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N926: Pharmacology > Inhalation Agents I > Flashcards

Inhalation Agents I Flashcards

1
Q

3 A’s of Anesthesia

A

Amnesia-Loss of memory
Analgesia-loss of sensation and pain control
Areflexia- lack of movement (minimizes sympathetic and parasympathetic changes in vital signs)

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2
Q

General Anesthesia Action

A 
Altered transmission in the cerebral cortex
Additional effects on:
-Brain stem arousal centers- amnesia
-Central thalamus-analgesia
-Spinal cord-areflexia
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3
Q

Stage I of Anesthesia

A

Amnesia & Anesthesia

Initiation of anesthesia to the loss of consciousness; patient able to follow simple commands, protective reflexes remain intact, eyelid reflex intact

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4
Q

Stage II of Anesthesia

A

Delirium & Excitation

Loss of consciousness and lid reflex, irregular breathing pattern, dilated pupils. Neurons that inhibit excitation are not functional and can lead to vomiting, laryngospasm cardiac arrest and emergence delirium. More exaggerated in younger individuals.

-Very pronounced in children, some adults
-Eyes become disconjugate, tachypneic, tachycardic, HTN
DO NOT WANT TO EXTUBATE DURING THIS STAGE
Pts go through this same process for emergence, need calm/quiet in OR prior to extubating

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5
Q

Stage III of Anesthesia

A

Surgical Anesthesia

Cessation of spontaneous respirations, absence of eyelash response and swallowing reflexes

Where you want to be during general anesthesia

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6
Q

Stage IV of Anesthesia

A

Anesthetic overdose

Cardiovascular collapse requiring provider intervention

Turn down gas

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7
Q

Sedation

A

Benzodiazepines-midazolam

Alpha 2 agonists-dexmedetomidine (good for emergence delirium)

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8
Q

Induction/Maintenance

A

Barbiturates, Propofol, Etomidate, Ketamine

Total intravenous anesthetic (TIVA)

Inhalation agents

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9
Q

Analgesics

A

Opioids- phenylpiperdines, dilaudid, morphine, meperidine

Non-opioids- NSAIDS, ERAS protocols (lidocaine, magnesium, etc)

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10
Q

Paralytics

A

Depolarizing-Succinylcholine

Non-depolarizing-Benzylisoquinoliniums and steroids

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11
Q

Adjuncts

A

Regional anesthetics

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12
Q

Choice of anesthesia based on:

A

Proposed surgery
Patient comorbidities
Provider experience
Surgeon

Periopertive considerations (preop, intraop, and postop)

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13
Q

Pharmacokinetics of Inhalation agents

A

Administration of an inhalation agent involves taking a liquid, vaporizing it and delivering it to the brain

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14
Q

The main factors in anesthetizing a patient are:

A 
Technical and machine related 
Drug specific 
Patient factors 
-Respiratory
-Circulatory
-Tissue
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15
Q

Absorption of inhalation agents are related to:

A 
Ventilation 
Blood uptake 
Cardiac output
Blood solubility
Alveolar to blood partial pressure difference
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16
Q

Assumptions regarding alveolar to blood partial pressure difference

A

The concentration or partial pressure of gas in the lungs is assumed to be equal in the brain

The dose of gas is expressed as minimal alveolar concentration, or MAC

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17
Q

MAC

A

Minimal alveolar concentration

% required to produce anesthesia (lack of movement) in 50% of the population

It is age dependent; peaks at 6 months, decreases with age

The faster the lung concentration rises, the faster anesthesia is achieved

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18
Q

Factors that increase MAC

A

Hyperthermia
Drug-induced increases in CNS activity
Hypernatremia
Chronic alcohol abuse

See Nagelhout pg. 74

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19
Q

Factors that decrease MAC

A 
Hypothermia 
Increasing age*
Alpha 2 agonists 
Acute alcohol ingestion
Pregnancy
Hyponatremia
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20
Q

Machine-related factors

A

Rubber and plastic machine pieces and CO2 absorbent can retain gas delaying initial uptake

Additionally, can retain small quantities of anesthetic gases

Liter flow of carrier gas
-air, oxygen, or nitrous oxide

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21
Q

What should you do if you have a patient who is at risk for malignant hyperthermia?

A

All inhalational agents except nitrous oxide can trigger malignant hyperthermia

A thorough flush at 10L/min for 20 minutes, replacement of all breathing circuits and CO2 absorbent and removal of vaporizers

Charcoal filters on inspiratory and expiratory limbs of anesthesia machine

22
Q

What does increasing liter flow of carrier gas do?

A

Increasing liter flows during induction accelerates agent intake.

23
Q

Blood:Gas Solubility

A

Describes the amount of gas that will dissolve, or bind to the blood versus the amount that will diffuse into the tissues

Soluble agents remain in the blood longer, so less is released into the tissues during uptake (it will be slower)

24
Q

Isoflurane

A

Has solubility coefficient of 1.4

This means that there is 1.4 times more gas soluble in the blood than available to the tissues, or a 1.4:1 ratio.

More of this gas is bound to blood, not available for tissues

25
Q

Desflurane

A

Has a solubility coefficient of 0.42

This means that only 0.42 stays in the blood for every molecule that is available to the tissues, or a 0.42:1 ratio

Will equilibrate faster than isoflurane

26
Q

What happens with lower blood gas solubility?

A

The lower the blood gas solubility coefficient the faster the rate of rise in the lung and brain concentrations.

Solubility is inversely related to MAC

27
Q

Ventilation-Related Factors

A

Inhalation agents move down a concentration gradient

Uptake is initially slow as drug redistributes into tissue

The rate and depth of ventilation influences the uptake on induction and removal on emergence

Ventilation-perfusion defects alter the rate of uptake
-gases with a low solubility coefficient affected to a greater extent

28
Q

Concentration effect

A

“Over-pressuring or concentration effect”

Administration of a higher concentration of gas than necessary to speed up initial uptake.

Greater effect on high solubility gases

29
Q

Second-Gas Effect

A

Co-administering a slower agent with nitrous oxide to speed the onset of the slower agent

Not completely understood; Large uptake of nitrous concentrates the second gas?

Also used during emergence to quickly remove slower gas.

30
Q

Oil:Gas Solubility

A

Indicator of potency

Highly lipid-soluble drugs tend to be more potent

Isoflurane most potent, nitrous oxide least potent

31
Q

What does blood:gas solubility indicate?

A

Determine how fast an anesthetic gas is delivered to the tissues

32
Q

What does oil:gas solubility indicate?

A

How efficiently the anesthetic gas can access the tissues to cause its effect

33
Q

Circulatory related factors

A

The circulatory system has two major influences on anesthetic gases; uptake and distribution.

Majority of blood leaving the heart is distributed to vessel rich organs, or central compartment

An increase in cardiac output slows uptake. Blood spends less time in lungs which slows the rise in lung/brain concentration.
-High solubility anesthetic gases are affected more (Isoflurane)

34
Q

Metabolism related factors

A

Modern anesthetics are minimally metabolized

Toxic metabolites are not a clinical issue.

Historically various agents were associated with toxic metabolites. (halothane=hepatoxicity, methoxyflurane=nephrotoxicity)

35
Q

Metabolism of nitrous oxide, desflurane, and isoflurane

A

Not metabolized

Inhaled through the lungs and exhaled through the lungs

36
Q

Sevoflurane

A

Approximately 5-8% is metabolized by the liver releasing free fluoride ions.

Clinically significant toxicity has not been seen. (Oxidation phase 1 metabolism)

Fluoride ions can be nephrotoxic, run higher flow rates of carrier gas @ 2L/minute.

37
Q

Decreases in temperature results in…

A

Increased potency and solubility.

Hypothermia decreases tissue perfusion resulting in slowed induction.
-This can be overcome by increasing gas concentration

Hypothermia increases tissue anesthetic capacity.
-This tends to slow recovery

38
Q

Hyperthermia’s effect on anesthesia

A

Increases cardiac output and anesthetic requirement

-This also slows induction

39
Q

Emergence related factors

A

Anesthetic leaves the blood via the lungs with ventilation

“Routine” practice is to administer 100% O2.
-Diffusion hypoxia- patients receiving nitrous oxide during a case should receive 100% O2 on emergence

Emergence tends to be smoother than induction. More so after longer cases, less so in younger patients.

40
Q

What is the result of longer use of an anesthetic gas?

A

The longer an anesthetic gas is used during the case, the slower the emergence.

The higher the solubility the slower the emergence.
-Isoflurane>Sevoflurane>Desflurane>Nitrous oxide

Differences are small, but most notable with the last 10% of anesthetic

Residual anesthetic can remain in the body for several days.

41
Q

Diffusion hypoxia

A

When high concentrations of insoluble anesthetics such as nitrous oxide are delivered, it quickly exits the lungs during emergence and is replaced by nitrogen resulting in dilution of less soluble gases such as oxygen and carbon dioxide.

Delivering 100% O2 for several minutes prior to emergence prevents this phenomenon.

42
Q

Emergence Phase 1

A

Cessation of anesthetic drugs

Reversal of neuromuscular blocking agents

Transition of apnea to breathing

Increased alpha and beta waves on EEG

43
Q

Emergence Phase 2

A

Increased heart rate and BP

Return of autonomic responses.

Responsiveness to pain, salivation, tearing, grimacing, swallowing, and gagging, defensive posturing.

Extubation possible (risk of laryngospasm)

44
Q

Emergence Phase 3

A

Eye opening

Response to verbal commands

Awake EEG patterns

Extubation possible

45
Q

Nitrous oxide and closed spaces

A

Nitrous oxide is 34 times more soluble than nitrogen.

When nitrous oxide is administered during a case, it will readily diffuse into air-containing cavities, increasing the volume

Rigid air-containing spaces will undergo increased pressure

  • tympanic space
  • intracranial vault
  • air-filled cuffs on airway devices and pulmonary artery catheters
46
Q

Pediatric related factors

A

Anesthetic uptake greater in pediatric patients than adults

Greater alveolar ventilation/wt ratio. (breathe at faster rate)

Infants have decreased muscle mass, anesthetic agents concentrate more in vessel rich tissue.

Anesthetic agents less soluble in children than adults.
-6 month old has 1.5-1.8 times the MAC requirement of a 40 year old adult

Emergence delirium more common infants, children and young adults.
-Attenuated with administration of dex, fent, and ketamine

47
Q

Obesity

A

Minimal impact on uptake

Prolonged cases may prolong emergence due to deposit of anesthetic into adipose tissue

48
Q

Pregnancy

A

Decreased MAC requirements

Higher minute ventilation ‘predicts’ a faster uptake BUT they also have increased cardiac output that slows uptake.

49
Q

Right to left shunt

A

Shunted blood mixes and dilutes blood coming from ventilated alveoli reducing anesthetic partial pressure and SLOWS induction

Insoluble agents are affected more

50
Q

Left to right shunt

A

Increases uptake of anesthetic in mixed venous blood

Slight increase in uptake to the brain, tissue and muscle

51
Q

Cardiopulmonary bypass

A

Higher concentrations required than under normal lung ventilation

Uptake and elimination is inversely related to blood:gas solubility

N926: Pharmacology (4 decks)

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