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Sub-tenon block: a learning curve of 100 cases. Whose benefit?

We read with considerable disquiet the article by Clarke, Roberton and Plummer, finding nothing whatsoever within it or evidence-based to justify such a radical change of practice (1). What could have possessed two successful, safe and experienced ('... both operators had each previously performed several thousand PBBs.') anaesthetists to change from using a technique with an enviable safety record and high efficacy to one with greater (though different) risk and, in their hands, a relatively poor outcome? Also, how did the Flinders Clinical Research Ethics Committee come to agree to such a study and, of probably more importance, what was the content of the informed consent?

The reasons for the increasing use of sub-Tenon's block, usually in routine phacoemulsification since the original description by Stevens (2), have escaped us. We are concerned that the relative complexity of what is a surgical procedure is unnecessary under these circumstances, it remaining 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. Considering retrobulbar block and peribulbar block together, as in this article, also serves to confuse rather than enlighten. The extraconal deposition of local anaesthetic has been shown to be effective and safe (3), indeed extremely safe (4). The effectiveness of peribulbar in comparison with sub-Tenon's block has also been confirmed, (5,6) and its safety profile with an extremely low incidence of major complications, orbital haemorrhage 0-0.09%, scleral perforation 0-0.006% and central nervous system complications 0.006-0.015% (3,4) hardly offers room for improvement. Minor complications such as bruising 2.6% are more related to operator and technique (3).

Compared with retrobulbar block, however, an improvement following the change to sub-Tenon's has been demonstrated by a prospective study from New Zealand involving 6000 blocks with high patient acceptance and only one major block-related adverse event recorded, but subconjunctival haemorrhage noted in 7% (7).

The suggestion by the authors that sub-Tenon's block has a 'substantially lower risk of major complications' is not supported by the evidence of an association with complications such as chemosis in 39.4% and subconjunctival haemorrhage in 32 to 56% of cases (8) and 6 to 12% in their series which is hardly insignificant. Even the use of diathermy has been considered to deal with the problem (9). Orbital bleeds, damage to vortex veins and local extravasation into the subconjunctival space make surgery difficult, and serious local complications such as orbital cellulitis may occur. 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 (10).

Ruschen reports five major complications in 7250 blocks, an incidence 0.068% (11). Sub-Tenon's block itself offers little advantage over topical anaesthesia in cataract surgery (12) and in this study it didn't work well with good blocks even at the end only 65-81%; hardly a success rate to write home about.

We remain strongly of the belief that for phacoemulsification and many other procedures including corneal grafting, the routine use of peribulbar, or topical anaesthesia in selected cases, is appropriate. Sub-Tenon's block may be the right choice for longer procedures such as vitreo-retinal surgery or if a catheter technique is required when administration under sterile conditions probably by the surgeon is recommended".

References

(1.) Clarke JP, Roberton G, Plummer J. Sub-Tenon Block: A Learning Curve of 100 Cases. Anaesth Intensive Care 2006; 34:450-452.

(2.) Stevens JD. A new local anaesthesia technique for cataract extraction by one quadrant sub Tenon's infiltration. Br J Ophthalmol1992; 76:670-674.

(3.) Hamilton RC, Gimbel HV, Strunin L. Regional anaesthesia for 12000 cataract extraction and intraocular lens implantation procedures. Can J Anaesth 1988; 35:615-623.

(4.) Davis DB, Mandel MR. Efficacy and complication rate of 16624 consecutive peribulbar blocks, a prospective multi centre trial. J Cataract Refract Surg 1994; 20:327-337.

(5.) Briggs MC, Beck SA, Esakowitz L. Sub-Tenon's versus peribulbar anaesthesia for cataract surgery. Eye 1997; 11:639643.

(6.) Azmon B, Alster Y, Lazar M, Geyer O. Effectiveness of sub-Tenon's versus peribulbar anaesthesia in extracapsular cataract surgery. J Cataract Refract Surg 1999; 25:1646-1650.

(7.) Guise PA. Sub-Tenon anesthesia: a prospective study of 6000 blocks. Anesthesiology 2003; 98: 964-968.

(8.) Canavan KS, Dark A, Garrioch MA. Sub Tenon's administration of local anaesthetic: a review of the technique. Br J Anaesth 2003; 90:787-793.

(9.) Kumar CM, Williamson S. Diathermy does not reduce subconjunctival haemorrhage during sub-Tenon's block. Br J Anaesth 2005; 95:562.

(10.) Redmill B, Sandy C, Rose GE. Orbital cellulitis following corneal gluing under sub-Tenon's local anaesthesia. Eye 2001; 15:554-556.

(11.) Ruschen H, Bremner FD, Carr C. Complications after sub-Tenon's block. Anesth Analg 2003; 96:273-277.

(12.) Zafirakis P, Voudouri A, Rowe S, Livir-Rallatos G, Livir-Rallatos C, Canakis C, Kokolakis S, Baltatzis S, Theodossiadis G. Topical versus sub-Tenon's anesthesia without sedation in cataract surgery. J Cataract Refract Surg 2001; 27:873-879.

(13.) Lake APJ, Puvanachandra K. Sub-Tenon's administration of local anaesthetic: a review of the technique. Br J Anaesth 2003; 91:921-923.

A. E J. LAKE

K. PUVANACHANDRA

St Asaph, Denbighshire,

United Kingdom

Sub-tenon block: a learning curve of 100 cases. Whose benefit?--Reply

Thank you for the opportunity to respond to Drs Lake and Pavanachandra's defence of peribulbar anaesthesia. We take issue with their presentation of the relative risks of peribulbar and sub-Tenon's block, which is the basis for ethical approval and patient consent.

In the case of globe perforation, which strongly correlates with visual loss, studies such as Hamilton (0 in 12000), show no room for improvement (1). On returning to the real world, data from the correspondents' country in a national survey showed a globe perforation rate of 1 in 874 cases (85% peribulbar block) (2). The same authors saw six cases of globe perforation in one month at a single centre (3).

It appears that a reality gap exists: on the one hand there are centres of excellence that report studies with very low perforation rates, whilst on the other hand the general rate of globe perforation is depressingly higher. Very few would accept a perforation rate of 1 in 874 as having no room for improvement. Moreover, this figure does not include other major complications such as retrobulbar haemorrhage, central nervous system anaesthesia and complications of sedation.

In their criticism, the correspondents cite the Ruschen et al study of five complications in 7350 sub-Tenon's blocks (4). However, of these, two were due to massaging the globe, one was central nervous system anaesthesia, one was unexplained visual loss and one was globe perforation from a peribulbar block top-up!

We believe sub Tenon's may offer a major improvement in risk profile over peribulbar block and well deserves to be 'written home about'.

The correspondents' initial question asks, why change practice having performed many peribulbar blocks? Firstly, we teach ophthalmic anaesthesia to trainees, and whilst we have low complication rates for peribulbar block, we strongly suspect the complication rate for others may not be so low and that future patients would be better served by anaesthetists trained in sub-Tenon's block. Secondly, vitroretinal surgery is a major component of our caseload, where high myopes are common. Even the correspondents accept the role of sub-Tenon's block in vitreoretinal surgery. Adding sub-Tenon's block to our skills allows us to offer the best approach to any given situation.

If any anaesthetist shares the concerns about the risks of peribulbar block, our study shows that proficient conversion to sub-Tenon's can be achieved in about 60 cases (5).

References

(1.) Hamilton RC, Gimbel HV, Strunin L. Regional anaesthesia for 12000 cataract extraction and intraocular lens insertion implantation procedures. Can J Anaesth 1988; 35:615-623.

(2.) Gillow JT, Aggarwal RK, Kirkby GR. A survey of ocular perforation during ophthalmic local anaesthetic surgery in the United Kingdom. Eye 1996; 10:537-538.

(3.) Gillow JT, Aggarwal RK, Kirkby GR. Ocular perforation during peribulbar anaesthesia. Eye 1996; 10:533-536.

(4.) Ruschen H, Bremner FD, Carr C. Complications after subtenants block. Anesth Analg 2003; 96:273-277.

(5.) Clarke JP, Roberton G, Plummer J. Sub-Tenon Block: A learning curve of 100 Cases. Anaesth Intensive Care 2006; 34:450-452.

J. CLARKE

G. ROBERTON

J. PLUMMER

Adelaide, South Australia
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Article Details
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Title Annotation:CORRESPONDENCE
Author:Lake, A.P.J.; Puvanachandra, K.; Clarke, J.; Roberton, G.; Plummer, J.
Publication:Anaesthesia and Intensive Care
Article Type:Letter to the editor
Date:Dec 1, 2006
Words:1373
Previous Article:Handbook of Anesthesiology, 2004-2005 Edition.
Next Article:Kidney stone movement during lithotripsy under general anaesthesia: High frequency jet ventilation versus spontaneous ventilation.


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