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The Effect of Clonidine on Peribulbar Block

Dhingra, Narendra, FRCSEd

doi: 10.1097/00000539-200211000-00071
LETTERS TO THE EDITOR: Letters & Announcements
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Department of Paediatric Ophthalmology

Alder Hey Hospital,

Liverpool, United Kingdom

Dr. Madan does not wish to respond.

To the Editor:

I read with interest the article by Madan et al (1) on the effect of clonidine on peribulbar block. There are a few comments that I would like to make.

  1. The authors have not commented whether adrenaline was used in the irrigating solution.
  2. The authors report that there was a mean decrease in mean arterial pressure and heart rate in patients after the peribulbar anesthesia was instituted, in both the 1.0-μg/kg and the 1.5-μg/kg groups. There are no values mentioned for the same. Does the reduction of mean arterial pressure also translate into reduced choroidal perfusion and effect retinal circulation? In an elderly population undergoing cataract surgery, this variable cannot be ignored.
  3. In a study by Hessemer et al. (2), it was found that the factors reducing the ocular pulsatile volume pressure, blood pressure, and ciliary perfusion pressure were volume of anesthesia, addition of adrenaline, and addition of hyaluronidase. This study was done in patients undergoing retrobulbar anesthesia. Whether adrenaline produces similar effect when used in peribulbar block is unknown. Skepticism regarding usage of clonidine instead of adrenaline will remain until the effect of clonidine on these factors is addressed in further studies.
  4. The authors comment that the use of epinephrine in orbital regional anesthesia is controversial because it may reduce the blood supply to vital organs. If clonidine also does the same (i.e., reduces the blood supply), then it cannot be argued to be better than adrenaline, although potentiation of myotoxicity with adrenaline remains a problem.

Narendra Dhingra, FRCSEd

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References

1. Madan R, Bharti N, Shende D et al. A dose response study of clonidine with local anaesthetic mixture for peribulbar block: a comparison of three doses. Anesth Analg 2001; 93: 1593–7.
2. Hessemer V, Heinrich A, Jacobi KW. Ocular circulatory changes caused by retrobulbar anesthesia with and without added adrenaline. Klin Monatsbl Augenheilkd 1990; 197: 470–9.
© 2002 International Anesthesia Research Society