Airway management Flashcards
Why do we need to secure an airway during anaesthesia?
Allows delivery of oxygen &inhaled anaesthetic gases
Prevents airway obstruction due to respiratory depression or loss of reflexes (all of which cause hypoxia)
Facilitates ventilation of patient
Protects airway from silent regurgitation
Helps in scavenging waste gases for environmental protection.
How do you select the correct endotracheal tube
- Palpate trachea to estimate diameter prior to intubation
- Choose 3 different sizes
- Measure tube from nares to point of shoulder
- Cut tubes to length to avoid intrathoracic placement
What are cuffed vs. uncuffed endotracheal tubes, and why are PVC/silicone preferred?
Cuffed: Prevent leakage & aspiration, inflated via pilot balloon
Uncuffed: Used in smaller patients to prevent tracheal damage
PVC/Silicone: More flexible & durable compared to red rubber tubes
What are the first steps in preparing for intubation of a cat?
- If tolerated, preoxygenate cat for 3 min using face mask or flow-by technique
- Administer IV induction drug
- Position cat in sternal recumbency & check for general muscle relaxation before assessing jaw tone
What are the techniques for positioning a cat for intubation?
Sternal or lateral recumbency:
- Extend head & neck using fingers or bandage around maxillary canines
- Gently pull tongue forward with fingers or dry swab
Dorsal recumbency:
- Use laryngoscope to lift mandible & tongue
- Enables visualisation of larynx without assistance but increases risk of regurgitation
How should lidocaine be applied during cat intubation?
- Use 1 ml syringe to drop ⩽0.2 ml of lidocaine onto arytenoid cartilages
- Wait 60–90s before proceeding
Avoid contact of syringe tip with arytenoid cartilages or vocal folds to prevent injury
What should you do if laryngospasm or resistance occurs during intubation?
- Stop the procedure
- Administer oxygen & assess anaesthetic depth
- Consider reapplying lidocaine after ensuring 60–90s have elapsed
Laryngospasm is usually self-limiting
How do you confirm correct endotracheal tube placement in a cat?
Observe arytenoid cartilages on either side of ETT
Check for condensation inside ETT with each breath
Ensure appropriate CO₂ waveform on capnograph
Palpate neck for 1 firm structure (trachea)
- If 2 tubes are felt, ETT is in oesophagus
How do you inflate the ETT cuff during intubation
- Inflate cuff in 0.5ml increments using 3ml syringe
- Stop inflating when no leak is heard at 16–18 cmH₂O circuit pressure
Use ETT cuff pressure measurement device for accurate inflation
What are the final steps after intubating a cat
- Secure ETT with gauze or tubing tied behind ears
- Attach to breathing circuit with oxygen flowing
- Check for heartbeat & assess mucous membrane colour
- Verify ETT placement with capnography or visual/physical signs (e.g., condensation or reservoir bag movement)
Describe equine ET tubes
Range from 14-30 mm
Cuffed
Gag required for intubation
Intubation without direct visualisation
Tube not cut to length
Lubricated
Describe equine intubation
- Induce anaesthesia & place horse in lateral recumbency
- Extend head & Insert gag
- Introduce tube to level of larynx
- Rotate & advance tube during inspiration (extend head further if difficult)
- Inflate cuff (tube is not usually secured)
What is Supraglottic airway device (V-gel)
Designed for cats, rabbits & dogs
Alternative to ET tubes; allows IPPV & airway protection
Ideal for short procedures & bronchoscopy
Channels to divert regurgitation can be incorporated
Always use capnography
(ETT remain gold standard)
Describe face masks as alternative to ETT
Available in range of sizes
Should cover nose & mouth
- not whole head
- avoid eyes
Beware of dead space
- choose the shape
Transparent masks preferable
Describe AMBU bags (self-inflating resuscitators)
Can use room air or connect oxygen
Essential in practice
Can connect to mask or ETT
What complications can arise from high pressure/low volume (red rubber) ETT cuffs?
Tracheitis: Inflammation of trachea
Pressure necrosis: Tissue damage from excessive cuff pressure
Tracheal rupture: Rare but severe in extreme cases
Why should the breathing system be disconnected when changing animals position?
To prevent trauma to trachea or airway caused by movement of ETT
How can ETT cuff inflation cause complications, and how can this be minimized?
Overinflation can damage trachea
Inflate carefully using manometer or by adding air in 0.5 ml increments until no leaks are heard at 16–18 cmH₂O.
What are the main functions of a breathing system during anaesthesia?
Connects patient to anaesthetic machine
Delivers oxygen & volatile anaesthetic agents (VAA) to patient
Removes CO₂ from expired gas
Provides means to ventilate patient
Label
What are the 2 types of breathing systems
Categorised by how they eliminate CO2 from expired gas
What is the function of adjustable pressure limiting (APL) valves in breathing systems
Also known as pop-off valve or exhaust valve
Allows exhaled gases & fresh gases to leave breathing system when pressure exceeds valve’s opening threshold
What is the purpose of corrugated tubing in a breathing system?
Increases flexibility & resistance to kinking
Can be smooth or corrugated on inside:
- Smooth inside reduces resistance to gas flow & prevents turbulence
What is the function of a reservoir bag in a breathing system?
Acts as gas reservoir for patient
Provides visual cue of patient’s breathing pattern
Must have volume 3–4x tidal volume of patient to accommodate inspiration
What are the features of a lack breathing system
Non-rebreathing system
Circuit factor (CF): 1
Patient size: >10 kg (mini Lack: 2–10 kg)
Advantages: More oxygen-efficient than T-piece or Bain
Not suitable for long-term IPPV
Label the lack breathing system
What are the features of a Bain breathing system?
Non-rebreathing system with coaxial arrangement (inner tube supplies fresh gas)
Patient size: 7–30 kg (mini Bain: <10 kg)
Circuit factor (CF): 2.5
Advantages: Excellent for IPPV
Higher fresh gas flow (FGF) than Lack
What are the features of a T piece breathing system
Non-rebreathing system, suitable for small patients (<10 kg)
Circuit factor (CF): 2.5
Advantages: Low resistance, suitable for IPPV
Requires higher fresh gas flow compared to Lack
How do you calculate fresh gas flow (FGF) for a breathing system?
- Calculate Minute Volume (MV):
- MV = TV × RR (Tidal Volume = approx. 10 ml/kg, RR = ~20 bpm) - Multiply MV × Circuit Factor × Patient Weight (kg)
Example: A 5 kg cat with T-piece → 5 × 2.5 × 0.2 = 2.5 L/min
FGF = MV x CF x Kg
What are the features of a circle breathing system?
Removes CO₂ using soda lime (must be changed often)
Patient sizes:
- Adult: 10–150 kg.
- Paediatric: 2–100 kg.
- Large animals: 30–1000 kg.
FGF:
Initial: 100 ml/kg/min for 10–15 mins.
Maintenance: 10–15 ml/kg/min.
Advantages: Less pollution, better for IPPV.
Label the circle breathing system
When should the FGF be increased during anaesthesia in a circle breathing system?
To change volatile anaesthetic agent (VAA) concentration quickly
At end of anaesthesia to encourage washout of gases.
What is IPPV
IPPV (intermittent positive pressure ventilation) is ventilating patient either manually (squeezing bag & opening/closing valve) or mechanically (via ventilator)
All breathing systems can be used for IPPV (short term)
How do you ventilate a patient using IPPV?
- Close pop-off valve or depress button on top
- Slowly squeeze reservoir bag while observing patient’s chest rise
- Open pop-off valve to allow exhalation
- Chest will fall due to passive recoil
What is the Humphrey ADE circle?
Versatile system: Can be used as non-rebreathing system for small patients & rebreathing system with soda lime for larger patients
Suitable for patients 2–100 kg
Compact, robust, easy to clean
Ideal for IPPV & low-flow anaesthesia
What precautions are needed for small animals during anaeshesia?
Use smallest chamber possible
Ensure volatile anaesthetic agent (VAA) enters at bottom & scavenges from top
Injectable anaesthesia is preferred to avoid excitement during chamber induction.
