Face and neck nerve blocks

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CHAPTER 7 Face and neck nerve blocks

Nerve blocks in the head and face are useful for the repair of lacerations and for scrubbing and debriding ‘roasties’. Nerve blocks in this region are less painful to the patient than local infiltration and they do not distort the anatomy. The supraorbital nerve, the infraorbital nerve and the mental nerve all exit their foramina along a line that can be drawn 25 mm lateral to the midline of the face through the pupil and the labial angle (Fig. 7.1).

Fig. 7.1 A line drawn through the pupil and the corner of the mouth will bisect the foramina of the supraorbital, infraorbital and mental nerves (from top to bottom).

Supraorbital and supratrochlear nerve blocks

The supraorbital and supratrochlear nerves supply sensation to the fontal aspect of the scalp (the forehead). The supraorbital nerve exits the skull through the supraorbital foramen that lies in the midpupillary line, which is approximately 25 mm lateral to the facial midline along the supraorbital ridge. The supratrochlear nerve exits the skull along the upper medial corner of the orbit in the supratrochlear notch, which is approximately 15 mm medial to the supraorbital foramen. Supraorbital and supratrochlear nerve blocks can be performed from either the area of the supraorbital foramen or the area of the supratrochlear notch. When in doubt, an ‘eyebrow block’ can be used to provide anaesthesia to virtually the entire ipsilateral forehead.

Ultrasound can also be used to identify the precise location of the supraorbital foramen.

Technique

Lateral or inferior approach

If performed from the side of the supraorbital foramen (Figs 7.2, 7.3):

• Identify the target area for needle insertion – just lateral to the notch on the supraorbital ridge in the midpupillary line.

• Raise a skin weal of local anaesthetic at the site with a 25G needle.

• Puncture the skin and advance the needle posteriorly and superiorly until the bone is contacted. Withdraw the needle by 1 mm. Do not attempt to enter the foramen.

• Aspirate. If no blood is detected, inject approximately 2 to 3 mL of local anaesthetic outside the foramen above the eyebrow.

• If blood is aspirated, reposition the needle slightly and aspirate again.

• If the patient complains of paraesthesias or severe pain with injection, withdraw the needle by 1 to 2 mm before the injection is continued.

• To block the supratrochlear nerve, redirect the needle medially, with the syringe held parallel to the eyebrow, and advance it to a position 15 mm lateral to the junction of the supraorbital ridge and the root of the nose.

• Aspirate. If no blood is withdrawn, inject 1 to 3 mL of local anaesthetic. Inject a further 1 to 3 mL as the needle is withdrawn.

Fig. 7.2 The supraorbital nerve block approached from the lateral side. The needle can be advanced to block the supratrochlear nerve more medially with a single needle insertion.

Fig. 7.3 The supraorbital nerve can be blocked from inferiorly. Be careful not to insert the needle into the foramen with this approach. The supratrochlear nerve will need to be blocked with a separate needle insertion.

Medial approach

If the block is performed from the area of the supratrochlear nerve (Fig. 7.4):

• Identify the target point for needle insertion – the root of the nose at the junction of the nasal root and supraorbital ridge.

• Raise a weal of local anaesthetic at the site with a 25G needle.

• Puncture the skin with the syringe held parallel to the eyebrow. Infiltrate the skin along the length of the entire eyebrow with frequent aspiration to avoid intravascular injection.

• For this field block, 2 to 4 mL of local anaesthetic solution per side is usually sufficient, and no more than 5 mL should be injected into either side.

• Warn patients about the possibility of swelling in the upper and/or lower eyelids. There is a risk of ecchymosis or haematoma formation with this injection.

Fig. 7.4 The supratrochlear and supraorbital nerves can be blocked from a medial needle insertion. An ‘eyebrow block’ will anaesthetise the entire ipsilateral forehead.

Ultrasound assistance

Ultrasound can be used to define the exact position of the supraorbital foramen (Figs 7.5, 7.6A&B). This position can then be marked on the skin and the procedure performed blind (an ultrasound-aided technique) or the out-of-plane approach can be used to advance the needle to a point just superficial to the foramen before injecting local anaesthetic (an ultrasound-guided technique).