Key reference:

Chua MJ, Lersch F, Chua AWY, Kumar CM, Eke T. Sub-Tenon’s anaesthesia for modern eye surgery-clinicians’ perspective, 30 years after re-introduction. Eye (Lond). 2021;35(5):1295-1304. doi:10.1038/s41433-021-01412-5

Demonstration of sub-Tenon block can be found on ABCs of Anaesthesia Youtube channel:

https://www.youtube.com/watch?v=k_bxA9GiGNs

Quick Summary

• Contemporary ophthalmic surgeries are increasingly being performed under regional and local anaesthesia with non-inferior analgesia, akinesia, safety profile and improved efficiency in list turnover.

• The sub-Tenon block (STB) presents an effective modality to achieve ocular analgesia and akinesia with superior safety profile compared to needle-based peribulbar and retrobulbar techniques.

• STB is associated with common but self-limiting complications including chemosis and subconjunctival haemorrhage.

• Nevertheless, retrobulbar haemorrhage (RBH), a sight-threatening ocular emergency resulting from rapid increases in intraocular pressure (IOP) from accumulated retrobulbar blood, remains a rare complication of STB.

• Prompt recognition of RBH is essential to expedite definitive lateral canthotomy decompression and minimise long-term sight impairment.

Preamble

You are a junior anaesthetic trainee on your first busy ophthalmology list. Your next patient is Mrs. CS, a 70 year old lady who has arrived for her elective left eye cataract surgery. She had her right eye cataract completed 2 months ago without any issues.

Her history is significant for ischaemic heart disease and atrial fibrillation, for which she is on aspirin 100mg daily and apixaban 2.5mg BD. Her preoperative visual acuity (VA) was 6/6 for right eye and hand movements-only for left eye. Both eyes had deep anterior chamber depths. Baseline IOP was 26mmHg for the right eye. After an unremarkable preoperative assessment, the patient was consented for a sub-Tenon block (STB).

What is a sub-Tenon Block (STB)?

STB is a regional eye block technique developed in 1884 and popularised in the 1990s. In contrast to needle-based peribulbar and retrobulbar blocks, STB utilises blunt-end cannula to deliver local anaesthetics into the episcleral potential space, targeting both sensory ocular nerves and all 6 extraocular muscle sheaths to produce anaesthesia and akinesia.

Tenon’s capsule is the fascial sheath that surrounds the globe. Anteriorly, it merges with the conjunctiva at the limbus, and posteriorly fusing with the meninges and sclera of the optic nerve. Between the Tenon’s capsule and the sclera contains the episcleral potential space, which is transverse by:

To access the sub-Tenon space, the infero-nasal quadrant is favoured as it is least likely to be traversed by the vortex veins or other neurovascular and muscular structures.

Once administered, the local anaesthetic hydro-dissects the episcleral space and creates a circumferential collection bathing the ciliary nerves. With larger volumes (>3mls), local anaesthetic spreads along the extraocular muscle sheath, as well as anteriorly to the facial plane of the lid to provide akinesia of the globe and eyelid muscles.

Steps to completing a STB

1. Patient consent

2. Position patient supine position

3. WHO block timeout

4. Standard ANZCA monitoring

5. IV access +/- anxiolysis/sedation if necessary, with IV midazolam/low dose propofol/ fentanyl

6. Hat/mask/sterile glove

7. 2-3 drops of topical anaesthetics of choice to target eye (e.g. 0.4% oxybuprocaine)

8. Skin prep with iodine-based antiseptic (e.g. betadine 1% solution), followed by sterile drape

9. Apply eye speculum

10. Ask patient to look superotemporally with the target eye to expose the inferonasal quadrant

11. Create a small tent of conjunctiva 5-7mm from the limbus using a conjunctival forceps (e.g. Moorfield’s), and make a small incision using Wescott spring scissors

    1. Non-snip techniques are also available using pencil point cannula or other plastic probes

12. Insert the blunt-end sub-Tenon cannula through the incision and up to the globe equator in depth, always hugging the sclera during the insertion

13. Slowly inject 3-5ml of local anaesthetic solution of choice into the sub-Tenon space (e.g. 2% lidocaine with 30 units/ml hyaluronidase), avoiding injecting if high resistance or discomfort encountered

    1. Hyaluronidase hydrolyses part of the extracellular matrix, improves local anaesthetic dispersion and penetration, reduces volume of LA required, and reduces time for onset of akinesia

14. Perform a post-block assessment, noting any immediate complications (e.g. chemosis, subconjunctival haemorrhage), pain, discomfort, periorbital swelling, proptosis etc.)

Sub-Tenon Block set up and equipment

Who is suitable for STB?

STB and other needle-based regional techniques are allowing patients to undergo low-risk ophthalmic procedures who would otherwise be at significant high risk for general anaesthetics. While STB is considered safe and effective for vast majority of patients, certain patient populations have relative and absolute contraindications to a STB:

Complications of STB

STB is a favoured eye block technique due to its superior safety profile. Two prospective studies in Australia and New Zealand with combined 8688 STBs observed no sight-threatening complications related to STBs. While STB is associated with higher rates of benign and transient complications such as chemosis and subconjunctival haemorrhage, sight and life-threatening complications are exceedingly rare and are 2.5 times less common than needle blocks. A Cochrane review of 605 patients undergoing cataract surgery found no evidence STB had a higher rate of intraoperative complications compared to non-invasive topical anaesthesia, albeit with limited statistical power.

…………………………..

Returning to Ms CS:

You successfully complete the STB for Mrs. CS in the holding bay. You note the patient’s bleeding risk whilst on both anticoagulant and antiplatelet therapy, but are reassured by your consultant of the low risk of sight threatening haemorrhage.

As you are waiting for the surgeons to prepare, Mrs CS reports increasing discomfort of the operative eye. You note that the eye has become tense with onset of periorbital swelling and resistance to retropulsion. Examination revealed proptosis of the right eye, with increased IOP up to 45mmHg. Your consultant immediately suspects a retrobulbar haemorrhage and reports to the ophthalmologist.

What is retrobulbar haemorrhage?

Retrobulbar haemorrhage (RBH) is a sight-threatening ophthalmic emergency, characterised by raised intraocular pressure (IOP) secondary to accumulating blood within the tight intraconal space, causing extrinsic compression of neurovascular structures, impairing orbital venous drainage and arterial supply, ultimately resulting in retinal ischaemia and optic nerve injury. RBH can be spontaneous, or through iatrogenic trauma such as with regional anaesthesia, which has a prevalence of 0.04% to 0.43%.

RBH is an extremely rare complication of STB, with isolated cases described in a small number of case reports and retrospective studies. The pathophysiology is attributed to iatrogenic injury to the vortex veins that traverses through the sub-Tenon space, causing slow ooze and gradual intraocular pressure rise. The use of metal cannulas, transient intraocular pressure rise from cough/Valsalva reflex, posterior vessel crowding from increased axial length, and use of antithrombotic therapy were respectively implicated as possible contributing factors. Due to the lack of case numbers, there is insufficient statistical power to-date to validate these risk factors.

Minimising RBH risk during STB

Using standard inferonasal approach

The inferonasal quadrant avoids the majority of neurovascular and muscular structures. Specifically, the vortex vein in the temporal region commonly loops around into the inner surface of the Tenon’s capsule, posterior to the insertion of the inferior rectus muscle. Thus, the inferonasal approach is usually preferred over inferotemporal to reduce the risk of vortex vein injury and RBH.

Using shorter, non-metal, blunt cannula

The vortex veins and ciliary vessels are concentrated in the posterior quadrant. As such, it is advisable to avoid cannula over-advancement beyond the globe equator and endangering posterior vascular structures. Anaesthetists should pay extra attention to the orbit’s axial length during their pre-operative assessment, which informs the required needle depth, as well as the risks of scleral thinning and irregularities. The use of shorter, flexible cannulas in favour of rigid metal cannulas has been suggested to avoid inadvertent vessel injury.

Using smaller local anaesthetic volume

Further risk minimisation through reducing volume (and speed of injection) of local anaesthetics to prevent shearing of sclerotic vessels and rise of intraocular pressure must be balanced with patient discomfort and suboptimal akinesia conditions associated with incomplete block.

Avoidance of “orbital massage”

Orbital massage is a technique used to disperse local anaesthetic throughout the sub-Tenon space by firm rocking pressure applied against the orbit. This has been shown to increase intraocular pressure abruptly to 400mmHg, significantly increasing shear stress on posterior vessels.

Management of RBH

Management of RBH requires early recognition of intraocular pressure, which may present as eye pain, proptosis, periorbital swelling, visual disturbance, impaired eye movements, or increased IOP. Immediate surgical decompression via lateral canthotomy/cantholysis, with adjunct medical management to reduce IOP is the first line of management, and is associated with only 0.14% rate of blindness if instituted promptly. Medical management commonly involves administration of acetazolamide, corticosteroids, and topical timolol to decrease aqueous humor production in the eye to further reduce IOP.

Returning to Ms CS

The ophthalmologist immediately sets up and performs a lateral canthotomy and cantholysis in theatre, with you administering procedural sedation. A small pocket of blood is evacuated.

Within minutes, Ms. CS’s symptoms improved, and proptosis is visibly reduced. Reassessment of the IOP showed a pressure of 15 mmHg.

You arrange for Ms. CS to be transferred to a tertiary eye centre for overnight observations. You instruct her to withhold her apixaban and aspirin for today. You commence her on acetazolamide (500 mg IV) and topical timolol to control her IOP. Immediate post-procedure monitoring noted no further signs of rebleeding or worsening of symptoms.

Ms. CS is discharged the next day. She returns 1 week later to complete her cataract surgery under general anaesthesia without complication, and fully recovers her VA.

Conclusion

STB continues to be a popular, safe and effective regional technique for ophthalmic surgery. While major complications are extremely rare, anaesthetists must be vigilant of signs and symptoms and follow techniques that minimise their risk. In the case of suspected RBH, prompt action must be taken to prevent permanent vision loss through surgical and medical management.

References

Chua MJ, Lersch F, Chua AWY, Kumar CM, Eke T. Sub-Tenon’s anaesthesia for modern eye surgery-clinicians’ perspective, 30 years after re-introduction. Eye (Lond). 2021;35(5):1295-1304. doi:10.1038/s41433-021-01412-5

Clarke JP, Plummer J. Adverse Events Associated with Regional Ophthalmic Anaesthesia in an Australian Teaching Hospital. Anaesthesia and Intensive Care. 2011;39(1):61-64. doi:10.1177/0310057X1103900109

Ernest JT, Goldstick TK, Stein MA, Zheutlin JD. Ocular massage before cataract surgery. Trans Am Ophthalmol Soc. 1985; 83: 205–217.

Lerch D, Venter JA, James AM, Pelouskova M, Collins BM, Schallhorn SC. Outcomes and Adverse Events of Sub-Tenon’s Anesthesia with the Use of a Flexible Cannula in 35,850 Refractive Lens Exchange/Cataract Procedures. Clin Ophthalmol. 2020;14:307-315. Published 2020 Jan 31. doi:10.2147/OPTH.S234807

Subbiah S, McGimpsey S, Best RM. Retrobulbar hemorrhage after sub-Tenon’s anesthesia. J Cataract Refract Surg. 2007;33(9):1651-1652. doi:10.1016/j.jcrs.2007.04.042

In our last article, we were tangled up in the brachial plexus. This time, we are looking at the lumbosacral plexus, a close cousin of the brachial plexus. In a similar vein, the lumbosacral plexus provides motor and sensory supply to the lower limb.

In this article, we will be looking at the anatomy and function of the main terminal branches of the lumbosacral plexus. This will set the backdrop for an article series on regional anaesthesia blocks. Knowing our anatomy for regional blocks helps us to locate the appropriate landmarks for anaesthetic injection.

The Lumbosacral Plexus

Figure 1. Schematic of the lumbosacral plexus, demonstrating relationship of nerve roots, divisions, and terminal branches.

Imagine a busy switchboard connecting calls between your spine and lower limbs. That’s the lumbar and the sacral plexi. Thanks to the lumbosacral trunk (the middleman), there is substantial overlap between the lumbar and sacral plexus, so much so that they are often collectively referred to as the lumbosacral plexus. This networking hub is formed from the ventral rami of L2-S3, making up the motor and cutaneous supply of our lower limbs.

The lumbar component of the lumbosacral plexus, originating from L1-L4, exits the spinal canal through the intervertebral foramen and enters into the psoas major muscle. Within this muscle, the roots split into the anterior and posterior divisions, reuniting to form the individual nerves of the lumbar plexus. Think of it as a nerve-themed family tree! (See image below which shows the branches of the lumbar plexus)

Figure 2. Close-up schematic of the lumbar component of the lumbosacral plexus

The sacral component of the lumbosacral plexus arises from the spinal nerves L4-S4, with some fibres from the lumbar plexus. Among these nerves, the largest is the sciatic nerve, comprising the common peroneal/fibular nerve and the tibial nerve, wrapped in a common sheath.

Due to its relatively deep location, the lumbosacral plexus is protected from acquired injuries. However, temporary deficiencies/ lesions may occur in the setting of pregnancy and childbirth, retroperitoneal pathology, and pelvic malignancies

Figure 3. Close-up schematic of the sacral component of the lumbosacral plexus. Note the close association of the two major terminal branches in forming the sciatic nerve: the common peroneal nerve (AKA common fibular nerve) and the tibial nerve.

Clinically, if there is damage to one of these nerves, the deficiency will be seen within the specific muscles and cutaneous innervation that the nerve supplies. At the spinal nerve level, this is commonly manifested as radiculopathy, which can comprise both positive (such as radicular pain, paraesthesia)and negative symptoms (such as numbness, weakness) that anatomically align with the supplied distribution of the affected nerve or nerve group. One of the most common lumbosacral pathologies is “sciatica”which describes the radicular pain originating from the lower back and hip region, radiating along the posterior thigh in the inferior direction – the very course of the sciatic nerve that is supplied by the lower lumbar and sacral nerve roots.

Additionally, injury of the distal terminal nerve branches can result in peripheral neuropathy with the same positive and negative symptoms and signs. For example, injury to the common fibular nerve, which commonly occurs due to its superficial location at the head and neck of the fibula, results in paresis/paralysis of the anterior and lateral leg muscle compartments, manifesting as foot drop and weakness in ankle eversion. Similarly, injury to the tibial nerve can result in paralysis of the calf muscles, leading to an inability to plantar flex the foot and the development of a shuffling gait.

Now equipped with our knowledge of the anatomy and pathology associated with the lumbosacral plexus, let’s delve a little deeper into the major nerves and their motor and cutaneous innervations.

Femoral nerve (L2-L4): The Overachiever

Obturator nerve (L2-L4): The Quiet Performer

Sciatic nerve (L4,L5, S1-3): The Beast

Tibial (L4,L5, S1-3): The Reliable Sidekick

Common Fibular Nerve (L4,L5,S1,S2): The Wanderer

Gluteal nerves (L4,L5,S1,S2): The Party Starters.

Pudendal nerve (S2,S3,S4)

That’s the introduction in the lumbosacral plexus and its anatomy. In our future articles, we will explore how this anatomy assists with lower limb regional blocks and the anaesthetic considerations of these blocks.

Keep a look out for them!

References:

Davies, K. (April 26, 2024). Lumbar Plexus. Teach Me Anatomy. https://teachmeanatomy.info/lower-limb/nerves/lumbar-plexus/

Davies, K. (July 8, 2024). The Sacral Plexus. Teach Me Anatomy. https://teachmeanatomy.info/lower-limb/nerves/sacral-plexus/

Palastanga, N., Field, D., & Soames, R. (2006). Anatomy and human movement: structure and function (Vol. 20056). Elsevier Health Sciences.

The brachial plexus. The harbinger of nightmares for all medical students (and junior doctors alike)

For me, I found it hard to conceptualise this phenomenally difficult yet important part of upper limb anatomy. Like many things in anatomy, the more practice and revision that is done, the easier it becomes to understand. In this article,we are going to break down the brachial plexus into smaller chunks so hopefully you can leave with a better understanding of it.

First stop, what is the brachial plexus?

The brachial plexus is a complex network of nerves arising from nerve roots C5 and T1 that ultimately gives rise to all the nerves that innervate the upper limb – both sensory and motor fibres – including arm, forearm, hand, shoulder, axilla, and some areas of the chest. From the spinal roots all the way to the peripheral nerves, the brachial plexus begins from the spinal nerves of C5 to T1 (roots or the ventral rami), then trunks, divisions and then cords. All throughout the brachial plexus smaller branches of nerves branch off to supply muscles and skin of the shoulder and superior thorax region.

Let’s delve into each component

The five roots run deep to the sternocleidomastoid muscle and make their way between the anterior and middle scalene muscles in between the clavicle and 1^st rib.The roots then intercalate to form the superior middle, and inferior trunks, which then divided into the anterior and posterior divisions. Drawing the brachial plexus is an excellent way to detangle the verbal descriptions and better visualise and understand the roots, divisions, and cords.

One of the ways I try to remember the stages of the brachial plexus is through the acronym ‘Really Tired? Drink Coffee.’ Roots Trunks Divisions Cords.

Ultimately the parts of the brachial plexus that enter into the axilla are the anterior and posterior divisions, which give rise to the lateral, medial and posterior cords winding along the axillary artery and forming an intimate relationship. I find it easier to visualise the divisions and cords in relation to the axillary artery. For example, the posterior division will be located relatively posterior to the axillary artery.

See that M shape when the cords begin to form? You should always look for that as it helps to orient yourself as to where you are. M for median nerve, and hence, the middle cord of the M will be the median nerve, the lateral cord will be the musculocutaneous and the medial cord will be the ulnar nerve. Once you find this ‘M’ then you’ll know what nerves form from these cords.

The main nerves of the upper limb rise from the lateral, medial and posterior cords. These nerves are the musculocutaneous, median, ulnar, radial, and axillary nerves.

Clinical implications of nerve blocks and injuries

When thinking about the consequences of injury or damage of the peripheral nerves, knowing its motor and sensory supply goes a long way into ascertaining the impairment of each and what results from regional anaesthesia to these nerves. Below we will go into all of these nerves, briefly, and what happens when it is damaged.

Axillary Nerve: branching from the posterior cords and running posterior to the surgical neck of the humerus. Innervating the deltoid and teres minor muscles and the skin/joint capsule of the shoulder.

Musculocutaneous Nerve: a major branch from the lateral cord, making its way through the anterior arm and supplying motor innervation to the biceps brachii, brachialis and coracobrachialis muscles. Beyond the elbow, its sensory innervation is the lateral forearm, hence the ‘cutaneous’ aspect of the musculocutaneous nerve.

Median Nerve: a very important nerve, the median nerve makes its way to the anterior forearm, traversing through the cubital fossa, supplying sensory fibres to the skin of the forearm and motor to the majority of muscles in the flexor compartment of the forearm. Additionally, it innervates the five intrinsic muscles of the lateral palm and has sensory fibres to 3 ½ lateral digits.

Ulnar Nerve: From the medial cord, the ulnar nerve descends into the forearm, behind the medial epicondyle and follows the course of the ulnar bone into the arm where it innervate the majority of the intrinsic hand muscles and sensation to the palmar and dorsal aspect of the medial 1 ½ digits. In the forearm it supplies the flexor carpi ulnaris and the medial part of the flexor digitorum profundus (the median nerve supplies the lateral aspect of the flexor digitorum profundus).

Radial Nerve: The radial nerve continues as an extension of the posterior cord and wraps around the humerus within the radial groove. Supplying the posterior skin of the dorsum of the hand and the posterior skin of the arm and forearm. It supplies

motor fibres to all the extensor muscles of the upper limb.

Ultimately, to test the peripheral nerves of the upper limb during an examination, you can quickly test the motor and sensory distribution in the following way:

Musculocutaneous – Flexion of the arm.

Radial – Supination and pronation.

Median – Flexion of the wrist.

Ulnar – Flexion at the interphalangeal joints.

Ulnar – Medial ½ digits and palmar surface of the hand.

Median – Lateral three and a half digits and palmar surface of the hand.

Radial – Majority dorsum of the hand.

Classic brachial plexus injury patterns

By Zheng Cheng Zhu

Erb palsy

You meet Mr. Smith, 25 yo gentleman, BMI 36, awaiting his left knee ACL repair. You note his right arm is held in a “waiter’s tip” position, with thinning of his shoulder muscles. He reports he has had weakness in his arm since childbirth…

Erb palsy, secondary to injury to the ipsilateral C5 and C6 nerve roots, typically occurs from excessive shoulder-neck distraction forces, most commonly encountered during difficult vaginal birth with macrosomia and shoulder dystocia preventing delivery of the superior shoulder.

C5 and C6 provide motor supply to deltoid (axillary), bicep brachii and brachialis muscles (musculocutaneous), and injury to these nerve roots correspondingly result in weakness in

• Shoulder abduction

• Shoulder and elbow flexion

• Shoulder external rotation

• Wrist supination

This results in the classical “waiter’s tip”, where the affected arm is held in unopposed adduction and internally rotated, with elbow extended, wrist pronated and palm facing outwards.

Klumpke palsy

You meet the next patient, Ms. Kim. She’s 35yo, left handed, having unfortunately fractured her left wrist and is awaiting her open reduction internal fixation. She tells you she was originally right handed, but after her bike accident 10 years ago she lost strength in her right hand and has a “claw hand”…

Klumpke palsy occurs from injury to the C8 and T1 nerve roots or the inferior trunk, typically from abrupt hyperabduction of the ipsilateral shoulder, like those sustained in high-force trauma.

C8 and T1 supplies the intrinsic muscles of the hand, including the lumbricals and interosseous muscles. Weakness of these muscles result in unopposed hyperextension at the metacarpophalangeal joints and flexion at the interphalangeal joints from extrinsic hand muscles, resulting in the classical “claw hand” deformity.

That’s a brief overview of the brachial plexus and remember, if you’re really tired, drink coffee!

In future articles, we will be delving into the specific upper limb regional blocks that can be performed, and now that we have an understanding of the brachial plexus, the regional blocks will extend on this knowledge.

References:

Basit H, Ali CDM, Madhani NB. Erb Palsy. [Updated 2023 Apr 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK513260/

Merryman J, Varacallo M. Klumpke Palsy. [Updated 2023 Aug 4]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK531500/

Marieb E.,, Hoehn, K. Human Anatomy and Physiology. Pearson Education. 2012.