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LETTERS TO EDITOR
Year : 2019  |  Volume : 63  |  Issue : 6  |  Page : 507-508  

Optic nerve sheath diameter assessment in obese patients undergoing robotic pelvic surgery


Department of Medicine, Surgery and Dentistry, “Scuola Medica Salernitana”, University of Salerno, Via Allende, Baronissi, Salerno, Italy

Date of Web Publication11-Jun-2019

Correspondence Address:
Dr. Maddalena De Bernardo
Department of Medicine, Surgery and Dentistry, “Scuola Medica Salernitana”, University of Salerno, Via Allende - 84081, Baronissi, Salerno
Italy
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ija.IJA_161_19

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How to cite this article:
Vitiello L, De Bernardo M, Rosa N. Optic nerve sheath diameter assessment in obese patients undergoing robotic pelvic surgery. Indian J Anaesth 2019;63:507-8

How to cite this URL:
Vitiello L, De Bernardo M, Rosa N. Optic nerve sheath diameter assessment in obese patients undergoing robotic pelvic surgery. Indian J Anaesth [serial online] 2019 [cited 2019 Sep 17];63:507-8. Available from: http://www.ijaweb.org/text.asp?2019/63/6/507/259935



Sir,

We are writing to congratulate Sujata et al. for their original and interesting case report on optic nerve sheath diameter (ONSD) guided extubation plan in obese patients undergoing robotic pelvic surgery in steep Trendelenburg position.[1] We consider it a really challenging article, but we would like to comment on some aspects of optic nerve sheath diameter assessment with ultrasound.

For their evaluation, the authors utilised ultrasound B scan technique, which has been employed for more than 50 years to identify several ocular and orbital diseases. Unluckily, it has been demonstrated to be quite untrustworthy for measurements of small structures such as ONSD, due to the so-called blooming effect.[2] It is caused by the absence of a standard sensitivity setting in performing this examination and this means that, when decreasing the gain, the ONSD will show larger measurements compared to the ones acquired with an increased gain.

However, this effect could be unimportant when large lesions need to be evaluated, but will definitely be very significant in case of lesions less than 0.5 mm, where also few microns could influence the interpretation of the ONSD.

For this reason, to overcome the aforesaid pitfalls, we would like to advise to use the Standardised A Scan. It is a blooming effect-free ultrasound technique that displays easily noticeable hyperreflective spikes from the interface between arachnoid and subarachnoidal fluid, making these measurements objective and exact, thereby providing more accurate and universal reference range values.[3]

Moreover, A scan examination permits to perform the '30 degrees test', which allows us to distinguish between an ONSD increase caused by raised intracranial pressure related to increased subarachnoidal fluid, and that one associated with other diseases, such as optic neuritis or optic nerve meningioma.[4],[5]

Lastly, we would like to suggest performing ocular ultrasonography with open eyelids, using methylcellulose and anaesthetic drops, to clearly visualise the eye, making the probe orientation much more accurate, which would help in avoiding errors in detecting gaze direction.[6]

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

1.
Sujata N, Tobin R, Mehta P, Girotra G. Optic nerve sheath diameter-guided extubation plan in obese patients undergoing robotic pelvic surgery in steep trendelenburg position: A report of three cases. Indian J Anaesth 2019; 63:138-41.  Back to cited text no. 1
[PUBMED]    
2.
Iaconetta G, De Bernardo M, Rosa N. Coronal axis measurement of the optic nerve sheath diameter. J Ultrasound Med 2017; 36:1073.  Back to cited text no. 2
    
3.
De Bernardo M, Rosa N. Measuring optic nerve sheath diameter as a proxy for intracranial pressure. JAMA Ophthalmol 2018; 136:1309-10.  Back to cited text no. 3
    
4.
Rosa N, De Bernardo M. Ultrasound assessment of optic nerve sheath diameter in healthy volunteers. J Crit Care 2017; 40:279.  Back to cited text no. 4
    
5.
De Bernardo M, Rosa N. Clarification on using ultrasonography to detect intracranial pressure. JAMA Ophthalmol2017; 135:1004-5.  Back to cited text no. 5
    
6.
Tenuta M, De Bernardo M, Rosa N. Comments on “Neuromuscular ultrasonography of cranial nerves”. J Clin Neurol 2017; 13:212-3.  Back to cited text no. 6
    




 

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