Difficult Airway Algorithm
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Direct answer
The Difficult Airway Society 2015 guidelines for unanticipated difficult intubation in adults run as a fixed cascade: Plan A is optimised laryngoscopy and tracheal intubation, limited to a maximum of three plus one attempts by the most experienced anaesthetist, declaring failure aloud; Plan B is supraglottic airway insertion — a second-generation device such as an i-gel, up to two attempts — to declare "failed intubation with supraglottic airway success"; Plan C is face-mask ventilation with a final attempt at re-establishing oxygenation, waking the patient if it fails; and Plan D is the can't intubate, can't oxygenate (CICO) emergency, resolved in adults by a scalpel cricothyroidotomy — scalpel, finger, bougie, then a cuffed 6.0 mm tube — because cannula techniques through the cricothyroid membrane have been abandoned for adults. The entire algorithm exists to stop clinicians repeating laryngoscopy while the saturation falls; oxygenation, not intubation, is the objective at every step.
What you must remember
- Plan A optimisation between attempts: change of head position, adjuncts, a bougie, external laryngeal manipulation, a different blade or videolaryngoscope, and a more experienced operator — the "3+1" limit exists because each repeated attempt worsens bleeding and oedema.
- Plan B device: a second-generation supraglottic airway, with the i-gel preferred; sizes 3, 4 and 5 fit roughly 30-50 kg, 50-70 kg and 70-100 kg, and success means oxygenation plus the decision to wake or proceed.
- Plan C options: with a working supraglottic airway but failed intubation, either wake the patient or proceed with an LMA-preferred technique (intubation through the i-gel or a flexible scope) depending on urgency, saturation and surgery.
- Plan D threshold: declaring CICO when oxygenation fails despite Plans A-C — declare it loudly, call for surgical and senior help, and start scalpel cricothyroidotomy without delay.
- Scalpel cricothyroidotomy sequence: transverse stab over the cricothyroid membrane, extend with scissors or the scalpel, pass a bougie, railroad a cuffed 6.0 mm tracheal tube, confirm with capnography — one attempt, then surgical airway by the ENT or general surgeon.
- Technician's CICO drill: know the exact drawer of the emergency airway box — scalpel (number 10 or 20 blade), bougie, cuffed 6.0 tube, and a size 4 i-gel — and be able to open and lay it out within sixty seconds, a genuine exam viva scenario.
- Anticipated difficulty runs a different path: awake fibreoptic intubation, or maintaining spontaneous ventilation with an inhalational induction, rather than paralysing an airway predicted as difficult.
Running the algorithm on a real list
A 58-year-old diabetic with a limited neck extension is induced for an emergency laparotomy; after rocuronium, laryngoscopy shows only the epiglottis (Cormack-Lehane grade III). The algorithm's discipline starts here. Attempt two is announced as the final attempt by this operator: head repositioned, bougie in hand, videolaryngoscope brought in, external laryngeal manipulation applied — the technician performing each requested change rather than waiting. It fails. The verbal declaration "failed intubation" is the algorithm's most important step because it forces the next plan while the SpO2 still reads the nineties.
Plan B: an i-gel size 4 is inserted and a clear capnography trace returns. The guidelines now frame the decision explicitly — wake or proceed: with a functioning i-gel in a paralysed patient for an emergency laparotomy, intubation proceeds through the device with a flexible scope or Aintree catheter. Had the i-gel failed, Plan C two-person face-mask ventilation buys time toward waking the patient; and if the mask fails too — the CICO moment — the declaration goes out and the scalpel cricothyroidotomy set is opened. Each plan is time-boxed and declared, and the person who runs out of plans gracefully is the one who moved between them early.
High-yield viva angles
Examiners probe three specific points. First, the attempt limit: quoting "three plus one" attempts in Plan A, and knowing that the guideline's real message is failure declaration, shows the algorithm was understood rather than memorised. Second, why the scalpel replaced the cannula in adults: narrow cannulae through the cricothyroid membrane kink, dislodge and deliver inadequate jet-ventilation flows, and transect with jet ventilation; the scalpel-finger-bougie technique creates a definitive cuffed airway in one step — this reasoning is a favourite discriminator question. Third, the paediatric divergence: in small children the algorithm permits supraglottic airway and face-mask optimisation for oxygenation but the front-of-neck rescue remains specialist territory, so the technician's role is calling for senior help early and preparing the rigid bronchoscope trolley.
Frequently asked questions
What are Plans A to D in the difficult airway algorithm?
Plan A optimised laryngoscopy with a maximum of three plus one attempts, Plan B supraglottic airway rescue, Plan C face-mask ventilation with waking the patient, and Plan D scalpel cricothyroidotomy for can't intubate, can't oxygenate.
How many intubation attempts does Plan A allow?
Three by the best available laryngoscopist plus one final attempt by a senior operator; each attempt must be different and better, and failure must be declared aloud.
Which front-of-neck rescue is recommended for adults?
Scalpel cricothyroidotomy — scalpel-finger (or bougie)-tube with a cuffed 6.0 mm tracheal tube — because cannula techniques have unacceptably high failure and complication rates in adults.
What sizes fit an i-gel in Plan B?
Size 3 for 30-50 kg, size 4 for 50-70 kg and size 5 for 70-100 kg, inserted without cuff inflation; a capnography trace through the device confirms ventilation.
When is waking the patient the correct strategy?
When oxygenation is achievable through mask or supraglottic airway, the patient is not paralysed beyond recovery, and the surgery is not immediately life-saving — the default choice over persisting in an elective case.