OCULAR Anesthesia
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Transcript of OCULAR Anesthesia
OCULAR ANESTHESIAModerator : DR. Padmajothi M S Presenter: Dr. Darshan S M
Objective
To assure safe surgical procedure by achieving akinesia, anesthesia & apropriate hypotony.
SURGICAL SPACES IN THE ORBIT Subperiosteal space : between the orbital bones
and the periorbita
Peripheral orbital space (anterior space) : bounded peripherally by periorbita and internally by 4 recti
Central space (muscular cone or retrobulbar space): Anteriorly : Tenon’s capsule peripherally: 4 recti posterior : continuous with peripheral space
Sub-Tenon’s space: between sclera and tenon’s capsule
Key feutures
Topical anesthesia
Local anesthesia
Local anesthetic agents
Lidocaine 2% > Onset of action : 5-10 mins > Duration of action : 1-2hrs
Bupivacaine 0.75% > Onset of action : 15-30mins > Duration of action : 5-10hrs
Epinephrine 1:100,000 > minimise systemic absorption
of anesthetic agents > prolong the duration of action > minimise bleeding > systemic effects may b harmfull.
Hyaluronidase
Enhances diffusion of anesthetic mixture through tissues
Use 75 units per 10ml anesthetic solution
Lidocaine 2% with or without epinephrine 1:100,000 (5ml)
Bupivacaine 0.75% (5ml)Hyaluronidase ( 75 units ) Therfore the final concentrations
in the anesthetic mixture are lidocaine 1%, bupivacaine 0.37%, epinephrine 1:200,000 & hyaluronidase 7.5 units per ml
Topical anesthesia
The first modern use of topical anesthesia was by Koller in 1884 with cocaine.
Benoxinate 0.4%, an ester (commonest & safest )
Other agents : tetracaine 0.5% , 1% amethocaine proparacaine (proxymetacaine) 0.5%; short acting (20 minutes) and are the least toxic to the corneal epithelium.
Lidocaine 4% and bupivacaine 0.5% and 0.75% have a longer duration of action but an increased associated corneal toxicity
Aim
To block the nerves that supply the superficial cornea and conjuctiva
> long & short ciliary nerve > nasociliary nerve > lacrimal nerve
Technique
The patient is asked to focus on the source of the light
> Small sponge soaked with the
drops can be kept in the inferior and superior fornix or a ring saturated with drops can placed in the paralimbal region to maintain corneal clarity
ADVANTAGES
• No risk associated at needle insertion
• No risk of periocular hemorrhage
• Functional vision is maintained
• No postoperative diplopia or ptosis
• Patients are fully alert
DISADVANTAGES
• An awake and talkative patient can be distracting for the surgeon
• No akinesia of the eye • If difficulties or problems
occur the anesthesia may not be adequate
Retrobulbar block
Aim to block the oculomtor
nerves before they enter the four muscles in the posterior intraconal space.
Local anesthetic is delivered within the muscle cone itself.
Into Central space
Using 22 G 35 mm long needle
In the Inferotemporal quadrant
At Junction of lateral 1/3rd and medial 2/3rd of inferior orbital margin
4-5 ml of local anaesthetic agent Bupivacaine 0.75% 5
ml Lidocaine 2% 5 ml with
adrenaline Hyaluronidase 75
units/m
Palpate inferior orbital rim. Place needle perpendicular
through skin , locate needle 1/3rd distance from lateral to medial canthus
Place just superior to inferior orbital rim
Inject 0.5ml of solution s/c to reduce pain when orbital septum is pierced
Advance needle parallel to orbital floor perforating the septum
After equater of globe is passed direct needle superonasally at 30 degree angle , advance ,piercing intermuscular septum and enter muscle cone,inject 4-5ml of anesthetic
Advantages
• A retrobulbar block is reliable for producing excellent anesthesia and akinesia
• The onset of the block is quicker than with peribulbar; it usually occurs within 5 minutes
• Low volumes of anesthetic ,results in a lower intraorbital tension and less chemosis than with peribulbar blocks
• Loss of visual acuity occurs in a greater number of patients compared to peribulbar blocks, though this can be volume dependent
Disadvantages
The main disadvantage of retrobulbar blocks is that the complication rate is higher than for peribulbar blocks – the reason for the development of the peribulbar block
Complications
There is a 1–3% chance that complications will occur with retrobulbar block.
Retrobulbar hemorrhage Ocular perforation (< 0.1%
incidence, but 1 in 140 injections in myopic eyes)[
Subarachnoid or intradural injection, leading to brainstem anesthesia in 1 in 350–500 patients
Muscle complications: ptosis from levator aponeurosis dehiscence, entropion and diplopia following extraocular muscle injection
Oculocardiac reflex, usually produced by pressure on the globe (vasovagal bradycardias are more common)
RETROBULBAR HEMORRHAGE Most common ,due to inadvertant puncture
of vessels within retrobulbar space. Simultaneous appearance of an excellent
motor block of the globe, closing of the upper lid, proptosis and a palpable increase in intraocular pressure.
It can lead to stimulation of the oculocardiac reflex.
the best course of action to postpone surgery for 2-4 days after hemmorhage
PUNCTURE OF THE GLOBERisk factors : High myopia (axial
length greater than 26 mm),Sharp injection needlePrevious scleral buckling Inexperience in performing local
blocks Poor patient complianceSIGNS: Sudden loss of
vision,hypotonia,poor red reflex
PERIBULBAR ANESTHESIAThe injection is outside the muscle cone
Spreads by way of diffusion to block the orbital nerves, including the IV nerve.
25 G ,25 mm long needle
Place needle perpendicular through skin
Locate needle 1/3rd distance from lateral to medial canthus
Technique 1st injection
Place just superior to the inferior orbital rim
Advance parallel to orbital floor,peforating orbital septum
Hub of needle should not go beyond inferior orbital rim.
Aspirate to avoid blood vessel and inject 3ml of anesthetic solution .
Apply pressure to prevent hemorrhage and facilitate diffusion of anesthetic
2nd injectionLocate needle by supraorbital
notch, place needle just Inferior to the superior orbital rim, advance needle straight back ,inject 3ml of anesthetic.
ADVANTAGES
The risk of complications associated with peribulbar block is low
Peribulbar block has all the advantages of retrobulbar block
DISADVANTAGES Peribulbar blocks have all the
disadvantages of retrobulbar blocks, but less frequently
The quality of akinesia and anesthesia may
not be as good as with retrobulbar block Often more than one injection is required
The block takes much longer to work—it can take up to 30 minutes
The Honan balloon may be uncomfortable for the patient
Chemosis occurs in 80% of cases, which makes operating conditions difficult
In 5.8% of both retrobulbar and peribulbar blocks, ptosis can remain for up to 90 days
PARABULBAR ANESTHESIASub Tenons block /pin point
anesthesia/medial episcleral block.
Post limbal, sub Tenon’s incision (1 mm)
Inferonasal quadrant - good fluid distribution,avoids damage to vortex vein
Short ciliary nerves are blocked
The conjunctiva is anesthetized first with drops of the local anesthetic of choice.
The commonest approach is by the infranasal quadrant
The eye is cleaned and the patient asked to look upwards and outwards.
Aseptically, the conjunctiva and Tenon’s capsule are picked up 3–5 mm away from the limbus using nontoothed forceps.
A small incision is made through these layers using scissors (Wescott scissors) exposing the sclera.
A sub-Tenon’s cannula is inserted
The cannula is advanced posteriorly halfway between the horizontal and vertical equators of the globe.
3 to 5milliliters of local anesthetic are injected; the greater the volume, the greater the akinesis.
Lignocaine 2% is the gold standard(2.5ml); bupivacaine 0.5% and articaine 2% .
Hyaluronidase can be added.
ADVANTAGES Less painful than peribulbar block Better analgesia than topical anesthesia Complications rarely serious No increase in intraocular pressure occurs
with the administration of local anesthetic Surgery can begin almost immediately
Lasts for 60 minutes and supplemental anesthetic agent can be given
The globe can be voluntarily moved at the surgeon’s instruction
Low dose and low volume of anesthetic agent are used
DISADVANTAGES The local anesthetic agent must be injected
into the capsule – double perforation of the capsule results in anesthetic leaking out, which decreases the effectiveness of the block
Although it is an advantage that the globe can be moved under instruction, it is important the eye is not moved at other times – the use of stabilizing sutures is advised
Post-op morbidity: Chemosis and subconjunctival haemorrhage.