a) What is the diameter of the connector (shown by the arrow)?

b) List 2 factors which predispose to obstruction of this tube in intensive care?

c) List 3 design features of this device which improve its safety.

d) Write down the formula to determine the size of the endotracheal tube required in children 1-10 yrs of age?

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College Answer

A photograph of a cuffed endotracheal tube with a connector was shown.

a) What is the diameter of the connector (shown by the arrow)?
15 mm

b) List 2 factors which predispose to obstruction of this tube in intensive care?

Lack of humidification
Infrequent physio/suctioning
Patients with large volumes of secretions

c) List 3 design features of this device which improve its safety.

i.  Clear non-toxic plastic
ii.  Low profile, high volume low pressure cuff
iii.  Radio-opaque line for identification of tip on xray iv.  Murphy’s eye
v.  Left bevelled atraumatic tip

d) Write down the formula to determine the size of the endotracheal tube required in children 1-10 yrs of age?

(Age in yrs/4) + 4        (Some use 4.25 or even 4.5 in the denominator and they are acceptable.

Discussion

The ETT and its various bits is discussed in greater detail elsewhere.

The connector pointed to is a 15mm connector, and there is a certain body which determines the size of connectors for airway equipment. The connectors are 15 and 22mm (internal diameters), conforming to ISO5356-1.

There are numerous factors which predispose the tubes to obstruction. The college has discussed the inspissation of secretions, and infrequent physiotherapy, but there are many other possibilities, such as clots due to pulmonary haemorrhage, or kinking because of patient chewing on the tube.

Safety features of the ETT are familiar. Question 30.1 from the second paper of 2013 asks this exact same thing. In summary:

  • 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

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.

References

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.