Inhaled Anesthetics Flashcards

2
Q

The depth of general anesthesia depends on partial pressure exerted by inhalational agent in the patient’s brain. This brain P depends on _______ partial pressure which depends on _________ partial pressure which depends on partial pressure of agent in the inspired gas.

A

ArterialAlveolar

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3
Q

What is the path an inhalational agent takes from the vaporizer to the brain?

A

Vaporizor->circuit->Lungs->Blood->Brainand then it goes back out

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4
Q

What is Relative affinity of an anesthetic for two phases and therfore the Partitioning of that anesthetic between the two phases is called…

A

Solubility

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5
Q

In a mixture of gases, each gas has a ______ ______ which is the pressure which the gas would have if it alone occupied the volume.

A

Partial pressure

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6
Q

What factors can we change to influence the amount of Inspired agent?

A

increase concentrationIncrease FGF(decrease the volume of the circuit and decrease the absorption by the machine are also listed but these are difficult to change)

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7
Q

What is a formula that describes alveolar partial pressure?

A

Input into alveoli - uptake into blood

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8
Q

How can we increase PA?

A

Increase ventilationIncrease concentration

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9
Q

What are two ways to increase initial concentration and uptake?

A

Concentration effectSecond gas effect

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10
Q

What is the definition of concentration effect?

A

Impact of the inspired partial pressure of the agent increases the rate of rise of the partial pressure of the alveolus(the higher the concentration of gas used the faster the alveolar concentration of that gas….or…. At 100 percent inspired concentration, the uptake of anesthetic creates a void, which draws gas down the trachea. This additional inspiration replaces the gas taken up.)

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11
Q

what is the second gas effect

A

High volume of uptake of one gas accelerates the rate of increase of the PA of the companion gas(During induction of general anesthesia when a large volume of nitrous oxide is taken up from alveoli into pulmonary capillary blood, the concentration of gases remaining in the alveoli is increased.)

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12
Q

What three factors affect anesthetic uptake?

A

Solubility, cardiac output, alveolar-venous difference

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13
Q

What is the formula for uptake?

A

Uptake = soulbility x CO x (PA-PV)

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14
Q

RElative affinity of inhale anesthetic for two phases at equilibrium?

A

Solubility

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15
Q

What happens to ithe PA/PI rise if soulbility is increased? How would this affect induction?

A

decreases PA/PI making induction slower, Halothane is given as the example for this

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16
Q

Rank the Partition coefficients from lowest to highest of Halothane, Sevoflurane, Desflurane, Nitrous Oxide and Isoflurane.

A

Desflurane (0.42)<Halothane (2.4)

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17
Q

The more soluble an anethesthetic agent is in the blood, the _____ the drug goes into the body, and the ________ the patient becomes anesthetised.

A

FasterSlower

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18
Q

How can you compensate for a more soluble agent to speed induction?

A

YOu can increase concentration, but it there are limits

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19
Q

Increased cardiac output has what effect on the rate of rise in PA/PI?

A

decreases

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20
Q

Increased cardiac output is more a concern for (soluble/insoluble) agents.

A

soluble. ON insoluble agents there is less of an effect

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21
Q

How does cardiac output influence its effect on uptake?

A

greater pulmonary blood flow remove more anesthetic and lowers PA. the alveoli will saturate faster if it is seeing less blood flow

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22
Q

What is responsible for alveolar venous difference?

A

absorption by the tissues

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23
Q

If gases were not absorbed by tissue what would the arterial venous difference be?

A

0

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24
Q

What affects the tissue uptake of anesthetic gases?

A

Tissue solubilityTissue blood flowDifference between partial pressure of blood and the specific tissue

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25
Q

Why do muscle and fat take longer for uptake and washout of gases compared to VRG?

A

Less blood flow (VRG is 10% of body mass and receives 75% of bf, whereas fat is 20% and receives only 6% of bf)

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26
How do we get rid of anesthetic gases?
biotransformation (small amount)transcutaneous lossEXHALATION
27
Which agent is the most metabolized?
Halothane
28
Which agent is the least metabolized?
Nitrous
29
Is there a concentration effect for elimination?
no
30
What are the partial pressures in the tissue during recovery?
All tissues have varying amounts
31
What changes pharmacokinetics of inhalational agents?
AgeLean muscleBody fatHepatic functionPulmonary gas exchangCardiac output
32
What MAC prevents movement in 95% of the population?
1.3
33
how does MAC change per decade?
6% decrease per decade
34
What is the definiton of MAC awake?
end tidal concentration of an anesthetic agent at which 50% of patients appropriately respond to verbal commands. It only applies to inhalation agents. ~10% of MAC
35
What may affect MAC awake?
Adjuctive needsagehypothermiaSedatives
36
What is MAC bar?
concentration required to block autonomic reflexes to nociceptive stimuli. 1.3 MAC
37
What factors increase mac?
HyperthermiaDrug-induced increase in catecholaminesHypernatremia
38
How does chronic alcohol abuse affect MAC?
no change
39
What are some factors that may decrease MAC?
OPIOIDSAcute alcohol intoxicationPregnancyLithiumNeuraxial opioidsOthers:Pre op medsincreased ageHypothermiaA-2 agonistsPaO2<40
40
Which inhaled anesthetics were available in 1840s?
Nitrous oxideEther Chloroform
41
Which anesthetics became available in 1951?
Halothanefloroxene
42
When did isoflurane become available? Des? Sevo?
1981, 1992 and 1994
43
how do anesthetic gases affect cerebral blood flow?
Increase vasodilation, decrease vascular resistance, increase CBF and ICP
44
Which causes more CBF, halothane or isoflourane?
Halothane can increase CBF by 166%d
45
What are inhaled anesthetics effect on siezures?
They will block siezure activity
46
What is burst suppression for isoflorane?
1.5 MAC. This will sacrifice blood pressure. all volatile agents cause burst supression at >2 MAC
47
what effect do inhaled anesthetics have on CSF production?
Sevo at 1 MAC may depress CSF production by up to 40%
48
Which hair color is associated with an increased mac?
red
49
what is the maximum for inhaled anesthetics for Evoked potential?
.5 MAC
50
How do inhaled anesthetics affect EEG
all may abolish EEG activity
51
How do inhaled anesthetics affect Cerebral blood flow?
All cause it to increase
52
HOw do Inhaled anesthestics affect Intercranial pressure?
Increased in all. Halogenated agents may increase it or remain the same
53
HOw do Inhaled anesthestics affect Cerebral perfusion pressure?
Nitrous oxide will decrease, all others increase
54
HOw do Inhaled anesthestics affect cerebral metabolic demands?
Nitrous increase all others decrease
55
HOw do Inhaled anesthestics affect CO2 reactivity?
No change
56
What effects do volatiles have on SVR and BP
Decrease SVR and BP
57
What effect do nitrous have on BP?
No change or slight increase
58
What effect do desflurane have on HR?
Causes tachycardia (and may cause HTN) due to stimulation of SNS
59
How do Iso and Sevo cause an increase in HR?
baroreceptor mediated
60
What effects do volatile have on CO?
decrease
61
What effect does Nitrous have on CO?
slight increase due to sympathomimetic activity
62
HOw do volatiles affect PVR?
decrease
63
what is coranary steal? which agent is associated with it and why?
Coronary steal is the diversion of blood from a myocardial bed with limited or inadequate perfusion to a bed with more adequate perfusion. Isoflurane has been associated with this because it is a potent coronary vasodilator (why the others are weak coronary vasodilators). However, no studies demonstrate an increas in ischemia with the use of ISO
64
what happens with administering halothane with epinephrine?
May cause arrhythmias
65
How do inhaled anesthetics affect MAP?
Nitrous remains the same or increases. All others decrease
66
How do inhaled anesthetics affect systemic vascular resistance?
Nitrous increases. Other decrease, except sevo stays the same
67
How do inhaled anesthetics affect Heart rate?.
Increase
68
How do inhaled anesthetics affect Miocardial function?
all decrease
69
How do volatile agents affect Vt, RR and MV?
RR increases, Vt and MV decrease--rapid shallow breathing
70
at what MAC do des and Sevo produce apnea?
1.5-2 MAC
71
How do volatile drugs affect AW resistance? Which is the exception?
Decrease AW resistance, except Des
72
HOw does anesthesia affect FRC?
decreases
73
HOw do inhaled anesthetics affect the kidneys?
decrease renal blood flow, GFR and urine output. May also lead to nephrotoxicity
74
How do the inhaled anesthetics affect the liver?
decrease hepatic blood flow and clearance, and can cause hepatic toxicity
75
What effects do inhaled drugs have the uterus?
decrease uterine smooth muscle contractility and blood flow.helpful to remove retained placentaMay increase blood loss during delivery
76
Can inhaled drugs cross the placenta?
Yes
77
What effects do inhaled drugs have on skeletal muscle?
Ether derived drugs pruduce muscle relaxation and potentiate paralyticsNitrous does not produce relaxation and may produce rigidity
78
How do volatile anesthetics lower body temp?
Lower the core temp set point at which thermoregulatory vasoconstriction is activatedVasodilation redistributes blood flow from central to peripheral compartmentsMetcabolic oxygen consumption is decreased-decreases heat generation
79
Which produces more compound A? baralyme or soda lime?
Baralyme
80
Which volatile agent leads to carbon monoxide?
Des--from dry dessicated absorber
81
What leads to nephrotoxicity from volatiles/
an inactive flouride metabolite--methoxyflurane
82
What are the two types of halothane hepatitis?
Mild self limiting form and a more rare life threatening hepatic necrosis
83
what % of halothane is metabolized by liver?
20%
84
What is the preservative used with halothane?
thymol
85
how much of Isoflurane is metabolized?
0.2%
86
Isoflurane has ____ cardiovascular changes at 1 MAC
minimal
87
Why is isoflurane a good choice for EEG?
2 MAC = isoelectric EEG
88
What patient should you avoid use of Des?
reactive Airways
89
Is des used with LMA?
No--AW irritant
90
Which volatile agent is least AW irritant?
Sevo
91
HOw much is Sevo metabolized?
2-5%. Associated with Compound A formation and renal tubular injury
92
What is the rule for sevo at low flows?
you can use low flows for 2 MAC hours
93
How does nitrous affect PVR?
increases
94
How does Nitrous affect CMRO2?
Increases
95
When shoudl nitrous be avoided?
enclosed air spaces--34x as soluble as nitrogenAvoid with: laparoscopic surgeryWorking on bowelsEye surgery with the gas buble