Breathing Systems & IVFT

Clinical Skills - Year 2

What are the aims of general anaesthesia?

to render the patient unconscious

to provide analgesia

to allow muscle relaxation

What are the stages of general anaesthesia?

1. preoperative assessment

2. premedication (pain relief and sedative typically)

3. induction

4. maintenance

5. recovery

What are the 2 main forms of anaesthetic agents?

injectable agents and inhalational agents

What are the features of injectable anaesthetic agents?

administered intravenously

easy to administer

allow a rapid, smooth induction

short-acting

can be used for maintenance but typically used for induction

What are the features of inhalational anaesthetic agents?

volatile liquids

liquids are vaporised and saturate oxygen

allows delivery of oxygen to the patient

allows a rapid change in depth of anaesthesia

typically used for maintenance

What are the 5 main components of an anaesthetic machine?

fresh gas supply

flowmeter with bypass valve

vaporiser

breathing system

scavenging system

What is the function of a bypass valve on an anaesthetic machine?

to bypass the anaesthetic and deliver only oxygen from the flowmeter to the patient (without anaesthetic)

Where on a flowmeter do you read the level of gas?

top of the bobbin or the centre of the ball

What does the scavenging system of an anaesthetic machine do?

collects and safely removes exhaled and excess waste anaesthetic gases from the patient’s breathing circuit and ventilator to prevent them from leaking into the operating room

What are the problems with using a face mask in an anaesthetic breathing system?

anaesthetic can leak out into the operating room

What is the function of breathing systems in an anaesthetic machine?

to delivery anaesthetic vapour

to deliver oxygen

to remove carbon dioxide

What are the 5 main components of breathing systems?

adapter that connects to an endotracheal tube

expiratory valve

reservoir bag to allow intermittent positive pressure ventilation

fresh gas tubing

expired gas tubing

What is the function of a soda lime canister in an anaesthetic machine?

to absorb carbon dioxide exhaled by the patient during anaesthesia

How do you know when a soda lime canister needs to be replaced?

it will change colour either from white to pink or pink to white when saturated with carbon dioxide

What are the features of a non-rebreathing system?

the patient does not rebreathe expired gas

expired gas is flushed from the system before the patient’s next breath

less economical

less resistance

At which weight must an animal use a rebreathing system instead of non-rebreathing?

above 25kg

Which patients are a Mapleson A breathing system used on?

patients over 10kg, as at this weight they can overcome the resistance of the system

Which patients are a Mapleson D breathing system used on?

patients under 10kg as this system has a lower resistance

What modifications were made to the Mapleson A breathing system to create the Parallel Lack system?

a second tube was added to allow the APL valve to be moved further away from the head during head surgery

this model can be used on patients over 7kg

What modifications were made to the Mapleson D system to create the Co-axial Bain system?

the fresh gas tubing was passed through the expiratory tubing

What is the pathway of gas flow in a non-rebreathing system?

1. fresh gas enters the system and fills the reservoir bag

2. patient inspires, filling lungs with fresh gas causing the reservoir bag to decrease in size

3. patient expires causing lungs to reduce in size and force expired gas into the tubing

4. the reservoir bag is now full of gas displaced from tubing by the expired gas

5. during the expiratory pause fresh gas continues to enter the system but cannot re-enter the lungs

6. pressure builds and opens the expiratory valve and expels expired and dead space gas

How do you ensure that the flow rate is correct in a non-rebreathing circuit?

ensure that the fresh gas flow rate exceeds the minute volume by a certain amount (depending on the circuit) in order to prevent rebreathing of expired gases

What is minute volume?

the volume of gas expired per minute

What is the approximate minute volume of a patient in a non-rebreathing system?

200 ml/ kg/ min

What are the features of a rebreathing system?

soda lime canister

expiratory valve and connector with one-way valves

patient rebreathes expired gas

economical

increased resistance

Which patients are suitable for rebreathing systems?

patients over 15kg

What is the approximate minute volume of a patient in a rebreathing system?

10-50 ml/ kg/ min

What is wrong with having a gas flow rate too high?

a lot of anaesthetic and gas will be wasted

What is wrong with having a gas flow rate too low?

expired gas will not be fully removed during the expiratory pause and the patient will rebreathe carbon dioxide

What are the different types of fluid used in IVFT?

crystalloids

colloids

protein-based solutions

What is the tonicity of a fluid?

the osmolarity of the solution relative to plasma

What is dehydration?

the loss of fluid from the intravascular and interstitial space

What is required to calculate the volume of isotonic fluid required to restore the body fluid of a patient to normal?

maintenance requirement

percentage dehydration (deficit)

ongoing losses

What clinical signs would you look for to identify dehydration?

demeanour

skin turgor

mucous membranes

globe/eye position

What is hypovolaemia?

loss of fluid from the intravascular space

What is the response to shock in a patient?

need to administer fluids as quickly as possible to increase intravascular volume to maintain cardiac output

What equipment do you need to administer an IV catheter?

catheter

bung

needle/ stylet

connector

cap

How should you set up a fluid giving set?

attach fluid bag to drip stand

note the volume of the drip (usually 20 drips/ml)

eliminate air bubbles

get fluids running at appropriate rate

stop fluid from running until ready to attach to the catheter

How do you calculate how much fluid to administer to a dehydrated patient?

1. calculate maintenance requirement: 2ml/kg/hr

2. calculate water deficit: % dehydration x bodyweight(kg) x 1000

3. factor in ongoing losses: volume per episode (ml) x frequency of loss per 24 hours

What equipment will you need for this skill?

anaesthetic machine

anaesthetic breathing systems

endotracheal tubes

scavenger

fluid bag

giving set

intravenous injection limb

calculator

intravenous catheter

catheter tape

Which stage of anaesthesia is associated with the greatest risk of mortality?

recovery

What are the 2 main types of breathing system?

rebreathing and non-rebreathing

Which component of a breathing system is shown here?

adapter to connect to an ET tube

Which component of a breathing system is shown here?

expiratory valve

Which component of a breathing system is shown here?

reservoir bag

Which component of a breathing system is shown here?

gas tubing

Which component of a breathing system is shown here?

soda lime (only in rebreathing)