4/10Exam 3 N. Inhaled (7) Flashcards
Site of action of inhaled anesthetics
multiple sites of action and protein targets probably exist;
When does loss of consciousness ensue?
Once a critical concentration of drug has entered the brain and spinal cord
VA with a chloride ion
Isoflurane
What are The primary factors that influence absorption of the inhalation anesthetics? (VUCSA)
Ventilation,
Uptake into the blood
Cardiac output,
Solubility of the anesthetic drug in the blood, and Alveolar-to-venous blood partial pressure difference.
The concentration or partial pressure of anesthetic in the lungs is assumed to be
the same as in the brain, because the drugs are highly lipid soluble and diffusible, and they quickly and easily reach equilibrium among the highly perfused body compartments.
Dose of an individual drug is expressed in terms of the
minimum alveolar concentration (MAC)
MAC is the
Minimum alveolar concentration needed to produce anesthesia (lack of movement) upon surgical stimulation
The faster the lung (and therefore brain) concentration rises, the_______Anesthesia is achieved
the faster
anesthesia is achieved.
The faster the lung (brain) concentration falls after discontinuation of the drug, _________the patient emerges
the more quickly the patient emerges
What do you do when preparing for a patient who is susceptible to malignant hyperthermia to avoid exposure resulting from residual trace amounts of gases *(TRI) ?
Thorough flush of the anesthesia machine with 100% oxygen at 10 L/min for at least 20minutes
Replacement of breathing circuits and the carbon dioxide canister, and draining, Inactivation or removal of vaporizers are
advised
MAC of Sevoflurane
2
Blood/Gas partition Coefficient of Sevo
0.6
MAC of Isoflurane
1.15
MAC of Nitrous oxide
105
Blood/Gas partition Coefficient of N2O
0.47
Desflurane MAC
5.8
Blood/Gas partition Coefficient of N2O
0.42
Is an indicator of the speed of uptake and elimination
The blood/gas solubility coefficient of an anesthetic
Concentration effect
The higher the concentration of anesthetic delivered, the faster anesthesia is achieved; this is also referred to as over-pressuring; as with any drug, the larger the initial dose administered, the faster the onset of action
Oil/gas Solubility coefficient
The blood/gas solubility coefficient is the indicator of an anesthetic’s speed of onset and emergence:
the higher the coefficient, the slower the anesthetic; conversely, the lower the coefficient, the faster
the anesthetic
Second-gas effect
The second-gas effect is a phenomenon in which two anesthetics of varying onset speeds are administered
together: a high concentration of a fast anesthetic such as nitrous oxide is administered with a slower second anesthetic gas; the slower gas achieves anesthetic levels more quickly than if it had been given alone
Diffusion Hypoxia
Diffusion hypoxia occurs when high concentrations of nitrous oxide are administered; at the end of the procedure, when nitrous oxide is discontinued, it leaves the body very rapidly, causing a transient
dilution of the oxygen and carbon dioxide in the lungs; hypocarbia and hypoxia may occur;
How to prevent diffusion hypoxia?
administration of 100% oxygen for approximately 3-5 min when nitrous oxide is discontinued alleviates this problem
Allow for an increase in deposition of anesthetics into fat and may prolong
recovery
Long procedures and morbid obesity
The MAC or required dose of Anesthetics is
higher in infants and children and decreases with increasing age.
Infants MAC vs adult
Infants aged 6 months have a MAC 1.5 to 1.8 times higher than
a 40-year-old adult.59
Diffusion of Nitrous Oxide into Closed Spaces
Nitrous oxide diffuses into air-containing cavities in the body during an anesthetic procedure.
These air-containing spaces are normally rich in nitrogen, which is_________Soluble than nitrous oxide.
34 times less soluble than nitrous
oxide.
NItrous oxide , If the space is expandable
it increases in volume.
Examples of expandable air cavities, include
Air embolism Pneumothorax Acute intestinal obtruction Intraocular air bubles Pneumoperitoneum
Avoid nitrous during these procedures
tympanomastoid procedures
and intracranial air during diagnostic or surgical intracranial procedures.
Cuff and nitrous
endotracheal tube cuff, laryngeal mask airway, and
balloon-tipped pulmonary artery catheters may expand during nitrous oxide anesthesia, and appropriate precautions and adjustments
should be considered
The uptake of anesthetic drugs is faster in which population?
children than in adults. In other words, a child goes to sleep faster than an adult patient
Child goes to sleep faster than an adult, whY?
Child has higher alveolar ventilation per weight accounts for this effect.
The higher the cardiac output
the slower the onset.
Less soluble anesthetic work
faster
In general, the longer an anesthetic is administered,
the slower the patient emerges.
The least soluble
Exhibits the fastest clinical recovery, Least to fast order
desfluranewith sevoflurane and isoflurane following in that order.
Intraocular hexafluoride gas and N2O
2-18 mmHg increase in pressure in 20 minutes
Middle ear pressure and N2O
Increased 1-7 mmHg in 1 hour
Pneumothorax and Nitrous
2-3 times the volume in 5-20
minutes
Intestinal gas and N2O
Double in 150 minutes
Air Bubble and N2O
Immediate increases in size occur
Least metabolize
nitrous
Least metabolize before nitrous
Desflurane Less than 0.1
Minimum alveolar concentration—BAR definition
block adrenergic responses
(MAC-BAR)The alveolar concentration of anesthetic that blunts the autonomic response to noxious stimuli;
approximately
MAC Bar level
1.6-2.0 MAC
The MAC suppressing appropriate response to commands in
50% of patients; memory is usually lost at MAC-awake; approximately 0.3-0.5 MAC
The MAC suppressing appropriate response to commands in
50% of patients; memory is usually lost at MAC-awake;
MAC awake level is
approximately 0.3-0.5 MAC
Are the least metabolized and do not result in metabolism-related toxicity.
Nitrous oxide, desflurane, and isoflurane
First, the majority of the blood leaving the lungs with anesthetic is normally distributed to the vital organs
Vessel rich group
The longer the anesthetic is given , the
Greater the saturation of all the body compartments.
During induction, increases in cardiac output effect on onset?
slow onset.
Hyperthermia and MAC
Increase
Drug induces increases in CNS and MAC
Increase
Hypernatremia and MAC
Increases
Chronic Alcohol abuse and MAC
Increase
Hypothermia and Increasing age and MAC
Decrease
Hyponatremia and MAC
Decrease
Hypoxia and MAC
Decrease MAC
Lidocaine and MAC
Decrease MAC
Lithium and MAC
decrease MAC
Cardiopulmonary bypass and MAC
Decrease
Hypotension and MAC
Decrease
Right to left shunt on induction of anesthesia
shunted blood mixed with blood coming from ventilated alveoli which results in reduction of alveolar partial pressure of the anesthetic. SLOW INDUCTION of anesthesia
Left to right shunt on induction of anesthesia
Left to right shunting causes the anesthetic partial pressure in mixed venous blood to increase more rapidly than it would in the absence of the shunts.
Cardiopulmonary bypass , it is necessary to administer a relative
Higher concentration of the volatile agent compared to that with normal lung inhalation.
The uptake of volatile agents administered by the oxygenator is dependent on 3 factors
Blood/gas solubility
tissue/gas solubility
Oxygenator intake
Blood gas solubility and temperature
Increases as temperature falls
Tissue/gas solubility and temperature
Increases as temperature falls.
Emergence Phase I : Resp
Transition from apnea to regular breathing
Emergence Phase II: Characteristics
Tearing, salivation Increase HR and BP Grimacing Response to Autonomic responsiveness Extubation possible Swallowing
Extubation possible in
Phase II and Phase III
Emergence Phase III characteristics: REEA
Eye opening
Response to oral commons
Awake patterns on EEG
Extubation possible.
General Anesthesia
Arousal not possible, unresponsive, eyes closed, reactive pupils
What is the Meyer-Overton rule
The more lipid soluble the anesthetic, the higher the potency.
What favors the genesis of cardiac dysrhythmias?
Increasing the number of halogen atoms.
2 Key players in the mechanism of anesthesia
Neurotransmitter gated-ion channels
2 pore K+ channels
The lipid solubility is
Directly proportional to potency
Gender on MAC
No effect
Metabolic alkalosis on MAC
No effect
VA causes immune suppresion
Nitrous oxide
Triggers for malignant Hyperthermia
Iso, des, sevo
Support combustion: VA
Nitrous
Gas likely to evaporate when left in an open container in the OR?
Desflurane
VP of desflurane
669 mmHg
VP of enflurane
172 mmHg
VP of Halothane
243 mmHg
VP of isoflurane
238 mmHg
VP of sevo
157 mmHg
Boiling point of Desflurane
22.8
Boiling point of Isoflurane
48.5
Boiling point of Sevoflurane
58.5
Which of the following physical properties best correlates with VA potency?
Lipid solubility
Nitrous can also inhibit this receptor
NDMA ; they are excitatory receptors, and their inhibition leads to decrease neuronal activity/
What is the boiling point of a liquid?
It is the temperature at which VP equals atmospheric pressure.
What VP and boiling point favors evaporation of the liquid phase into a vapor phase?
HIgh VP and low boiling point.
VA effects on the neuro physiology and metabolism
Increase CBF, decrease in CMRO2./
Nitrous on CMRO2
Increases CMRO2, CBF, and ICP
Gas most likely to produce seizure like activity on the EEG
Enflurane.
Causes a reflex increase in HR (gas favor)
Isoflurane
Nitrous oxide has a direct
negative inotropic effect despite this, it has the lest effect on the CV
NITROUS and SNS
Sympathetic stimulator, and increases level of catecholamines, present during nitrous anesthesia produces a slight compensatory increase in arterial BP and HR so that CO remains same.
Sevoflurane, Desflurane and isoflurane are all
Vasodilators and decrease the SVR.
Sensitize the myocardium
Halothane.
C1H2CIF5O.
Isoflurane
C3H2F6O
Desflurane
Desflurane and sevoflurane are halogenated exclusively with
fluorine
Halogenated exclusively with fluorine are
less soluble in blood.
Halogenated exclusively with fluorine are
less soluble in blood.
Which modern volatile agent differs from isoflurane only in the replacement of the chlorine with fluorine?
Desflurane differs from isoflurane only by the substitution of a fluorine
atom for the chlorine atom. This one change increases the vapor pressure
dramatically
Methyl ethyl ethers.
Enflurane, isoflurane, and desflurane
Fluorinated methyl isopropyl ether.
Sevoflurane
Is the only brominated modern volatile anesthetic agent
Halothane
4 contraindications to the use of N2O
Closed pneumothorax
Tympanoplasty or middle ear surgery
Pneumocephalus
Venous Air embolism
May promote aplastic anemia
Nitrous oxide
N20 can cause a decrease in blood pressure and cardiac output when added to high dose of what intravenous anesthetics?
Opioids
Does ETC02 increase, decrease, or remain unchanged when N 10 is turned off? Why? What law applies?
ETC02 decreases. When N2O is discontinued, N20 rushes into the alveoli from the blood. The alveoli enlarge and gases that are present, including
C02, are diluted. Fick’s law of diffusion applies.
Does nitrous oxide administered alone increase cerebral blood flow and intracranial pressure?
Yes
Which inhaled agent is most associated with postoperative nausea and vomiting (PONY). Rank the inhaled agents, from greatest to least. with respect causing PONY.
Nitrous oxide has the greatest capacity to cause postoperative nausea and vomiting (PONY). From greatest to least, the likelihood of an inhaled agent •
causing PONV is: nitrous oxide > desflurane;; isoflurane = sevoflurane.
Nitrous oxide is turned on and held at the same concentration for 6 hours. At 6 hours, is the uptake of nitrous oxide increasing, decreasing, or remaining
unchanged?
Nitrous oxide equilibrates with all tissues within 6 hours, so uptake of nitrous oxide remains unchanged at this time; the amount of nitrous oxide inhaled essentially equals the amount of nitrous oxide exhaled
In general, how much does N20 reduce
the MAC of a volatile agent?
There is approximately a I% reduction in MAC for every 1% of nitrous oxide delivery.
Which two volatile anesthetics most decrease systemic vascular resistance (SVR)?
Isoflurane and desflurane.
By what mechanism does isoflurane cause hypothermia?
Depresses the temperature regulating centers of the hypothalamus, there is heat loss, because no shivering occurs.
How may an increase in ICP with isoflurane can be prevented?
Hyperventilate the patient during isoflurane administration
Which volatile agent is LEAST likely to produce potentially dangerous increases in intracranial pressure if modest hypocapnian is present?
lsoflurane.
These agents have similar effects on cerebral blood flow.
Iso, sevo, enflurane and desflurane
How do VA alter the ventilatory response to CO2? to hypoxia>
Dose dependent decrease in ventilatory response to CO2/
What MAC completely blocked at low concentration of volatile agent?
0.1 MAC
Have volatile inhalational agents been shown to inhibit hypoxic pulmonary vasoconstriction (HPV) in patients?
HPV is inhibited by a high concentration of a volatile agent, possibly at 1.0-1.5 MAC, or higher.
You are providing LMA anesthetic delivery during maintenance anesthesia and the patient begins to cough. What volatile agent has the highest incidence
of causing the patient to cough?
Isojlurane has a slightly higher incidence of causing cough during anesthetic delivery through LMA
Several minutes after induction, during mechanical ventilation, the vaporizer is delivering 2% isoflurane but the gas analyzer is only reading end-tidal concentration
at 0.5%. Why
the alveolar uptake of isoflurane is relatively slow because of its reasonably high blood solubility. This argument holds for enflurane and halothane as well. The greater the blood solubility of an inhalational agent, the slower the increase in partial pressure in the
alveoli
Which volatile agents most depress ventilation?
Least depress ventilation?
Desflurane and enflurane most depress ventilation. Halothane least depresses ventilation
Which volatile agents most depress the baroreceptor reflex, and which least depress it?
Halothane and sevoflurane most depress the baroreceptor reflex(there are no increases in heart rate despite decreases in blood pressure with these
agents).
Which volatile agents least depress the baroreceptor reflex,
Heart rate tends to increase reflexly with the decreases
in blood pressure produced by these agents
Which volatile agent is most degraded
by soda lime? Which is least degraded?
Sevoflurane is most degraded by soda lime and desflurane least.
What volatile inhalational agent least potentiates muscle relaxants?
All, but halothane does it the least.
What volatile agent produces the greatest
increase in cerebral blood flow
Halothane
What effect does acute alcohol intoxication
have on MAC
MAC is decreased in the patient who is acutely intoxicated
Which inhalational agent has no halogen
N2O
Clinically, what is the most important Fluoride ions. Inorganic fluoride ions cause nephrotoxicity? Why?
Fluoride ions. Inorganic fluoride ions cause nephrotoxicity
Are isoflurane, enflurane, sevoflurane and desflurane metabolized by oxidative or reductive processes
Oxidative.
The modern inhaled anesthetics are primarily excreted via the
lungs
The minimal amount of biotransformation ( 0.02% to 5%) of modern volatile anesthetics takes place in the liver by the
cytochrome P450 enzyme system
Desflurane how many atoms
6 fluorine atoms
Sevoflurane how many atoms
7 fluorine atoms
Vapor pressure is directly proportional to
Temperature