Mohd Ali, Mohd Raffiz
(2015)
Optic nerve sheath diameter: a mean of detecting raised intracranial pressure in adult traumatic and non-traumatic patients.
Masters thesis, Universiti Sains Malaysia.
Abstract
(ONSD) is emerging as a non-invasive technique to evaluate and predict raised intracranial pressure (ICP). It has been shown in previous literature that ONSD
measurement has good correlation with surrogate findings of raised ICP such as clinical and radiological findings suggestive of raised ICP.
Objectives: The objective of the study is to find a correlation between sonographic
measurement of ONSD value with ICP value measured via the gold standard invasive
intracranial ICP catheter, and to find the cut-off value of ONSD measurement in
predicting raised ICP, along with its sensitivity and specificity value. Finally, we
would also like to assess if this bedside non-invasive technique is more accurate in
predicting raised ICP in traumatic or non-traumatic causes of raised ICP.
Methods: A prospective observational study was performed using convenience
sample of 41 adult neurosurgical patients treated in neurosurgical intensive care unit
with invasive intracranial pressure monitoring placed in-situ as part of their clinical
care. Portable SonoSite ultrasound machine with 7MHz linear probe were used to
measure optic nerve sheath diameter using the standard technique. Simultaneous ICP
readings were obtained directly from the invasive monitoring. Spearman rank
correlation coefficient was used to assess the correlation between ONSD value and
ICP value. High ICP was defined as ICP>20mmHg, and a receiver operator
characteristic (ROC) curve was performed to find the ONSD cut-off point in
predicting raised ICP, and to measure the sensitivity and specificity of both groups.
Results: 75 ONSD measurements were performed on 41 patients. The non-parametric
Spearman’s correlation test revealed a significant correlation at the 0.01 level between
the ICP and ONSD value, with correlation coefficient of 0.820. The receiver operator
characteristic (ROC) curve generated an area under the curve with the value of 0.964,
and with standard error of 0.22. At 95% confidence interval, the lower boundary for
this area under the curve is 0.921 and the upper boundary is 1.000. From the ROC
curve, we found that the ONSD value of 5.205mm is 95.8% sensitive and 80.4%
specific in detecting raised ICP. When similar ONSD value was analyzed; 5.47mm vs
5.48mm, the sensitivity and specificity of this value in predicting raised ICP is higher
in the Traumatic group (94.4% sensitive and 95.2% specific) compared to Nontraumatic
group (83.3% sensitive and 93.3% specific).
Conclusions: ONSD value of 5.205 is sensitive and specific in detecting raised ICP.
Bedside ultrasound measurement of ONSD is readily learned, and is reproducible and
reliable in predicting raised ICP in both trauma and non-trauma group. This noninvasive
technique can be a useful adjunct to the current invasive intracranial catheter
monitoring, and has wide potential clinical applications in district hospitals,
emergency departments and intensive care units.
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