Airway management Flashcards
Sizing a nasopharyngeal airway
Tip of the nose to the tragus of the ear
Thickness –> 5th digit on the hand
Complications of NP airway
Epistaxis (C/I in bleeding diathesis)
Submucosal placement (false tract)
C/I in BOS fractures
How is inward displacement of the NP airway attained
Safety pin
Optimal position for laryngoscopy
Extension of upper cervical spine
- Reverse the recession of the mandible
- Increase submandibular space/space in hypopharynx
- Raises the larynx
Flexion of lower cervical spine
REDUCED DISTANCE FROM MOUTH TO LARYNGEAL INLET
LINE OF SITE TO THE LARYNX OPTIMIsED
What are the mnemonics used to assess for a difficult airway
Difficult BVM - BOOTS
Difficult laryngoscopy and intubation - MMAP
What factors are predictive of difficult BVM
BOOTS
Beard/Body piercings Obese/Obstetrics Older Toothless/Trauma Snore/Stridor/Syndromes
What are the predictive factors for difficult laryngoscopy and intubation
MMAP
Measure 3:3:1
- 3 fingers - hyomental distance
- 3 fingers incisor gap
- 1 finger - underbite test
Mallampati 1 - Complete visualisation soft palate 2 - Complete visualisation uvula 3 - Visible uvula base 4 - Soft palate not visible
Atlanto-occipital extension limitation
Pathology - upper airway (and neck: surgical airway)
What are the predictive factors for difficult extraglottic device (e.g. LMA)
MOODS
Mouth Opening (Can you get the device in?) Obstructed airway (Seating over larynx?) Disrupted airway (Seating over larynx?) Stiff lungs (COPD/asthma) (Chance of leak?)
What are the predictive factors for difficult surgical cricothyroidotomy
DART
Distortion (Can the cricothyroid membrane be identified)
Access (Can the trachea be accessed through the CT membrane)
Radiation
Tumor
Describe the Cormack Lehane grading system for laryngoscopy
Grade 1 Most of the glottis visible
Grade 2 < 50% glottis visible
Grade 2a Part of the vocal cords visible
Grade 2b Only posterior elements visible (Arytenoids/posterior commissure)
Grade 3 Glottis not visible. Epiglottis visible
Grade 3a Epiglottis can be lifted
Grade 3b Epiglottis cannot be lifted
Grade 4 Neither glottis nor epiglottis visible
When is use of cLMA indicated?
- Elective anaesthesia in patients at low risk of regurgitation
- Difficult airway management
- as a conduit for intubation
- rescuing an obstructed airway - Airway management during CPR
What is a preferred choice of LMA if choosing to use IPPV
The Proseal LMA with oesophageal venting tube
What are the two major limitations of the LMA
- Risk of aspiration if regurgitation occurs in elective anaesthesia
- Inadequate ventilation due to airway leak
What is the incidence of aspiration when using a cLMA during elective anaesthesia and how does this compare to the endotracheal tube. What other factors does the risk of aspiration depend on?
1 in 4000 - 11 000
Similar to ETT
Depends on: CASE SELECTION and QUALITY OF INTRA-OPERATIVE CARE
Does the cLMA provide protection against aspiration? How does this compare to the degree of protection from aspiration offered by the Proseal LMA
Cadaveric studies indicate some protection is conferred but considerably lower than that afforded by the Proseal LMA
What is the airway seal pressure provided by the cLMA
16 - 20 cmH2O (Similar to tone of upper oesophageal sphincter)
With pressures above 20 cmH20
- Gas leak out through mouth
- Gas leak into oesophagus/stomach –> distension –> splint diaphragm –> decr. lung compliance –> Increasing required pressures –> vicious cycle
How are the risks of gastric insufflation, pulmonary aspiration and oropharyngeal injury risk mitigated
- Careful case selection
- Pressure controlled ventilation
- Good insertion technique
- Cuff pressure management
Steps for LMA insertion?
- Fully deflate
- Water-soluble lubricant posterior surface
- Anaesthesia before insertion (no response to jaw thrust)
- Patient ‘Sniffing the morning air’
- Hold cLMA like a pen with index finger at joining of stem and bowl
- Non-dominant hand on occiput
- Press the bowl of the LMA against the hard palate
- Advance cLMA along hard palate into the supraglottic region
- Final push: dominant hand remains in place –> non-dominant hand removed from occiput and applies force to the airway tube whilst the dominant hand directs this final push
- Inflate cuff - Monitor intracuff pressures ≤60cmH2O (the recommended volumes on the packaging are maximum -> start with half)
What is the maximum cuff pressure for an LMA vs endotracheal tube cuff?
LMA < 60 cmH2O
ETT < 30 cmH2O
How long after the initiation of N2O should the cuff pressure be checked again
30 mins - N2O diffuses to equilibrium
How is correct placement of cLMA confirmed
- Posterior black line of airway tube remains in midline
- Look - chest rise
- Listen - for leaks
- Feel - the anaesthetic reservoir bag (inspiration = low resistance and expiration –> rapid refilling)
Describe how the cLMA is removed
Clear secretions during the light planes of anaesthesia
The cLMA should only be removed when the patient is able to open mouth to command
Do not deflate the cuff when removing the LMA
How does the cLMA compare to the endotracheal tube airway with regard to airway protection
Better airway protection once inserted
Worse airway protection during insertion and removal
Classify supraglottic airways
Sealing mechanism
Miller
1. Cuffed perilaryngeal sealer
2. Cuffed peripharyngeal sealer (King larngeal tube/combi tube)
3. Cuff-less Anatomically pre-shaped sealers
Generation (incorporates previous features with each generation)
1st generation
- breathing tube with laryngeal mask
2nd generation
- mechanism for gastric drainage and prevention against aspiration (advantage in emergency setting)
Proposed principle 3rd generation
- some kind of mechanism for dynamic sealing
Supraglottic devices that allow for intubation
e.g. fast-track intubating LMA
What are the arguments against the use of the cLMA
No protection against aspiration
Stimulates ‘swallowing reflex’ and hence opens LOS
Channel regurgitant material into the larynx
Which surgery may require single use LMAs and why?
During tonsillectomy, there is an intermediate risk of transmission of variant Creutzfeldt-Jakob disease due to incompletely removed proteins on re-used LMAs during the standard cleaning, decontamination and cleaning processes. All other procedures are considered low risk and there is no documented case of viral or vCJD transmission.
What were the reasons for the development of single use laryngeal masks?
Economic competition
vCJD risk was overstated
What does the number for the size of endotracheal tube represent: sizes 2 - 9
The internal diameter of the tube in mm
What is the Murphy’s eye on the ETT and what is its function
It is a hole on the right aspect of the left-facing beveled tip of the ETT. This is to ensure ventilation continuous if the left facing beveled tip becomes obstructed
What is the purpose of reinforced and flexible ETT
Provide flexibility and resist kinking –> popular for head and neck, thyroid and prone surgery, though unproven necessity
What are microlaryngeal tracheal tubes (MLT) and what is their use?
Small internal diameter tubes (4-5.5mm ID), but of adult length, and with larger cuff volume.
Useful for laryngeal inlet surgery
Intubating through LMA
What are the most common problems experienced with LMAs
Twisting in the hypopharynx
Inserted too deep
Inserted too superficial
Tip bending over or inserting into the glottis
How can one establish when the LMA is incorrectly positioned?
Spontaneous ventilation
- Airway noise
- Tracheal tug
- See-saw respiration
Controlled ventilation
- leak noises during manual ventilation
- poor chest expansion
- High airway pressures
- abnormal capnograph
What are the benefits and limitations of capnography
- Breath by breath confirmation of airway patency
- RR
- Adequacy of ventilation
- Detection of re-breathing
- Disconnection alarm
- Identify low cardiac output states
Limitations
- Delay
- Patient/machine factors may alter accuracy
In an obstructed airway, how long does it take for SaO2 to fall from 85% to 50% vs 99% to 90%? Explain.
85% to 50%: 30 - 60 seconds
100% to 85 %: 3 - 10 minutes (After full pre-oxygenation)
Sigmoid shape of OHDC
Which patients become hypoxic more rapidly
Those with increased O2 consumption and/or lower FRC
- Acutely ill patients
- Children
- Elderly
- Obese
- Pregnant
- Septic
- Anaemic
- Raised intra-abdominal pressure
Describe the effects of thiopental, propofol, ketamine, Opioids, Volatile agents, NMB on the airway
Thiopental
- Airway tone: decreases
- Airway reflexes: Sometimes increases. Sometimes decreases (bronchospasm and laryngospasm are more likely)
Propofol
- Airway tone: decreases
- Airway reflexes: decreases (less laryngospasm and less bronchospasm)
Ketamine
- Airway tone: decreased far less compared to other agents
- Airway reflexes: unchanged
All opioids
- Airway tone: Decreased
- Airway reflexes: Decreased
- Respiratory drive: Decreased
Volatiles
- Airway tone: decrease
- Airway reflex: irritate (may cause laryngospasm/bronchospasm)
NMB
- Obliterate airway tone
Classify the causes of Upper Airway Obstruction
Anatomical causes
Physiological causes
Anaesthetic causes
Others
Anatomical causes of airway obstruction?
Oral cavity lesions
Nasopharyngeal cavity lesions
Hypopharynx and larynx lesions
Lesions below the larynx
Physiological causes of airway obstruction?
Loss of tone
Loss of reflexes
Laryngospasm
Anaesthetic causes of airway obstruction?
Drugs
Obstruction of anaesthetic circuit
Airway device malfunction
Other causes of airway obstruction?
Secretions/blood/regurgitation
External compression of the airway (hematoma)
Which patients are at increased risk for airway obstruction?
History of failed ventilation/failed intubation
OSA or severe obesity
Upper airway pathology/craniofacial abnormality
Bleeding in the upper airway
What are the cardinal signs of airway obstruction in adults
See-saw respiration
Tracheal tug
Airway noise
Reduced movement of the anaesthetic bag
What are additional findings to suggest airway obstruction in children
Head bobbing
Sternal recession
Intercostal recession
Subcostal recession
What is see-saw respiration
“Stomach in, Chest out”
Inspiration with a closed airway:
Diaphragm moves inferiorly –> abdominal contents displaced and abdomen expands + negative intrathoracic pressure with now air movement leads to collapse of the chest wall. Abdomen out, chest in.
Expiration against a closed airway
Diaphragm moves superiorly –> abdominal contents restored to original position + Increase intrathoracic pressure against closed airway –> Abdomen in, chest out.
What is tracheal tug
Tracheal and neck structures are drawn downward during inspiration against a closed airway due to the negative intrathoracic pressure generated during inspiration against a closed airway
How can inspiratory vs expiratory airway obstruction be distinguised?
Inspiratory obstruction: High airway pressures
Expiratory obstruction: Anaesthetic bag refills slowly
These usually coexist
Describe the changes on the capnograph in partial to complete airway obstruction
Partial obstruction - Narrowed trace tending toward a shark fin with higher gradient in plateau phase as less CO2 is exhaled into the airway.
As degree of obstruction worsens, amplitude of capnograph wave decreases until complete obstruction when the capnograph wave is absent
Describe the spirometry loop in airway obstruction
SPONTANEOUS VENTILATION
Inspiratory limb –> reducing amplitude of oval flow-volume observed
Expiratory limb –> Reducing amplitude and concave morphology
IPPV
Inspiratory limb –> Reducing amplitude and box shaped inspiratory flow volume loop
Expiratory limb –> Reducing amplitude and concave morphology
List and describe the 6 key steps to Rx of airway obstruction
- 100% FiO2 and get help (NMB may be required)
- Airway clearing/opening manoeuvres
- Attach BVM to establish general location of problem (patient | machine/circuit)
- If problem with patient airway: troubleshoot the airway
- Chest exam: (?bronchospasm/pneumothorax/pulmonary aspiration/laryngospasm)
- CICV –> insert LMA and prepare for surgical access
Is it safe to paralyze a patient when difficulty in mask ventilation is encountered after induction?
Difficult BVM usually corresponds with difficult intubation.
Patient’s who are anticipated high risk of airway complications should have their airway secured awake.
If a decision is made to paralyze a patient with difficult BVM –? anaesthetist must be prepared (willing, trained, equipped) to manage CICV
What complication should be actively sought and excluded subsequent to airway obstruction
Negative pressure pulmonary oedema
What is the treatment and course of negative pressure pulmonary edema
Rx: O2 + CPAP (also diuretics and opioids)
Px: Usually settles in 24 hours –> may require ICU for a period of ventilation
