6. Airway Assessment Flashcards
How do you assess a patient’s airway prior to anaesthesia?
Remember:
History
Examination
Investigations
This is easy to forget in examination conditions.
History
Any history of previous problems with airway
management must be elicited and the anaesthetic
charts reviewed.
Exam
Anatomical
Mallampati
Forward mandibular movement
Anatomical problems
Obesity
Large breasts
Prominent teeth
Short, thick neck
Syndromes associated with difficult intubation
Trauma, local infection, radiotherapy
Mallampati score
This assesses the visibility of the pharyngeal structures
and assumes the view is related to the size of the tongue base.
The further assumption is that a large tongue base may
hinder exposure of the larynx.
Initially there were three proposed classes,
but Samsoon and Young added a fourth in 1987 and
this has gained common acceptance.
Mallampati score
Technique – patient sitting, head neutral, mouth fully open and tongue
fully extended, no phonation. Some suggest conducting the test twice.
Class I
Exposure of soft palate, uvula and tonsillar pillars
Class II
Exposure of soft palate and base of uvula
Class III
Exposure of soft palate only
Class IV
No visualisation of pharyngeal structures except hard palate
Forward mandibular movement
- Cervical spine movement
Assesses atlanto-occipital and atlanto-axial joint mobility.
The patient is asked to extend the head with the neck in full flexion.
- Thyromental distance
- Sternomental distance
- Prayer sign
- Thyromental distance
Described in 1983 by Patil et al. and
defined as the distance from the chin
to the notch of the thyroid cartilage
with the head fully extended.
If this is less than 6 cm,
it may be associated with difficult intubation
- Sternomental distance
Described in 1994 by Savva and defined as the distance from the
tip of the chin to the sternal notch.
If this is less than 12 cm, it may be associated with difficult intubation
- Prayer sign
Difficult intubation has been associated with the inability to place both palms
flat together and seems to be more common in diabetics
Wilson risk score
Wilson risk score:
This gives a score from 0–2 for each of the following risk factors:
Weight
Head and neck movement
Jaw movement
Receding mandible
Buck teeth
A score of 3 or more predicts 75% of difficult intubations (with 12% incidence of false-positives).
Combined predictors
Individually, these tests have only moderate sensitivity and specificity. More
recently, investigators have looked at combined predictors to try and increase
the usefulness of these tests.
The combination of Mallampati class III/IV
with a thyromental distance of less than
7 cm is predictive of a grade IV
laryngoscopy with high sensitivity and specificity
Investigations
Plain X-rays of head and neck
CT scan
Fibre-optic laryngoscopy
Some useful terms
Difficult intubation
Difficult laryngoscopy
Difficult mask ventilation
Failed oxygenation
When placement of an endotracheal tube requires more than 3 attempts
and/or more than 10 min (ASA)
Laryngoscopy
As described by Cormack and Lehane
Difficult mask ventilation
Less clearly defined but certainly a different entity to the concepts above.
One study showed a 15% incidence of difficult mask ventilation in
patients who had difficult or failed intubation.
Failed oxygenation
SpO2 < 90% with FiO2 1.0 (DAS)
How would you manage a difficult airway?
A difficult airway may be recognised pre-operatively as described above
A difficult airway may be recognised pre-operatively as described above or
may be unrecognised, presenting itself when the patient is anaesthetised +/− paralysed.
These two situations warrant different management.
The basic principles common to both include:.
Maintain oxygenation
Call for experienced (in difficult airway) senior anaesthetic help
Call for experienced surgical help
Ensure difficult airway adjuncts are available
Have working knowledge of a difficult airway algorithm.
Recognised difficult airway
With anticipated difficult airway management,
the airway should be secured with the patient awake.
Preparation in this case is essential.
Consideration should be given to the following:
- Psychological preparation of the patient
- Monitoring
- Drying agents
- Aspiration prophylaxis
- Sedation
- Oxygen supplementation
- Topical local anaesthesia +/− nerve blocks
- Topical vasoconstrictors
- Appropriate equipment
If intubation fails in recognised difficult airway , options include:
- Cancellation of surgery
- Regional anaesthesia
It must be recognised that this could result in the
need for general anaesthesia and airway control
in suboptimal conditions should the regional
block fail. - Surgical airway
