What is this device? Describe its safety features.
(This is one of the older vivas, back when the college did not even bother to give you their stem text. Their entry for this viva simply reads "Miscellaneous Equipment including a tracheostomy tube, an ECG electrode, a double lumen tube, and defibrillation pads. Roles, advantages and disadvantages were requested." As the consequence of this, most of what you see here is generated de novo by yours truly.)
So: safety features?
Question 30.1 from the second paper of 2013 asked for six of these.
- Single use item, no risk of cross-infection
- Standardised 15mm connector to fit all airway devices
- Low-allergen PVC construction, free of latex
- Transparent body,to see blood or vomit
- Markings to indicate depth of insertion
- Black line to guide insertion to appropriate depth
- High volume low pressure cuff to seal the trachea
- Size labelling on pilot balloon
- Pilot cuff to gauge cuff pressure
- Rounded atraumatic edges
- Murphy's eye to protect against occlusion
- Bevelled tip to assist insertion
- Radio-opaque line to help gauge position on chest X-rays
What are the indications for the use of this device?
This might sound like a stupid question, but it's important to be able to generate a list of these so that you might sound like some sort of airway expert.
Thus, indications for intubation are:
- To overcome an airway obstruction and to protect the airway
- To allow access to the lower airway for suctioning of secretions
- To allow mechanical ventilation in a patient in whom non-invasive ventilation is contraindicated.
What are the contraindications for the use of this device?
Actually there are few real hard contraindications to intubation.
- Absence of upper airway (eg. radical laryngectomy)
- Laryngeal trauma which would be exacerbated by ETT insertion (eg. fractured larynx)
- Transection of the airway which could be exacerbated by ETT insertion
Additionally one might include "futility" in that list.
What are the possible complications associated with the use of this device? What steps might you take to prevent these?
Failure of intubation
Right main bronchus intubation
Pneumothorax and tension pneumothorax
Increased intracranial pressure
Increased intraocular pressure
How would you confirm the position of this device when it is correctly placed?
- By end-tidal capnometry
- By ventilator waveforms consistent with tracheal placement
- By "balloting the cuff", where gentle pressure on the trachea just above the suprasternal notch is transmitted via the ETT cuff to the pilot balloon
Radiologically, how does one identify an appropriate ETT tip position?
The ETT is well placed when:
- The cuff is below the cords
- The cuff does not block any of the main bronchi
With more subtlety:
- It is recommended that the endotracheal tube tip be fixed at 5cm above the carina, with the head in a neutral position (we know that as the patient flexes and extends their neck, the endotracheal tube moves up and down by about 2 cm in either direction).
- Thus, the ETT tip should be around the T3-T4 level, going by fixed bony landmarks. This corresponds to a carina position at around T5-6.
(a "neutral" head position corresponds to a mandible at the level of C5-C6. This level is also where the vocal cords are located).
What is the role of the air-filled cuff?
Two main roles:
- To seal the trachea, so that positive pressure cannot escape from the lower airway
- To seal the upper airway, so that material above the glottis cannot enter the trachea
What are appropriate cuff dimensions, volume and internal pressure?
The cuff is usually filled with 10ml of air.
This inflates it to a diameter of approximately 30mm.
The normal cuff pressure should be around 20-30mmHg.
What are the possible reasons for a cuff pressure reading of zero mmHg?
- The cuff has ruptured,
- The pilot balloon tube has been chewed through
- The balloon inflation lumen is occluded. Ventilation parameters are eerily stable in spite of a "zero" reading.
What is the purpose behind the design of the ETT tip?
The candidates are expected to comment on Murphy's eye and the bevelled tip.
- Murphy's eye:
- Ensures that the ETT is more difficult to block
- Ventilates the right upper lobe bronchus when it abnormaly takes its origin from the right tracheal wall ( in about 0.5% of the population, the right upper lobe bronchus takes its origin anomalously straight from the trachea)
- Bevelled tip:
- The left-sided bevel offers a profile which promotes the greatest amount of cord visibility during laryngoscopy
- It also prevents occlusion by direct contact with the carina or bronchial wall
- It also is easier to insert through partially adducted cords
Apparently, Magill originally cut his tubes at an angle because it made nasal insertion easier.
What factors predispose to ETT blockage?
To rephrase, "what are the causes of a blocked ETT"?
- Inadequate humidification
- Inspissation of secretions
- Infrequent physiotherapy
- Excessive secretions with adequate cough and humidification
- Clots due to pulmonary haemorrhage
- Kinking of ETT due to position
- Patient chewing on the ETT
How would you correctly select the size of ETT for children?
This is examined in Question 18.2 from the first paper of 2008.
There are actually several methods to guide ETT selection in children:
- diameter of the pinky finger
- (Age in years + 16)/4
- The Khine formula: (Age /4) + 3
- Broselow paediatric tape
The formula quoted by the college is also the one they teach you in the APLS course, so perhaps it has been locally accepted as the right formula for any young Australian larynx.
That formula is:
ETT diameter = (Age / 4) + 4
What is the definition of a difficult intubation?
The airway is difficult IF:
- It is difficult to bag-mask ventilate
- i.e. no seal, excessive leak, or excessive resistance due to obstruction
- It is difficult to intubate:
- None of the vocal cords are visible (Grade IV direct laryngoscopy)
- Multiple attempts are required for intubation
- The operator is a “conventionally trained anesthesiologist”
What features on history might alert you to the possibility of a difficult intubation?
- History of difficult intubation in previous attempts
- History of airway-altering changes since the last anaesthetic, eg. significant weight gain, C-spine surgery, head and neck radiotherapy, etc.
Specific pathologies associated with difficult intubation, which may be available as history:
- Recent intubation (oedema, trauma, etc)
- Airway trauma
- Airway infection
- Mediastinal mass, eg. retrosternal goitre
- Ankylosing spondylitis
- Degenerative arthritis (i.e. of the C-spine or jaw)
- Subglottic stenosis
- Lingual hypertrophy (i.e. big fat tongue)
- Syndromic appearance:
- Treacher-Collins syndrome: Auricular and ocular defects, malar and mandibular hypoplasia
- Pierre Robin syndrome: micrognathia, macroglossia, cleft soft palate
- Down syndrome: small mouth; macroglossia
- Goldenar’s syndrome: malar and mandibular hypoplasia
- Kippel-Feil syndrome: congenital C-spine fusion
What features on examination might suggest that intubation will be difficult?
- Level of consciousness (i.e. is the patient cooperative enough for an awake intubation?)
- Level of comfort (i.e. can the patient be positioned properly, or are they to short of breath?)
- Pregnancy (makes everything difficult)
- Syndromic appearance
Mouth, face and jaw
- Long upper incisors (“buck teeth”)
- No teeth (edentulous patients are easier to intubated, but harder to bag-mask ventilate)
- Prominent overbite
- Inability to “prognath”, i.e to voluntarily protrude the mandible
- Small mouth opening (3cm is the minimum to comfortably admit a laryngoscope blade).
- Mallampati score more than 2 (i.e. a barely visible uvula)
- Arched or narrow palate
- Compliance of the mandible and mandibular space (i.e. is it possible to manipulate it, or is it relatively fixed by some sort of disease process, eg. a submandibular abscess)
- Patency of nares: polyps, deviated septum etc.
Neck and posture
- Thyromental distance (“three ordinary finger breadths”, or 6cm)
- Mandibulo-hyoid distance of less than 4cm
- Sternomental distance of less than 12cm
- Thick short neck
- Restricted range of neck motion
The candidate may simply list the components of the LEMON screening tool, which would be enough to pass:
- Does the patient look like the stereotypical difficult intubation?
Evaluate: 3:3:2 rule
- 3 fingers width of mouth opening
- 3 fingers width of thyromental distance (from the thyroid cartilage to the mental process of the mandible, colloquially referred to as the chin)
- 2 fingers width of distance from the hyoid to the thyroid
- amount of pharynx which can be seen by opening the mouth
Obesity and obstruction
- Is the patient morbidly obese?
- is there some sort of obstruction, eg abscess?
- this determines how easy it will be to align the planes