Retrobulbar Block Anesthesia - Techniques, Indications, Contraindications and Treatment

Introduction

Regional or local anesthesia means injecting a local anesthetic drug to numb a small body area. For eye surgeries, only regional anesthesia is sufficient to obtain akinesia of the eyeball (loss of ability to move the eye voluntarily due to paralysis of ocular muscles) and sensory block.

The anesthetic techniques for eye surgeries also include general anesthesia.

What Is Retrobulbar Block Anesthesia?

A retrobulbar block is a regional anesthetic nerve block administered behind the globe of the eyeball, which is called retrobulbar space. Herman Knapp first described the technique in the year 1884.

The Nerves Anesthetized in This Technique Are:

• 3rd cranial nerve or Oculomotor nerve.

• 4th cranial nerve or Trochlear nerve.

• 6th cranial nerve or Abducens nerve.

• Ciliary nerves.

• Ciliary ganglion (collection of nerve bodies).

The Structures Anesthetized in This Technique Are:

• Cornea.

• Uvea.

• Conjunctiva.

• Extraocular muscles.

• Levator palpebrae suprioris.

• Superior oblique.

• Inferior oblique.

• Lateral rectus.

• Medial rectus.

• Superior rectus.

• Inferior rectus.

What Is the Technique of Retrobulbar Anesthesia?

Materials Needed:

• Atkinson or retrobulbar needle (23 or 25-gauge and 38 mm in length).

• 5 ml or 10 ml syringe.

• 5 percent ophthalmic Betadine.

• An anesthetic agent.

• A gauze pack.

Patient Preparation:

• The technique starts with proper patient preparation to minimize complications. Intravenous sedation is often used to maximize patient cooperation and obtain amnesia and analgesia.

• The anesthetic commonly used is short-acting. A topical agent can numb the surface of the eye before the surgery.

• All the vital signs-pulse, body temperature, breathing rate, and blood pressure, are monitored.

• The patient's position is supine, with the head on a flat surface. Oxygen Supplementation is given. The next crucial thing is the choice of an anesthetic agent, which depends on the duration of surgery.

• Lidocaine 2 percent with Bupivacaine 0.75 percent is the most commonly used combination of drugs. Hyaluronidase can be used as an additional drug to fasten the spread of anesthesia.

Technique:

• Firstly proper patient preparation, vital signs monitoring, and positioning are done.

• The patient is placed in the primary gaze position looking straight forward.

• The lower eyelid is sterilized with Betadine solution. The inferior orbital rim is palpated and located, pushing the eyeball slightly to clear the site for needle insertion. The site of needle insertion is approximately ⅓ from the eye corner.

• The needle bevel should face downwards towards the globe to prevent perforation.

• The needle is inserted perpendicularly through the lower eyelid in the sagittal plane. Then the needle is advanced with an inclination angle of 10 50 15 degrees and parallel to the orbital floor.

• After advancement of 1 cm, when a 'pop' is felt in the orbital septum, an inclination of 30 to 45 degrees is taken superonasal and inserted for 2.5 to 3.5 centimeters intraconal.

• After the needle is in place, the globe is checked for any perforation, and aspiration is done.

• With no blood with aspiration, slowly deposit 2 to 4 ml of anesthesia and retract the needle.

• Then apply pressure over the site of injection for 5 minutes with eyes closed to ensure fast diffusion and prevent retrobulbar hemorrhage.

• Check for induction and extent of akinesia and anesthesia after 5 minutes.

What Are the Indications of Retrobulbar Anesthesia?

Retrobulbar anesthesia is used in various surgical procedures:

Intraocular Surgery: Surgery performed on the eye and its associated structures)

• Cataract surgery (replacement of damaged cloudy lens with a clear artificial lens).

• Vitrectomy (surgery to remove the vitreous humor and access the retina).

• Tube shunt placement (placement of a flexible plastic tube for drainage of aqueous humor from the eye).

Cyclodestructive Procedures: They are a group of modalities used to destroy the ciliary body to lower the aqueous humor secretion and intraocular pressure.

• Diathermy.

• Cryotherapy.

• Cyclophotocoagulation.

• Endocyclophotocoagulation.

• Ultrasound and lasers.

Corneal Procedures:

• Corneal transplant.

• Pterygium surgery.

Strabismus Surgery: It is an eye alignment surgery done to correct misaligned eyes.

Orbital Surgery.

Enucleation and Evisceration.

What Are the Contraindications of Retrobulbar Anesthesia?

• Infection - Any active infection in the eye is a contraindication. The infection needs to be treated for the local anesthetic drug to work.

• Hypersensitivity - Any known allergy to any anesthetic drug or its components should be considered a contraindication.

• Nystagmus - Uncontrolled, rapid, and repetitive movements made by the eye are called nystagmus.

• Increased axial eye length.

• Thyroid associated with orbitopathy.

• Scleral buckling.

• Anticoagulant therapy.

• Bleeding diathesis.

What Are the Complications of Retrobulbar Anesthesia?

• Allergy: It can happen with an ester type of local anesthesia.

• Retrobulbar Hemorrhage: It means a collection of blood in the retrobulbar space behind the eye. It is the most common complication in this technique. It can cause an immediate rise in intraocular pressure, proptosis, and drooping of upper eyelids. It can further lead to obstruction of the central retinal artery.

• Intradural or Subarachnoid Injection: This is the spread of local anesthesia to the central nervous system characterized by vomiting, drowsiness, blindness, convulsion, respiratory failure, and cardiac arrest.

• Diplopia: Diplopia means double vision that occurs secondary to local anesthetic toxicity.

• Ocular Perforation: Penetrating injuries to the eye can lead to a severe loss of vision. It is more common with a myopic eye (longer and thinner than normal). Symptoms include sudden loss of vision and pain during the block.

• Cardiorespiratory Distress: It includes rapid breathing, shortness of breath, low blood pressure, and extreme fatigue.

• Oculocardiac Reflex: It is also called Aschner or trigeminal vagal reflex. It is the phenomenon of a decrease in heart rate due to direct pressure on extraocular muscles or conjunctiva. It can happen after hemorrhage; hence patients with hemorrhage should be observed.

• Damage to Optic Nerve: Damage made to the optic nerve can be either a contusion (direct injury due to trauma) or atrophy causing blurred vision; a reduction is the sharpness of vision and loss of ability to see colors and react to light.

• Vascular Retinal Occlusion: It is the block in the blood supply to the eye's retina. It will be a consequence of dural penetration and injection of the local anesthetic drug into the subarachnoid space.

• Chemosis: The swelling of the conjunctiva is called chemosis. It can be avoided when anesthesia is given slowly, and it can interfere while giving stitches.

• Corneal Abrasion: A scratch on the corneal layer is called a corneal abrasion.

• Ptosis: Drooping of the upper eyelids is ptosis.

• Postoperative strabismus.

What Are the Other Local Anesthetic Techniques of the Eye?

• Topical Anesthesia: It is superficial anesthesia without the complications caused due to injections. It will anesthetize the superficial cornea and conjunctiva by blocking nasociliary and lacrimal nerves. It has the advantages of being safe, avoiding the use of needles, and does not cause vision changes.

• Peritubular Block: In this block, local anesthesia is injected into the peribulbar space (space present behind the eye).

• Parabulbar or Sub-Tenon Block: The anesthesia is given into the sub-tenon space.

• Intracameral Block: It is given as an adjunct to local anesthesia.

Conclusion

There is a possibility of death with retrobulbar anesthesia present when the drug is accidentally injected into the optic. Then this spreads to subarachnoid space, leading to the brainstem and brain. With that patient will show signs of brainstem anesthesia. However, with proper emergency treatment, the patient can recover completely.