Kinetic anaesthesia for laser surgery

Local anaesthetic is widely used in ophthalmic surgery and more recently in vitreoretinal surgery. Akinesia is a useful effect of local anaesthetic blocks, but there are situations where some residual globe movements are of benefit. We looked to see whether reducing the volume of anaesthetic solution used in a block could retain some kinesia while achieving good analgesia.

We compared two groups of patients undergoing panretinal photocoagulation (PRP) with an indirect laser. The control group received 5 ml of anaesthetic solution in a single injection by a standard intraconal technique; a second group received a lower volume of solution by the same technique. We recorded the adequacy of anaesthesia and the amount of residual kinesia for the two groups. Differences between groups were analysed using the Student's t-test and chi(2) tests.

The low-volume group received an average of 2.8 ml, compared to 5 ml in the control group. There was no significant difference in the adequacy of analgesia achieved, however 16/18 (89%: 95% confidence intervals (CI)=81.5-96.3%) of the low-volume group had good perioperative kinesia compared to just 3/21 (14%: 95% CI=6.6-21.9%) of the controls (P<0.001).

We have shown that low-volume intraconal blocks retain some perioperative kinesia without compromising their analgesic effect.