Basic Anesthetic Blocks

Introduction

Regional anesthetic blocks can be a valuable supplement or even replacement to the more common field block used in plastic surgery. The principle behind a regional nerve block is to anesthetize a sensory nerve that supplies innervation to the area of injury at a single more proximal site. The advantages of this technique over a field block are that it is usually much faster, it requires a smaller volume of local anesthetic, and it avoids distortion of the surgical site, as well the bleeding that often ensues after multiple needle sticks. It does, however, require a thorough knowledge of the anatomy of the nerve, and it does not always provide complete anesthesia to the desired site secondary to collateral innervation.

This chapter will focus on regional nerve blocks in two key anatomic regions: the face and hands.

Choice of Anesthetic Agent

The previous chapter discussed the various anesthetic agents in detail. Briefly, most blocks can be achieved using 1% lidocaine with epinephrine (1:100,000). The addition of epinephrine prolongs the duration of action of the anesthetic, as well as providing vasoconstriction of the site. Epinephrine can be used anywhere in the face; however it should not be used in the fingers or penis. The addition of bupivicaine to the lidocaine solution can prolong the duration of anesthesia for several hours, providing additional post-procedure pain relief. Furthermore, sodium bicarbonate can be added to the lidocaine solution to cut back on the burning sensation from the injection.

Choice of Syringe and Needle

A 5 ml syringe is usually sufficient for most blocks since rarely is more than this amount required. The smaller syringe is also easier to maneuver. The needle should be a 25 or 27 gauge. The length of the needle must be sufficient to reach the target. For example, the infraorbital foramen is usually reached through the oral cavity, requiring at least a 1 inch needle.

Regional Block of the Scalp

Indication

Anesthesia of the scalp down to the periosteum.

Technique

The scalp is innervated by branches of the trigeminal and cervical nerves. These nerves can be anesthetized as they penetrate the scalp. They become subfascial along

a line that encircles the head (like a skull-cap). This line passes just above the tragus and through the glabella and occiput. A wheal should be raised in the subdermal plane along this line. About 10 ml of lidocaine is required every few centimeters.

Supraorbital Nerve Block

Indication

Anesthesia of the upper eyelid and medial forehead.

Technique

Palpate the supraorbital notch/foramen at the junction of the medial and middle thirds of the orbital ridge (about 2.5 cm off the midline of the face). Raise a wheal using a 25 gauge 1 inch needle. Advance the needle until the tip meets the foramen, and inject 1-2 ml while withdrawing.

Infraorbital Nerve Block

Indication

Anesthesia of the lower eyelid, medial cheek region or upper lip.

Extraoral Technique

Place the index finger in the canine fossa pointing caudal towards the infraorbital foramen. Raise a wheal using a 25 gauge 1 inch needle about 1 cm lateral to the ala of the nose. Advance the needle towards the tip of the finger until the tip meets the foramen on the maxilla. Inject 1-2 ml into the foramen and while withdrawing. The infraorbital canal runs in a superolateral direction.

Intraoral Technique

Retract the cheek with the thumb and introduce the needle into the upper gingival sulcus above the second bicuspid. Rest the syringe on the lower lip of the patient. Aim slightly laterally away from the midline along the maxilla until the infraorbital foramen is encountered. Inject 1-2 ml into the foramen and inject while withdrawing. The infraorbital canal runs in a superolateral direction.

Mental Nerve Block

Indications

Anesthesia of the lower lip, anterior portion of the lower jaw (including the anterior lower teeth).

Extraoral Technique

The mental foramen is located directly below the root of the second lower bicuspid at the midpoint between the lower and upper margins of the mandible. The needle is inserted into the skin and a wheal is raised. It is aimed inferolaterally towards the mental foramen, and anesthetic is injected while the needle advances until bone is met. After instilling 1 ml of anesthetic, the needle is used to palpate the mental foramen after which an additional 1 ml is injected into the foramen.

Intraoral Technique

With the mouth closed, the cheek is retracted and needle inserted into the gingivobuccal sulcus below the bicuspids. A wheal is raised, and the needle is aimed towards the root of the second bicuspid and advanced at 45˚ until bone is reached. After instilling 1 ml of anesthetic, the needle is used to palpate the mental foramen after which an additional 1 ml is injected into the foramen.

Regional Block of the External Nose

Indications

Anesthesia of the skin of the nose.

Technique

The two sides of the nose should be anesthetized separately. The needle is introduced into the skin about 1 cm lateral to the alar base. A wheal is raised, and the needle is advanced towards the radix; 2-3 ml is injected along this line. The needle is withdrawn almost completely and then directed downward towards the oral commissure. An additional 1-2 ml is injected along this course. The entire procedure is repeated for the other side of the nose.

Regional Block of the External Ear

Indication

Anesthesia of the ear.

Technique

The anterior ear is supplied by the auriculotemporal nerve and the posterior ear by the greater auricular nerve and occipital nerve (including its mastoid branch). These nerves all reach the ear from the superior, posterior and inferior directions only. A needle is inserted 2 cm above the helix and advanced anteroinferiorily and posteroinferiorily. The needle is removed and inserted 3 cm posterior to the ear and advanced anterosuperiorily and anteroinferiorily. The needle is removed and inserted 1 cm below the ear, advancing it posterosuperiorily and anterosuperiorly. When these three injections are completed, a continuous infiltration around the entire ear (excluding the anterior portion) has been achieved.

Radial Nerve Block

Indication

Anesthesia of the radial dorsum of the hand and proximal thumb, index and middle finger. The ring finger should also be blocked with an ulnar nerve block.

Technique

Identify extensor pollicus longus (dorsal tendon of the anatomical snuffbox).
Insert the needle over the tendon at the base of the first metacarpal.
Inject superficial to the tendon (about 2 ml) and over the snuffbox (1 ml).

Median Nerve Block

Indication

Anesthesia of the palmar side of the thumb index finger and middle finger, and radial side of the ring finger. Also, the nailbeds of the above fingers can be blocked with this technique. The thenar region (palmar cutaneous branch of the median nerve) can also be blocked.

Technique

Identify flexor carpi radialis and palmaris longus by having the patient make a clenched fist and slight wrist flexion.
Insert the needle 2 cm proximal to the proximal wrist crease.
As the needle passes through the flexor retinaculum, 3 ml of anesthetic is injected.
Injection of an additional 1 ml above the retinaculum will anesthetize the palmar cutaneous branch supplying the thenar eminence.

Ulnar Nerve Block

Indications

Anesthesia of the little finger and ulnar side of the ring finger.

Technique

Identify flexor carpi ulnaris by having the patient forcefully ulnar deviate the wrist slightly with the fingers fully extended.
The ulnar nerve lies radial to the flexor carpi ulnaris tendon.
Insert the needle 2 cm proximal to the wrist on the radial side of the tendon directed towards the midline.
After parasthesias are felt, inject 4 ml of anesthetic in a fanwise fashion along the course of the nerve.

Digital Nerve (Ring) Block

Indications

Anesthesia of the digit.

Technique

With the dorsum of the hand facing upward, insert the needle into the dorsal skin at the midpoint between the digits (the apex of the “V” of the web space) and raise a wheal.
Advance the needle towards the palm perpendicular to the skin and infiltrate along this course about 2 ml of anesthetic.
Withdraw the needle almost completely and then begin advancing the needle towards the middle of the digit, infiltrating the skin on the dorsum of the finger base.
The digital nerves on either side of the finger should be anesthetized in this manner.

Pearls and Pitfalls

The supraorbital, infraorbital and mental foramena all lay along a vertical line that also includes the pupil in the midgaze position. Therefore, if any two of the foramena have been located, the third can be easily found.
Epinephrine requires about 10 minutes until full effect, and the same is true for lidocaine used in a regional block. Therefore, one should administer the block in advance.
Several studies reviewing thousands of cases of digital anesthesia have found that using epinephrine in the digits is entirely safe, with almost no cases of digital ischemia secondary to the epinephrine. However, until a prospective trial demonstrates the absolute safety of this practice, epinephrine should not be used in the digits.
An adequate block is not always 100% successful at eliminating pain from the site of injury. Often a supplemental field block is required after the initial regional block has taken effect.

Plastic Surgery