Endotracheal tube

Apart from being a ubiquitous part of the ICU househould, the ETT seems to be a regular favourite of the CICM examiners. Its features are frequently asked about in the written papers and the vivas. One example of this is Question 30.1 from the second paper of 2013, "List six design features of a standard endotracheal tube which improve its safety".  Another question (Question 28.2 from the first paper of 2011) asks about the above-cuff suction port. Question 18.2 from the first paper of 2008 also asks the candidate to estimate a paediatric tube size. This is a brief exam-oriented summary, shaved down to naked point form. A more indepth discussion of the ETT is available in the massive and excessively detailed chapter dedicated to this device.

ETT size calculation 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:

Indications for intubation:

• 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.

Indications for mechanical ventilation:

• To manipulate PaO₂ and PaCO₂
• To decrease the work of breathing (whether to reduce respiratory distress or to decrease total body oxygen demand)
• To increase the functional residual capacity (FRC)
• To stabilize the chest wall in serious chest injuries

Contraindications to intubation

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

Safety features of the ETT

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

Factors which predispose the ETT to blockage

• 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

Complications of intubation

• Failure of intubation
• Oesophageal intubation
• Obstruction of the tube (be it kinked by teeth or clogged with phlegm)
• Dislodgement above the glottis (tube falling out)
• Endobronchial intubation (tube falling in)
• Cuff rupture, pressure loss
• Trauma due to intubation (eg. tracheobronchial injury, even perforation)
• Mucosal ulceration and necrosis from prolonged intubation

The above-cuff subglottic suction port

• enables the aspiration of secretions which collect above the tube cuff.
• Apparently, no improvement in duration of ventilation or mortality.
• The risk of VAP is somewhat reduced.
• The risk of tracheal mucosal damage is somewhat increased.
  • This risk is predominantly associated with continuous suction.