Inhalation Agents - Apex and Dr. C PP Flashcards
Has a single specific receptor been found for inhalational agents, mechanism of action
No
Once a critical concentration of inhalation agent enters the brain and spinal cord, what ensues
Loss of Consciousness
what is minimum alveola concentration?
The dose of an individual drug expressed in terms of the concentration required to produce immobility and 50% of patients to surgical stimulation
What are the primary factors that influence the absorption of inhalational anesthetics?
Ventilation
Uptake into the blood, cardiac output, solubility of the anesthetic drug in the blood, Alviola to Venous blood partial pressure difference
The blood :gas solubility coefficient is an indicator of?
The speed of uptake and elimination
The blood: gas solubility coefficient, reflects the proportion of anesthetic that will be?
Soluble in the blood and not readily enter the tissues
The more soluble, the drug, the faster or slower the uptake in the brain and spinal cord?
The slower the uptake, the anesthesia is achieved slower
In pediatrics, does crying result in faster or slower loss of consciousness when inhaled anesthesia is being administered
Faster due to increase respiratory rate entitled volume
Over pressuring can speed the effect of which agents? what happens after the first few minutes.
Can speed the effect of slow agents such as isoflurane. After the first few minutes, the dose is decreased to the normal maintenance level.
During induction, how does an increase in cardiac output affect anesthetic onset??
Increases in cardiac output, slow onset. Increased cardiac output removes more anesthetic from the lungs, which slows the rise in lung and brain concentrations.
Hypothermia and hyperthermia both have what effect on induction of inhalation anesthetics
Both slow induction for different reasons
In general, which agent would have the slowest emergence and why
Isoflurane is the most soluble agent making its emergence longer because it wants to stay in the blood
Is inhalation anesthetic, uptake, slower or faster in children? why?
Uptake faster in children than adults child’s higher alveolar, ventilation per weight accounts for this effect.
Increase cardiac output usually delays speed of induction. Why doesn’t this occur in children?
Infants and children have higher cardiac output per weight than adults. This would normally slow onset; however, cardiac output distributed to vessel-rich groups in children more than in adults, as well as a lower muscle mass, meaning more agent is delivered to vital organs.
Does midazolam, serotonin, antagonists, or parental presence have an effect on emergence agitation
no
Theoretically, how may obesity effect emergence of inhaled anesthesia
Long procedure in morbid obesity allow for an increase in an aesthetic agent deposition into fat may prolong recovery
During cardio, pulmonary bypass are higher or lower concentrations of tile agents needed
Higher concentrations needed compared to normal lung inhalation
Why is MAC a useful tool among inhalation agents
Useful to compare potencies
What is the definition of a “response” when assessing MAC level
Response is defined as gross purposeful movement of the head or extremities
What is Mac-awake?
The Mac at which 50% of subjects or respond to command “open your eyes”
How is regular Mac different than Mac-bar?
MAC-Bar is the Mac necessary to block adrenergic response to skin incision, whereas regular Mac is response via movement to surgical stimulation
Movement is prevented in 95% of the population at what MAC
~1.3 MAC
Inhalational anesthetics produce what affects in general
amnesia
Loss of consciousness mobility, modulate autonomic function, may provide some analgesia
Volatile inhalation agents generally increase or decrease the cerebral metabolic rate of oxygen consumption
Decrease CMRO2.
But only to the extent that they reduce electrical activity
What Mac is required to produce an isoelectric state
1.5-2 MAC
Are inhalational, anesthetics, cerebral vasodilators or vasoconstrictors
Vasodilators
Inhalation agents decrease CMRO2, when metabolic demand decreases the brains blood vessels constrict, however, volatile agents are vasodilators as well. Therefore we say volatile anesthetics do what to CMRO2 and CBF?
Uncouples CMRO2 and Cerebral Blood Flow
At concentrations above 0.5 MAC volatile anesthetics ______ cerebral blood flow, even though they _______ CMRO2
increase cerebral blood flow even though they decrease CMRO2
What is the advantage and disadvantage of volatile anesthetics uncoupling CMRO2 and cerebral blood flow?
The upside is that it produces a favorable cerebral oxygen supply-demand ratio, but the downside is that it increases ICP
Does nitrous oxide uncouple CMRO two and cerebral blood flow
No nitrous oxide is different. It increases cerebral blood flow as a function of increased CMRO2.
How do Desflurane and Isoflurane impact cerebral uncoupling?
“Uncoupling does not seem to occur with 1 MAC or less of Des or Iso” - Dr. C Powerpoint
What is the normal physiological response of cerebral vascular to carbon dioxide levels
Vasculature constricts in the presence of hypocarbia and vasodilates with hypercarbia
If a patient has an increased ICP, what can we do with ventilation to reduce the pressure?
We can hyperventilate for an etCO2 around 30 to 35 mmHg. This will cause cerebral vasculature to vasoconstrict due to hypocarbia. This can be effective for approximately 4 to 6 hours.
Volatile agents produce dose-dependent suppression or activation of EEG activity.?
Suppression
Burst suppression can be achieved at what MAC of Desflurane
1.5-2
Burst suppression can be achieved at what MAC of Isoflurane or Sevoflurane
2
Volatile agents in nitrous oxide produce a dose-dependent reduction in evoke potential. Which are more sensitive, and which are more resistant?
Visual-evoked most sensitive
Brainstem-evoked most resistant
What changes are seen on EEGs or evoke potential if using volatile agents
An increase in latency or decrease in amplitude of evoke potential can reflect ischemia or could be secondary to the volatile agent
What two volatile agents can cause emergence agitation in children? how long does it usually last?
Sevo and Des
Usually lasts ~ 15min
Iso, Des, and Sevo all have what effect on cardiac output and cardiac index
Reduce cardiac output in cardiac index in a dose-dependent fashion.
Iso, Des, and Servo all have what effect on MAP via ____?
Reduce map via reduction in SVR
Nitrous oxide activates the sympathetic nervous system and has an effect on SVR
Increases SVR
Which inhalational agent between iso, Des and Sevo has the least effect on heart rate
Sevo
Rapid increases in inhaled concentrations of which two inhalational anesthetics can lead to an increase in heart rate and blood pressure due to sympathetic activation via an irritant effect
Isoflurane and ***Des
What is coronary steal? How can it be prevented?
Theoretically, coronary steel is a reduction in the perfusion of ischemic myocardium with simultaneous improvement of blood flow to non-ischemic tissue. A sort of taking from the poor and giving to the rich.
When normotension is maintained, a steal phenomenon is avoided.
Volatile agents reduce the quantity of catecholamine necessary to evoke arrhythmias to avoid this. What should you keep your epinephrine dose at?
Keep epinephrine dose less than 10 µg per kilogram
True or false: all inhalation agents prolong the QT interval
True
Which inhalation agent would be most likely to cause bradycardia or AV nodal conduction disturbance
Sevo
Volatile agents have what effect on pulmonary artery pressure and PVR?
Decrease PA pressures and PVR
nitrous oxide has what effect on PVR
In normal adults, small increase in PVR however, those with pre-existing pulmonary hypertension result in a larger increase in PVR
how do volatile agents affect CO2 responsiveness
CO2 responsiveness is depressed and the apneic threshold is increased (the co2 @ which a pt is stimulated to breathe)
how do volatile agents affect title volume and respiratory rate?
Agents reduce title volume as concentration of agent increases. There’s a compensatory increase in respiratory rate, however not enough to prevent elevations in CO2.
You have a V/Q mismatch, which usually is compensated for by hypoxic pulmonary vasoconstriction. Which agent has the most effect on reducing HPV?
Isoflurane
what are the inhalational agents effects on airway smooth muscle?
Inhalational agents relax airway smooth muscle and produce bronchodilation when there is increased airway resistance.
Sevo is the best at this.
Once the patient is anesthetized, Iso can bronchodilate, and nitrous oxide.
Effects of volatile anesthetics on upper airway patency
Agents impair the airway dilator muscles, such as the genioglossus or tensor Palatine, leading to upper airway obstruction
Impaired pulmonary muscles, which decreases functional residual capacity and effectiveness of ventilation
Which inhalation agent impaired the hypoxic drive the least? Because of this when might you choose to use it?
Des. One of the best choices for patients who rely on the hypoxic drive to breathe such as those with emphysema or sleep apnea.
As a general rule, you should be concerned about nerve ischemia when measuring evoked potential when amplitude decreases by greater than _____% or latency increases by _____%
When amplitude decreases by greater than 50% or latency increases by greater than 10%
According to Apex Anesthesia, the best anesthetic technique to preserve evoked potential is?
TIVA w/o Nitrous Oxide
When using a volatile agent during EVP studies, using less than what Mac is recommended and supplement with what?
Use < 0.5MAC and supplement with IV agents such as propofol and opioids. Do not use N2O.
how do volatile anesthetics impact the kidneys
Autoregulation of renal circulation generally remains intact.
Reductions in SBP are accompanied by decreased renal vascular resistance, which could result in a decline in GFR. This could be why we have a reduction in urinary output intraop.
How do the volatile aesthetics influence the neuromuscular system?
Of volatile agents produce Dossi pendant relaxation of skeletal muscle, as well as an additive effect with both the depolarizing and nondepolarizing muscle relaxants
Which inhalation agents can trigger malignant hyperthermia
All agents except nitrous oxide
What medication treats malignant hyperthermia
Raynodex and Dantrolene
What is the connection between nitrous oxide use and pregnancy?
Nitrous oxide exposure has been linked to both spontaneous abortion and reduced fertility and workers
If a pregnant patient needs non-urgent surgery which trimester should the surgery be performed in?
Second trimester
