Optic nerve sheath diameter, intracranial pressure and acute mountain sickness on Mount Everest: a longitudinal cohort study

Abstract

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.Despite the fact that acute mountain sickness (AMS) has been recognised as a specific condition since the early 20th century, the mechanisms underlying its development remain unclear.

Distal enlargement of the optic nerve sheath in the hyperacute stage of intracerebral haemorrhage

“…In the present study the range was 2.6–4.4 mm, while other studies17 24 have reported a range of 2.2–4.9 mm, and a range of 2.1–4.8 mm was recorded in untreated post mortem specimens 6. It therefore appears more useful to measure relative ONSD enlargement in patients in the hyperacute stage of increased ICP when enlargement affects only the distal part of the optic nerve sheath.…”

Ultrasonography of optic nerve sheath diameter for detection of raised intracranial pressure: a systematic review and meta-analysis

“…One ongoing study (MOONSTRIP: measurement of optic nerve sheath diameter in traumatic raised intracranial pressure) was also identified on clinicaltrials.gov. Among the eligible studies, 675 were excluded because the abstracts did not mention ultrasonography of ONSD and 17 were excluded because ultrasonography of ONSD was not compared with ICP monitoring [17,[32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. Finally, another study [47] was excluded because we were not able to distinguish the subgroup of patients who had the reference standard test.…”

Quantification of Optic Disc Edema during Exposure to High Altitude Shows No Correlation to Acute Mountain Sickness

“…Underlying mechanisms of AMS are still under debate with some research groups favoring cerebral edema of varying degree as the underlying mechanism for all forms of the disease [13]. In addition, indirect evidence suggests brain edema as a possible cause of AMS [14], [15]. However, another study measuring intracranial pressure by lumbar puncture during hypoxia exposure was not able to detect significant differences in subjects with or without AMS [16].…”