Circuits and Flows

Question 1

what 3 factors influence uptake and distribution and therefore the anesthetic % delivered to the patient

Answer 1

1) vaporizer setting
2) anesthetic circuit
3) patient

Question 2

what is oxygen consumption (VO2)

Answer 2

amount of oxygen required by cells to carry on normal aerobic metabolism

Question 3

how do we ensure carbon dioxide production (VCO2) elimination

Answer 3

by ensuring FGF is high enough to remove CO2 with or without the soda lime absorber (depending on type of circuit)

Question 4

you should use at least what FGF regardless of patient size… why?

Answer 4

1L/min… because precision vaporizers are less accurate in their output of anesthetic at flows of < 300-500 mL/min

Question 5

what is the oxygen consumption for all species

Answer 5

5-10 ml/kg/min

Question 6

oxygen consumption is within the (lower/higher) dose range for large animals and within the (lower/higher) dose range for small animals because of degree of __________

Answer 6

lower; higher; metabolism

Question 7

in terms of CO2 removal, a rebreathing system can be (higher/lower/equal to) minute ventilation whereas a non-breathing system should be (higher/lower/equal to) minute ventilation

Answer 7

lower; equal

Question 8

what is the equation for minute ventilation

Answer 8

VE = Vt x RR

Question 9

what is tidal volume in most species

Answer 9

10-20 ml/kg/breath

Question 10

do we more commonly use VIC or VOC

Answer 10

VOC: safer and more accurate

Question 11

where is VIC located

Answer 11

between the inspiratory unidirectional valve and the patient

Question 12

is anesthetic diluted more if the vaporizer is VIC or VOC

Answer 12

VOC

Question 13

what is the effect of FGF on dilution of anesthetic for the following:

VIC
VOC

Answer 13

VIC: increased FGF = increased dilution (more slowly overcome)

VOC: Increased FGF = decreased dilution (more quickly overcome)

Question 14

T/F both rebreathing and non-rebreathing systems can use co-axial tubing

Answer 14

T: for rebreathing would be an F circuit and for non-rebreathing is a Bain

Question 15

how can you identify a bain system easily

Answer 15

it contains FGF tubing to connect to the common gas outlet of the anesthetic machine

Question 16

what are the consequences of higher FGF in a non-rebreathing system (think of the properties of oxygen)

Answer 16

lower body temperature and less humidification

Question 17

it is recommended to use a rebreathing system if patients are what size and non-rebreathing is patients are what size

Answer 17

rebreathing > 10kg
non-rebreathing < 10kg

Question 18

what 3 things influence circuit dilution

Answer 18

1) size of circuit
2) FGF
3) vaporizer setting

Question 19

why do we use higher FGF than VO2

Answer 19

1) to overcome dilution from the system and the patient
2) to reach dialed anesthetic % faster so that FA approaches FI faster

Question 20

What are the FGF for a rebreathing system during the following:
- induction
- maintenance
- recovery

Answer 20

• induction: 100 ml/kg/min
• maintenance: 50 ml/kg/min
• recovery: 100 ml/kg/min (with iso off)

Question 21

what are the FGF for large animals in the following:
- induction
- maintenance
- recovery

why are they different?

Answer 21

induction: 20 ml/kg/min
maintenance: 10 ml/kg/min
recovery: 20 ml/kg/min

flowmeters only reach 10L/min in anesthetic machines, so if we used the 100, 50, 100 metrics the flow would exceed that amount

Question 22

with large animals it is mandatory to use

Answer 22

rebreathing system and fresh/active soda lime

Question 23

what FGF do we use for a non-rebreathing system

Answer 23

200 ml/kg/min UNLESS the calculated amount is < 1L/min, in which case we use 1L/min

Question 24

the FGF for a non-rebreathing system is about the same as what

Answer 24

minute ventilation (VE)