Topical anesthesia of the airway is generally required in two situations:
1. Preparation for nasal or oral awake fiberoptic intubation, especially when minimal or no sedation is used
2. When endotracheal intubation is performed without muscle relaxation in anesthetized patients
Two types of 'equipment' are needed to establish topical anesthesia of the airway, these are drugs and devices to deliver those drugs.
Drugs used for topical anesthesia of the airway are primarily local anesthetics (obviously), vasoconstrictors/ decongestants, and anti-sialogogues.
- Local anesthetics
Lidocaine is the most commonly used local anesthetic due to its relatively fast onset of action and superior safety profile. A higher-strength 4% (topical-only) Lidocaine preparation is available, as are various formulations of viscous Lidocaine/ Lidocaine gel.
- Vasoconstrictors/ decongestants
A number of agents have been successfully used as nasal decongestants. They are all sympathomimetic vasoconstrictors and include cocaine, phenylephrine, ephedrine, oxymetazoline and xylometazoline.
Care must be taken with regards to unwanted systemic sympathomimetic effects of these drugs, i.e. tachycardia, vasoconstriction and central nervous system stimulation. This is paricularly true in patient with hypertension and cerebrovascular or coronary artery disease.
Unless the patient has a cardiovascular contraindication to receiving glyocopyrrolate, we suggest to give 0.2- 0.4 mg intravenously to reduce secretions in the oro- and hypopharynx. For best effect do this before administering topical local anesthetics.
Many practitioners like to supplement their airway anesthesia technique with intravenous sedation, using hypnotic drugs such as Dexmedetomidine, Propofol and Benzodiazepines or centrally-acting drugs which suppress laryngeal reflexes such as Remifentanil or Alfentanil. While there is nothing wrong with this in principle, please do not rely on sedatives to compensate for poor local anesthetic technique. In addition, in cases where you provide topical airway anesthesia for awake fiberoptic intubation, please consider carefully why you chose this approach in the first place. Most likely you expect a difficult airway and want to maintain spontaneous respiration until intubation is achieved. Think for a minute about what would happen if you got your iv sedation wrong and the patient became apneic! Would you have a 'plan B'?
Also bear in mind that patients with critical airway obstruction requiring awake fiberoptic intubation might be retaining CO2 and be very sensitive to the effects of intravenous sedation.
Amount of intravenous sedation given should be inversely related to the anticipated difficulty of the airway!
2. Drug delivery devices
These include a range of purpose-designed nebulizers, atomizers, nasal pledgets, etc. and some devices which have been designed for other applications but are usefule for 'topicalizing' the airway. They are described here.
A large variety of techniques to deliver local anesthetics to the airway has been described. We'll first list a selection of these methods and then suggest a sequence/ combination of these techniques which works in our experience.