Nitrous oxide anaesthesia and intraocular gases

E-mail: akwan78071{at}aol.com

Editor—I read with great interest the article by Lee,1 and like to thank the author for highlighting the important issue of nitrous oxide anaesthesia and intraocular gases. Long-acting gases, such as sulphur hexafluoride or perfluoropropane, have been used in the treatment of retinal detachment for over 30 years,2 and animal experiments with intraocular long-acting gas showed that the intraocular pressure could rise by 100% during nitrous oxide anaesthesia (75%) in an average of 24.1 min.3 This may lead to retinal artery occlusion, retinal ischaemia, and eventually visual loss. The first case of adverse effect of nitrous oxide anaesthesia on intraocular pressure in a patient with intraocular gas was reported in 1975.4 To my knowledge, the longest reported duration between a retinal operation with intraocular gas injection and subsequent visual loss from nitrous oxide anaesthesia was 6 weeks (42 days),5 which is a longer period than the one reported by Lee.

With such a long documented history of problem, it is unfortunate and worrying that the risk of visual loss from nitrous oxide anaesthesia in patients with intraocular gas is not better recognized. One of the reasons may be that the majority of the reports on this complication is published in ophthalmic journals. Our unit had previously addressed this complication and recommended such patients should carry cards giving details of possible complications of intraocular gas.6 The use of information cards or bracelets may be useful in patients who are not forthcoming with their history of recent intraocular surgery, or in the event of emergency anaesthesia. Lastly, vitrectomy for retinal detachment is not the only way to introduce long-acting gases into the eye. Pneumatic retinopexy for repair of retinal detachment involves injecting a small amount of long-acting gas into the vitreal cavity followed by laser treatment or cryotherapy.7 The gas bubble will enlarge slowly over a few days to partially fill the vitreal cavity. This is arguably a clinic/office based procedure, and patients who undergo this procedure may not feel they have had an ‘operation’, and therefore may not inform the anaesthetist before a subsequent operation.5 Unfortunately, the resultant expanding gas bubble poses the same danger to the eye in nitrous oxide anaesthesia as the intraocular gas after vitrectomy operation. It is important to enquire about all ocular procedures before the use of nitrous oxide as an anaesthetic agent. I hope with Lee's latest report, we have drawn the attention of our anaesthetic colleagues, especially those in training, to the danger of nitrous oxide anaesthesia and intraocular gas.

A. S. L. Kwan

London, UK

References

1 Lee EJ. Use of nitrous oxide causing severe visual loss 37 days after retinal surgery. Br J Anaesth 2004; 93: 464–6[Abstract/Free Full Text]

2 Norton EW. Intraocular gas in the management of selected retinal detachments. Trans Am Acad Ophthalmol Otolaryngol 1973; 77: 85–98

3 Smith RB, Carl B, Linn JG Jr, Nemoto E. Effect of nitrous oxide on air in vitreous. Am J Ophthalmol 1974; 78: 314–17[ISI][Medline]

4 Fuller D, Lewis ML. Nitrous oxide anesthesia with gas in the vitreous cavity. Am J Ophthalmol 1975; 80: 778–9

5 Seaberg RR, Freeman WR, Goldbaum MH, Manecke GR Jr. Permanent postoperative vision loss associated with expansion of intraocular gas in the presence of a nitrous oxide-containing anesthetic. Anesthesiology 2002; 97: 1309–10[CrossRef][ISI][Medline]

6 Yang YF, Herbert L, Ruschen H, Cooling RJ. Nitrous oxide anaesthesia in the presence of intraocular gas can cause irreversible blindness. Br Med J 2002; 325: 532–3[Free Full Text]

7 Assi AC, Chateris DG, Gregor ZJ. Practice patterns of pneumatic retinopexy in the United Kingdom. Br J Ophthalmol 2001; 85: 244.





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