Clinical Relevance of Transorbital Ultrasonographic Measurement of Optic Nerve Sheath Diameter (ONSD) for Estimation of Intracranial Pressure Following Cerebrospinal Fluid Diversion Surgery

Abstract

Background and aim Raised intracranial pressure (ICP) can be estimated by various invasive as well as non-invasive techniques. Optic nerve sheath diameter (ONSD ) is a bedside non-invasive technique for assessment of ICP as a regular follow-up tool and has added advantage over CT scan/MRI, which require patient transfer to the suite. Cerebrospinal fluid (CSF) diversion procedures such as a ventriculoperitoneal shunt or external ventricular drainage are commonly done to relieve symptoms of patients with raised ICP. Change in ICP measured through ONSD after CSF diversion procedures may guide the proper functioning of the shunt and immediate post-operative management. The present study was conducted to compare ONSD before and after CSF diversion procedures and correlate the ONSD with ICP. Our secondary objective was to determine the ONSD cutoff for the prediction of ICP >20mm Hg. Setting, design, and methods This prospective, comparative, and observational study was carried out at Dr. Ram Manohar Lohia Institute of Medical Sciences, Lucknow, India. The present study was conducted on 40 adult patients undergoing CSF diversion surgery under general anaesthesia. Ultrasonographic measurement of the ONSD was performed before induction, after induction, after endotracheal intubation, after completion of shunt surgery, and then every two hours for 12 hours. The direct ICP was measured by the neurosurgeon at the time of the initial ventricular puncture. Statistical analysis The Wilcoxon signed-rank test was used to compare pre and post variables. Qualitative variables were compared using the Chi-Square test/Fisher’s exact test as appropriate. Spearman's rho statistical measure of linear association was applied to measure the strength of linear association between parameters to show how close the points lie to a straight line. A p-value of <0.05 was considered statistically significant. Results The mean value of ONSD before induction and after induction was 6.36 ± 0.61 mm and 6.29 ±0.64 mm, respectively. After endotracheal intubation, ONSD slightly increased to 6.34 ±0.62mm, followed by a consistent decrease in ONSD values. The mean direct ICP recorded was 30.93±6.22 mmHg. Comparison of mean ONSD before induction, after induction, and after intubation with ONSD after surgery was statistically significant (p <0.001). We found a strong positive correlation between direct ICP and ONSD after intubation with a correlation coefficient of 0.969 (P <0.001). Receiver operating characteristic (ROC) curve analysis showed an ONSD cutoff of >5.85, predicted ICP>20 mmHg with a sensitivity of 92.3%, and specificity of 85.7%. Conclusion Measurement of ONSD by ultrasonography is an important and reliable tool in the assessment of normalization of ICP post CSF diversion procedure.

Non-Invasive Intracranial Pressure Monitoring

“…An experimental study revealing that ONSD decreases with lumbar puncture also demonstrated the ability to collect real-time ONSD measurements [ 218 ]. Similar results were shown by studies before and after ventriculo-peritoneal shunt surgery [ 219 ] and during surgery [ 220 ].…”

Comparison of Optic Nerve Sheath Diameter (ONSD) Measurements Obtained from USG Before and After Placement of Ventriculoperitoneal Shunt in Obstructive Hydrocephalus as a Surrogate Marker for Adequacy of Shunt Function: A Prospective Observational Study

“…The authors also found that an ONSD cutoff value of 5.85 mm was able to predict ICP > 20 mm Hg with a sensitivity of 92.3% and a specificity of 85.7%. 4 In a recently published prospective study conducted by Sahu et al on 30 adults scheduled for surgical procedures for the management of intracranial hypertension, the authors observed that an ONSD cutoff value > 5.5 mm predicted ICP > 20 mm Hg with a sensitivity of 100% and a specificity of 75%. The authors also identified ONSD cutoffs of 6.3, 6.5, and 6.7 mm for predicting ICP greater than 25, 30, and 35 mm Hg, respectively.…”

“…CSF diversion procedures such as ventriculoperitoneal (VP) shunt surgery, endoscopic third ventriculostomy (ETV), or placement of an external ventricular drain are frequently performed to relieve raised ICP in patients with hydrocephalus. 4 While invasive methods continue to remain the proverbial "gold standard" for monitoring ICP, they are associated with several complications such as infection, hemorrhage, and device failure or disconnection. 5 In addition, invasive ICP monitoring is relatively contraindicated in the presence of coagulopathy, which is commonly encountered in patients with traumatic brain injury.…”