Efficacy of Sub-Tenon's block using an equal volume of local anaesthestic administered either as a single or as divided doses
Our hypothesis was that a divided injection into the Sub-Tenons space would achieve greater, more consistent and more rapid motor blockade then a single injection using equal volumes and mixtures of local anaesthetic solution.
Ethics Committee of Cork University Hospital, approval received in 2003.
Single blinded, prospective, randomised controlled trial
Primary study design
Secondary study design
Randomised controlled trial
Patient information sheet
On arrival in the induction room, intravenous excess was secured and monitoring with non-invasive blood pressure (NIBP), electrocardiogram (ECG), and pulse oximetry (Datex AS3) established. Topical anaesthesia was established by instillation of benoximate eye drops and after 2 minutes an eye speculum inserted. With the eye in neutral position, the conjunctiva was lifted in the infranasal quadrant with the help of Moorsfields forceps and using Westcott's scissors a small incision was made in the conjunctiva. A 19 gauge Stephens's cannula was carefully placed subconjuctivally into the Sub-Tenon's space.
In group 1, 5 ml of local anaesthetic solution comprising 2.5 ml of 2% lignocaine with 1:200,000 adrenaline, 15 IU/ml of hyaluronidase and 2.5 ml of 0.5% bupivacaine was injected over thirty seconds. After the injection orbital pressure was applied for two minutes.
In group 2, 3 ml of the same anaesthetic solution described above was injected and cannula withdrawn followed by application of orbital pressure for 2 minutes. A further 2 ml of the same anaesthetic solution was injected through the same conjunctival incision with approx three minutes between the two injections.
Intraocular pressures were measured by a hand held tonometer (knowa) prior to injection and six minutes after the first (or sole) injection and compared with pre-injection value.
Benoximate, lignocaine, adrenaline, hyaluronidase, bupivacaine
Primary outcome measure
Measurement of movement was performed by the operating surgeon who was unaware of the anaesthetic technique used in all four quadrants (inferior, superior, redial, lateral) using a vernier calliper and scored according to movement:
0 = no movement
1 = movement of less than 2 mm
2 = movement of more than 2 mm
Motor function was evaluated at two time intervals, 3 and 6 minutes after the initial injection. Overall movement score was obtained by combining the scores of these four muscles. This score ranged from 0 (no movement) to 8 (complete movement) and was categorised into two groups, akinesia (score 0 - 4) and no akinesia (score 5 - 8).
All measured during the surgery.
Secondary outcome measures
Chemosis and subconjuctival haemorrhage were also assessed by surgeons before starting surgery as mild, moderate or severe. All measured during the surgery.
Overall trial start date
Overall trial end date
Reason abandoned (if study stopped)
Participant inclusion criteria
1. American Society of Anaesthesiologists (ASA) I - III patients undergoing cataract surgery
2. No age range, both male and female patients
Target number of participants
Participant exclusion criteria
1. Allergy to any of the drugs administered
2. Impaired mental status
3. Uncontrolled glaucoma
4. Clotting abnormalities
5. Recent surgical procedure on the same eye
Recruitment start date
Recruitment end date
Countries of recruitment
Trial participating centre
South Infirmary Hospital
Investigator initiated study - no extra funding required as Sub-Tenon's block is routinely used
Funding Body Type
Funding Body Subtype
Results and Publications
Publication and dissemination plan
Not provided at time of registration
Intention to publish date
Participant level data
Not provided at time of registration
Basic results (scientific)