Breathing Systems - Anesthesia

Question 1

What is the use of a breathing system?

Answer 1

to conenct the patient’s airway to the anesthesia machine and deliver O2 + anesthetic gases (or in conjunction with injectable anesthesthetic drugs)

ET tube if gases, O2 mask if injectable

Question 2

Difference between rebreathing (circle) and non-rebreathing systems

Answer 2

Rebreathing system (circle): has soda lime cannister that absorbs the exhaled CO2

Non-rebreathing system: uses the high O2 flow-by to flush out the exhaled CO2

Question 3

Mechanical dead space

Answer 3

any length from Y-piece to the ET tube

hose length is NOT mechanical dead space

Question 4

How does the non-rebreathing system ensure not rebreathing of exhaled O2?

Answer 4

Fresh Gas Flow (FGF) volume is always more than minute ventilation volume (to avoid rebreathing the exhaled CO2)

Question 5

Answer 5

flexible tubing that connects the common gas outlet (tube) to the fresh gas inlet (on machine)

Question 6

Answer 6

Inspiratory unidirectional valve

Question 7

Answer 7

Coaxial tube- inspiratory limb is placed within the expiratory limb; reduces bulk and the expiratory gases also help warm the inspired gases

Question 8

Answer 8

Expiratory unidirectional valve

Question 9

Calculation for selecting reservoir bag size. Solve this example: reservoir bag needed for a 20kg dog.

Answer 9

Reservoir bag should be 5-6x the patient’s normal tidal volume (Vt = 10-20mL/kg)

E.g., for a 20kg dog:
- normal minute volume 10-2020mL/kg:
- 20kg x 10-20ml/kg = 200-400mLs = minute volume
- need a reservoir bag 5-6x BIGGER than the minute volume (1L-2L bag)

Question 10

Consequences of using a reservoir bag that is too large

Answer 10

second bullet point: 2% isoflurane and 2L per minute of O2 -> change iso to 3% -> over next 3-4 minutes, patient will start to breathe deeper as the new iso % distributes through breathing system

If 5L per minute of O2 -> change in iso % will take longer//be slower to reflect in patient

Question 11

When is APL (pop-off valve) open/closed?

Answer 11

Open: spontaneous breathing
Closed: mechanical ventilation

Question 12

when to change CO2 absorber? (soda lime)

Answer 12

• when you see rebreathing of CO2 on Capnograph
• canister feels hot
• when indicator color changes
• when granules become hard-to-break (= exhausted)

Question 13

Clinical signs that soda lime needs to be changed?

Answer 13

rebreathing CO2 (on capnograph), hypertension, tachycardia

Question 14

What is the highest content of soda lime?

Answer 14

Calcium hydroxide

Question 15

Critical step when setting up non-rebreathing system?

Answer 15

Disconnect rebreathing tube from fresh gas inlet and replace with the non-rebreathing system’s tube

Question 16

Purpose of Scavenging System

Answer 16

to help avoid personnel exposure to anesthetic gases via a passive system that conducts wasted gases (e.g., CO2) into charcoal filter