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Ocular Ultrasound an effective non-invasive estimator of intracranial pressure

Ocular Ultrasound an effective non-invasive estimator of intracranial pressure

Usually, the gold standard for intracranial pressure (ICP) measurement is invasive intracranial devices (IEDs).But lately, ultrasonography of the optic nerve sheath diameter (ONSD) has been suggested as a potential non-invasive ICP estimator. Chiara Robba and associates performed a meta-analysis to evaluate the diagnostic accuracy of sonographic ONSD measurement for assessment of intracranial hypertension (IH) in adult patients and arrived at the conclusion. Ultrasound measurement of the optic nerve sheath diameter has been proposed as a test for elevated ICP, but studies have generally been small and with variable results.

Increased intracranial pressure (ICP) may be difficult to be detected as its associated symptoms such as a headache and vomiting are nonspecific, and because available tests are either insensitive (fundoscopy) or highly invasive (lumbar puncture, intracranial pressure monitor).In addition, Papilledema is an unreliable sign of elevated ICP and unpleasant for many patients.

The authors conducted a systematic review and meta-analysis to determine ultrasound’s test characteristics for elevated ICP.

They searched on electronic databases (MEDLINE/PubMed, Scopus, Web of Science, ScienceDirect, Cochrane Library) until 31 May 2018 for comparative studies that evaluated the efficacy of sonographic ONSD vs. ICP measurement with IID. The data were extracted independently by two authors and the QUADAS-2 tool was used for assessing the risk of bias (RB) of each study. After that a  diagnostic meta-analysis following the bivariate approach and a random-effects model was performed.

The researchers evaluated seven prospective studies (320 patients)  for IH detection (assumed with ICP > 20 mmHg or > 25 cmH2O). The accuracy of included studies was around 95 %. Elevated ICP was defined as a pressure >20 mm Hg or 25 cm H2O.

Despite a  wide 95% CI in the pooled DOR for exercising caution, it was found that ultrasonographic ONSD may be a potentially useful approach for assessing IH when IIDs are not indicated or available.

Seven studies were identified that compared ultrasound to simultaneous (within 1 hour) invasive ICP measurement (lumbar puncture or intraparenchymal or intraventricular pressure monitoring) in at least 15 hospitalized adults (total number of patients, 320).

They concluded that ocular ultrasound may be conducted to measure the optic nerve sheath diameter. Up to  3 mm behind the globe is ok but when the nerve sheath is >5 mm wide,  further testing may be pursued.However, the authors suggest that included studies used different cut-offs to determine whether the optic nerve was enlarged, and this is an important limitation for this meta-analysis.

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Source: With inputs from Intensive Care Medicine

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