There is a place for regional anaesthesia in the patient with the difficult airway when it is used by a clinician who has a clear understanding of the risks involved and a clear definition of the type and likelihood of difficulty which may be experienced with intubation or ventilation. The anaesthetist must also be both proficient in regional anaesthesia and be prepared to maintain ventilation in a patient with a difficult airway who has become accidentally paralyzed.
Specifically, the risk is that a regional anaesthetic (eg subarachnoid block) may extend high enough to cause respiratory paralysis lasting for a prolonged period in a patient who cannot be intubated or ventilated.
Every candidate for major regional anaesthesia or muscle relaxation anaesthesia must be assessed with regard to the likelihood of difficult intubation. Emphasis should be placed on reduced mouth opening, enlarged tongue and restricted head extension (1, 2, 3, 4, 5).
As only about 10% of difficult or impossible intubations can be predicted with certainty, the possibility of a difficult intubation should be kept in mind even in those patients for whom regional anaesthesia is planned. Because the parturient is at particular risk of oesophageal reflux, all the equipment required to deal with a difficult intubation or airway soiling should be functional and immediately available.
Respiratory embarassment is possible following epidural or spinal anaesthesia. Low spinal (eg. saddle block) and mid-spinal (eg. to T10) have a lower risk of respiratory compromise.
Measures to reduce the risk of respiratory impairment include:
1. test dosing if an epidural is to be used,
2. care with the dose of the drug used for subarachnoid anaesthesia and,
3. appropriate posturing of the patient.
If an airway emergency occurs during regional anaesthesia in a woman with a difficult airway, there are many alternatives to intubation with the Macintosh laryngoscope. These include:
1. Belscope angulated laryngoscope (6),
2. Bullard laryngoscope,
3. flexible fibreoptic laryngoscope,
4. light wand (not practical in the emergency case),
Other intubation aids such as a flexible copper wire introducer or gum elastic bougie may also be useful.
Measures which permit ventilation of the patient without the benefit of a cuffed endotracheal tube include:
1. bag and mask,
2. laryngeal mask airway,
3. crico-thyroid puncture and
4. tracheostomy.
None of these methods should be used in an emergency by someone who is not skilled in their use.
References:
1. Bellhouse CP, Dore C. Criteria for estimating likelihood of difficulty of endotracheal intubation with the Macintosh laryngoscope. Anaesthesia and Intensive Care 1988;16:329- 337.
2. Rocke DA, Murray WB, Rout CC, Gouws E. Relative risk analysis of factors associated with difficult intubation in obstetric anesthesia. Anesthesiology 1992;77:67-73.
3. Wilson ME, Spiegelhalter D, Robertson JA, Lesser P. Predicting Difficult Intubation. British Journal of Anaesthesia, 1988; 61:211-216.
4. Frerk, CM. Predicting difficult intubation. Anaesthesia, 1991;46:1005-1008.
5. Pottecher T, Velten M, Galani M, Forrler M. Valeur comparee des signes cliniques d'intubation difficile chez la femme. Ann Fr Anesth Reanim 1991;10:430-5.
6. Bellhouse CP. A new laryngoscope for routine and difficult intubations. Anesthesiology 1988;68:126-129.