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Clinical Anesthesia > Inhaled and Gaseous Agents > Flashcards

Inhaled and Gaseous Agents Flashcards

1
Q

Define Saturated Vapor Pressure

A

The pressure exerted by a vapour when it is completely saturated and in equilibrium with its liquid form, and is a measurement of volatility

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2
Q

Define Solubility

A

the ability of a liquid or gas solute to dissolve into a liquid or gas solvent

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3
Q

Define Partition Coefficient (blood:gas and oil:gas)

A

Blood Gas solubility coefficient (e.g. alveolar-blood interface) –> related to the rate of induction and recovery

  • High solubility = halothane = slower speed of induction and recovery
  • Low solubility = sevoflurane

Oil Gas solubility coefficient (e.g. blood-brain interface) –> is a measure of anesthetic potency i.e. how much is required to cause anesthesia in the brain

  • High solubility = halothane = lower MAC value required to achieve anesthesia = more potent the agent is
  • Low solubility = desflurane
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4
Q

Define MAC

A

The Minimum concentration of anesthetic agent in the alveoli at which 50% of patients will not exhibit a gross purposeful reponse (movement) to a particular surgical stimulus (tail clamp/ skin incision)
- This measurement allows for the comparison of potency of inhalational anesthetics

The higher the MAC, the larger the mount of agent is needed to produce anesthesia, thus the lower the potency

  • Halothane MAC = 0.8% = very potent
  • Desflurane MAC = 7% = less potent
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5
Q

Isoflurane, Sevoflurane and Desflurane are all __________

A

Halogenated ethers (Vapours)

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6
Q

Nitrous Oxide and Xenon are both _______

A

Inhaled Gases

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7
Q

Which of the Halogenated ethers can be used in food-producing animals?

A

Isoflurane

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8
Q

Isoflurane, Sevoflurane and Desflurane are all __________

A

Halogenated ethers (Vapours)

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9
Q

Which of the Halogenated ethers can be used in domestic animals?

A

Isoflurane

Sevoflurane

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10
Q

Why is Nitrous Oxide not used in vet medicine anymore?

A
  • Negative environmental effects
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11
Q

Why is Xenon rarely used in vet medicine?

A

VERY expensive to purchase and use

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12
Q

What factors increase the speed of induction with inhaled agents?

A

1) Increase inspired anesthetic concentration
2) Increase alveolar ventilation
3) Decrease removal from alveoli

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13
Q

How can you increase the anesthetic concentration being delivered to a patient?

A

1) turn up the dial on the vaporizer
2) increase the fresh gas flow (in a circle system)
3) increase vaporization of the agent
4) decrease gas volume of the breathing circuit

note: in order for any of these to work, the patient has to be breathing properly

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14
Q

How can you increase the alveolar ventilation of the anesthetic agent?

A

1) Increase tidal volume, respiratory rate or both

2) Decrease residual capacity/ dead space ventilation

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15
Q

How can you decrease the removal of the anesthetic agent from the alveoli?

A

1) Use agents with lower blood:gas solubility coefficients
2) Decrease cardiac output
3) Decrease solubility in tissues

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16
Q

What are the effects on the CNS, CVS, RS, GIT and Renal system of using Inhaled Anesthetics?

A

CNS: depression + increase blood flow to the brain due to vasodilation –> Increase in intracranial pressure despite lower metabolic activity

CVS: Lower blood pressure + tissue perfusion due to vasodilation, lower cardiac contractility and HR
+/- arrhythmias especially with Halothane and Desflurane

RS: depressed ventilation, resulting in respiratory acidosis and an increased blood flow to the brain

Renal + Cerebral perfusion: both decreased

GIT: reduced lower esophageal tone, thus more likely to regurgitate under anesthesia

17
Q

What are the effects of Isoflurane specifically on the RS, CVS and environment?

A

RS: Depressant, leading to hypoventilation

CVS: drop in total peripheral resistance due to vasodilation, and a drop in BP

Environment: has the LEAST ozone-depletion potential of all anesthetics

18
Q

What are the effects of Sevoflurane specifically on the RS, CVS and environment?

A

RS: less depression than iso

CVS: similar to isoflurane- drop in total peripheral resistance due to vasodilation, and a drop in BP

Environmental: is the LEAST global warming potential

19
Q

What are the effects of Desflurane specifically on the RS, CVS and environment?

A

RS: respiratory depression, airway irritation

CVS: doesnt sensitize the myocardium, but can cause sympathetic storms (arrhythmias)

20
Q

Why is Sevoflurane stored in plastic bottles instead of glass?

A

Stored in plastic bottles as the aluminium impurities in glass can lead to reactions with the anesthetic + render it useless

21
Q

Why does Desflurane need a fancy vaporizer?

A

This is because Desflurane boils at 22.8 C, unlike the other agents

22
Q

Why was Halothane taken off the market?

e.g. what were its risk factors?

A
  • Had a profound depression on RS
  • Lead to a large drop in blood pressure due to reduced contractility and stroke volume of the heart
  • Sensitizes the myocardium, leading to arrhythmias
  • Hepatotoxic = halothane hepatitis
23
Q

What are the gaseous agents used in vet medicine?

A

Nitrous Oxide

Xenon

24
Q

What are the benefits of using Xenon over Nitrous Oxide?

A
  • Fewer environmental effects
  • Lower blood:gas coefficient = rapid onset of induction
  • Stable CVS effects
  • Provides profound analgesia at the NMDA receptors
  • Does NOT activate the SNS, thus no increase in cortisol
  • Produces the highest regional blood flow to the brain, liver and kidneys
25
Q

Can Xenon be used in vet medicine?

A

Yes, just not readily available. Likely only seen in vet colleges

26
Q

Can Xenon be used in vet medicine?

A

Yes, just not readily available due to cost. Likely only seen in vet colleges

27
Q

What is the lifespan of Sevoflurane, Desflurane and Nitrous Oxide in the environment?

A

Sevoflurane = 1 year
Desflurane = 14 years
Nitrous Oxide = 114 years

28
Q

What factors are MAC-sparing, and thus reduce the requirement for volatile agent ?

A
  • The use of sedative and opioid drugs and local techniques
  • Other anesthetics (PIVA, CRI’s or N2O)
  • Age: the very young and old have reduced requirements
  • Temperature: for every 1C lower, this reduces requirement by 5-10%
  • Pregnancy: due to the effects of progesterone in the pregnant dam
  • Species
  • Conditions such as hypotension, anemia and hypoxemia
29
Q

What are the greatest advantages of using Sevoflurane over Isoflurane?

A
  • Faster speed of induction + recovery
  • ## Speed of changing depth of anesthesia is quicker due to less solubility
30
Q

What are the greatest advantages of using Sevoflurane over Isoflurane?

A
  • Faster speed of induction + recovery
  • Speed of changing depth of anesthesia is quicker due to less solubility
  • Neuroanesthesia is better: ideal for MRI, CSF tap
31
Q

What are the advantages of Nitrous Oxide?

A
  • It provides some analgesia
  • Reduces MAC of other inhalant agents
  • Causes minimal cardiopulmonary depression
  • Is not metabolized
  • Non-irritating
  • Non-arrhythmogenic
  • Increases the speed of uptake of other inhaled agents especially at the beginning of anesthesia
32
Q

Why is Nitrous Oxide not popular in vet medicine?

A
  • Cause easily cause hypoxemia as a minimim of 33% oxygen is needed
  • It collects in gas-filled cavities e.g. gastro-intestinal tract and phenomothorax
  • At the end of anesthesia it can cause diffusion hypoxia by replacing oxygen in the alveoli
  • Health hazards to humans
  • Additional monitoring equipment is needed to use it safely
  • It is expensive
  • Is a green house gas
33
Q

What MAC-sparing techniques do we have now that have largely replaced Nitrous Oxide in vet medicine?

A

Analgesia:

  • Local blocks (e.g. epidural)
  • CRI’s: Medetomidine, ketamine, morphine, lidocaine, fentanyl and various combinations (e.g. MLK = Morphine + Lidocaine + Ketamine)
34
Q

Describe the use, bolus dose and CRI dose of using a (Dex)Medetomidine CRI

A

Bolus Dose: 0.5 - 2 ug/kg IV
CRI dose: 1-2 ug/kg/hr

Use:

  • Often helps make anesthesia more stable
  • Used in combination with opioids to reduce the requirements
  • Used when NSAIDs cannot be used
35
Q

Describe the use, bolus dose and CRI dose of using a Ketamine CRI

A

Bolus Dose: 0.2-0.5 mg/kg IV
CRI dose: 5-10 ug/kg/min

Use:

  • Useful for neuropathic pain
  • Reduces the requirement for opioids

caution: bolus dose may cause transient (2min) apnea, which can be handled with positive pressure ventilation

36
Q

Describe the use, bolus dose and CRI dose of using a Lidocaine CRI

A

Bolus Dose: 1 mg/kg IV
CRI dose: 15-50 ug/kg/min

Use:

  • anti-arrhythmic = Tx for ventricular tachycardia
  • pro-kinetic = tx for gut stasis
  • reduces inhalent requirements

note: above doses are NOT anti-arrhythmic

caution: may cause CVS depression/ hypotension
caution: only use in dogs, not cats!

37
Q

Describe the use, bolus dose and CRI dose of using a Morphine CRI

A

Bolus Dose: 0.1 - 0.2 mg/kg IV
CRI dose: 0.1-0.12 mg/kg/hr

Use:
- USeful post-op in combination with very low dose of acepromazine for increased sedation: must monitor mentation + regurgitation

38
Q

Describe the MLK and FLK Infusion combination

A 
MLK = Morphine + Lidocaine + Ketamine
M 60mg
L 500mg
K 60 mg
- In a 500mL 0.9% saline bag
- Infused at 1ml/kg/hr (intra or post op)

FLK = Fentanyl + Lidocaine + Ketamine

Clinical Anesthesia (17 decks)

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