OSCE 11

Created on Thu, 06/04/2015 - 00:44
Last updated on Wed, 08/30/2017 - 01:17

What is this device?  Describe its safety features.

an endotracheal tube

(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.)

Anatomy of the endotracheal tube

markings on the ETT

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?

Complication

Preventative measure

Failure of intubation

Oesophageal intubation

  • Visual confirmation of ETT position
  • Capnometry
  • Auscultation of the chest

Right main bronchus intubation

  • auscultation of both lungs
  • chest Xray
  • Bronchoscopic confirmation

Bronchospasm

  • Pre-intubation nebulised salbutamol or adrenaline

Hypoxia

  • Pre-oxygenation
  • Continuous pulse oximetry

Aspiration

  • Cricoid pressure (debatable)
  • Aspiration of stomach contents by NG tube
  • Fasting the patient in preparation
  • Careful bag-mask ventilation to prevent gastric inflation
  • Alternatively: do not bag-mask ventilate (RSI)

Pneumothorax and tension pneumothorax

  • Use of moderation in bag-mask ventilation volumes
  • Post-intubation CXR

Cuff leak

  • Select a size-appropriate tube

Myocardial ischaemia

  • Use of opiate analgesics as part of intubation drug cocktail to prevent the sympathetic response to laryngoscopy
  • Anaesthtising the vocal cords

Spinal injury

  • Correctly identify patients at risk of spinal injury, and use of inline stabilisation
  • Fiberoptic bronchoscopy

Increased intracranial pressure

  • Use of opiate analgesics as part of intubation drug cocktail to prevent the sympathetic response to laryngoscopy
  • Hyperventilation with bag to decrease CO2 post intubation

Increased intraocular pressure

  • Use of opiate analgesics as part of intubation drug cocktail to prevent the sympathetic response to laryngoscopy
  • Anaesthtising the vocal cords

Structural damage:

-lips
-teeth
-tongue

  • Skilled practitioner
  • Limit the number of attempts by unskilled practitioners
  • Videolaryngoscopy
  • Avoid the use of stylet or bougie
  • Ensure the tip of the stylet is well within the ETT when it is advanced (i.e. not sticking out past the end of the ETT)
How would you confirm the position of this device when it is correctly placed?
  • Auscultation
  • Radiologically
  • 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.

Ideal position of the Endotracheal tube on a plain mobile Xray

(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.

influence of ETT cuff pressure on tracheal mucosal perfusion

What are the possible reasons for a cuff pressure reading of zero mmHg?
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

AND:

  •  The operator is a “conventionally trained anesthesiologist
What features on history might alert you to the possibility of a difficult intubation?

 Anaesthetic history:

  • 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)
  • Angioedema
  • Airway trauma
  • Airway infection
  • Mediastinal mass, eg. retrosternal goitre
  • Ankylosing spondylitis
  • Acromegaly
  • 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?

General features

  • 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)
  • Beard
  • 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
  • Kyphosis

The candidate may simply list the components of the LEMON screening tool, which would be enough to pass:

Look:

  • 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

Mallamati score

  • 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?

Neck mobility

  • this determines how easy it will be to align the planes

Disclaimer: the viva stem above is the original CICM stem, acquired from their publicly available past papers. However, because the college do not make the rest of the viva text or marking criteria available, the rest has been confabulated. It sounds like a plausible viva and it can be used for the purpose of practice, but all should be aware that it does not represent the "true" canonical CICM viva station. 

 

References

Griesdale, Donald EG, et al. "Complications of endotracheal intubation in the critically ill."Intensive care medicine 34.10 (2008): 1835-1842.

Rashkin, Mitchell C., and Tern Davis. "Acute complications of endotracheal intubation. Relationship to reintubation, route, urgency, and duration." CHEST Journal 89.2 (1986): 165-167.

Divatia, J. V., and K. Bhowmick. "Complications of endotracheal intubation and other airway management procedures." Indian J Anaesth 49.4 (2005): 308-18.

King, Brent R., et al. "Endotracheal tube selection in children: a comparison of four methods." Annals of emergency medicine 22.3 (1993): 530-534.

Duracher, Caroline, et al. "Evaluation of cuffed tracheal tube size predicted using the Khine formula in children." Pediatric Anesthesia 18.2 (2008): 113-118.

Davis, D. I. A. N. E., L. Barbee, and D. Ririe. "Pediatric endotracheal tube selection: a comparison of age-based and height-based criteria." AANA journal66 (1998): 299-303.

Souza, Carolina Ramos de, and Vivian Taciana Simioni Santana. "Impact of supra-cuff suction on ventilator-associated pneumonia prevention." Revista brasileira de terapia intensiva 24.4 (2012): 401-406.

DePew, Charlotte L., and Mary S. McCarthy. "Subglottic secretion drainage: a literature review." AACN advanced critical care 18.4 (2007): 366-379.

Arne, J., et al. "Preoperative assessment for difficult intubation in general and ENT surgery: predictive value of a clinical multivariate risk index." British journal of anaesthesia 80.2 (1998): 140-146.

Wilson, M. E., et al. "Predicting difficult intubation." British Journal of Anaesthesia 61.2 (1988): 211-216.

Cattano, D., et al. "Anticipation of the difficult airway: preoperative airway assessment, an educational and quality improvement tool." British journal of anaesthesia 111.2 (2013): 276-285.

Reed, M. J., M. J. G. Dunn, and D. W. McKeown. "Can an airway assessment score predict difficulty at intubation in the emergency department?." Emergency medicine journal 22.2 (2005): 99-102.

Apfelbaum, Jeffrey L., et al. "Practice Guidelines for Management of the Difficult AirwayAn Updated Report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway." The Journal of the American Society of Anesthesiologists 118.2 (2013): 251-270.

Nørskov, Anders Kehlet, et al. "Diagnostic accuracy of anaesthesiologists’ prediction of difficult airway management in daily clinical practice: a cohort study of 188 064 patients registered in the Danish Anaesthesia Database." Anaesthesia 70.3 (2015): 272-281.

Williamson, Dominic, and Jerry Nolan. "Airway assessment." Emergency Airway Management(2015): 41.