Nerve Block

Nerve block anesthesia is effected by an injection of a small amount of local anesthetic around a nerve, resulting in anesthesia within the area supplied by that nerve. The volume of anesthetic used in these procedures is small and so there is a low risk of systemic toxicity. In contrast to the infiltrative method, there is almost no imbalance with nerve blocks and it is associated with less discomfort. However, this method requires good technical and anatomical knowledge to obtain optimal results with few injections and to avoid adverse events. There is the possibility of inadvertent laceration of the nerve and blood vessel injuries. Long-lasting dysesthesia and hematoma or ecchymosis may occur in a few patients, which may be quite distressing (Laskin 1984).

The sensitivity and motion of the face are dependent on the fifth pair of cranial nerves (Fig. 4.1). The main trigeminal branches have independent exits from the skull. The ophthalmic branch is more superior and passes inside the orbit, forming the frontal branch, which bifurcates into the supraorbital and supratroch-lear nerves. The other two branches are the maxillary nerve, which produces the infraorbital nerve, and the mandibular nerve, which is the largest and the only one to contain motor fibers, and which produces the mental nerve. Nerve block is usually achieved with 1 or 2% lidocaine. A combination of epinephrine and lidocaine is preferable when a quicker and longer-lasting anesthetic response is required. Care should be taken not to inadvertently inject this into the blood vessels. Epinephrine should also be avoided in patients with hypertension or cardiovascular diseases.

Pain results from tissue expansion during the injection and as a result of irritation from the anesthetic itself. Gentle injections are preferable and provide a quite tolerable nerve block.

Fig. 4.1 The areas supplied by the main facial nerves (de Maio 2004)

Supraorbital Nerve Territory

Fig. 4.1 The areas supplied by the main facial nerves (de Maio 2004)

4.6.1 The Supraorbital Nerve

4.6.2 The Supratrochlear Nerve

4.6.1.1 Anatomy and Territory

4.6.2.1 Anatomy and Territory

The supraorbital nerve exits the skull through the supraorbital foramen, which lies along the supraorbital ridge in the midpupillary line. It supplies the forehead.

The supratrochlear nerve exits the skull along the medial corner of the orbit.

It supplies the medial portion of the forehead.

4.6.2.2 Technique

4.6.1.2 Technique

Inject 0.5-1 ml lidocaine right into the depression in the internal third of the eyebrows (supraorbital notch) with the needle pointed toward the forehead (Figs. 4.2 and 4.3).

Inject 0.5-1 ml lidocaine at the junction of the root of the nose and the upper rim of the orbit, just below the medial portion of the eyebrow

Supraorbital Nerve Block
Fig. 4.2 Anatomy and blocking of the supraorbital nerve. 1=external branch of the frontal nerve; 2 and 3=internal branch of the frontal nerve (de Maio 2004)
Supraorbital Block
Fig. 4.3 Blocking of the supraorbital nerve
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Responses

  • gundolpho
    Where to inject lidocaine for facial nerve blocks?
    8 years ago

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