Sub-Tenon’s administration of local anaesthetic: a review of the technique

S. J. B. Nicoll1, J. M. I. Hickman Casey1, A. P. J. Lake2, K. Puvanachandra2, C. M. Mather3, J. N. P. Kirkpatrick3, K. Canavan4, A. Dark4 and M. A. Garrioch4

1 Eastbourne, UK 2 Rhyl, UK 3 Cheltenham, UK 4 Glasgow, UK

Editor—The review article by Canavan and colleagues1 cites inability to lie flat, deafness and mental incapacity as absolute contraindications to sub-Tenon’s anaesthesia. Our department performs 2000 cataract operations per year; we use this technique in 98% of patients.

In individuals who present with severe chronic obstructive pulmonary disease, it is our practice to perform sub-Tenon’s blocks with the patient semi-recumbent. Supplementary oxygen is delivered via a Hudson mask. Profoundly deaf patients are provided with information and instructions written on cards in large, bold type.

Excessive anxiety can be managed using propofol i.v. in small increments (e.g. 10–30 mg). Patients with early dementia can be operated on using sub-Tenon’s anaesthesia if handled sympathetically; speed is of the essence!

Although hyaluronidase promotes spread of local anaesthetic,2 it is not essential for a successful block. In a prospective audit carried out in this hospital in 2001, 71 patients received sub-Tenon’s blocks using a mixture of 2 ml 2% lidocaine and 2 ml 0.5% bupivacaine. Hyaluronidase was added in 34 cases (47.9%). There was no difference in pain scores between the groups during the block or subsequent surgery. Operating conditions were acceptable in both groups. The use of hyaluronidase has been associated with problems such as allergy,3 and pseudotumour, and should perhaps be avoided.

A small incision should be made in the conjunctiva to minimize leakage during injection of local anaesthetic. Asking the patient to change the direction of gaze from upwards and outwards to the primary position, and rotating the syringe until almost upright, positions the tip of the sub-Tenon’s cannula further into the posterior sub-Tenon’s space. Top-up injections have not been necessary with this technique.

No mention is made of the minor but distressing problem resulting from a large conjunctival incision, which is slow to heal. This will close spontaneously but may require a longer course of postoperative steroid eye drops.

S. J. B. Nicoll

J. M. I. Hickman Casey

Eastbourne, UK

Editor—We read the review article by Canavan and colleagues1 with interest because the reasons for the increasing use of sub-Tenon’s block, usually in routine phacoemulsification, since the original description by Stevens4 have escaped us. We are concerned that the relative complexity of what is, in effect, and as described in the article, a surgical procedure, may be unnecessary under these circumstances. It is a general principle of surgical practice that tissue planes should only be opened if there is a clear advantage in so doing due to the potential for resultant complications. The article further identifies the number of different approaches to the technique. Considering retrobulbar block and peribulbar block together in many cases also serves to confuse rather than enlighten.

Retrobulbar block combined with facial nerve block was the standard local anaesthetic technique until the demonstration by Davis and Mandel5 that extraconal deposition of local anaesthetic was as effective and safe,6 indeed extremely safe.7 Recent publications have confirmed the effectiveness of peribulbar block in comparison with sub-Tenon’s block.8 9 With the move from retrobulbar block to peribulbar block because of the latter’s excellent safety profile, there was an untrammelled expansion in its provision particularly by anaesthetists, and problems identified therefrom supported the promotion of topical anaesthesia,10 11 which is also effective in comparison with sub-Tenon’s block.12

Starting from a safety profile as good as peribulbar block with an extremely low incidence of major complications, orbital haemorrhage 0–0.09%, scleral perforation 0–0.006% and CNS complications 0.006–0.015%,6 7 where do you go? Minor complications such as bruising 2.6%6 are more related to operator and technique and reduced by the use of short, fine needles and orbital compression.

Compared with retrobulbar block, an improvement following the change to sub-Tenon’s block has been ably demonstrated by a prospective study from New Zealand involving 6000 blocks,13 which showed good or perfect block in 96% of patients, but 7% experienced pain during surgery and 20% experienced discomfort from the subconjunctival injection of antibiotic. Patient acceptance is reported as 98.8% but pain during block insertion occurred in 32%. Only one major block-related adverse event was recorded but subconjunctival haemorrhage was noted in 7%.

Sub-Tenon’s block ‘perceived as having an acceptable safety profile because a sharp needle is not placed within the orbital cavity’ despite the fact that ‘the serious complications associated with sharp-needle techniques are rare’ is associated with complications too, as Canavan and colleagues1 remind us. Chemosis in 39.4% and subconjunctival haemorrhage in 32–56% of cases is hardly insignificant. Ruschen14 reports five major complications in 7250 blocks, an incidence of 0.068%. Orbital bleeds, damage to vortex veins, and local extravasation into the subconjunctival space make surgery difficult. Serious local complications such as orbital cellulitis may occur and because the technique involves a significant breach of the conjunctiva, consideration should be given to administering sub-Tenon’s block after sterile preparation and immediately before the start of surgery.15 Indeed, perhaps, if invasive local anaesthesia is not necessary, it should not be used.16

Sub-Tenon’s block itself offers little advantage over topical anaesthesia.17 The New Zealand study13 conclusion that further support is provided for the view that sub-Tenon’s block poses a very low risk of injury to the globe could also be applied to peribular block, which provides a very effective regional block of short duration. Entering the orbital space with a 27G Atkinson tip needle is less disturbing to tissue planes than the dissection needed for sub-Tenon’s block, as practised by many.

Is the move from peribulbar block, which is so safe and effective in the right hands, to sub-Tenon’s block really in order to reduce the already low incidence of complications from the use of sharp needles, or is the procedure now just considered too low key?

After careful consideration of the available evidence, we believe that for phacoemulsification and many other procedures including corneal grafting, the routine use of peribulbar block or topical anaesthetic in selected cases is appropriate. Sub-Tenon’s block may be the right choice for longer procedures such as vitreoretinal surgery or if a catheter technique is required, when administration under sterile conditions, probably by the surgeon, is recommended. Perhaps, as Rubin states,18 an urgent need for a well-planned, double-blind randomized study or detailed audit remains.

A. P. J. Lake

K. Puvanachandra

Rhyl, UK

Editor—We would like to compliment Canavan and colleagues for their article reviewing the technique of sub-Tenon’s local anaesthesia (STLA).1 This technique is endorsed by the Royal College of Ophthalmologists as a standard method for providing effective local anaesthesia for many types of ocular surgery. In our experience, it provides reliable and safe conditions for the operating surgeon with minimal patient discomfort.

There are two areas where we would like to contribute to the discussion. First, there is no absolute requirement for i.v. access for patients receiving STLA, and readers are referred to RCOphth and RCA guidelines in this area.19 The risk of intravascular or intradural injection is so rare (unreported) that we do not believe that the ‘lack of intravenous access’ is an ‘absolute contraindication’ to performing STLA.

Secondly, we believe that there is a small but significant risk of extraocular muscle trauma with STLA. We have reported three cases with muscle fibrosis (two involving the inferior rectus and one the medial rectus) that required exploration and squint surgery to relieve postoperative diplopia.20 The anaesthetist who performs STLA should be aware of the absolute care required to avoid any risk of dissection or injection in areas adjacent to the rectus muscle insertions that may lead to this complication. We support the use of the inferomedial quadrant for STLA, and the importance of ensuring that the direction of the cannula is equidistant between the horizontal and vertical meridia of the globe. With careful training and attention to detail, the technique of STLA is highly recommended.

C. M. Mather

J. N. P. Kirkpatrick

Cheltenham, UK

Editor—Our article was written as a referenced review to guide all anaesthetists practising or considering taking up the practice of sub-Tenon’s anaesthesia. We consider it sensible to be cautious in the use of regional anaesthetic techniques in patients with predictable difficulties with either communication or comprehension. Nicoll and Hickmann-Casey are to be applauded for their efforts to overcome these difficulties. Readers of the article should not be discouraged from considering general anaesthesia when they feel this is appropriate however. This may still be the technique of choice for many such patients.19

We agree that there are adequate reports to conclude that hyaluronidase is not essential for a successful sub-Tenon’s block. However, the use of hyaluronidase does aid an effective block, especially with regard to paresis of the orbicularis oculi muscle.21 This minimizes the potential for eyelid movement during the surgical procedure, making use of hyaluronidase worthwhile.

We have not been aware of the difficulties caused by the conjunctival incision and thank Drs Nicoll and Hickmann-Casey for reporting it. We look forward to bringing it to the attention of our ophthalmic surgical and anaesthesia colleagues.

Thank you for the opportunity to respond to Drs Lake and Puvanachandra’s defence of peribulbar and topical anaesthesia. We take issue with the assertion that peribulbar block has a safety profile that cannot be improved upon. Any reductions in the risks of globe perforation and dural puncture conferred by sub-Tenon’s anaesthesia are clear advantages. These serious complications of peribulbar block more than justify the cautious and careful opening of the sub-Tenon’s space under sterile conditions in selected patients. Compared with topical anaesthesia, we referred in our review to evidence for the superior performance of sub-Tenon’s block with regard to akinesia and analgesia.

Peribulbar anaesthesia may be a relatively safe technique in the hands of experienced practitioners. We agree that comparison of local anaesthetic techniques by an appropriate randomized, controlled trial is warranted and thank the correspondents for reiterating this point.

We thank Drs Mather and Kirkpatrick for their compliments. The insertion of a peripheral i.v. line is useful not only to manage adverse events specific to local anaesthetic procedures but also any general complications such as arrhythmias or hypotensive episodes which can occur peri-operatively. Eke reports similar incidences of such non-specific adverse events with all local anaesthetic techniques and we therefore believe that it is good practice to obtain i.v. access prior to their administration.22

The important report of extraocular muscle trauma is noted.20 We discussed a similar case in our review23 and agree that assiduous attention to detail is required during the performance of sub-Tenon’s block.

K. Canavan

A. Dark

M. A. Garrioch

Glasgow, UK

References

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