Sub‐Tenon's block: are fasting and intravenous access necessary?

Abstract

Editor—You recently published a thorough and informative review of the sub‐Tenon's block by Canavan and colleagues.1Canavan KS Dark A Garrioch MA. Sub‐Tenon's administration of local anaesthetic: a review of the technique.Br J Anaesth. 2003; 90: 787-793Crossref PubMed Scopus (62) Google Scholar We applaud their fine effort, but were disappointed that they did not discuss the issue of preoperative fasting. We would also like to take issue with their assertion that lack of i.v. access is a contraindication to the procedure. Canavan and colleagues correctly point out that sub‐Tenon's block is safe, effective, and usually painless.1Canavan KS Dark A Garrioch MA. Sub‐Tenon's administration of local anaesthetic: a review of the technique.Br J Anaesth. 2003; 90: 787-793Crossref PubMed Scopus (62) Google Scholar Complications are rare and when they occur they do not require i.v. access or medication as part of their immediate management. Indeed, the guidelines on Local Anaesthesia for Intraocular Surgery compiled by the Royal Colleges of Ophthalmologists and Anaesthetists do not specifically recommend i.v. access for sub‐Tenon's block.2The Royal College of Anaesthesists and the Royal College of Ophthalmologists Report on Local Anaesthesia for Intraocular Surgery. 2001Google Scholar In our institution, ∼250 vitreoretinal procedures are performed annually, of which 41% are performed under sub‐Tenon's block administered by an anaesthetist, and 37% under a block performed by a surgeon without an anaesthetist present. Only 22% of procedures are performed under general anaesthesia. For those cases performed under local anaesthesia, we do not routinely secure i.v. access and have not had a case where this has compromised patient care or safety. Our view is that the discomfort, cost and additional risk, albeit minor, of cannulation are not justified, particularly when there is no anaesthetist present. In our hospital, only staff nurses are authorized to remove i.v. cannulae, and the presence of an i.v. cannula sometimes causes delays in discharge if an ‘appropriately’ trained nurse is not available to remove the cannula! Fasting before surgical procedures has extensive implications for patients. This is particularly true of diabetic patients, who form a large proportion of the ophthalmic surgery workload. Insulin‐dependent or poorly controlled non‐insulin dependent diabetics who are fasted require infusions of insulin and dextrose (a hypotonic solution), with inherent risks of hypo‐ and hyperglycaemia, and hyponatraemia. As Canavan and colleagues point out,1Canavan KS Dark A Garrioch MA. Sub‐Tenon's administration of local anaesthetic: a review of the technique.Br J Anaesth. 2003; 90: 787-793Crossref PubMed Scopus (62) Google Scholar the incidence of failure of sub‐Tenon's block is minimal—thus it is extremely rare that an unplanned general anaesthetic is required. We believe that the risks of fasting diabetic patients far outweigh the risks of performing the block and surgery on unfasted patients, and do not insist that patients undergoing vitreoretinal surgery are fasted. In fact, diabetic patients are offered a drink and a snack just before their operation. Editor—We thank Sidery, Absalom and Burton for their constructive comments. We have previously justified our position regarding our requirement for the insertion of an i.v. cannula before insertion of sub‐Tenon's block.3Nicoll SJB Hickman Casey JMI Lake APJ et al.Sub‐Tenon's administration of local anaesthetic: a review of the technique.Br J Anaesth. 2003; 91: 921-923Crossref PubMed Scopus (2) Google Scholar However, current practice at the Southern General Hospital in Glasgow has changed in that i.v. cannulae have been abandoned. We suspect that this is commonplace and welcome the updated reference provided.2The Royal College of Anaesthesists and the Royal College of Ophthalmologists Report on Local Anaesthesia for Intraocular Surgery. 2001Google Scholar It has been our practice to fast patients for ophthalmic procedures under local anaesthetic. We recognize that it is rarely necessary to convert a sub‐Tenon's block to general anaesthesia, and indeed lack of fasting may confer advantages in some patients, especially diabetics. It would be useful, however, to consider a study comparing fasted and non‐fasted subjects undergoing sub‐Tenon's anaesthesia to clarify this point. K. Canavan M. Garrioch Glasgow, UK