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07 / Anaesthesia · Airway

The airway lab

The mouth as the anaesthetist sees it, the larynx as the laryngoscope sees it, the sizes as arithmetic, the 4 plans as a ladder, the rapid sequence as 10 steps to be put in order, and the 9 bedside tests with what each one is worth.

Two laryngoscope handles laid out beside an assortment of straight Miller blades of increasing size.
Laryngoscope handles and straight Miller blades, the sizes side by side.

Photograph: DiverDave, CC BY-SA 3.0, via Wikimedia Commons.

A hand in uniform holds a video laryngoscope whose small screen shows the vocal cords of a training manikin.
A video laryngoscope in a class: the manikin's cords on the screen, the blade doing the looking.

Photograph: U.S. Marine Corps, Public domain, via Wikimedia Commons.

An adult size 4 single-use laryngeal mask airway, cuff deflated as it comes from the packet, with its pilot balloon, on a white surface.
A size 4 laryngeal mask, the adult default, cuff down as it comes out of the packet.

Photograph: ICUnurses, CC BY-SA 4.0, via Wikimedia Commons.

Look, then grade

The views

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Sitting up, mouth open, tongue out, no phonation

Which class is this?

Class I
Class II
Class III
Class IV

At the bedside

The assessment, test by test

How: Ask directly: has anyone ever had trouble with a breathing tube? Previous anaesthetic records, a difficult airway alert card, snoring or sleep apnoea, radiotherapy or surgery to the neck, stridor, rheumatoid disease of the neck, and syndromes with a small jaw or a large tongue.

Worry when: A previous difficult intubation, or any airway surgery or radiotherapy

Because: A documented difficult intubation outweighs every bedside test combined. It changes the plan from 'try and see' to a stated strategy, usually an awake technique or a videolaryngoscope from the first attempt.

Records are often missing. If the patient remembers being told, believe them.

Difficult mask ventilation

MOANS

  • MMask seal. A beard, facial trauma, a nasogastric tube, or a face that does not fit the mask.
  • OObesity or obstruction. BMI above 26 in the original study; upper airway obstruction from tumour, abscess or angioedema.
  • AAge over 55. Loss of upper airway muscle tone and elasticity.
  • NNo teeth. The mask has nothing to seat against. Dentures in for mask ventilation.
  • SStiff lungs or snorer. High airway pressures from asthma, COPD or fibrosis; a history of sleep apnoea.

The adjuncts

  • Oropharyngeal (Guedel) airway. Measured from the incisors to the angle of the jaw. Sizes 2, 3 and 4 for most adults. Lifts the tongue off the posterior pharyngeal wall during mask ventilation. Only tolerated once the gag reflex has gone.
  • Nasopharyngeal airway. Measured from the nostril to the tragus; 6 to 7 mm for most adults. Tolerated in the lighter patient. Avoided in base of skull fracture and severe coagulopathy; the nose bleeds.
  • Bougie. 15 French adult, with the angled coude tip. Passed blind under an epiglottis in a grade 3 view; tracheal rings are felt as clicks and it stops at the carina. The tube is railroaded over it with the bevel rotated to the left.
  • Videolaryngoscope. Macintosh-shaped or hyperangulated blades; the latter needs a stylet. Improves the view in almost every difficult airway. A good view is not the same as an easy tube: the tube still has to turn the corner.
  • Second-generation supraglottic airway. By weight: 3 for 30 to 50 kg, 4 for 50 to 70 kg, 5 for 70 to 100 kg. A gastric drainage port and a higher seal pressure. Plan B in the difficult airway and the everyday airway for most day-case surgery.

Sizes

The tube and the mask for this patient

Sex, for the adult sizes

Tracheal tube

5.0 cuffed

5.5 uncuffed · depth 15 at the lips (18 nasal)

Uncuffed ID = age/4 + 4. Cuffed ID = age/4 + 3.5. Oral depth = age/2 + 12 cm.

Have the size above and below ready. The narrowest point of a child's airway is the cricoid ring, so a tube that passes the cords can still be too big: check for a leak at 20 to 25 cmH2O.

Laryngeal mask

Size 2.5

20 to 30 kg · cuff up to 14 mL

11.522.53456

Seat it, inflate to a seal rather than to the maximum, and check the capnograph. A second-generation device adds a gastric port.

Why preoxygenation matters

Time to desaturation during apnoea

at 3.0 min
1009080706050400246810minutes of apnoea
  • Healthy 70 kg adult: 8.7 min to 90%. A full functional residual capacity of oxygen against a resting consumption of about 250 mL a minute.
  • Moderately ill 70 kg adult: 5 min to 90%. A smaller effective reservoir and a higher oxygen consumption: sepsis, fever, and shunt all eat into the margin.
  • Healthy 10 kg child: 3.7 min to 90%. A high metabolic rate against a small reservoir. Children desaturate fast and then bradycardia follows.
  • Obese 127 kg adult: 2.7 min to 90%. The functional residual capacity is squeezed by the abdomen and the chest wall, and oxygen consumption is higher. Ramping and head-up positioning are what buy time.

When it is difficult

Plan A, B, C, D

Plan A

Make the first attempt the best attempt, and stop after three.

  1. 1Position: ramped so the ear is level with the sternal notch, neck flexed on the chest, head extended on the neck.
  2. 2Preoxygenate to an end-tidal oxygen above 0.85, and give apnoeic oxygen through nasal cannulae at 15 L/min throughout laryngoscopy.
  3. 3Full neuromuscular blockade before laryngoscopy: a partly relaxed larynx is the commonest self-inflicted difficulty.
  4. 4Direct or video laryngoscopy, with a bougie or stylet from the outset if any difficulty is predicted.
  5. 5Each further attempt changes something: blade, position, external laryngeal manipulation, or the operator. Remove cricoid pressure if it is worsening the view.
  6. 6Confirm placement with sustained waveform capnography, and nothing else.

The limitThree attempts, plus one by a more experienced colleague.

ThenDeclare failed intubation out loud and move to Plan B.

Rapid sequence induction

Put the ten steps in order

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Tap the next step

The sequence so far

  1. 1…
  2. 2…
  3. 3…
  4. 4…
  5. 5…
  6. 6…
  7. 7…
  8. 8…
  9. 9…
  10. 10…
Drill itCannot intubate, cannot oxygenateDrill itLaryngospasmRead itThe airway ladder, taught