Ophthalmic Anesthesia Flashcards
Nerves that innervate the upper lid
supraorbital
supratrochlear
lacrimal
zygomaticotemporal
Nerves that innervate the lower lid
Zygomaticofacial
Nerves that innervate the globe
Long ciliary
Nerves that innervate the medial canthus
Infratrochlear
Nerves that innervate the lateral canthus
Zygomaticofacial
Indications for retrobulbar block
Intraocular surgery
Corneal surgery
Evisceration, enucleation
Complications of a retrobulbar block: orbital
- Corneal abrasions
- Chemosis
- Ecchymosis
- Retrobulbar hemorrhage
- Globe perforation
- Optic N damage
Complications of retrobulbar block: systemic
- Manifestation of OC reflex
- LA toxicity
- IV/intrathecal injection complications ie seizures, brainstem ax, CPA
RBA: volumes recommended
Dogs: 2-3mL
Cats: 1mL
No widely agreed volume/local agent for recommended use
RBA: important to note
- does not provide complete analgesia of eyelids bc some branches of ophthalmic/maxillary N pass intraconally
- Must combine with eyelid, conjunctival infiltration for enucleation/evisceration
RBA: ITP Approach
- Dogs
- 22g, 3.81cm spinal needle bent at midpoint at approx 20* angle
- Inserted through lower lid at junction of middle and temporal thirds
- Needle advanced until slight pop detected –> piercing of orbital fascia
- Needle then advanced another 1-2cm dorsally, nasally
- Reported 1-2mL 2% lidocaine
RBA: superior nasal approach
- Cats
- 22g, 3.81cm spinal needle bent at midpoint at approx 20* angle
- Needle inserted through the upper eyelid at dorsomedial orbit
- Needle advanced 3/4” length toward caudal pole of the globe
- Inject 1mL LA
PBA approach: canine
ventrolateral, medial canthus, dorsomedial +VL orbit
Want to scrape the bony orbit when pass needle
Small dogs: 25g, 5/8” needle
Medium to large breeds: 23g, 1” needle
Giant breeds: 23 1-1.5” needle
0.2-0.8mL/kg with larger dose in small breed dogs, smaller dose in large breed dogs DT body surface area to volume ratio
PBA approach: cats
DM single injection
25g 5/8” needle inserted in close proximity to the orbital wall
Up to 4mL but watch toxicity –> may need to dilute further
Peribulbar block
- Gold standard in human medicine
- Has replaced RBA bc the needle is further away from the globe and other intraconal structures
Indications for a PBA
-Intraocular surgery
Complications of PBA
- Transient increase in IOP –> not a concern if enucleation planned but should not be used in animals with glaucoma or globes at risk of rupture
- Exophthalmos
- Chemosis, ecchymosis from rostral spread of injectate volume, damage to small blood vessels
- Large volume required for adequate intraconal distribution may exceed maximal LA dose in small/cachexic K9, Fl
Sub-Tenon’s Anesthesia (STA)
- Safer alternative to needle-based techniques
- Blunt cannula inserted under sterile conditions along curvature of sclera into Tenon’s space via small incision in the conjunctiva and Tenon’s capsule several mm from the limbus
- LA diffuses along Tenon’s space to block short and long ciliary nerves to produce pupil dilation (short) and analgesia (long)
STA in Dogs
- incision in DM portion of bulbar conjunctiva, 5mm from the limbus
- 19g STA cannula inserted
- Incision allowed to heal by second intention
Consequences of postoperative ophthalmic pain
- self-trauma
- possible dehiscence of surgical site
Perioperative pain management of ophthalmic procedures in dogs and cats
- Systemic use of opioids +/- NSAIDS
- regional anesthesia blocks nociception –> More complete analgesia than systemic analgesics
Goal of regional anesthesia
Reduce need for preoperative administration of systemic analgesics
Also reduces requirements for GA during surgery
Other benefits of regional anesthesia during ocular surgery
- Akinesia of extra ocular muscles, resulting in globe centralization
- Mydriasis may facilitate some ophthalmic procedures
- Trigeminal N, ciliary ganglion block may decrease incidence of oculocardiac reflex –> bradycardia, systole
Orbit
In carnivores, incomplete
-medial orbit present with a partial orbital rim
Bony extensions of the orbital rim longer in cats > dogs
DL component replaced by supraorbital ligament - more extensive in dogs > cats
