Optic nerve sheath diameter, intracranial pressure and acute mountain sickness on Mount Everest: a longitudinal cohort study
- 1Nuffield Department of Surgery, John Radcliffe Hospital, University of Oxford, UK
- 2Royal Victoria Infirmary, Queen Victoria Rd, Newcastle upon Tyne, UK
- 3Division of Community Health Sciences, St George’s, University of London, UK
- 4Nuffield Laboratory of Ophthalmology, University of Oxford, UK
- 5Research Division, Altitude Research Center, University of Colorado Denver Health Sciences Center, Mail Stop F-524, PO Box 6508, Aurora, Colorado, USA
- Dr A Sutherland, Wellcome Research Training Fellow, Nuffield Department of Surgery, Level 6, John Radcliffe Hospital, Oxford OX3 9DU, UK;
- Accepted 5 December 2007
- Published Online First 8 January 2008
Objective: To investigate the association of optic nerve sheath diameter (ONSD), as a correlate of intracranial pressure (ICP), with acute mountain sickness (AMS).
Design: Longitudinal cohort study of mountaineers from sea level to 6400 m.
Setting: Mount Everest (North side).
Participants: 13 mountaineers (10 men, 3 women; aged 23–52 years) on a British expedition to climb Mount Everest.
Interventions: ONSD was measured ultrasonically, 3 mm behind the globe using B scans recorded with an OTI-Scan 3D scanner (Ophthalmic Technologies, Canada). Serial binocular scans were recorded at sea level, and 2000, 3700, 5200 and 6400 m. All ONSDs were measured by a blinded observer.
Main outcome measures: ONSD, AMS score (using the Lake Louise scoring system), heart rate, and oxygen saturation levels.
Results: All results were analysed by regression analysis with adjustment. ONSD was positively associated with increasing altitude above sea level (0.10 mm increase in ONSD per 1000 m, 95% CI 0.05 to 0.14 mm) and AMS score (0.12 mm per score, 95% CI 0.06 to 0.18 mm); further associations were found with resting heart rate (0.29 mm per 20 beats/min, 95% CI 0.17 to 0.41 mm) and oxygen saturations (0.20 mm per 10% decrease, 95% CI 0.11 to 0.29 mm).
Conclusions: ONSD increases at high altitude, and this increase is associated with more severe symptoms of AMS. Given the linkage between ONSD and ICP, these results strongly suggest that intracranial pressure plays an important role in the pathophysiology of AMS.
Funding: A small project grant was received from the Carnegie Trust for the Universities of Scotland. AIS is funded by a Wellcome Research Training Fellowship. The authors are independent from the funders.
Competing interests: None.
Ethics approval: This study was approved by the Oxford Tropical Research Ethics Committee (Ref: 015–06 ”Investigation of Intracranial Pressure at High Altitude”).