Factors associated with optic nerve sheath diameter during exposure to hypobaric hypoxia.
OBJECTIVE
To monitor the changes in optic nerve sheath diameter (ONSD) induced by acute exposure to hypobaric hypoxia and to investigate factors associated with these changes, including development of acute mountain sickness.


METHODS
In this cohort study, neurologic signs and symptoms, cardiovascular parameters, and ultrasonography of ONSD were prospectively assessed in 19 healthy lowlanders at baseline and after ascent to 3,830 m (3 hours, 9 hours, 24 hours, 48 hours, 72 hours, and 8 days) by blinded investigators. Potential confounding factors (e.g., altitude variations, physical effort) were minimized. A multivariate analysis of factors associated with ONSD was performed by means of generalized estimating equations.


RESULTS
ONSD increased with exposure to altitude in all participants (p < 0.001). The increase between 9 and 24 hours was larger in patients who developed acute mountain sickness (p = 0.001). There was no influence of sex, oxygen saturation, or acclimatization on ONSD.


CONCLUSIONS
Both physiologic and pathologic responses to hypobaric hypoxia were independently associated with changes in ONSD. Studies on a larger cohort, at a range of altitudes, and with baseline neuroimaging techniques are necessary to further understand the clinical significance of increased ONSD during exposure to hypobaric hypoxia.
From the EURAC Institute of Mountain Emergency Medicine (G.S., H.B., T.D.C., E.P.), Bolzano; Department of Anesthesiology and Critical Care Medicine (G.H.), General Hospital of Silandro; Department of Neurology (P.L.), General Hospital of Merano, Italy. giacomo.strapazzon@eurac.edu.
Giacomo
G
Strapazzon
From the EURAC Institute of Mountain Emergency Medicine (G.S., H.B., T.D.C., E.P.), Bolzano; Department of Anesthesiology and Critical Care Medicine (G.H.), General Hospital of Silandro; Department of Neurology (P.L.), General Hospital of Merano, Italy.
Hermann
H
Brugger
From the EURAC Institute of Mountain Emergency Medicine (G.S., H.B., T.D.C., E.P.), Bolzano; Department of Anesthesiology and Critical Care Medicine (G.H.), General Hospital of Silandro; Department of Neurology (P.L.), General Hospital of Merano, Italy.
Tomas
T
Dal Cappello
From the EURAC Institute of Mountain Emergency Medicine (G.S., H.B., T.D.C., E.P.), Bolzano; Department of Anesthesiology and Critical Care Medicine (G.H.), General Hospital of Silandro; Department of Neurology (P.L.), General Hospital of Merano, Italy.
Emily
E
Procter
From the EURAC Institute of Mountain Emergency Medicine (G.S., H.B., T.D.C., E.P.), Bolzano; Department of Anesthesiology and Critical Care Medicine (G.H.), General Hospital of Silandro; Department of Neurology (P.L.), General Hospital of Merano, Italy.
Georg
G
Hofer
From the EURAC Institute of Mountain Emergency Medicine (G.S., H.B., T.D.C., E.P.), Bolzano; Department of Anesthesiology and Critical Care Medicine (G.H.), General Hospital of Silandro; Department of Neurology (P.L.), General Hospital of Merano, Italy.
Piergiorgio
P
Lochner
D000328:Adult; D000532:Altitude Sickness / Q000000981:diagnostic imaging* / Q000503:physiopathology; D015331:Cohort Studies; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000000981:diagnostic imaging* / Q000503:physiopathology; D008297:Male; D009900:Optic Nerve / Q000000981:diagnostic imaging*; D011446:Prospective Studies; D014463:Ultrasonography