:gas coefficient = ______ induction/wakeup
Rapid
_______ of volatile agents correlates with the physical property of lipid solubility.
The more soluble= the more _______.
Potency;
potent.
The higher the MAC the _____ the B:G coefficient.
lower
Decrease in potency is associated with a decrease in the _______ partition coefficient.
oil:gas
____ MAC = _____ soluble = ______ potent.
High;
Less; Less
Increase in CO, increase in blood flow through the lungs, more rapid uptake, increasing the amount removed from:
alveolar concentration.
Increased CO = _______ for inhalational to reach an equilibrium between the alveoli and brain therefore ______ induction time
longer; prolonged.
Decreased CO or blood flow through the lungs = _______ anesthetic taken up by the blood, ________ rate of rise in the PA.
Less; increased