Optic Nerve Sheath Diameter Increase on Ascent to High Altitude: Correlation With Acute Mountain Sickness.
OBJECTIVE
Elevated optic nerve sheath diameter on sonography is known to correlate with increased intracranial pressure and is observed in acute mountain sickness. This study aimed to determine whether optic nerve sheath diameter changes on ascent to high altitude are associated with acute mountain sickness incidence.


METHODS
Eighty-six healthy adults enrolled at 1240 m (4100 ft), drove to 3545 m (11,700 ft) and then hiked to and slept at 3810 m (12,500 ft). Lake Louise Questionnaire scores and optic nerve sheath diameter measurements were taken before, the evening of, and the morning after ascent.


RESULTS
The incidence of acute mountain sickness was 55.8%, with a mean Lake Louise Questionnaire score ± SD of 3.81 ± 2.5. The mean maximum optic nerve sheath diameter increased on ascent from 5.58 ± 0.79 to 6.13 ± 0.73 mm, a difference of 0.91 ± 0.55 mm (P = .09). Optic nerve sheath diameter increased at high altitude regardless of acute mountain sickness diagnosis; however, compared to baseline values, we observed a significant increase in diameter only in those with a diagnosis of acute mountain sickness (0.57 ± 0.77 versus 0.21 ± 0.76 mm; P = .04). This change from baseline, or Δ optic nerve sheath diameter, was associated with twice the odds of developing acute mountain sickness (95% confidence interval, 1.08-3.93).


CONCLUSIONS
The mean optic nerve sheath diameter increased on ascent to high altitude compared to baseline values, but not to a statistically significant degree. The magnitude of the observed Δ optic nerve sheath diameter was positively associated with acute mountain sickness diagnosis. No such significant association was found between acute mountain sickness and diameter elevation above standard cutoff values, limiting the utility of sonography as a diagnostic tool.
University of Utah, Salt Lake City, Utah USA (N.C.K.); Stanford University School of Medicine, Palo Alto, California USA (G.S.L., S.R.W.); Tacoma General Hospital, Tacoma, Washington USA (B.B.C.); University of Hawaii, Honolulu, Hawaii USA (P.S.H.); and Royal Perth Hospital, Perth, Western Australia, Australia (J.F.P.). kanaan2@gmail.com.
Nicholas C
NC
Kanaan
University of Utah, Salt Lake City, Utah USA (N.C.K.); Stanford University School of Medicine, Palo Alto, California USA (G.S.L., S.R.W.); Tacoma General Hospital, Tacoma, Washington USA (B.B.C.); University of Hawaii, Honolulu, Hawaii USA (P.S.H.); and Royal Perth Hospital, Perth, Western Australia, Australia (J.F.P.).
Grant S
GS
Lipman
University of Utah, Salt Lake City, Utah USA (N.C.K.); Stanford University School of Medicine, Palo Alto, California USA (G.S.L., S.R.W.); Tacoma General Hospital, Tacoma, Washington USA (B.B.C.); University of Hawaii, Honolulu, Hawaii USA (P.S.H.); and Royal Perth Hospital, Perth, Western Australia, Australia (J.F.P.).
Benjamin B
BB
Constance
University of Utah, Salt Lake City, Utah USA (N.C.K.); Stanford University School of Medicine, Palo Alto, California USA (G.S.L., S.R.W.); Tacoma General Hospital, Tacoma, Washington USA (B.B.C.); University of Hawaii, Honolulu, Hawaii USA (P.S.H.); and Royal Perth Hospital, Perth, Western Australia, Australia (J.F.P.).
Peter S
PS
Holck
University of Utah, Salt Lake City, Utah USA (N.C.K.); Stanford University School of Medicine, Palo Alto, California USA (G.S.L., S.R.W.); Tacoma General Hospital, Tacoma, Washington USA (B.B.C.); University of Hawaii, Honolulu, Hawaii USA (P.S.H.); and Royal Perth Hospital, Perth, Western Australia, Australia (J.F.P.).
James F
JF
Preuss
Sarah R
SR
Williams
D000208:Acute Disease; D000328:Adult; D000368:Aged; D000532:Altitude Sickness / Q000000981:diagnostic imaging* / Q000188:drug therapy / Q000453:epidemiology*; D015984:Causality; D015897:Comorbidity; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007052:Ibuprofen / Q000627:therapeutic use; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009798:Ocular Hypertension / Q000000981:diagnostic imaging* / Q000453:epidemiology* / Q000517:prevention & control; D009900:Optic Nerve / Q000000981:diagnostic imaging* / Q000187:drug effects; D015990:Placebo Effect; D015203:Reproducibility of Results; D018570:Risk Assessment / Q000379:methods; D012680:Sensitivity and Specificity; D013223:Statistics as Topic; D016896:Treatment Outcome; D014463:Ultrasonography / Q000379:methods / Q000706:statistics & numerical data*; D014481:United States; D055815:Young Adult
D007052:Ibuprofen
acute mountain sickness; emergency ultrasound; high altitude; intracranial pressure; ocular ultrasound; optic nerve sheath diameter