Postoperative visual loss following prone spinal surgery

* E-mail: thgeeraerts{at}hotmail.com

Editor—We read with interest the article by Kamming and Clarke1 on a case report of postoperative visual loss in a 60-yr-old man after prolonged decompressive laminectomy in the prone position. We completely agree with the discussion about aetiology of postoperative visual loss, but we would like to add some commentaries on retrobulbar circulation physiology. The authors assumed that the vessels involved in vascular supply of the posterior portion of the optic nerve (branches of the ophthalmic artery) are ‘incapable of autoregulatory control’. As we discussed in a recent article published in the British Journal of Anaesthesia,2 although the ocular circulation does not have any autonomic nerve supply, the ophthalmic and central retinal arteries have an autoregulation of their own blood flow.3 4 The central retinal artery is tightly autoregulated by retinal endothelium derived factors as prostaglandin or endothelin.5 The ophthalmic artery may have a different autoregulatory mechanism and vasoreactivity seems to be lower but the autoregulation in this artery is also efficient.6 Effects of anaesthetic agents (i.v. or inhaled) on retrobulbar circulation are not well known. We demonstrated in children that high alveolar concentrations of sevoflurane (2 MAC) may enhance alterations in ophthalmic artery blood flow.2 At 2 MAC sevoflurane, end diastolic velocity in the ophthalmic artery decreased to 70% of that at 1 MAC, whereas mean arterial pressure decreases only by 4%. In the case reported by Kamming and Clarke,1 anaesthesia was induced with midazolam, propofol and remifentanil, and maintained with isoflurane (0.9–1.2%) and remifentanil for more than 6 h. In their case, with only a minor anaesthesia-related decrease in systolic blood pressure, the oculovascular effect of inhalated anaesthetic such as isoflurane may have contributed to alterations in ophthalmic artery blood flow, even if a major decrease in perfusion pressure to the eye did not occur. In addition, isoflurane has a more important intrinsic cerebral vasodilatory effect compared with sevoflurane.7 The specific oculovascular effect of isoflurane is unknown, but we can hypothesize a similar or greater effect than sevoflurane. The discussion of this case report should consider the possibility of important vasodilatory effect of isoflurane in ophthalmic artery. If perfusion pressure decreases in an artery vasodilated by isoflurane, the ocular blood flow will be compromised, and optic nerve ischaemia may occur.

In conclusion, and in addition to this carefully discussed case report of postoperative visual loss, we could suggest for an explanation of ischaemic optic neuropathy, the possible isoflurane-induced alteration in ophthalmic artery autoregulation in combination with moderate hypotension, anaemia, and increased intraocular pressure.

T. Geeraerts* and J. M. Devys

Paris, France

References

1 Kamming D, Clarke S. Postoperative visual loss following prone spinal surgery. Br J Anaesth 2005; 95: 257–60[Abstract/Free Full Text]

2 Geeraerts T, Devys JM, Berges O, Dureau P, Plaud B. Sevoflurane effects on retrobulbar arteries blood flow in children. Br J Anaesth 2005; 94: 636–41[Abstract/Free Full Text]

3 Best M, Gerstein D, Wlad N, Rabinovitz AZ, Hiller GH. Autoregulation of ocular blood flow. Arch Ophthalmol 1973; 89: 143–8[CrossRef][ISI][Medline]

4 Tachibana H, Gotoh F, Ishikawa Y. Retinal vascular autoregulation in normal subjects. Stroke 1982; 13: 149–55[Abstract]

5 Delaey C, Van De Voorde J. Regulatory mechanisms in the retinal and choroidal circulation. Ophthalmic Res 2000; 32: 249–56[CrossRef][ISI][Medline]

6 Bornstein NM, Gur AY, Geyer O, Almog Y. Vasomotor reactivity in the ophthalmic artery: different from or similar to intracerebral vessels? Eur J Ultrasound 2000; 11: 1–6[CrossRef][Medline]

7 Matta BF, Heath KJ, Tipping K, Summors AC. Direct cerebral vasodilatory effects of sevoflurane and isoflurane. Anesthesiology 1999; 91: 677–80[CrossRef][ISI][Medline]





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