Sub-Tenon's anaesthesia: complications and their prevention.

The advent of a new technique that is considered much safer than previously established one leads to its rapid adoption. This usually leads to the identification of previously unreported complications of the new technique, and a re-assessment of its position in clinical care, which is precisely the state of play with the sub-Tenon's block. The sub-Tenon's block was introduced into the clinical practice in early 1990. A systematic recent search of subject headings such as complications of sub-Tenon's block, subtenon, orbital block, orbital block complications, and orbital anaesthesia was performed in Medline, EMBASE, and Cochrane database. Indeed there are complications of sub-Tenon's block published as case reports and the exact incidence of these complications is not known. Management and preventive measures of these complications are described. Although the sub-Tenon's block appears to be relatively safer than needle-based blocks but a proper prospective, randomized, double-blind controlled trial is essential for scientific proof that sub-Tenon's block is better than needle-based blocks.

Conscious sedation during ophthalmic surgery under local anesthesia.

Sedation during ophthalmic local anesthesia helps to ensure comfort and cooperation during eye surgery. Sedation requirements of ophthalmic patients have changed with the popularization of newer surgical and anesthetic techniques. Many sedative agents are available to anesthesiologists including benzodiazepines, intravenous anesthetic induction agents, narcotic analgesics and a-adrenoreceptor agonists. However, there is no single ideal sedative agent, regime or protocol that can completely cater to the wide spectrum of ophthalmic procedures performed in a heterogeneous patient population. Moreover, the clinical practice of sedation during ophthalmic surgery under local anesthesia is varied and not without risk of complications and adverse events. Hence, balanced sedative techniques should only be used after careful consideration of patient profile, the type of eye surgery, and patient and surgeon preferences. Good knowledge of the pharmacology of sedative agents is fundamental to their useful clinical application.

Sedation during ophthalmic surgery.

Sedation is frequently used during ophthalmic regional anaesthesia. There is no 'ideal' drug for sedation or analgesia. Various drugs either alone or in combination have been used with different methods of administration. This review includes the roles of sedation, the pharmacology of drugs and the safety of sedation in patients undergoing ophthalmic surgery.

A comparison of three sub-Tenon's cannulae.

PURPOSE: To compare the quality of anaesthesia and complication rates between three sub-Tenon cannula of increasing length (anterior Greenbaum, mid Kumar-Dodds, and posterior Steven's sub-Tenon's cannulae). METHODS: A total of 150 patients undergoing cataract extraction were randomised to receive a sub-Tenon injection of 5 ml of 2% lidocaine with hyaluronidase with one of the three cannulae. The development of akinesia was assessed every 2 min over a 6-min period. Complications were also recorded. RESULTS: There was no difference in the onset of akinesia, with 46, 50, and 46 patients achieving adequate akinesia within 6 min for the anterior, mid, and posterior groups respectively (P>0.05). There was an increase in retained lid opening with anterior compared to mid and posterior cannulae (P=0.0001). There was significantly less retained lid closure with the posterior compared to the mid or anterior cannulae (P<00001). The mean (range, SD) scores for pain during injection were 0.4 (0-5, 0.83), 1.2 (0-9, 1.96), and 1.1 (0-6, 1.19) for the anterior, mid, and posterior groups, respectively. These were not significantly different between the anterior and mid groups, or the mid and posterior groups (P>0.05), but there was significantly more pain on injection with the posterior compared to the anterior groups (P<0.01). All patients scored intraoperative pain as zero. There was significantly more chemosis in the anterior group (76%) compared to the mid (20%) and posterior (32%) groups (P<0.0001). There were significantly (P=0.0004) more conjunctival haemorrhages in the anterior group (56%) than the mid (20%) or posterior (20%) groups. CONCLUSIONS: We have shown that all three cannulae provide high-quality anaesthesia with minor differences in retained muscle activity, chemosis, and haemorrhage rates.

Subjective visual experience during phacoemulsification cataract surgery under sub-Tenon's block.

In a prospective survey, 121 patients received sub-Tenon's block and were interviewed on the same day after their phacoemulsification cataract surgery regarding their visual experience in the operated eye during surgery. Majority of patients (81%) reported that they could see some light during surgery and various colours were seen by 56%. Movements of various descriptions were also reported by 40% of patients. The majority of patients (93%) found the visual experience acceptable but 4% thought it to be unpleasant and 3% found it frightening. Patients undergoing phacoemulsification surgery under sub-Tenon's block experience a variety of visual sensations and some patients may be frightened. All patients should receive appropriate preoperative warning.

Evaluation of the Greenbaum sub-Tenon's block.

A prospective, randomized blind study was conducted in 40 patients undergoing phacoemulsification and posterior chamber intraocular lens implantation. They received anaesthetic infiltration of 2% lidocaine with 1:200,000 epinephrine and hyaluronidase 150 U ml(-1) in a volume of 2, 3, 4 or 5 ml into the sub-Tenon's fascial space through a Greenbaum cannula after a conjunctival incision. Reduction of ocular movements, anaesthesia, pain on injection and any incidental complications were recorded. Akinesia and anaesthesia occurred within 5 min with 4 and 5 ml of local anaesthetic, and no supplementary injections were required. There were marked reductions in the frequency of forced eyelid movements with these volumes. Chemosis and conjunctival haemorrhage were noted in the majority of patients but caused no intraoperative problems. Approximately 10-15% of patients reported slight discomfort at the time of injection. Four to 5 ml of 2% lidocaine with 1:200,000 epinephrine and 150 U ml(-1) of hyaluronidase is the optimum volume to achieve adequate akinesia, anaesthesia and reduction of lid movements during the Greenbaum sub-Tenon's block.