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Veterinary Nursing VN06 > Anaesthetic equipment > Flashcards

Anaesthetic equipment Flashcards

1
Q

What is the function of anaesthetic circuits?

A

They have several functions:
- to take fresh gas and deliver it to the patient
- to remove exhaled carbon dioxide
- to supply oxygen
- to supply volatile agent
- to be used during IPPV (for certain circuits)

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2
Q

Define IPPV

A

Intermittent positive pressure ventilation - a method of delivering breaths to patients who cannot deliver their own

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3
Q

What is the system used for classification of circuits and when was it established?

A

The Mapleson classification system. It was established in 1954, and focuses on classifying based non rebreathing systems based on their appearance, in particular the position of the reservoir bag and valve

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4
Q

Describe a Mapleson A circuit and give an example

A

The gas enters the bag before it reaches the patient. It contains an expiratory valve, which lets air out.
Examples are the Lack, Mini Lack and Magill circuits

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5
Q

Describe a Mapleson D circuit and give an example

A

The gas enters the bag after leaving the patient and the bag is full of expired gas.
Examples:
Bain and Paediatric T-piece

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6
Q

Describe a Mapleson E circuit and give an example

A

Has no reservoir bag and no valve, only tubing.
Example is the classic Ayres T-piece

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7
Q

Describe a Mapleson F circuit and give an example

A

These have no valve but an open ended reservoir bag.
Example: Ayres T-piece with Jackson Rees modification

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8
Q

What is the significance of the placement of the reservoir bag?

A

If the reservoir bag is on the inspiratory limb, where the fresh gas foes in, the circuit will have a low circuit factor, and IPPV is usually not possible
If the reservoir bag is on the expiratory limb, where expired gas comes out, the circuit factor will be higher, but IPPV will be possible

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9
Q

How do rebreathing systems work?

A

The patient’s exhaled gases are reused after passing over soda lime to remove carbon dioxide after absorption
Flow rate and volatile agent usage are lower

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10
Q

What are the two different types of rebreathing systems?

A

Closed - the valve is completely shut and the flow rate is taken up by the patient
Low flow systems - the valve is left slightly open - arguably easier to manage as excesses are accounted for by the open valve

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11
Q

Which gas cannot safely be used in rebreathing circuits?

A

Nitrous oxide - it can only safely be used in these circuits when monitoring arterial oxygen tensions or using high flow rates.
Benefits are often outweighed by the risks

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12
Q

Describe a circle anaesthetic circuit

A

AKA the hamster wheel circuit. Carbon dioxide is removed from expired gas by being pushed over soda lime canisters, which absorbs it and conserves oxygen, moisture and heat.
It is very efficient, and FGF is based on the requirements of the animal
Used for patients over 10kg, have unidirectional valves which increase resistance
Can be used for IPPV

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13
Q

What are some advantages of circle circuits?

A
  • very efficient
  • low cost
  • reduce heat loss, meaning it is easier to maintain normothermia
  • inspired gases are moistened and the risk of burns from pure, dry oxygen is lower
  • very easy to do IPPV
  • soda lime cannister is kept far away from patient and is less of an irritant risk
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14
Q

What are some disadvantages of circle circuits?

A
  • the circuits themselves are expensive to buy
  • the soda lime cannisters can be difficult to fill, and requires PPE
  • the plastic can become weak and leak, presenting a health and safety risk
  • only suitable for patients over 10kg
  • may be unsuitable for hyperthermic patients
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15
Q

What does soda lime consist of?

A

80% sodium hydroxide
18% calcium hydroxide
silicates
pH indicators

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16
Q

What PPE should be worn when changing soda lime in a circuit?

A

It is an irritant alkali so full PPE (gloves, mask, apron, goggles) should be used

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17
Q

When is the best time to check a soda lime cannister?

A

After a theatre session - granules can return to their original colour even if expire if left for a long time, e.g. overnight

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18
Q

Why is use of a closed circuit not recommended?

A

Most veterinary anaesthetic machines do not have flow meters that allow accurate delivery of very low fresh gas flow rates.

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19
Q

What is the aim in rebreathing systems?

A

To provide fresh gas flow comparable to oxygen consumption

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20
Q

What is a general rule for reservoir bag sizing for patients?

A

Generally up to 10kg can have a 0.5 litre bag; 10-20kg a 1 litre bag; 20-30kg a 2 litre bag, and 30-40kg a 3 litre bag

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21
Q

What can the effects of nitrous oxide be?

A

It is not absorbed by soda lime or by the patient - it pools in body cavities, and can cause hypoxia as it takes up the space where oxygen should be perfused.

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22
Q

Define HYPOXIA

A

Reduced amount of oxygen in the tissues of the body

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23
Q

What is denitrogenation?

A

Also called preoxygenation - it is to counter the effects of nitrous oxide and prevent it pooling in the patient’s body. Fresh oxygen is given for a period of time before and after surgery, at high flow rates

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24
Q

Describe the Humphrey ADE system

A

Introduced to the UK in 2000 and was previously popular in medical practice. It has several different modes to allow the benefit of the characteristics of several different circuit types.
It is a Mapleson A circuit when the level is up, and the reservoir bag and reservoir valve are used
It is a Mapleson D circuit when the lever is down, and the reservoir bag and valve are bypassed
It is a Mapleson E system if no ventilator is attached to the ventilator port

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25
What are some of the benefits of recycling gases with the ADE system?
It is much more efficient and cost effective, especially for larger animals, and fresh gas flow requirements do not need to be calculated
26
What is the circuit factor?
It indicates how many times the minute volume must be multiplied to meet gas requirements
27
What is the circuit factor of the most common nonrebreathing circuits?
In a Bain and Ayres T-Piece (all versions), the circuit factor is 2.5-3.0 In a Lack and Mini Lack, the circuit factor is 1.0-1.5
28
Describe the Ayres T-piece
Comes in several different versions. Whether modified or not, it is used for patients that are under 10kg. The classic T-Piece has no bag and no valve - it is a Mapleson E Gas enters the breathing system close to the patient (at the T) and fills all the tubing from which the patient inhales. When the patient exhales, gases move directly down the expiratory limb where they leave the system into a scavenging system
29
Describe the Ayres paediatric T-piece
It is a Mapleson D circuit. It has an APL valve and a closed reservoir bag. It can be used for IPPV
30
Describe the Ayres T-piece with Jackson Rees modification
It has an open bag, to which the waste bag is directly attached. It has no APL valve and is a Mapleson F circuit
31
At what ratio can nitrous oxide be used in an Ayres t-piece?
At a ratio of 1:2, Oxygen:nitrous
32
What are some disadvantages of the Ayres T-piece?
- circuit drag - the weight of the circuit means there is potential for the ET tube to be pulled out of the patient and cause trauma - the Jackson Rees modification can twist easily, blocking the open end and meaning there is no where for the expired gas to go, which is potentially catastrophic
33
Define CO-AXIAL
A circuit that has tubes inside tubes
34
Describe the Bain circuit
It is a Mapleson D system and works similarly to the T-piece. It has a circuit factor of 2.5-3.0. The inner inspiratory limb is surrounded by an outer expiratory hose. Used for patients over 10kg due to resistance, suitable for IPPV. Has low circuit drag, although the system is still heavy, with fairly low mechanical dead space. Uses high oxygen and volatile agent flow rates
35
Describe the Lack circuit
May be parallel or coaxial. It is a Mapleson A system. Has a circuit factor of 1-1.5. Only suitable for patients over 10kg, but not suitable for IPPV, as only one tube can be occluded at a time. Can be used with nitrous
36
What is a coaxial lack circuit?
The inspiratory and expiratory limbs are switched (when compared with the Bain system) and the expiratory limb is on the inside. Both limbs are also much thicker; has a circuit factor of 1-1.5
37
Describe a Mini Lack circuit
Has the same conventional design as a normal Lack but its narrower tubes and smaller reservoir bag means it is suitable for patients under 10kg. It has a circuit factor of 1-1.5 and is not suitable for IPPV
38
Describe a Magill circuit
Used for patients over 10kg. It is the original Mapleson A circuit
39
What are some advantages of the Magill circuit?
Inexpensive and reasonably efficient gas wise
40
What are some disadvantages of the Magill circuit?
The position of the valve close to the patients head may make orofacial surgery difficult/ Only for patients over 8kg Difficult to perform IPPV correctly
41
What are some specific additions to a circuit that should be considered?
The APL valve (adjustable pressure limiting valve), the pop off valve, and the IPPV button
42
Describe the APL valve
The adjustable pressure limiting valve. It controls the amount of gas contained in the reservoir bag and how much escapes from the breathing system through scavenging The valve opens at 60cm/H2O for adults, and 35cm/H2O for paediatric The valve gives the user more control
43
Describe the pop off valve
A pressure valve that will lift off when the pressure if too high, to prevent overfilling and bursting of the lungs and associated barotrauma
44
Describe the IPPV button
An additional button added specially to use for IPPV - not all machines have them, and there are now other mechanisms used for IPPV instead
45
What is the point of intubation?
It is an effective method of maintaining a patent airway when a patient's reflexes are lost under GA. An intubated airway can still become obstructed, so it is important to observe the patient's breathing patten and tidal volume
46
How is the appropriate size of a tube determined?
The tube should fit snugly within the trachea, and should extend from the incisors to the scapula when measured from the outside. Generally choose a size, and one up, and one down to trial
47
What are some risks with intubation?
- increases risk of morbidity - increased risk of tracheal ischaemia and necrosis
48
What is tracheal ischaemia?
Restriction of blood supply to the trachea, can lead to tissue necrosis
49
How can risk of tracheal trauma be limited?
- use a suitably sized tube - use a supreglottic device, such as a v-gel - use lidocaine based spray for cats, to reduce risk of laryngospasm - use of a manometer to measure the pressure in the area - taking care when inflating cuffs - securely tie tubes in - disconnect the animal when moving to prevent twisting
50
What are some advantages of tracheal intubation?
- provides a patent airway - gives full control to the anaesthetist - allows IPPV in an emergency - reduced theatre pollution, good for health and safety and everyone in theatre
51
What are some disadvantages of tracheal intubation?
- reduced lumen in the trachea, and increased resistance - the animal has to breathe harder - tubes can be occluded or twist - risk of laryngeal paralysis in cats - mechanical dead space if tube too big - risk of tracheal necrosis - can cause reactions in patients if cleaning solutions used are too abrasive
52
What are some common types of ET tube?
Magill tubes, Cole tubes
53
Describe a Magill ET tube
Most common. They are curved and have a bevelled tip. Available in sizes 3mm-40mm. Often supplied too long and can increase mechanical dead space - should be cut to size but are often not.
54
Describe a Cole ET tube
Designed for emergency use in paediatric anaesthesia, but also used in rabbits and cats. The design is such so that the shoulder of the tube should impact the larynx and provide a gas tight seal, however any kind of movement of IPPV tends to dislodge it, meaning they are not ideal for routine use
55
What materials may ET tubes be made out of?
Red rubber, polyvinyl chloride, silicone rubber, latex
56
Describe red rubber ET tubes
Can be autoclaved, but can disintegrate and be dangerous if the shedding is allowed to access the patient's lungs. Can have issues keeping them clean
57
Describe PVC ET tubes
Intended to be single use only but often are not. Less likely to cause reactions
58
Describe silicone rubber ET tubes
Designed for repeated use, have relatively thick walls. Inserted using a stylet (called a bougie). They are hypoallergenic
59
Describe latex ET tubes
Very soft and perishes rapidly. Mainly used for armoured tubes (which are corrugated to prevent kinking). Generally have been superseded by silicone rubber
60
What are some possible complications of intubation?
- oesophageal intubation - endobronchial intubation - impaction - herniation of the cuff - compression of the lumen of the ET tube - stretching of the tracheal wall
61
What is oesophageal intubation and how can it be recognised?
Occurs when the ET tube does not pass between the vocal folds and instead enters the oesophagus. Recognised by: - unusually small amount of movement in the reservoir bag - audible respiratory sounds in the mouth - occasional cyanosis - lack of a gas tight seal when cuff inflatated - light anaesthesia, due to lack of uptake of inhalational agent
62
What are signs of endobronchial intubation?
- potential cyanosis - strange or laboured breathing - barotrauma of the intubated lung
63
What is endobronchial intubation?
Occurs if a tube that is too long is placed, and it enters into one of the mainstream bronchi. The unintubated lung does not contribute to gas exchange and the large volume of blood flowing through this lung contributes to a significant right to left shunt
64
How many times maximum should the ET tube be reintroduced?
No more than once or twice more following initial intubation
65
How may endobronchial intubation be avoided?
Can be prevented by using a correctly trimmed tube and securely tying it in, ideally to the patients muzzle
66
What is the impact of impaction of the tip of the ET tube against the tracheal wall?
Possibly respiratory obstruction, particularly where the trachea contains a sharp bend, such as at the thoracic inlet
67
What is a Murphy's Eye?
A small hole incorporated in to the end of many modern ET tubes that allows the passing of gas even with less than ideal tube placement or obstruction
68
What is herniation of the ET tube cuff and what is its effect?
It may be more likely in old, perished tubes - the lumen of the tube is obstructed by the cuff if it is overinflated
69
What is the effect of compression of the lumen of the ET tube?
The tube is squashed. May be caused by over inflation of the cuff, or by gradual diffusion of nitrous oxide onto the cuff during the course of anaesthesia. More common with silicone rubber tubes as they are thinner
70
What is the effect of stretching of the tracheal wall during intubation?
Can result in tracheal trauma and result in tracheal necrosis as well as tracheal rupture
71
What are the benefits of an inflated cuff?
It will prevent theatre pollution, prevent the patient breathing in normal air, help to manage regurgitation, and gives the nurse/anaesthetist more control over the anaesthetic
72
When should a patient not be cuffed?
In times of respiratory distress, as it could cause problems and damage
73
What is the risk of ET intubation in rabbits?
It is generally a blind process and can involve a lot of poking around, which can cause tracheal trauma and injury
74
What is the supraglottis?
The upper part of the laynrx, including the epiglottis, the area above the vocal cords
75
What is a v-gel?
A supraglottic device - a tube which forms a pharyngeal seal, and are not placed into the trachea - they sit over the top of the larynx. Suitable especially for cats and rabbits
76
What are some benefits and risks of using a v-gel?
Take the mystery out of intubating rabbits and cats, and allows fast oxygenation. Can flip and cause damage within the larynx/pharynx
77
What is a laryngoscope?
A tool to facilitate laryngeal visualisation, aiding quick intubation and reducing the risk of laryngeal trauma
78
What is a heat moist exchanger?
Often placed between the ET tube and the breathing system to absorb the heat and moisture from exhaled air It reduces tracheal dryness and heat loss to the patient

Veterinary Nursing VN06 (16 decks)

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