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Pharm Test 2 > Circuits and Flows > Flashcards

Circuits and Flows Flashcards

1
Q

Anesthetic % delivered to the patient is affected by:

A
  • Vaporizer setting (dial %)
  • Anesthetic Circuit
  • Patient

FACTORS TO KEEP IN MIND
§Vaporizer setting and location
§Circuit and dilution
§Patient and dilution

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2
Q

§ Uptake and distribution of anesthetic depends on:

A
  • Inspired concentration (up)
  • Alveolar ventilation (up)
  • Solubility (down)
  • Cardiac output (down)
  • Alveolar to venous tension difference (down)
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3
Q

how are alveolar concentration and amount of anesthetic in the brain related?

A

Alveolar concentration reflects the amount of anesthetic in the brain
>directly proportional

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4
Q

how does vaporizer dial setting effect effect anesthetic delivery to the brain?

A

The higher the dialed %, the faster dilution is
overcome in the circuit and patient

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5
Q

where is the vaporizer located in the circuit and why?

A

In (VIC- vaporizer in the circuit)
-Between the inspiratory one-way valve and patient
-Rarely used

Out (VOC- vaporizer out of the circuit)
-Most commonly used due to safety and accuracy

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6
Q

in VIC, how does free gas flow effect the delivered % of anesthetic?

A

§ The higher the fresh gas flow, the lower the delivered % of anesthetic
* DILUTION

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7
Q

in VIC, how do resp rate and depth of breathing effect anesthetic concentration?

A
  • Faster rates and deeper breaths increase the delivery of anesthetic to the patient (Alveolar Ventilation as per Uptake)
  • Dial setting does not indicate %
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8
Q

What are the properties of VOC vaporizers?

A

§ Precision vaporizers that deliver the concentration dialed on them)
* Dilution caused by the anesthetic circuit and patient will affect the speed at which FA approaches FI (FA/FI)

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9
Q

in VOC, what does higher flow correspond to?

A

§ The higher the flow, the faster dilution is overcome
* More molecules of inhalant are delivered to the patient which helps with saturation of tissues and equipment

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10
Q

in VOC, what does higher flow correspond to?

A

§ The higher the flow, the faster dilution is overcome
* More molecules of inhalant are delivered to the patient which helps with saturation of tissues and equipment

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11
Q

what are rebreathing circuits used with, in terms of other equipment?

A
  • Unidirectional valves
  • CO2 absorber
  • Lower Fresh gas flows (FGF)
  • Preserve humidity and patient temperature
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12
Q

what patients are rebreathing circuits recommended for?

A
  • Patients > ≈10 kg
    • arbitrary preference
  • NOT an absolute
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13
Q

what patients are rebreathing circuits recommended for?

A
  • Patients > ≈10 kg
    • arbitrary preference
  • NOT an absolute
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14
Q

what are the types of rebreathing circuits?

A

§ Circle circuit:
* 2 limbs joined by “Y” piece

§ F-circuit:
* Co-axial system
* Inspiratory limb is the inner tube * Expiratory limb is the outer tube

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15
Q

what is the Bain system? what are the characteristics of its tubing?

A

Non-rebreathing circuit
* Co-axial system
* Inspiratory limb is the inner tube
* Notice is the fresh gas flow tubing
* Expiratory limb is the outer tube

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16
Q

main 3 differences with non-rebreathing circuits? what do they offer? who are they recommended for?

A
  • No valves
  • No CO2 absorber
  • Higher FGF to eliminate CO2

§ They offer:
* Less resistance (no valves)
* Higher FGF may result in lower body T and less humidification (cool and dry O2)

§ Recommended for:
* Patients < ≈10 kg (some recommend lower BW)

17
Q

what is circuit dilution affected by?

A

§ Circuit needs to be saturated by delivered concentration from vaporizer
§ Affected by:
*Size of circuit
* Hoses, reservoir bag, sodalime canister
* Higher impact in larger circuits (as per Large Animals)
*Fresh gas flow dialed in flowmeter
*Vaporizer setting

18
Q

what is fresh gas flow? what is the quantity of O2 required by cells to carry on normal function?

A

§ Oxygen consumption (VO2)
* Quantity of O2 required by cells to carry on normal function
* 5-10 mL/kg/min

19
Q

what amount of O2 should be included as FGF in a rebreathing system?

A
  • Quantity of O2 required by cells to carry on normal function
  • 5-10 mL/kg/min
    § This is the minimum amount of O2 that should be
    included as FGF in a rebreathing system
  • F-circuit, Circle system
  • Usually, this flow rate is exceeded for safety and to increase the number of molecules of inhalant anesthetic carried by it
20
Q

how do we calculate minimum FGF? What is it for a 20 kg dog?

A
  • 5-10 mL/kg/min

§ 20 kg dog
* 20 kg x 10 mL/kg/min = 200 mL/min

21
Q

how do we calculate minimum FGF? What is it for a 450kg horse?

A
  • 5-10 mL/kg/min
    § 450 kg horse
  • 450 kg x 5 mL/kg/min = 2.25 L/min
22
Q

what values for minimum oxygen consumption should we use for small and large animals and why?

A

§ Metabolism is greater in smaller patients, therefore use the higher value of VO2 (5-10 mL/kg/min)
ie. use 10 for small and 5 for large

23
Q

why would we use a FGF that is higher than VO2?

A

FGFs more commonly used
§ Higher flows than VO2
* To overcome dilution* and to reach dialed anesthetic % faster**, so that FA approaches FI faster

§ *Dilution from system and patient

§ ** A higher FGF allows for vaporization of a larger amount of inhalant anesthetic, even though the same % is present
* 1L/min at 2% isoflurane versus 5L/min at 2% isoflurane

24
Q

what FGFs do we more commonly use in rebreathing systems?

A

100 mL/kg/min immediately after induction
50 mL/kg/min during maintenance
100 mL/kg/min during recovery

25
Q

what FGFs would we commonly use for a 20kg dog during anesthesia?

A
  • Induction
  • 20 kg x 100 mL/kg/min = 2 L/min
  • Maintenance
  • 20 kg x 50 mL/kg/min = 1 L/min
  • Recovery
  • 20 kg x 100 mL/kg/min = 2 L/min
26
Q

what FGFs would we commonly use for a 450kg horse during anesthesia? what problem will we encouter and how do we deal with this?

A
  • Induction
  • 450 kg x 100 mL/kg/min = 45 L/min
  • Maintenance
  • 450 kg x 40 mL/kg/min = 18 L/min
  • Recovery
  • 45 L/min
    § Flowmeters reach only 10 L/min in Large Animal
    Anesthetic machines
  • Therefore, the above flows cannot be achieved

§ Instead, we use FGF that are closer to VO2 approximate values
§ Recommended FGF in full size LA

  • Induction
  • 500 kg x 20 mL/kg/min = 10 L/min
  • Maintenance
  • 500 kg x 10 mL/kg/min = 5 L/min
  • Recovery
  • 500 kg x 20 mL/kg/min = 10 L/min

§ This emphasizes that VO2 is all is needed; however, time to achieve vaporizer settings % are a factor due to dilution especially in larger patients (Patient Dilution)

27
Q

what is different about FGF in non breathing systems? what additional purpose does it serve?

A

§ No soda lime absorber, no unidirectional valves
§ CO2 eliminated by means of high FGF

28
Q

what should FGF be in a non-rebreathing system? eg for a 5kg cat? 20kg dog?

A

§ Flows
* 100-300 mL/kg/min
* Greatly exceed VO2
* Applicable and feasible in smaller patients with flowmeter capabilities and cost of anesthesia

  • 5kgcat
  • 5kgx200mL/kg/min=1L/min
  • 20 kg dog
  • 20 kg x 200 mL/kg/min = 4 L/min
29
Q

when will alveolar concentration equilibriate with brain concentration? what patient characteristics do we nee to keep in mind?

A

§ Patient needs to be saturated by anesthetic
* Alveolar concentration will only equilibrate with brain concentration when tissues are mostly saturated
§ Larger patients take longer to equilibrate (saturate) than smaller ones
* More obvious comparing a horse/cow to a dog/cat

30
Q

During induction and maintenance, the higher the FGF (vaporizer dial >0%):

A
  • Dilution from the system is overcome faster
  • Patient is saturated faster
    > Alveolar concentration rises faster
    > Brain concentration rises faster
31
Q

Changes in anesthetic % take longer in larger animals. why?

A
  • Dilution from the patient (slower saturation)

Pharm Test 2 (16 decks)

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