Postoperative visual loss occurs more commonly in patients placed prone. The mechanism may be raised intraocular pressure (IOP) causing an ischemic oculopathy.
IOP was measured in 20 patients undergoing spinal surgery. The IOP was measured prior to intubation, immediately after pronation, and at the end of surgery before the patient was returned to the supine position. Duration of surgery, method of head stabilization and standard physiological parameters were recorded.
Both measurements of median IOP in the prone position were significantly higher than that in the supine position (P < 0.001). There was no evidence of a relationship between rise in IOP and duration of surgery, age, or body mass index. There was weak evidence of a tendency for patients whose heads were on pillows to have higher values of IOP at the end of surgery than patients whose heads were supported in pins.
IOP increases when anesthetized patients are placed in the prone position.
From the Departments of *Anaesthesia and ‡Ophthalmology, National Hospital for Neurology and Neurosurgery, London, UK; and †UCLH Research and Development Directorate, London, UK.
Received for publication April 16, 2004; accepted June 9, 2004.
Abstracts presented at the Southwest Thames Anaesthesia Updates, La Plagne, France, January 2003, and the Neuroanaesthetic Society of Great Britain and Ireland, Manchester, UK.
Reprints: Katharine Hunt, FRCA, Department of Anaesthesia, National Hospital for Neurology and Neurosurgery, Queen Square, London WC1N 3BG UK (e-mail: Kath.Hunt@dial.pipex.com).