Anaesthesia Breathing Systems

Question 1

What is meant by rebreathing?

Answer 1

1. First 1/3rd of exhaled breath has NOT undergone gas exchange (dead space gas) > Okay to be rebreathed
2. Remember the other 2/3rds have undergone GE and so have more CO2 than O2 (NOT FOR REBREATHING)

Question 2

How do we prevent rebreathing of CO2 rich gases?

Answer 2

1. Flow rates which are high enough to get rid of the CO2 rich gas
2. Soda-lime canisters which absorb the CO2
3. One-way valves near the patient to vent CO2 from the patient

Question 3

Which non-rebreathing circutes are commonly used by vets?

Answer 3

Mapleson A,D,E,F

Question 4

Mapleson A is also known as…

Name the modification of this circuit.

What flow rate is required of this circuit?

Answer 4

Magill

Parallel Lack/ coaxial lack

FR = 1xMV

Question 5

What is the difference between between a magill and parallel lack?

Answer 5

In a parallel lack the over-spill valve has been nearer the machine, away from the patient

Question 6

What is the difference between a Mapleson E and F?

What is the name of Mapleson F?

Answer 6

An F has a reservoir bag - increases resistance but allows IPPV

Jackson-Rees

Question 7

How can you identify a Mapleson E/ F circuit

Answer 7

Fresh gas flow is right next to the patient

F has a reservoir bag

Question 8

Which circuits would be most appropriate for patients:

1. <10kg?
2. >10kg?

Answer 8

1. <10kg - Ayre’s T-piece (E)
2. >10kg - Bain (D), Magill/ Lack (A)

Question 9

Minute volume

Answer 9

The volume of gas exhale and inhaled in one minute

MV = TV x RR

Question 10

What is the average tidal volume and breathing rate of dogs and cats?

Answer 10

1. TV = 10-20mls/kg
2. RR = 10-20 breaths per minute

Question 11

What figure is usually used for minute voume in dogs and cats?

Answer 11

200 ml/kg/mi

Question 12

Outline the flow rates required for A, D, E, F during spontaneous breathing.

Answer 12

• A - 1 - 2 x MV
• D - 2 - 2.5 MV
• E, F - 2.5 - 3.5 MV

Question 13

Outline the flow rates required for A,D,E,F during IPPV.

Answer 13

• A - 2 - 4 x MV
• D, E, F - 1 - 2 MV

Question 14

What flow rate is required for Rebreathing anaesthetic systems?

Answer 14

4-10 ml/kg/minute

(lower for large animals)

Question 15

What are the two main types of rebreathing system?

Answer 15

• To and fro
• Circle - one way valve

Air flow is OBVIOUS

Question 16

What is the main problem with to and fro rebreathing systems?

Answer 16

As the soda lime canister exhausts dead space increases

Question 17

Why is it common for high flow rates to be used at the beginning of rebreathing system use?

Answer 17

• Removes nitrogen from the air in the system and patients lungs/body
• Allows replenishing of anaesthetic vapour more quickly (when it is being taken up more quickly)

Question 18

How long and what high flow rates would be used at the beginning of anaesthesia using a rebreathing circuit?

Answer 18

For 5-20 mins

2-5 L/min for dogs

10 L/min for horses

Question 19

Which inhalation agent is the only one to provide analgesia to patients?

Answer 19

N2O

Question 20

Define the second gas effect.

Answer 20

Due to N2Os highly soluble properties in blood, it is very rapidly absorbed into the blood.

When combined with otehr anaesthetic agents this rapid absorbtion causes alveolar conc of the inhalation agent to increase quickly.

Leads to quicker uptake of anaesthetic agent (high concentration gradient)

Question 21

Why should you turn of N2O before oxygen during anaesthesia?

Answer 21

Once turned off N2O rapidly leaves the blood (can dilute gases in alveolus including oxygen)

Diffusion hypoxia