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Entonox as an analgesic agent
  1. S Sandramouli,
  2. M Kurli
  1. Wolverhampton and Midland Counties Eye Infirmary, Compton Road, Wolverhampton WV3 9QR, UK
  1. Correspondence to: Mr S Sandramouli; smouli{at}

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We read with great interest the paper on Entonox as an analgesic agent by Cook et al.1 We congratulate the authors for their work. However, we would like to clarify certain aspects of the study.

We recently performed a randomised, placebo controlled, double blind study with 100 patients on the analgesic effect of Entonox for pain relief during local anaesthetic injections in minor eyelid procedures (accepted for publication). We administered Entonox for 30 seconds in our study and found no statistically significant difference in the pain scores between the control and the study groups. No side effects were reported but in our pilot study, where the patients were given Entonox for 60 seconds, all the Entonox group patients reported light headedness and required prolonged observation before being discharged. We attributed our results of lack of statistically significant pain relief with Entonox to less than 50 seconds‘ administration of Entonox. Waud et al2 have shown that optimal administration of Entonox should cover 50 seconds, based on theoretical calculations for effective pain relief. Based on the above experience, we would like to know if the authors administered Entonox throughout the laser treatment and, if so, did it not interfere with the laser delivery since the inhalation process is likely to be associated with head movements? If the Entonox was given for a shorter duration, we need to know the duration of administration since that would be of practical benefit to the readers.

The authors have concluded that Entonox is useful in young patients, those undergoing re-treatments, and in patients who have previously not been able to tolerate the full treatment. We would like to know how the authors came to this conclusion, as there is no mention of the type of patients selected for their study.