The interincisor distance recorded at the preoperative visit is the one everyone plans from, and it is the wrong one. Mouth opening changes with induction - relaxation can improve it, and loss of the patient's voluntary effort can make it worse - so the number you assessed the airway on may not be the number you have when the laryngoscope goes in.
So measure it again after induction, before the first attempt, in any patient whose airway you were already concerned about. It takes seconds and it is the last point at which the plan can still change cheaply. If the opening has shrunk below what your chosen device needs, that is the moment to pick a different blade or a different technique, not after two failed attempts.
Record both numbers. A patient whose mouth opening falls under anaesthesia will do so again, and an alert card or an anaesthetic record that says 'mouth opening 30 mm awake, 20 mm after induction' tells the next anaesthetist something that no preoperative assessment can.
- Measure the interincisor distance awake, and again after induction before the first attempt, in any anticipated difficult airway
- Use the post-induction figure to choose the device, not the preoperative one
- Be particularly alert in degenerative cervical spine disease, where the fall is most likely
- Record both numbers in the anaesthetic chart and on any alert card you issue
- Have the alternative device physically in the room before induction, not in a trolley down the corridor
Why it matters
The airway assessment everyone plans from is made under conditions that no longer apply at the moment of intubation.
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