Peribulbar Block

The peribulbar block:

Indications

Anaesthesia and akinesia of the globe for:

  • Cataract extraction
  • Trabeculectomy
  • Vitrectomy
  • Strabismus repair

Contraindications

Should be avoided when:

  • Axial length is >26mm
    ↑ risk of globe perforation, particularly due to risk of posterior staphylomas.
  • Severe coagulopathy
  • Perforated globe
  • Infected eye
  • Inability to lie flat
  • Staphyloma
    ↑ risk of globe perforation.

Anatomy

The orbit:

  • Takes a truncated pyramid shape
  • Contains mostly fat
  • Is divided into three parts, based on their contents:
    • Intraocular compartment contains the globe:
      • Lies anteriorly
      • Equator of the globe lies at the lateral border.
    • The intraconal compartment contains the six extraocular muscles
      The inferior and lateral rectus muscles sit at inferiorly and nasally respectively, so the greatest gap between them lies is inferonasally.
      • The four rectus muscles form the retrobulbar cone
        Contact the walls of the orbit.
        • The intraconal space lies within these muscular attachments
          Intraconal injection of local anaesthetic produces anaesthesia and akinesia of the globe and extraocular muscles.
        • The extraconal space is a potential space lying between these muscles and the orbital wall
    • The extraconal compartment
      Consists of fat sitting between the extraocular muscles and the bony walls of the orbit, and communicates freely with the intraconal component.

The globe is:

  • Spherical
  • Covered in three layers:
    • Cornea and sclera
      • Cornea is translucent and covers the iris
      • Sclera is opaque, and covers the rest
        The circumferential junction of the cornea and the sclera is called the limbus.
    • Tenon’s capsule covers the scleral portion
      Connective tissue layer acts as the fascial sheathe of the globe. The capsule:
      • Lies deep to the conjunctiva
      • Superficial to the sclera
      • Anteriorly merges ~1mm with the limbus
      • Posteriorly merges with the optic nerve sheathe
  • Attached to each of the extraocular muscles
  • Divided into the anterior and posterior segments:
    • Anterior segment
      Small, containing:
      • Aqueous humor
    • Posterior segment
      Large, containing:
      • Lens
      • Vitreous
      • Retina
      • Macula
      • Optic nerve
    • Segments are separated by the iris, and communicate via the pupil

Equipment

  • Gauze
  • Antiseptic
    Typically 50% saline with 50% aqueous betadine
  • Topical local anaesthetic drops
  • Mix LA solution
    Many different options exist.
    • Lignocaine/Ropivacaine
      • Take 40mls of 1%% ropivacaine, 10ml 10% lignocaine, and 1500 units of hyaluronidase
      • Into a 50ml syringe, draw up the local anaesthetics and mix in the hylauronidase
      • This gives a combination of 0.8% ropivacaine, 2% lignocaine, and 30U/ml hyaluronidase
        Hyaluronidase concentrations of 30U/ml or greater are associated with periorbital cellulitis.
    • Ropivacaine alone
      0.75-1% ropivacaine with 75-150 U/ml hyaluronidase.
  • A needle
    Typically 23-27G.
  • A syringe
    Typically 10ml.
  • Minimum volume extension
    Removes weight of syringe from needle improving manual dexterity.

Technique

Avoid oversedation - patients are usually frail, and the very fine needles are minimally painful. A small dose of midazolam and alfentanil are adequate for good conscious sedation.

Assumes monitoring, IV access, time-out, topical local anaesthetic drops, and conscious sedation have been performed, as discussed here.

  • Apply antiseptic
    Ensure there is some antiseptic under the lower lid and in the conjunctival sac.
  • Ask the patient to look directly ahead
  • Perform block:
    • Palpate medial two-thirds and lateral one-third of the inferior rim of the orbit
      This should be lateral to the limbus, to avoid damaging the fragile extra-ocular muscles.
    • Using a 23-27G needle, advance directly backwards
      Parallel to orbital floor. Limit insertion depth to 25mm.
      • Avoid displacing the globe with a finger - this may cause globe rotation and the posterior part to move into the path of the needle
      • Bevel should be orientated supero-medially
      • If contacting bone, redirect slightly superiorly
      • If the globe rotates, this suggests scleral contact
        Ensure patient can move eye freely once in at desired depth.
      • Slight superior and medial angulation can be performed once past the equator of the globe
    • Aspirate, then inject 4-10ml of LA
      • Cease injection if the globe becomes tense
  • Use digital pressure or a Honan balloon to compress the globe, reducing LA volume and therefore IOP
  • Assess for block efficacy
    Assess:
    • Eye opening
      Levator block is usually a good indication of block efficacy.
    • Eye movements
    • Eye closing
    • Vision
      Difficult to interpret; normal findings include:
      • Normal vision
      • Grayscale vision
      • Flashing lights
  • If required, a top-up block can be performed with a different technique:
    • Using a 30G 13mm needle
    • Place needle between the caruncle and medial canthus
    • Aim directly back, perpendicular to the coronal plane
    • Inject 3-4ml LA

Complications

Minor complications:

  • Chemosis
    Subconjunctival swelling. Transient.
  • Venous haemorrhage
    Cosmetic but rarely significant.
  • Arterial haemorrhage
    May be dramatic, leading to rise in IOP. Usually requires postponing OT, but may require canthotomy.

Major complications:

  • Globe perforation
    Due to direct trauma.
    • ↑ risk with myopia, repeated injections
    • Presents with ocular pain, intraocular haemorrhage, restlessness
      May not be immediately obvious.
  • Retrobulbar haemorrhage
    Due to direct trauma.
    • Presents with bruising, propotosis, and pain
      Inadequate retinal artery flow may require a lateral canthotomy to relieve IOP and prevent loss of vision.
    • May be subtle, occasionally presents as rapid orbital swelling and proptosis.
  • Optic nerve damage
    Due to direct injury or vascular occlusion.
    • Presents with visual loss
  • Intraarterial injection
    Flow down the ICA may result in the dose of LA being delivered directly to midbrain structures.
    • May present with seizure or CVS toxicity
  • Brainstem anaesthesia
    Due to needle passing through the nerve sheath, resulting in subarachnoid deposition of LA.
    • May present with a broad array of symptoms, including respiratory or CVS arrest, agitation, ptosis, dysphagia, confusion
  • Oculocardic reflex
    Due to raised intraocular pressure.
    • Presents with bradycardia, which may be profound.

References

  1. Ripart J, Mehrige K, Rocca RD. Local & Regional Anesthesia for Eye Surgery. NYSORA.
  2. Chuan A, Scott DM. Regional Anaesthesia: A Pocket Guide. 1st Ed. Oxford University Press