This review published in the October issue of the British Journal of Ophthalmology discusses the use of adjuvants to local anesthesia for ophthalmic regional anesthesia. The author, Dr. Lee Adams, concludes that there is no consensus on this issue but provides a summary of current data with the goal of allowing eye surgeons and anesthesiologists to make their own informed decisions.
The article reviews the literature on the use of hyaluronidase, bicarbonate, epinephrine, muscle relaxants, opiates and clonidine on their own and in combination as adjuvants to ophthalmic regional anesthesia. Dr. Adams focuses on their efficacy with regard to improving akinesia, analgesia, speed of onset and reducing block failure. He discusses their pharmacological action, related randomized control trials, notable papers and dosage.
He says that multiple studies indicate that adding hyaluronidase to low-volume retrobulbar blockade improves both akinesia and analgesia. However, the heterogenous nature of the studies does not allow a consistent measure of akinesia or analgesia for comparison, and it is debatable that a minor improvement in akinetic onset time has clinical relevance.
He says that the weight of evidence suggests that bicarbonate adds to the quality of local anesthesia when combined with hyaluronidase. He concludes that the addition of bicarbonate could provide a significantly cheaper and “pleasingly simple alternative to hyaluronidase that does not run the risk of allergic reaction.”
However, he says that there are insufficient data to draw conclusions on the use of opiates or muscle relaxants. The large number of randomized trials using hyaluronidase, on the other hand, suggests the usefulness of a meta-analysis. He says that an important factor in the analysis would be the decision to treat the different anatomical blocks (retrobulbar, peribulbar and sub-Tenon) as a homogenous group or to recognize that the appropriate use of hyaluronidase may depend on its exact site of application and the volume and type of local anesthetic it is carried within.
He also concludes that adjuvants, such as clonidine, show promise as they may improve analgesia and provide useful light sedation in low doses. However, further work needs to be done to assess their suitability for outpatient surgery.