Ultrasonography of the optic nerve in neurocritically ill patients

Optic nerve sheath diameter and eyeball transverse diameter in severe head injury and its correlation with intracranial pressure

BACKGROUND

Gold standard for determining intracranial pressure (ICP), intraventricular catheter, is invasive with associated risks. Non-invasive investigations like magnetic resonance imaging and ultrasonography have demonstrated correlation between optic nerve sheath diameter (ONSD) and raised ICP. However, computed tomography (CT) is accessible and less operator-dependent. Literature shows variable results regarding correlations between ICP and ONSD on CT. The study aimed to investigate correlations between raised ICP and ONSD, eyeball transverse diameter (ETD), and ONSD/ETD ratios on CT scan(s) of severe head injuries.

METHODS

A retrospective review of a three-year prospectively-maintained database of severe traumatic head injuries in patients who had ICP measurements and CT scans was conducted. Glasgow Coma Score (GCS), ICP, ONSD 3 mm and 9 mm behind the globe, ETD, ONSD/ETD ratios, CT Marshall Grade, and Glasgow Outcome Score (GOS) were recorded. Statistical analysis assessed correlations between ICP and CT measurements.

RESULTS

Seventy-four patients were assessed; mortality rate: 36.5 %. Assault (48.6 %) and pedestrian-vehicle collisions (21.6 %) were the most common mechanisms. CT Marshall Grade correlated significantly with 3 mm and 9 mm ONSD, ONSD/ETD ratios, GCS, and GCS motor score, which correlated significantly with GOS. No significant correlation was found between ICP and ONSD, ETD or ONSD/ETD ratios. Marshall Grade was not significantly associated with ICP measurements but correlated with injury severity.

CONCLUSIONS

Unlike previous studies, our study not only investigated the correlation between ICP and single variables (ONSD and ETD) but also the ONSD/ETD ratios. No correlations were observed between raised ICP and ONSD, ETD or ONSD/ETD ratio on CT in neurotrauma patients.

Optic nerve sheath diameter as a non-invasive tool to detect clinically relevant raised intracranial pressure in children: an observational analytical study

BACKGROUND

Raised intracranial pressure (ICP) contributes to approximately 20% of the admissions in the paediatric intensive care unit (PICU) in our setting. Timely identification and treatment of raised ICP is important to prevent brain herniation and death in such cases. The objective of this study was to examine the role of optic nerve sheath diameter (ONSD) in detecting clinically relevant raised ICP in children.

METHODS

A hospital-based observational analytical study in a PICU of a tertiary care institute in India on children aged 2-14 years. ONSD was measured in all children on three time points that is, day 1, day 2 and between day 4 and 7 of admission. ONSD values were compared between children with and without clinical signs of raised ICP.

RESULTS

Out of 137 paediatric patients recruited, 34 had signs of raised ICP. Mean ONSD on day 1 was higher in children with signs of raised ICP (4.99±0.57 vs 4.06±0.40; p<0.01). Mean ONSD on day 2 also was higher in raised ICP patients (4.94±0.55 vs 4.04±0.40; p<0.01). The third reading between days 4 and 7 of admission was less than the first 2 values but still higher in raised ICP patients (4.48±1.26 vs 3.99±0.57; p<0.001). The cut-off ONSD value for detecting raised ICP was 4.46 mm on the ROC curve with an area under curve 0.906 (95% CI 0.844 to 0.968), 85.3% sensitivity and 86.4% specificity. There was no difference in ONSD between the right and the left eyes at any time point irrespective of signs of raised ICP.

CONCLUSION

We found that measurement of ONSD by transorbital ultrasound was able to detect clinically relevant raised ICP with an excellent discriminatory performance at the cut-off value of 4.46 mm.

Monitoring of optic sheath diameter during acute migraine attack: an objective criteria for the severity of disease

BACKGROUND

The etiology of migraine can be complex and multifactorial but not clear, also, intracranial pressure has been already associated with migraine attacks. This study aimed to monitor intracranial pressure during migraine attack to understand the possible relations with disease and severity.

METHODS

A prospective randomized study was designed. Patients with a definitive diagnosis of migraine underwent ultrasonography for optic nerve sheath diameter (ONSD) measurement before treatment and were re-measured after the attack was resolved. The severity of the migraine was assessed with Headache Impact Test-6 (HIT-6) and Migraine Disability Assessment (MIDAS) questionnaire before the treatment and after the symptoms regressed. ONSD values and scores from the questionnaires were compared before and after the migraine attack.

RESULTS

The study included 11 (52.4%) women and 10 (47.6%) men, and 42 eyes were evaluated. ONSD was detected as 4.23 ± 0.26 mm in the right eye and 4.10 ± 0.32 mm in the left eye during the migraine attack and decreased to 3.65 ± 0.41 mm in the right eye and 3.50 ± 0.33 mm in the left eye after the attack was treated (p < 0.001, both). A similar statistical improvement was found in HIT-6 and MIDAS scores with ONSD after treatment (p < 0.001). A significant positive correlation was found between the ONSD value in both eyes and HIT-6/MIDAS scores during the migraine attack, and also, after the migraine attack.

CONCLUSION

A subjective increase of ONSD values during the migraine attack decreased after the disease resolved, also changes in ONSD values were significantly correlated with the severity of symptoms.

Measurement of Optic Nerve Sheath Diameter by Computed Tomography in the Pediatric Population: Normal Values

PURPOSE

To determine the normal values of optic nerve sheath diameter (ONSD) by computed tomography (CT) in the pediatric population.

METHODS

The CT scans of pediatric patients aged 1 to 16 years who underwent brain CT for different reasons, who did not have intracranial pathology or increased intracranial pressure, and who had no pathology on CT were included in the study. Four age groups were defined with the following ranges: 1 to 2, 3 to 6, 7 to 10, and 11 to 16 years. ONSD was measured from axial CT images, 3 and 10 mm behind the optic globe.

RESULTS

The normative values of ONSD measured on CT imaging in children aged 1 to 16 years were reported. The change in ONSD according to age was investigated. ONSD was found to increase with age at both levels measured. The difference was statistically significant.

CONCLUSIONS

Normal values should be known to detect pathologies that may cause an increase in optic nerve diameter. The values reported in this study can serve as a reference for normal optic nerve sheath diameter in the pediatric age group. [J Pediatr Ophthalmol Strabismus. 2024;61(1):38-43.].

Is optic nerve sheath diameter diagnostic in methanol intoxication?

BACKGROUND AND AIM

Methyl alcohol intoxication causes severe morbidity and mortality, especially in developing countries. Formic acid is formed as a result of methanol metabolism. Formic acid accumulation and inhibition of adenosine triphosphate synthesis result in ophthalmic issues. This study aimed to demonstrate that the optic nerve sheath diameter (ONSD) measurement is an accurate prognostic marker and can be helpful in the diagnosis of methanol intoxication.

MATERIALS AND METHODS

This prospective study was conducted with 52 patients who were admitted to the emergency department after alcohol consumption and agreed to participate in the study. Age, gender, comorbid diseases, vital signs, ONSD ultrasonography measurements, hospitalization and discharge status, in-hospital mortality status, dialysis need, presence of visual impairment, blood gas parameters, respiratory status, time since alcohol intake, ethanol levels, urea levels, and creatinine levels were analyzed.

RESULTS

ROC curve analysis was performed to evaluate the predictive power of ONSD to diagnose methanol intoxication. The area under the curve was 0.857 for the cut-off value of 5.05 mm (95 % CI: 0.728-0.985; p < 0.001), with a sensitivity of 80.8 % and a specificity of 100 %. In the regression analysis performed to determine the prognostic value of the parameters in estimating mortality in methanol intoxication cases, an increase in ONSD (OR: 3.619; 95 % CI: 0.057-0.199; p = 0.001), an increase in lactate levels (OR: 5.653; 95 % CI: 0.040-0.085; p < 0.001), and increased duration after alcohol intake (OR: 2558; 95 % CI: 0.004-0.034; p = 0.014) were identified as independent predictors of mortality, but pH, HCO3, and base deficit levels were not significant predictors.

CONCLUSIONS

We believe that ONSD can be helpful for the differential diagnosis and prognosis of patients with suspected methanol toxicity who presented with alcohol intake.

Automation of ultrasonographic optic nerve sheath diameter measurement using convolutional neural networks

BACKGROUND AND PURPOSE

Ultrasonographic optic nerve sheath (ONS) diameter is a noninvasive intracranial pressure (ICP) surrogate. ICP is monitored invasively in specialized intensive care units. Noninvasive ICP monitoring is important in less specialized settings. However, noninvasive ICP monitoring using ONS diameter (ONSD) is limited by the need for experts to obtain and perform measurements. We aim to automate ONSD measurements using a deep convolutional neural network (CNN) with a novel masking technique.

METHODS

We trained a CNN to reproduce masks that mark the ONS. The edges of the mask are defined by an expert. Eight models were trained with 1000 epochs per model. The Dice-similarity-coefficient-weighted averaged outputs of the eight models yielded the final predicted mask. Eight hundred and seventy-three images were obtained from 52 transorbital cine-ultrasonography sessions, performed on 46 patients with brain injuries. Eight hundred and fourteen images from 48 scanning sessions were used for training and validation and 59 images from four sessions for testing. Bland-Altman and Pearson linear correlation analyses were used to evaluate the agreement between CNN and expert measurements.

RESULTS

Expert ONSD measurements and CNN-derived ONSD estimates had strong agreement (r = 0.7, p < .0001). The expert mean ONSD (standard deviation) is 5.27 mm (0.43) compared to CNN mean estimate of 5.46 mm (0.37). Mean difference (95% confidence interval, p value) is 0.19 mm (0.10-0.27 mm, p = .0011), and root mean square error is 0.27 mm.

CONCLUSION

A CNN can learn ONSD measurement using masking without image segmentation or landmark detection.

Non-invasive intracranial pressure estimation using ultrasonographic measurement of area of optic nerve subarachnoid space

OBJECTIVE

To verify whether the area of the ONSAS (ONSASA) obtained by transorbital ultrasonography can be used to accurately evaluate the intracranial pressure (ICP).

METHODS

The recorded indexes included the optic nerve diameter, the optic nerve sheath diameter (ONSD), the width of both sides of the ONSAS (ONSASW) at 3 mm from the optic nerve head and the entire ONSASA outlined between 3 and 7 mm. After exploring and comparing five models to describe the relationship between body mass index (BMI), mean arterial blood pressure (MABP), ONSASA and ICP, the best model was determined.

RESULTS

In all, 90 patients with neurological diseases undergoing continuous invasive ICP monitoring were included in the study. In the training group, the correlation coefficient for the association between the ICP and ONSASA (Pearson's correlation r=0.953) was higher than that for the association of the ICP with the ONSD (r=0.672; p<0.0001) and ONSASW at 3 mm behind the globe (r=0.691; p<0.0001). In the training group, the weighting function for prediction of the ICP was as follows: non-invasive ICP=2.050×ONSASA-0.051×BMI +0.036*MABP-5.837. With 20 mm Hg as the cut-off point for a high or low ICP, the sensitivity and specificity of ONSASA predicting ICP was 1.00 and 0.92. Receiver operator curve analysis revealed that the calculated cut-off value for predicting elevated ICP was 19.96 (area under curve= 0.960, 95% CI 0.865 to 1.00).

CONCLUSION

Measurement of the ONSASA using ultrasonography can serve as a practical method for rapid and non-invasive quantification for evaluating ICP through an accurate mathematical formula with the BMI and MABP considered as contributing parameters.

TRIAL REGISTRATION NUMBER

The study was registered in the Chinese Clinical Trial Registry (Study no ChiCTR2100045274).

Effect of Tourniquet Deflation on Intracranial Pressure Measured by Ultrasound of the Optic Nerve Sheath Diameter in Patients Undergoing Orthopedic Surgery Under Spinal Anesthesia: An Observational Study

Background Orthopedic surgeries of the lower extremities frequently require exsanguination and the use of pneumatic tourniquets. However, the deflation of the tourniquet is accompanied by predominant metabolic changes such as an increase in PaCO2. Prior studies have reported the existence of a correlation between tourniquet deflation and an increase in intracranial pressure in patients undergoing surgery under general anesthesia. However, there is a dearth of literature demonstrating such relationships among patients undergoing surgery under subarachnoid block in the Indian setting. The present research was conducted to study the variations in intracranial pressure after the deflation of the tourniquet by measuring the optic nerve sheath diameter (ONSD) using ultrasound among patients undergoing orthopedic surgery of the lower limb under spinal anesthesia at a tertiary care hospital in eastern India. Methodology After obtaining clearance from the Institutional Ethics Committee, this prospective observational study was conducted among 45 patients undergoing orthopedic surgeries of the lower limb using a pneumatic tourniquet. Changes in intracranial pressure following tourniquet deflation were recorded by measuring ONSD by ultrasound in these patients. Heart rate (HR), mean arterial pressure (MAP), SpO2, EtCO2, and ONSD were noted 15 minutes before administration of subarachnoid block (T0), just before tourniquet deflation (T1) and at 5, 10, and 15 minutes after tourniquet deflation (T5, T10, and T15, respectively). Results The ONSD varied significantly at each point of observation (p < 0.05). The ONSDs at 5 and 10 minutes after the deflation of the tourniquet were significantly greater than that at T0 (p = 0.002). EtCO2 showed a significant increase compared to baseline values at every point of observation intraoperatively whereas MAP showed a significant decrease (p < 0.05). For all parameters (ONSD, HR, systolic blood pressure, diastolic blood pressure, MAP, and EtCO2), the most significant change in observation was noted at T10, i.e., 10 minutes after the deflation of the tourniquet.   Conclusions The significant finding in this study was that the ONSD measurements recorded by ultrasound were increased after the deflation of the tourniquet and that this change can be attributed to an increase in EtCO2. However, the results obtained cannot be validated outside the present research owing to the observational nature of the study and limited sample size. Thus, it is difficult to arrive at a definitive conclusion. Further large-scale multicentric studies may be needed to substantiate the findings of this study.

Prognostic role of optic nerve sheath diameter in stroke in emergency department, A case control study

Background

Sonographic measurement of optic nerve sheath diameter (ONSD) can reflect intracranial pressure (ICP) indirectly and determine the neurology intensive care unit (NICU) requirement and mortality in acute ischemic stroke (AIS).

Aim

To demonstrate the effectiveness of ONSD to determine mortality, morbidity, and NICU requirement on patients with the AIS.

Methods

The sonographic ONSD measurements were performed on each patient with AIS, over 18 years old. All patients were categorized according to the Oxfordshire Community Stroke Project (OCSP) classification system. MRI images were examined for increased ICP, and the patients were categorized into two groups as increased ICP (i-ICP) and normal ICP. The ONSD results were evaluated in terms of classifications, outcomes, and prognosis of the patients.

Results

One hundred and five patients were included and 31 (35.2%) were in the i-ICP group. The median ONSDs were 5.26 mm in the i-ICP group and 4.62 mm in the normal ICP group (P < 0.001). The median ONSDs were 5.13 mm in the NICU group and 4.69 mm in the neurology ward (NW) group (P = 0.001). The total anterior circulation infarction (TACI) subgroup had higher ONSDs than the others (TACI: 5.27 mm; PACI: 4.73 mm; POCI: 4.77 mm; and LACI: 4.64 mm, P < 0.001). The NICU requirements were higher in the TACI subgroup. The median ONSD was 5.42 mm in the deceased group (survived: 4.77 mm, P < 0.001).

Conclusion

ONSD may be favorable for predicting the increased ICP and the NICU requirement in OCSP subgroups. Moreover, ONSD can be used to foresee the mortality of AIS.

Does prolonged prone position affect intracranial pressure? prospective observational study employing Optic nerve sheath diameter measurements

BACKGROUND

Our aim in this observational prospective study is to determine whether the prone position has an effect on intracranial pressure, by performing ultrasound-guided ONSD (Optic Nerve Sheath Diameter) measurements in patients with acute respiratory distress syndrome (ARDS) ventilated in the prone position.

METHODS

Patients hospitalized in the intensive care unit with a diagnosis of ARDS who were placed in the prone position for 24 h during their treatment were included in the study. Standardized sedation and neuromuscular blockade were applied to all patients in the prone position. Mechanical ventilation settings were standardized. Demographic data and patients' pCO₂, pO₂, PaO₂/FiO₂, SpO₂, right and left ONSD data, and complications were recorded at certain times over 24 h.

RESULTS

The evaluation of 24-hour prone-position data of patients with ARDS showed no significant increase in ONSD. There was no significant difference in pCO₂ values either. PaO₂/FiO₂ and pO₂ values demonstrated significant cumulative increases at all times. Post-prone SPO2 values at the 8th hour and later were significantly higher when compared to baseline (p < 0.001).

CONCLUSION

As a result of this study, it appears that the prone position does not increase intracranial pressure during the first 24 h and can be safely utilized, given the administration of appropriate sedation, neuromuscular blockade, and mechanical ventilation strategy. ONSD measurements may increase the safety of monitoring in patients ventilated in the prone position.

Detection of increased intracranial pressure in trans-oral robotic thyroidectomy using optic nerve sheath diameter measurement

BACKGROUND

During transoral robot-assisted thyroidectomy, there is a risk of increasing intracranial pressure because the site of CO₂ insufflation is narrow and close to the brain.

METHODS

We analyzed the pre- to post-CO₂ neck insufflation change in the optic nerve sheath diameter during transoral robot-assisted thyroidectomy. Changes in vital-signs, airway pressure, and arterial carbon dioxide pressure were analyzed along with postoperative complications.

RESULTS

Among the 30 participants, the post-CO₂ inflation mean optic nerve sheath diameter (5.64 ± 0.54 mm) was higher than the pre-induction diameter (4.81 ± 0.37 mm) with a mean difference of 0.83 (95% CI, 0.69-0.97; p < 0.001), but returned to baseline after CO₂ deflation in most cases. One participant had sustained increased optic nerve sheath diameter (6.35 mm) associated with severe new-onset postoperative headache.

CONCLUSION

Transient elevation in the intracranial pressure during low-pressure CO₂ neck insufflation in the transoral robot-assisted thyroidectomy did not appear to adversely affect patients.

The Effects of Lateral 45° Head-Down Position and Carbon Dioxide Pneumoperitoneum on the Optic Nerve Sheath Diameter in Patients Undergoing Laparoscopic Transperitoneal Nephrectomies: A Prospective Observational Study

Background: The aim of this study is to assess the extent of the increased intracranial pressure resulting from lateral decubitus and 45° downward positioning using sonographic optic nerve sheath diameter (ONSD) in patients undergoing laparoscopic transperitoneal nephrectomy. In addition, we evaluated the effect of the carbon dioxide pneumoperitoneum (CO₂PP) on ONSD. Materials and Methods: Twenty-four adults were enrolled in this prospective observational study. Longitudinal and transverse ONSDs were measured for each eye by ocular ultrasonography. The values were noted in supine position (T0), 20 minutes after induction of anesthesia (T1), after insufflation of the abdomen in lateral 45° head-down position (T2), at 30-minute intervals during surgery (T3-T4-T5), during lateral 45° head-down position after CO₂ exsufflation (T6), before awakening while supine (T7), and at postoperative 24th hour (T8). Hemodynamic and respiratory parameters were investigated at the measurement time points. Results: Average ONSD values for the lower eye was T0 = 4.27 ± 0.4 mm, T1 = 4.56 ± 0.6 mm, T2 = 4.84 ± 0.6 mm, T3 = 4.91 ± 0.4 mm, T4 = 4.99 ± 0.5 mm, T5 = 4.97 ± 0.5 mm T6 = 4.96 ± 0.5 mm, T7 = 4.76 ± 0.4 mm, T8 = 4.36 ± 0.5 mm and for the upper eye was T0 = 4.24 ± 0.4 mm, T1 = 4.39 ± 0.5 mm, T2 = 4.54 ± 0.5 mm, T3 = 4.60 ± 0.4 mm, T4 = 4.66 ± 0.4 mm, T5 = 4.72 ± 0.7 mm, T6 = 4.68 ± 0.4 mm, T7 = 4.52 ± 0.4 mm, T8 = 4.30 ± 0.4 mm (P < .001). Conclusion: In our study, we observed a significant increase in ONSD within minutes after the patient was placed in a head-down position. We also observed that the difference increased more with CO₂PP and was proportional to the length of the surgery. We found that it regressed to initial levels at the postoperative 24th hour. Clinicaltrials.gov: NCT05185908.

Correlation between the Optic Nerve Sheath Diameter Measurement and Intracranial Hypertension Tomographic Findings from a Colombian Hospital

Objective In the present study, we aimed at determining the correlation between tomographic findings of intracranial hypertension and ultrasound measurement of the optic nerve sheath diameter (ONSD).

Methods Observational, descriptive, prospective, cross-sectional pilot study. The present research was performed in a tertiary hospital in Cali, Colombia, from March 2019 to October 2019. Twenty-five patients constituted the intracranial hypertension group, and 25 patients without intracranial hypertension constituted the control group. Ultrasound measurements of the ONSD were assessed using a Sonosite Turbo (SonoSite Inc., Bothell, WA, USA) ultrasound. The computed tomography (CT) images obtained from each patient diagnosed with intracranial hypertension were available in the software of the hospital. The primary outcome was the ultrasound measurement of the ONSD.

Results The ONSD values of the right eye of the intracranial hypertension group ranged from 5.2 to 7.6 mm, and the ONSD of the left eye ranged from 5.3 to 7.3 mm. The global ONSD values, obtained from the average between the right and left eye, were recorded between 5.25 and 7.45 mm. Overall, our study indicated that ultrasound measurements of the ONSD were effective in differentiating a group with intracranial hypertension, previously diagnosed by CT scan images, from patients without this condition. According to the ROC curve, the optimal cutoff point for detecting intracranial hypertension was 5.2 mm.

Conclusions Ultrasound measurements of the ONSD correlated with the measurements obtained from CT scan images, suggesting that the ultrasound technique can be efficient in identifying patients with intracranial hypertension and valuable in cases when CT scan images are not an available option.

The role of sonographic optic nerve sheath diameter measurements in pediatric head trauma

PURPOSE

To determine the accuracy of bedside sonographic measurements of optic nerve sheath diameter (ONSD) and ONSD/eyeball transverse (ETD) diameter ratios to predict space-occupying lesions (SOLs) or elevated intracranial pressure (ICP) in pediatric head trauma.

METHODS

Children who presented to the emergency department with head trauma and underwent cranial computed tomography (CT) were enrolled and examined by ocular ultrasonography (US), and the ONSD was measured at 3 mm posterior to the globe and ETD were measured. Ratios of ONSD at 3 mm/ETD were calculated. All ONSD measurements and ratios were calculated from cranial CT images.

RESULTS

Subjects with elevated ICP had increased ONSD measurements and ratios. To predict elevated ICP, the AUC for ONSD at 3 mm was 0.956 (95% CI 0.896-1). At a cut-off level of 5.1 mm, the sensitivity and specificity of ONSD 3 mm values for elevated ICP were 92.9% and 94.0%. For the ONSD 3 mm/ETD ratio, it was 0.980 (95% CI 0.959-1). At a cut-off level of 0.22, the sensitivity and specificity were 100% sensitivity and 88.0%. All sonographic ONSD measurements and ratios were significantly correlated with readings calculated from cranial CT images.

CONCLUSION

Sonographic ONSD measurements and ratios were found to be quite sensitive to detect elevated ICP on cranial CT images. Additionally, there was a significant correlation between measurements calculated by ocular US and cranial CT scans. Bedside ocular US seems to be a promising and useful tool to determine ICP in children with head trauma.

Ultrasonographic Changes in Transorbital Measurement of Optic Nerve Sheath Diameter in Magnesium Sulfate-Treated Severely Preeclamptic Patients: A Prospective Observational Study

Introduction

Severe preeclampsia can lead to various complications including increased intracranial pressure (ICP) which can be catastrophic but difficult to detect because of variable nonspecific symptoms. Ultrasonography has been used as noninvasive measure to monitor optic nerve sheath diameter (ONSD) as a marker of raised ICP. Effect of MgSO4 on ICP can modify the management approach, need for additional monitoring, targeting hemodynamic goals, timing of delivery, and choice of anesthesia. We evaluated the effect of MgSO4 on raised ICP in severely preeclamptic patients using ultrasound-guided ONSD as a surrogate marker of ICP.

Methodology

This prospective observational study was conducted after ethical committee approval and written informed consent from patients. Ultrasound-guided ONSD was measured and compared in 47 severe preeclamptic patients before and at 1 h, 4 h, 12 h, and 24 h after starting MgSO4 therapy. The analysis of data was done by one-way analysis of variance using Statistical Package for the Social Science.

Results

Mean ONSD was 5.56 ± 0.30 mm in our study group. ONSD above 5.8 mm was seen in 17 (36.17%) patients and was considered as marker of raised ICP. There was a significant decrease in ONSD after 4 h of administration of MgSO4. No significant correlation was observed between mean arterial pressure, serum magnesium level, and ONSD.

Conclusion

Ultrasound-guided ONSD measurement can be used as a quick, noninvasive bedside tool in severe preeclamptic patient on MgSO4 treatment as marker of ICP which help us in determining clinical severity, therapeutic response, and to decide further course of management.

Quality assessment of optic nerve sheath diameter ultrasonography: Scoping literature review and Delphi protocol

BACKGROUND AND PURPOSE

The optic nerve is surrounded by the extension of meningeal coverings of the brain. When the pressure in the cerebrospinal fluid increases, it causes a distention of the optic nerve sheath diameter (ONSD), which allows the use of this measurement by ultrasonography (US) as a noninvasive surrogate of elevated intracranial pressure. However, ONSD measurements in the literature have exhibited significant heterogeneity, suggesting a need for consensus on ONSD image acquisition and measurement. We aim to establish a consensus for an ONSD US Quality Criteria Checklist (ONSD US QCC).

METHODS

A scoping systematic review of published ultrasound ONSD imaging and measurement criteria was performed to guide the development of a preliminary ONSD US QCC that will undergo a modified Delphi study to reach expert consensus on ONSD quality criteria. The protocol of this modified Delphi study is presented in this manuscript.

RESULTS

A total of 357 ultrasound studies were included in the review. Quality criteria were evaluated under five categories: probe selection, safety, positioning, image acquisition, and measurement.

CONCLUSIONS

This review and Delphi protocol aim to establish ONSD US QCC. A broad consensus from this process may reduce the variability of ONSD measurements in future studies, which would ultimately translate into improved ONSD clinical applications. This protocol was reviewed and endorsed by the German Society of Ultrasound in Medicine.

Optic Nerve Sheath Diameter Ultrasound: A Non-Invasive Approach to Evaluate Increased Intracranial Pressure in Critically Ill Pediatric Patients

Early diagnosis of increased intracranial pressure (ICP) is crucial for prompt diagnosis and treatment of intracranial hypertension in critically ill pediatric patients, preventing secondary brain damage and mortality. Although the placement of an external ventricular drain coupled to an external fluid-filled transducer remains the gold standard for continuous ICP monitoring, other non-invasive approaches are constantly being improved and can provide reliable estimates. The use of point-of-care ultrasound (POCUS) for the assessment of ICP has recently become widespread in pediatric emergency and critical care settings, representing a valuable extension of the physical examination. The aim of this manuscript is to review and discuss the basic principles of ultra-sound measurement of the optic nerve sheath diameter (ONSD) and summarize current evidence on its diagnostic value in pediatric patients with ICP. There is increasing evidence that POCUS measurement of the ONSD correlates with ICP, thus appearing as a useful extension of the physical examination in pediatrics, especially in emergency medicine and critical care settings for the initial non-invasive assessment of patients with suspected raised ICP. Its role could be of value even to assess the response to therapy and in the follow-up of patients with diagnosed intracranial hypertension if invasive ICP monitoring is not available. Further studies on more homogeneous and extensive study populations should be performed to establish ONSD reference ranges in the different pediatric ages and to define cut-off values in predicting elevated ICP compared to invasive ICP measurement.

Non-invasive intracranial pressure assessment using shear-wave elastography in neuro-critical care patients

OBJECTIVE

To determine if Young's modulus of the optic nerve (ON) structure as measured by shear-wave elastography can suggest changes in intracranial pressure (ICP) in neuro-critical care patients.

MATERIALS AND METHODS

Thirty-one healthy volunteers and twenty-two neuro-critical care patients were enrolled. ON sheath (ONS) diameter (ONSD) values and Young's modulus measurements of volunteers were collected in a calm state and during a Valsalva maneuver (VM). Ultrasound measurements and ICP values of patients were collected on operation day and at 24 and 48 h after the operation; measurements were thereafter assigned to three groups: severely elevated (ICP greater than 22 mmHg), mildly elevated (ICP = 14-22 mmHg), and normal (ICP ≤ 13 mmHg).

RESULTS

ONSD and Young's modulus for the ON and ONS of volunteers during VM were higher than those in the calm state (all P < 0.001). In contrast to ONSD, Young's modulus for ON and ONS did not correlate with age, body mass index, or sex. The best cutoff values of Young's modulus for ON for predicting elevated and severely elevated ICP were 16.67 kPa and 22.74 kPa, respectively. Accordingly, the sensitivity values were 96.7% and 88.9%, and the specificity values were 86.1% and 73.7%, which had the same diagnostic performance as ONSD.

CONCLUSION

Young's modulus of the ON accurately reflects changes in ICP. It is not confounded by age, sex, or body mass index compared to ONSD.

Optic Nerve Sheath Diameter Ultrasound for Raised Intracranial Pressure: A Literature Review and Meta-analysis of its Diagnostic Accuracy

Optic nerve sheath diameter (ONSD) ultrasound is becoming increasingly more popular for estimating raised intracranial pressure (ICP). We performed a systematic review and analysis of the diagnostic accuracy of ONSD when compared to the standard invasive ICP measurement.

METHOD

We performed a systematic search of PUBMED and EMBASE for studies including adult patients with suspected elevated ICP and comparing sonographic ONSD measurement to a standard invasive method. Quality of studies was assessed using the QUADAS-2 tool by two independent authors. We used a bivariate model of random effects to summarize pooled sensitivity, specificity, and diagnostic odds ratio (DOR). Heterogeneity was investigated by meta-regression and sub-group analyses.

RESULTS

We included 18 prospective studies (16 studies including 619 patients for primary outcome). Only one study was of low quality, and there was no apparent publication bias. Pooled sensitivity was 0.9 [95% confidence intervals (CI): 0.85-0.94], specificity was 0.85 (95% CI: 0.8-0.89), and DOR was 46.7 (95% CI: 26.2-83.2) with partial evidence of heterogeneity. The Area-Under-the-Curve of the summary Receiver-Operator-Curve was 0.93 (95% CI: 0.91-0.95, P < .05). No covariates were significant in the meta-regression. Subgroup analysis of severe traumatic brain injury and parenchymal ICP found no heterogeneity. ICP and ONSD had a correlation coefficient of 0.7 (95% CI: 0.63-0.76, P < .05).

CONCLUSION

ONSD is a useful adjunct in ICP evaluation but is currently not a replacement for invasive methods where they are feasible.

Arterial and Venous Cerebral Blood Flow Velocities and Their Correlation in Healthy Volunteers and Traumatic Brain Injury Patients

BACKGROUND

Few studies have explored the cerebral venous compartment or the correlation between venous and arterial cerebral blood flows. We aimed to correlate cerebral blood flow velocities in the arterial (middle cerebral artery) and venous (straight sinus) compartments in healthy volunteers and traumatic brain injury (TBI) patients. In addition, we determined the normative range of these parameters.

MATERIALS AND METHODS

A total of 122 healthy volunteers and 95 severe TBI patients of both sexes were included and stratified into 3 age groups as follows: group 1 (aged, 18 to 44 y); group 2 (aged, 45 to 64 y); group 3 (older than 65 y). Transcranial Doppler systolic cerebral blood flow velocity, diastolic cerebral blood flow velocity, and mean cerebral blood flow velocity (FVs, FVd, FVm, respectively) were measured in the middle cerebral artery and peak cerebral venous blood flow velocity (FVVs) was measured in the straight sinus. The arteriovenous correlation was assessed on the basis of a positive relationship between FVs and FVVs.

RESULTS

There was an arteriovenous correlation (FVs vs. FVVs) in healthy volunteers (R=0.39, P<0.0001). We found no arteriovenous correlation in the TBI cohort overall, but FVs and FVVs were correlated in age group 1 (R=0.28, P=0.05) and in males (R=0.29, P=0.01). In healthy volunteers, FVs and FVm were significantly higher in males compared with females; and FVs, FVm, FVd, FVVs all increased across the age spectrum. There were no significant differences in any of these parameters in TBI patients.

CONCLUSIONS

There are age and sex differences in arterial and venous cerebral blood flow velocities in healthy volunteers. Arteriovenous correlation is present in healthy volunteers but absent in TBI patients.

Effect of a neck collar on brain turgor: a potential role in preventing concussions?

BACKGROUND

Mild internal jugular vein (IJV) compression, aimed at increasing intracranial fluid volume to prevent motion of the brain relative to the skull, has reduced brain injury markers in athletes suffering repeated traumatic brain injuries. However, an increase in intracranial volume with IJV compression has not been well demonstrated. This study used transorbital ultrasound to identify changes in optic nerve sheath diameter (ONSD) as a direct marker of accompanying changes in intracranial volume.

METHODS

Nineteen young, healthy adult volunteers (13 males and 6 females) underwent IJV compression of 20 cm H₂O low in the neck, while in upright posture. IJV cross-sectional area at the level of the cricoid cartilage, and the change in right ONSD 3 mm behind the papillary segment of the optic nerve, were measured by ultrasound. Statistical analysis was performed using a paired t-test with Bonferroni correction.

RESULTS

Mean (SD) cross-sectional area for the right IJV before and after IJV compression was 0.10 (0.05) cm² and 0.57 (0.37) cm², respectively (p=0.001). ONSD before and after IJV compression was 4.6 (0.5) mm and 4.9 (0.5) mm, respectively (p=0.001).

CONCLUSIONS

These data verify increased cerebral volume following IJV compression, supporting the potential for reduced brain 'slosh' as a mechanism connecting IJV compression to possibly reducing traumatic brain injury following head trauma.

High-resolution MRI assessment of optic nerve sheath diameter in adults: optic nerve sheath variation and a new diagnostic tool for intracranial hypertension

BACKGROUND

Assessment of optic nerve sheath diameter (ONSD) is a non-invasive measure of intracranial pressure (ICP). However, it is not clear whether healthy individuals exhibit ONSD variation or whether factors other than ICP affect the ONSD.

PURPOSE

To investigate whether ONSD was correlated with age, sex, height, weight, eyeball transverse diameter (ETD), or body mass index (BMI), and to develop a new diagnostic model to increase the diagnostic accuracy of intracranial hypertension (IH).

MATERIAL AND METHODS

A total of 145 relatively healthy adults and 40 patients with acute IH who underwent high-resolution magnetic resonance imaging (MRI) were enrolled in this study. Linear regression analyses were used to determine the relationship between ONSD and these variables. If correlations were identified, an index ONSD_Δ removing variables effects was calculated. ROC analysis was used to assess the IH predictive value of ONSD_Δ in terms of sensitivity and specificity.

RESULTS

In relatively healthy adults, there was a correlation between ONSD and BMI (P = 0.002), which can be presented as an index ONSD_Δ. The ONSD_Δ model better predicted IH than the ONSD model (P = 0.035), with a sensitivity of 70.00%, a specificity of 71.72%, and an AUC of 0.755.

CONCLUSION

A correlation between ONSD and body mass index (BMI) was found using high-resolution MRI. This result indicates that the effects of BMI should be considered along with the ONSD during ICP monitoring. Meanwhile, the index ONSD_Δ was better than the ONSD in predicting IH and could be used to obtain a more precise estimation of ICP.

Effects of Venoconstrictive Thigh Cuffs on Dry Immersion-Induced Ophthalmological Changes

Neuro-ophthalmological changes named spaceflight associated neuro-ocular syndrome (SANS) reported after spaceflights are important medical issues. Dry immersion (DI), an analog to microgravity, rapidly induces a centralization of body fluids, immobilization, and hypokinesia similar to that observed during spaceflight. The main objectives of the present study were 2-fold: (1) to assess the neuro-ophthalmological impact during 5 days of DI and (2) to determine the effects of venoconstrictive thigh cuffs (VTC), used as a countermeasure to limit headward fluid shift, on DI-induced ophthalmological adaptations. Eighteen healthy male subjects underwent 5 days of DI with or without VTC countermeasures. The subjects were randomly assigned into two groups of 9: a control and cuffs group. Retinal and optic nerve thickness were assessed with spectral-domain optical coherence tomography (OCT). Optic nerve sheath diameter (ONSD) was measured by ocular ultrasonography and used to assess indirect changes in intracranial pressure (ICP). Intraocular pressure (IOP) was assessed by applanation tonometry. A higher thickness of the retinal nerve fiber layer (RNFL) in the temporal quadrant was observed after DI. ONSD increased significantly during DI and remained higher during the recovery phase. IOP did not significantly change during and after DI. VTC tended to limit the ONSD enlargement but not the higher thickness of an RNFL induced by DI. These findings suggest that 5 days of DI induced significant ophthalmological changes. VTC were found to dampen the ONSD enlargement induced by DI.

The assessment of the effect of different intraabdominal pressures used for laparoscopic cholecystectomy surgery on optic nerve sheath diameter: a prospective observational cohort study

Background/aim

During laparoscopic cholecystectomy operations, increases in intraabdominal, intrathoracic, and intracranial pressures (ICP) can be seen after pneumoperitoneum created for surgical imaging. Orbital ultrasonography (USG), which has been developed in recent years, is a method that can evaluate the ICP by measuring the optic nerve sheath diameter (ONSD) from the eyeball. In our study, we aimed to evaluate whether different intraabdominal pressure values created during laparoscopic cholecystectomy operations correlate with ICP by measuring ONSD.

Materials and methods

The study included a total of 90 patients with American Society of Anesthesiologists (ASA) physical status classification I (ASA I) and II (ASA II) and ages from 18 to 65 years with laparoscopic cholecystectomy planned. After the patients were intubated, at the 5th min, bilateral ONSD measurements were performed. The same measurements were performed at the 15th and 30th min after CO2 insufflation and additionally 10 min after CO2 was released at the end of the operation. During intrabdominal CO2 insufflation, patients with 10 mmHg pressure applied comprised Group 1, patients with 12 mmHg pressure applied comprised Group 2, and patients with 14 mmHg pressure applied comprised Group 3.

Results

The study was completed with 89 patients, 51 female and 38 males. One patient was excluded from the study due to erroneous values. The variations in ONSD measured in the right-left eye before pneumoperitoneum and at the 15th and 30th min after abdominal CO2 insufflation were observed to be statistically significant (p < 0.01). In all three groups, the right and left eye ONSD values were not identified to be statistically significantly different (p > 0.01). A significant increase was observed in ONSD values in direct proportion to the increase in intraabdominal pressure in patients undergoing laparoscopic cholecystectomy surgery.

Conclusion

USG-guided ONSD measurements appear be a guide to ensure optimization of intraabdominal pressures and safe anesthesia administration for patients, especially those at risk of ICP increase, during laparoscopic surgery.

Bedside sonographic measurements of optic nerve sheath diameter in children with diabetic ketoacidosis

BACKGROUND

Bedside sonographic assessment of the optic nerve sheath has gained popularity for evaluating intracranial pressure in recent years.

OBJECTIVE

To investigate the bedside sonographic measurements of optic nerve sheath diameter (ONSD) and ONSD/eyeball diameter ratios, which are related with cerebral edema (CE), in children with diabetic ketoacidosis (DKA) before and after treatment.

METHODS

Children aged 12 months to 18 years, who were diagnosed with DKA were included. The ONSD was measured at 3 mm posterior to the globe in the anterior axial transbulbar view. The eyeball transverse diameter (ETD) and eyeball vertical diameter (EVD) were measured and ratios of ONSD/ETD and ONSD/EVD were calculated. Bedside ultrasound (US) examinations were performed at the beginning and at the end of fluid therapy.

RESULTS

About 43 patients were enrolled. About 12 (27.9%) patients had mild, 14 (32.6%) moderate, and 17 (39.5%) severe DKA. At baseline, the ONSD measurements and ratios were significantly higher in severe DKA group than in those with mild or moderate DKA group. All ONSD measurements, ONSD/ETD, and ONSD/EVD ratios at the end of therapy were significantly lower compared with baseline measurements. At the end of therapy, ONSD measurements and ratios were similar among DKA severity groups.

CONCLUSION

The ONSD measurements and ratios decreased from the beginning of DKA treatment, which could be considered as an indicator of an increase in intracranial pressure at the time of admission. Ocular US may serve as a promising tool to perform further risk stratification of children with DKA and to identify DKA-related CE.

Comparison of the effects of normal and low blood pressure regulation on the optic nerve sheath diameter in robot assisted laparoscopic radical prostatectomy

Background

Robot-assisted laparoscopic radical prostatectomy is an advanced and popular surgical technique. However, increased intracranial pressure which is caused by CO₂ pneumoperitoneum and Trendelenburg position is the main cerebrovascular effect. Measurement of optic nerve sheath diameter using ocular ultrasound is a noninvasive and reliable method for the assessment of intracranial pressure. The primary endpoint of this study was to identify whether low blood pressure regulation has any benefit in attenuating an increase of optic nerve sheath diameter during robot-assisted laparoscopic radical prostatectomy.

Methods

Optic nerve sheath diameter and cerebral oxygen saturation were measured at baseline (supine position), one and two hours after pneumoperitoneum and Trendelenburg position respectively, and after return to supine position in normal (n = 27) and low blood pressure groups (n = 24).

Results

Mean optic nerve sheath diameter values measured at one and two hours after pneumoperitoneum and Trendelenburg position were significantly increased compared to the baseline value (P < 0.001 in normal blood pressure group; P = 0.003 in low blood pressure group). However, the mean optic nerve sheath diameter and cerebral oxygen saturation measured at any of the time points as well as degrees of change between the two groups did not show any significant changes. The peak values of optic nerve sheath diameter in normal and low blood pressure groups demonstrated 14.9% and 9.2% increases, respectively.

Conclusions

Low blood pressure group demonstrated an effect in maintaining an increase of optic nerve sheath diameter less than 10% during CO₂ pneumoperitoneum and Trendelenburg position.

Dynamic Optic Nerve Sheath Diameter (ONSD) guided management of raised intracranial pressure in pediatric acute liver failure

BACKGROUND AND AIMS

The objectives were to evaluate the role of optic nerve sheath diameter (ONSD) to detect raised intracranial pressure (ICP) in pediatric acute liver failure (PALF), study the variations in ONSD with ICP-lowering measures and to evaluate its prognostic role.

METHODS

PALF with clinical evidence of raised ICP were enrolled as cases, while those without raised ICP were control group A. ONSD was measured at admission and repeated regularly. It was also measured at time of each new episode of raised ICP and 2 h after the management of such episode.

RESULTS

31 PALF with raised ICP were included as cases and 15 without as control group A. ONSD was significantly higher in cases: 5 mm (IQR: 4.7-5.4) as compared to control group A: 3.8 mm (IQR: 3.3-4). ONSD greater than 4.55 mm at baseline diagnosed clinically raised ICP with 87.5% sensitivity and 100% specificity. The mean ONSD was 5.44 ± 0.49 mm during a total of 90 events of acute raised ICP. Clinical responders had a decrease in ONSD by 0.59 ± 0.24 mm by 2 h, whereas non-responders showed a decrease of 0.18 ± 0.23 mm, p < 0.0005. ONSD persisting more than 4.6 mm by 24 h of management predicted poor outcome with sensitivity and specificity of 83.3% and 72.7%.

CONCLUSION

ONSD is a simple, bedside, inexpensive, reproducible and repeatable modality to assess ongoing change in ICP in PALF. ONSD more than 4.55 mm suggests raised ICP. The goal should be to bring ONSD down to less than 4.6 mm within 24 h by aggressive anti-ICP therapy to achieve favourable outcome.

Efficacy of Noninvasive Technologies in Triaging Traumatic Brain Injury and Correlating With Intracranial Pressure: A Prospective Study

BACKGROUND

There is interest in methods of measuring noninvasive intracranial pressure (ICP), including pupillometry, ultrasonographic transcranial Doppler (TCD), and optic nerve sheath diameter (ONSD), for diagnosing traumatic brain injury (TBI) in limited resource environments. Whether these technologies have diagnostic agreement is unknown. We hypothesized that ONSD, pupillometry, and TCD could both distinguish severe TBI and correlate with ICP.

METHODS

A prospective study of 135 patients was conducted at a level 1 trauma center. Four test groups were established: nontrauma patients with ICP monitoring, trauma patients without TBI, trauma patients with mild TBI, and trauma patients with severe TBI with ICP monitoring. All patients underwent daily measurements of ONSD, pupillometry, and TCD with both CX50 Sonosite and the Spencer ST3 Yi Pencil probe.

RESULTS

ONSD differed significantly in patients with severe TBI compared with patients with mild and no TBI, but did not correlate with ICP. Pupillometric constriction velocity, dilation velocity, and percent change in pupil diameter were significantly different in patients with severe TBI, but also did not correlate with ICP. TCD did not differ among TBI severities, but middle cerebral artery peak systolic velocity, middle cerebral artery flow velocity, and carotid flow velocity correlated with ICP.

CONCLUSIONS

This is a novel study of four noninvasive tests to screen for severity of TBI and measure ICP. Our analysis indicates that no single device can do both. However, ONSD and pupillometry may be used as a supplementary screening tool for severe TBI, whereas TCD could be used to estimate and follow ICP in patients with severe TBI.

Variability of the Optic Nerve Sheath Diameter on the Basis of Sex and Age in a Cohort of Healthy Volunteers

Many studies have demonstrated that the optic nerve sheath diameter (ONSD) is a good indicator of intracranial pressure (ICP). There are uncertainties regarding the optimal ONSD threshold, considering age and sex differences in the healthy population, and these differences could lead to uncertainties in evaluation of ONSD in pathological conditions.The aim of this prospective observational study was to investigate if age and sex could influence ONSD in a cohort of healthy Italian volunteers recruited during preanesthetic assessment for low-risk surgical procedures.The population was stratified for sex (males versus females) and for age (18-44 years, 45-64 years, and ≥65 years). The axial and longitudinal ONSD diameters were measured by two trained investigators.A significant difference in ONSD between males and females was found (median 4.2 (interquartile range 3.9-4.6) versus 4.1 (interquartile range 3.6-4.2) mm, P = 0.01), and a positive correlation between ONSD and age was found (R = 0.50, P < 0.0001).It was concluded that ONSD increases with age and is significantly larger in the healthy male population. These discrepancies should be taken into consideration when ONSD measurement is performed.

Optic Nerve Sheath Diameter in Preterm Infants: Suggested Values

OBJECTIVE

Timely detection of elevated intracranial pressure (ICP) in highrisk preterm infants may be critical to avoid permanent neurologic sequelae. Size of optic nerve sheath diameter (ONSD) is highly correlated with changes in ICP. Normal ultrasonographic ONSD values for preterm infants have been published. This study sought to compare these data with MRI measured OSND and to propose suggested ultrasonographic ONSD values.

METHODS

The ONSD in preterm MRIs were retrospectively measured and related to pre-existing ultrasonographic ONSD. Data were stratified for corrected gestational age. Simple linear regression between ONSD mean values and age was modeled for both eyes, and R2 was calculated. Suggested values for ultrasonographic ONSD were ascertained through linear regression and calculated prediction intervals.

RESULTS

ONSD measurements demonstrated R2 values of 0.95 (right ONSD MRI), 0.95 (left ONSD MRI), 0.96 (right ONSD ultrasound), and 0.93 (left ONSD ultrasound). Suggested ONSD values were incremental with corrected gestational age.

CONCLUSION

ONSD measurements with MRI and ultrasound are similar. The proposed suggested ONSD values may be helpful in clinical situations where ICPs are suspected or known.

Correlation Between Invasive and Noninvasive Technique of Intracranial Pressure Measurement in Children With Traumatic Brain Injury: An Observational Study

BACKGROUND

Direct measurement of intracranial pressure (ICP) is an invasive technique with potential complications, which has prompted the development of alternative, noninvasive, methods of ICP assessment. The aim of this study was to determine the relationship between noninvasive ultrasound-based measurement of optic nerve sheath diameter (ONSD), transcranial Doppler-derived pulsatility index (PI), and invasive ICP measurements in children with traumatic brain injury (TBI).

METHODS

Children aged 1 to 18 years undergoing invasive ICP monitoring following TBI were included in the study. Noninvasive ONSD and PI measurements were compared with simultaneous invasive ICP.

RESULTS

In all, 406 measurements of ONSD and PI were obtained in 18 patients. ONSD and PI correlated with ICP (r=0.76 and 0.79, respectively), combining ONSD and PI resulted in an even stronger correlation with ICP (r=0.99). Formulas were derived from mixed-effect models that best fitted the data for noninvasive ICP estimation. A combination of ONSD and PI had the highest ability to detect ICP >20 mm Hg (area under the receiver operating characteristic curve=0.99, 95% confidence interval: 0.99-1.00). Optimal cutoff values for the prediction of intracranial hypertension were 5.95 mm for ONSD (sensitivity, 92%; specificity, 76%) and 1.065 for PI (sensitivity, 92%; specificity, 87%).

CONCLUSIONS

In children with TBI, a combination of ONSD and PI strongly correlates with invasive ICP and has potential to screen for intracranial hypertension noninvasively. ONSD and PI may be useful tools for assessing ICP where invasive monitoring is unavailable or contraindicated.

Neuromonitoring during general anesthesia in non-neurologic surgery

Cerebral complications are common in perioperative settings even in non-neurosurgical procedures. These include postoperative cognitive dysfunction or delirium as well as cerebrovascular accidents. During surgery, it is essential to ensure an adequate degree of sedation and analgesia, and at the same time, to provide hemodynamic and respiratory stability in order to minimize neurological complications. In this context, the role of neuromonitoring in the operating room is gaining interest, even in the non-neurolosurgical population. The use of multimodal neuromonitoring can potentially reduce the occurrence of adverse effects during and after surgery, and optimize the administration of anesthetic drugs. In addition to the traditional focus on monitoring hemodynamic and respiratory systems during general anesthesia, the ability to constantly monitor the activity and maintenance of brain homeostasis, creating evidence-based protocols, should also become part of the standard of care: in this challenge, neuromonitoring comes to our aid. In this review, we aim to describe the role of the main types of noninvasive neuromonitoring such as those based on electroencephalography (EEG) waves (EEG, Entropy module, Bispectral Index, Narcotrend Monitor), near-infrared spectroscopy (NIRS) based on noninvasive measurement of cerebral regional oxygenation, and Transcranial Doppler used in the perioperative settings in non-neurosurgical intervention. We also describe the advantages, disadvantage, and limitation of each monitoring technique.

Effects of low- and high-pressure carbon dioxide pneumoperitoneum on intracranial pressure during laparoscopic cholecystectomy

BACKGROUND

Laparoscopic surgeries are a risk factor for raised intracranial **pressure and neurological complications. Even though rare, the consequences may be severe.

METHODS

One hundred and one patients of laparoscopic cholecystectomy were enrolled and were randomized into two groups: low-pressure 8 mm Hg (Group A) and high-pressure 14 mm Hg (Group B) carbon dioxide pneumoperitoneum during surgery. Fifty patients were in group A and 51 patients were in group B. Intracranial pressure was measured by measuring the optic nerve sheath diameter (ONSD) using ultrasound examination. Baseline ONSD was recorded followed by ONSD recording at various intervals: at the induction of anesthesia; 30 min, 45 min, at the end of surgery; and 30 min post surgery.

RESULTS

The groups were comparable in terms of demographics and comorbidities. The mean age of group A was 45 years and for group B it was 45.75 years. Most common indication for surgery was symptomatic gall stone disease. Baseline ONSD in group A was 0.427 ± 0.0459 mm, whereas it was 0.412 ± 0.0412 mm in group B. There was a significant rise of ONSD (p < 0.05) 30 min after induction of pneumoperitoneum and up to 30 min post anesthesia. In the low-pressure group 7 (14%) patients had a significant rise of ICP, whereas in the high-pressure group 20 (39%) patients had a significant rise of ICP (p < 0.05).

CONCLUSIONS

High-pressure pneumoperitoneum causes significant rise in intracranial pressure in comparison to low-pressure pneumoperitoneum during laparoscopic cholecystectomy, which can be monitored by ONSD measurement by ultrasound examination and is totally non-invasive.

Ultrasonographic measurement of the optic nerve sheath in the differential diagnosis and follow-up of migraine with and without aura: A pilot study

OBJECTIVE

Headache continues to be a common cause of emergency admissions. At first glance, primary headaches may not be distinguished from secondary headaches. This study aimed to evaluate the use of ultrasonic measurement of optic nerve sheath diameter (ONSD) in the clinical diagnosis of migraine patients during attack and during periods without attacks.

PATIENTS AND METHODS

This prospective study was conducted at the emergency department and neurology outpatient clinic of a tertiary hospital between October 2019 and January 2020. Patients diagnosed with episodic migraine and between ages 18-60 were included in the study. Migraine diagnosis and classification were based on criteria from the 2018 International Classification of Headache Disorders. ONSD measurement was performed with ultrasonography. ONSD measurements of the same migraine patients during attack and attack-free periods were compared with measurements of healthy volunteers.

RESULTS

A total of 82 participants consisting of 42 migraine patients and 40 control subjects were evaluated. In the control group, mean ONSD of the right eye was 4.88 ± 0.31 mm and mean ONSD of the left eye was 4.86 ± 0.31 mm. Mean ONSD measurement of the left eye was 4.80 ± 0.36 mm and mean ONSD of the right eye was 4.82 ± 0.37 during the attack period of the migraine patients. There was no significant difference between the migraine patients and the control group according to right and left eye ONSD measurements (attack-free period: p = 0.200, p = 0.448; attack period: p = 0.338, p = 0.660, respectively). There was no significant difference between ONSD measurements during the attack period and attack-free period in migraine patients (right eye p = 0.32; left eye p = 0.532).

CONCLUSION

The results of our study indicate that ONSD measurements may provide clinical insight into differential diagnosis preceding neuroimaging in migraine patients. On the other hand, since our study is the first on this topic, it should be noted that further studies are needed to come to a conclusion.

Effects of Age and Sex on Optic Nerve Sheath Diameter in Healthy Volunteers and Patients With Traumatic Brain Injury

The measurement of optic nerve sheath diameter (ONSD) has been reported as a non-invasive marker for intracranial pressure (ICP). Nevertheless, it is uncertain whether possible ONSD differences occur with age and sex in healthy and brain-injured populations. The aim of this study was to investigate the effects of sex and age on ONSD in healthy volunteers and patients with traumatic brain injury. We prospectively included 122 healthy adult volunteers (Galliera Hospital, Genova, Italy), and compared age/sex dependence of ONSD to 95 adult patients (Addenbrooke's Hospital, Cambridge, UK) with severe traumatic brain injury (TBI) requiring intubation and invasive ICP monitoring. The two groups were stratified for sex and age. Age was divided into 3 subgroups: (1) young adults: 18–44 years; (2) middle-aged adults: 45–64 years; (3) old adults: >65 years. In healthy volunteers, ONSD was significantly different between males and females [median (interquartile range): 4.2 (3.9–4.6) mm vs. 4.1 (3.6–4.2) mm (p = 0.01), respectively] and was correlated with age (R = 0.50, p < 0.0001). ONSD was significantly increased in group 3 compared to groups 2 and 1, indicating that ONSD values are higher in elderly subjects. In TBI patients, no differences in ONSD were found for sex and the correlation between ONSD and age was non-significant (R = 0.13, p = 0.20). ONSD increases with age and is significantly larger for males in healthy volunteers but not in TBI patients. Different ONSD cut-off values need not be age- or sex-adjusted for the assessment of increased ICP in TBI patients.

Ultrasound measurement of optic nerve sheath diameter pre- and post-lumbar puncture

BACKGROUND

To test the hypothesis that optic nerve sheath diameter (ONSD) correlates with real-time changes in intracranial pressure, we performed ultrasound measurements of the ONSD in ambulatory patients undergoing elective lumbar puncture (LP). We conducted a prospective cohort study, including adult patients undergoing LP in a non-emergent setting. We measured ONSD perpendicular to the optic nerve at 3 mm behind the globe in both eyes in the traverse and sagittal planes, with the patient supine. The primary outcome was change in ONSD from pre-LP to post-LP. We calculated association of opening and closing LP pressures with changes in the pre- and post-LP ONSD measurements.

RESULTS

The mean patient age was 49.0 years (SD = 37-61, range 19-67) with 21 females (72.4%) and 26 (89.7%) white American (not Hispanic or Latino). The average opening pressure and closing pressures were 20.4 cm and 13.5 cm with a difference of 6.9 cm, (95% CI 3.9-10.0 cm). Pressures between the participants with baseline ONSD measurement > 5 mm (average opening pressure = 21.3 cm) to those < 5 mm (20.2 cm) differed by 1.1 cm (95% CI - 5.7 to 8.0). Linear regression revealed no association between the sagittal, transverse, average, and change in ONSD measurements with the observed LP opening pressure, change in LP pressure, or volume of cerebral spinal fluid (CSF) drained.

CONCLUSIONS

In this study of ambulatory patients undergoing rapid decreases in ICP via elective LP, we detected no acute changes in ultrasonographic measurement of the ONSD.

Epidural bolus versus continuous epidural infusion analgesia on optic nerve sheath diameter in paediatric patients: A prospective, double-blind, randomised trial

The use of programmed intermittent epidural bolus for postoperative analgesia may have greater analgesic efficacy than continuous epidural infusion. However, the rapid delivery speed used with an epidural bolus is more likely to increase intracranial pressure. We compared the effects of lumbar epidural bolus versus continuous infusion epidural analgesia on intracranial pressure in children using optic nerve sheath diameter as a marker. We randomly assigned 40 paediatric patients to bolus or infusion groups. Epidural analgesia (0.15% ropivacaine 0.3 ml·kg⁻¹) was administered via bolus or infusion. Ultrasonography was used to measure the optic nerve sheath diameter before (T0), at 3 min (T1), 10 min (T2), and 70 min (T3) after starting the pump. There were statistically significant between-group differences in optic nerve sheath diameter over time (P_{Group x Time} = 0.045). From T0–T3, the area under the curve values were similar between the two groups. Although there were differences in the patterns of optic nerve sheath diameter change according to the delivery mode, the use of lumbar epidural bolus did not increase the risk of intracranial pressure increase over that of continuous infusion. Further research is needed to investigate intracranial pressure changes after continuous application of each delivery mode.

Optic nerve sheath diameter in children with acute liver failure: A prospective observational pilot study

BACKGROUND & AIMS

Early detection of raised intracranial pressure (ICP) improves outcome in acute liver failure (ALF). We evaluated the feasibility of bedside, ultrasound-guided measurement of optic nerve sheath diameter (ONSD) in normal and ALF children and correlation of ONSD with grade of hepatic encephalopathy (HE), international normalized ratio (INR) and blood ammonia (BA).

METHODS

Forty-one ALF and 47 healthy children (5-18 years) were prospectively enrolled and 12 hourly clinical evaluation was done. Laboratory parameters including INR and BA were recorded. ONSD was measured at admission, change in HE grade and at recovery in ALF, and once in controls.

RESULTS

One hundred and twenty-one ONSD measurements (ALF-74, controls-47) were taken without complications. ONSD was 4.2 (3.9-4.3), 4.4 (4.0-4.6), 5.2 (4.8-5.8) and 3.9 (3.3-4.1) mm in controls, ALF without HE, with HE and at recovery respectively. ONSD was significantly higher in ALF with HE than those without HE. ALF without HE and at recovery had ONSD similar to controls. ONSD was higher in ALF with the clinical signs of raised ICP than those without (5.4 [4.9-5.7] vs 4.6 [4.1-5.3] mm; P = .01). ONSD of 4.6 mm differentiated ALF with HE vs without HE and 5.1 mm between poor vs good non-transplant outcome with ≥80% sensitivity and specificity. ONSD positively correlated with INR (r = .53, P < .001) and BA (r = .42, P = .002).

CONCLUSIONS

ONSD can be safely and easily measured in ALF children and correlates with HE grade, INR and BA. Normal ONSD in children (>4 years) is <4.5 mm and value of >5.1 mm in ALF requires urgent attention.

Optic Nerve Sheath Diameter Ultrasound: Optic Nerve Growth Curve and Its Application to Detect Intracranial Hypertension in Children

PURPOSE

First, to create an optic nerve growth curve from normal optic nerve sheath diameter (ONSD) values measured by using B-scan ultrasonography in subjects 0-18 years of age. Second, to identify age-appropriate cutoff values of ONSD to be used in the diagnosis of intracranial hypertension (IHT).

DESIGN

Prospective cross-sectional study.

METHODS

B-scan ocular ultrasonography was performed on both eyes of 215 subjects 0-18 years of age, divided into 3 groups: 165 healthy children, 29 children with IHT (all >4 years of age), and 21 children with optic disc drusen (ODD).

RESULTS

There were no statistically significant differences in between the ONSDs of healthy children and those in subjects with ODD. An optic nerve growth curve was created by using ONSDs measured in healthy subjects 0-18 years of age, using the equation: ONSD = ln [33.15] - (-0.18 × ln [children's age]). The curve showed a progressive increase of ONSD up to 10 years of age, and it remained constant until the age of 18. For this reason, 2 different cutoff values were calculated for age groups 4-10 and 11-18. Values were 4.10 mm and 4.4 mm, respectively, with a 100.0% sensitivity and a specificity ranging from 83.9% to 98.8%. A sensitivity of 28.6% was reached for the population of subjects 4-18 years of age with a threshold value of 5 mm, as used in published reports.

CONCLUSIONS

The ONSD continued to enlarge gradually until the age of 10. Therefore, 2 different cutoff values for the age groups 4-10 and 11-18 were calculated, considering the ONSDs of subjects 11-18 years of age overlapping with those of adults. No patients with IHT <4 years old were found. Further studies are needed to evaluate the correct cutoff values for these ages.

The effect of prolonged steep head-down laparoscopy on the optical nerve sheath diameter

Both the steep head-down position and pneumoperitoneum increase the intracranial pressure (ICP), and their combination for a prolonged period during laparoscopic radical prostatectomy (LRP) might influence the central nervous system homeostasis. Changes in optic nerve sheath diameter (ONSD) may reflect those in ICP. This study aims to quantify the change in ONSD in response to peritoneal CO₂ insufflation and steep Trendelenburg position during LRP. ONSD was measured by ultrasound in 20 patients undergoing LRP and ten awake healthy volunteers. In patients, ONSD was assessed at baseline immediately after induction of general anesthesia in supine position, 10 and 60 min from baseline in a 25° head-down position during pneumoperitoneum, and after deflation of pneumoperitoneum with the patient supine at 0° angle. ONSD in controls was assessed at baseline with the patient lying supine, after 10 and 60 min of 25° head-down position, and 10 min after repositioning at 0° angle. ONSD increased significantly in both patients and controls (p < 0.0001) without between-group differences. The mean increase was 10.3% (95% CI 7.7-12.9%) in patients versus 7.5% (95% CI 2.5-12.6%) in controls (p = 0.28), and didn't affect the time to recovery from anesthesia. In the studied patients, with a limited increase of end-tidal CO₂ and airway pressure, and low volume fluid infusion, the maximal ONSD was always below the cut-off value suspect for increased ICP. ONSD reflects the changes in hydrostatic pressure in response to steep Trendelenburg position, and its increase might be minimized by careful handling of general anesthesia.

Neurocritical care monitoring of encephalopathic children with acute liver failure: A systematic review

Research on non-invasive neuromonitoring specific to PALF is limited. This systematic review identifies and synthesis the existing literature on non-invasive approaches to monitoring for neurological sequelae in patients with PALF. A series of literature searches were performed to identify all publications pertaining to five different non-invasive neuromonitoring modalities, in line with PRISMA guidelines. Each modality was selected on the basis of its potential for direct or indirect measurement of cerebral perfusion; studies on electroencephalographic monitoring were therefore not sought. Data were recorded on study design, patient population, comparator groups, and outcomes. A preponderance of observational studies was observed, most with a small sample size. Few incorporated direct comparisons of different modalities; in particular, comparison to invasive intracranial pressure monitoring was largely lacking. The integration of current evidence is considered in the context of the clinically significant distinctions between pediatric and adult ALF, as well as the implications for planning of future investigations to best support the evidence-based clinical care of these patients.

Effect of neck extension on ultrasonographic optic nerve sheath diameter as a surrogate for intracranial pressure in patients undergoing palatoplasty: A prospective observational study

Palatoplasty is performed with neck extension in patients with a cleft palate. The neck extension required for a better surgical view during palatoplasty can affect intracranial pressure. We evaluated the effect of neck extension on intracranial pressure by measuring the optic nerve sheath diameter using ultrasonography during palatoplasty. The optic nerve sheath diameter was measured in 30 patients at 10 min after anesthetic induction in the supine position (T1), at 10 min after neck extension before preparing for a sterile field (T2), at the end of surgery with neck extension (T3), and at 10 min after the supine position (T4). Hemodynamic and respiratory variables such as systolic blood pressure, heart rate, end-tidal carbon dioxide partial pressure, and peak airway pressure were also measured at the same time points. In comparison with the optic nerve sheath diameter measured at 10 min after anesthetic induction in the supine position (T1), the mean optic nerve sheath diameters were significantly increased at 10 min after neck extension before preparing for a sterile field (T2), at the end of surgery with neck extension (T3), and at 10 min after the supine position (T4; 4.19 ± 0.26, 5.20 ± 0.29, 4.38 ± 0.36, and 4.35 ± 0.30 mm, respectively). However, hemodynamic and respiratory variables were not significantly different at all time points. We found that the optic nerve sheath diameter, an indicator of intracranial pressure, was increased during palatoplasty with neck extension, which suggests that the position may affect the intracranial pressure of patients with a cleft palate.

The Measurement of Elderly Volunteers' Optic Nerve Sheath Diameters by Ocular Ultrasonography

BACKGROUND AND OBJECTIVES

The optic nerve is a component of the central nervous system, and the optic nerve sheath is connected to the subarachnoid space. For this reason, intracranial pressure (ICP) increases are directly transmitted to the optic nerve sheath. Knowing the normal optic nerve sheath diameter (ONSD) range in a healthy population is necessary to interpret this measurement as a sign of intracranial pressure in clinical practice and research. In this study, we aimed to determine the standard ONSD value in healthy adultsaged65 years of age or older who had not previously been diagnosed with a disease that could increase the ICP.

MATERIALS AND METHODS

The right and left ONSD values and ONSD differences were compared, according to the gender of the patients. The patients were divided into 3 groups, according to their age. The age groups were assigned as follows: Group 1: 65-74 years of age; Group 2: 75-84 years of age; and Group 3: 85 years of age or older. The ONSDs and the ONSD difference between the left and right eyes of Group 1, Group 2 and Group 3 were compared.

RESULTS

The study included 195 volunteers. The mean ONSD of both eyes was 4.16±0.69 mm, and the difference between the ONSD of the left and right eyes was 0.16±0.18 mm. There was no difference between genders in terms of right ONSD, left ONSD, mean ONSD and ONSD difference between the left and right eyes. There was no correlation between age and ONSD and ONSD difference. When the age groups and ONSD were compared, no difference was found between the groups.

CONCLUSIONS

In conclusion, the ONSDs of both eyes do not vary with age in healthy adults aged65 years or older. ONSD does not vary between genders. The calculation of ONSD difference can be used to determine ICP increase.

Diagnosis of elevated intracranial pressure in critically ill adults: systematic review and meta-analysis

OBJECTIVES

To summarise and compare the accuracy of physical examination, computed tomography (CT), sonography of the optic nerve sheath diameter (ONSD), and transcranial Doppler pulsatility index (TCD-PI) for the diagnosis of elevated intracranial pressure (ICP) in critically ill patients.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

Six databases, including Medline, EMBASE, and PubMed, from inception to 1 September 2018.

STUDY SELECTION CRITERIA

English language studies investigating accuracy of physical examination, imaging, or non-invasive tests among critically ill patients. The reference standard was ICP of 20 mm Hg or more using invasive ICP monitoring, or intraoperative diagnosis of raised ICP.

DATA EXTRACTION

Two reviewers independently extracted data and assessed study quality using the quality assessment of diagnostic accuracy studies tool. Summary estimates were generated using a hierarchical summary receiver operating characteristic (ROC) model.

RESULTS

40 studies (n=5123) were included. Of physical examination signs, pooled sensitivity and specificity for increased ICP were 28.2% (95% confidence interval 16.0% to 44.8%) and 85.9% (74.9% to 92.5%) for pupillary dilation, respectively; 54.3% (36.6% to 71.0%) and 63.6% (46.5% to 77.8%) for posturing; and 75.8% (62.4% to 85.5%) and 39.9% (26.9% to 54.5%) for Glasgow coma scale of 8 or less. Among CT findings, sensitivity and specificity were 85.9% (58.0% to 96.4%) and 61.0% (29.1% to 85.6%) for compression of basal cisterns, respectively; 80.9% (64.3% to 90.9%) and 42.7% (24.0% to 63.7%) for any midline shift; and 20.7% (13.0% to 31.3%) and 89.2% (77.5% to 95.2%) for midline shift of at least 10 mm. The pooled area under the ROC (AUROC) curve for ONSD sonography was 0.94 (0.91 to 0.96). Patient level data from studies using TCD-PI showed poor performance for detecting raised ICP (AUROC for individual studies ranging from 0.55 to 0.72).

CONCLUSIONS

Absence of any one physical examination feature is not sufficient to rule out elevated ICP. Substantial midline shift could suggest elevated ICP, but the absence of shift cannot rule it out. ONSD sonography might have use, but further studies are needed. Suspicion of elevated ICP could necessitate treatment and transfer, regardless of individual non-invasive tests.

REGISTRATION

PROSPERO CRD42018105642.

Prediction of Early Intracranial Hypertension After Severe Traumatic Brain Injury: A Prospective Study

OBJECTIVE

This study aimed to assess the reliability of clinical features, noninvasive transcranial Doppler-related pulsatility index (PI) calculation, and optic nerve sheath diameter (ONSD) measured by ultrasound (US) and initial computed tomography (CT) scan (Marshall CT scan classification) in predicting the occurrence of early (<24 hours) high intracranial pressure (EHICP) (>20 mm Hg) after severe traumatic brain injury (TBI).

METHODS

We conducted an observational prospective study in a level 1 trauma center. Patients were measured simultaneously for PI and US ONSD in the triage zone. Patients were categorized into 2 groups: those who had EHICP after TBI (EHICP+) and those who did not (EHICP-).

RESULTS

Fifty-four patients were included; 32 were categorized as EHICP+ and 22 as EHICP-. PI >1.4 did not correlate with EHICP+ patients (69% vs. 46%, P = 0.09). US ONSD measurement was higher in the EHICP+ group (6.25; range, 6-6.95 vs. 5.7; range, 5.2-6.4; P = 0.005). The area under the receiver operating characteristic curve for US ONSD as a predictor of developing EHICP was 0.73 (95% confidence interval [CI], 0.59-0.86). CT ONSD measurement was higher in the EHICP+ group (6.71; range, 6.35-7.87 vs. 6.25; range, 5.8-6.93; P = 0.04). The area under the receiver operating characteristic curve for CT ONSD measurement as a predictor for EHICP+ was 0.67 (95% CI, 0.53-0.81). The diffuse injury III and IV categories in the Marshall CT scan classification were associated with the occurrence of EHICP (P = 0.004).

CONCLUSIONS

None of the clinical features or noninvasive tools assessed in this study enabled clinicians to strictly ascertain EHICP. Further studies are needed to establish their potential role before intracranial pressure probe insertion.

The Use of Ultrasound-Measured Optic Nerve Sheath Diameter to Predict Ventriculoperitoneal Shunt Failure in Children

OBJECTIVE

The goal of this study was to assess the accuracy of ultrasound-measured optic nerve sheath diameter (ONSD) as a screen for ventriculoperitoneal shunt failure.

METHODS

We prospectively enrolled a convenience sample of children presenting to the ED with suspected shunt failure. The ONSD was measured by ultrasound and compared with computed tomography/magnetic resonance imaging (CT/MRI) and neurosurgical impression. We defined shunt failure on ultrasound as an ONSD greater than 4.0 mm in infants 12 months and younger or greater than 4.5 mm in children older than 12 months. A single emergency radiologist at our institution read all CTs and MRIs for categorical determination of shunt failure. We defined shunt failure based on neurosurgical impression as a decision to admit and perform shunt revision. We report test characteristics and 95% confidence intervals of ONSD as a predictor for shunt failure.

RESULTS

We enrolled 32 subjects. The sensitivities of ONSD compared with CT/MRI and neurosurgical impression, 60.0% and 75.0%, respectively, were low. However, the negative predictive values of ONSD compared with CT/MRI and neurosurgical impression were 90.0% and 95.0%, respectively.

CONCLUSIONS

Optic nerve sonography may be a useful tool to identify children presenting with suspected ventriculoperitoneal shunt failure who do not require further imaging. This would reduce the use of CT scan and exposure to ionizing radiation in children with suspected shunt malfunction who do not require neurosurgical intervention. Consideration of additional risk factors and a larger sample size may yield stronger results.

Optic nerve sheath diameter ultrasonography at admission as a predictor of intracranial hypertension in traumatic brain injured patients: a prospective observational study

OBJECTIVE

Intracranial hypertension and impaired cerebral autoregulation are common causes of secondary injuries in patients with traumatic brain injury (TBI). The primary outcome of this study was to assess whether a noninvasive method to estimate intracranial pressure (ICP) based on the ultrasonography of the optic nerve sheath diameter (ONSD) measured at the time of neurocritical care unit (NCCU) admission is correlated with the mean ICP during NCCU stay. Secondary outcomes were to assess whether ONSD is correlated with the dose of ICP > 20 mm Hg and impaired autoregulation during NCCU stay and with instantaneous ICP and whether ONSD is associated with NCCU mortality.

METHODS

This prospective observational monocentric study included adults with severe TBI. ONSD was measured at NCCU admission, immediately after invasive ICP insertion. ONSD-predicted noninvasive ICP (nICPONSD) was calculated according the formula: nICPONSD = 5 × ONSD - 14 (nICPONSD in mm Hg, ONSD in mm). Autoregulation was measured using the pressure reactivity index (PRx).

RESULTS

In total, 100 patients were included in this study. ONSD was significantly correlated with mean ICP (r = 0.46, p < 0.0001), with mean PRx (r = 0.21, p = 0.04), and with the dose of ICP > 20 mm Hg during NCCU stay (r = 0.49, p < 0.0001). Admission nICPONSD was shown to be significantly correlated with instantaneous ICP (r = 0.85, p < 0.001). ONSD at admission was significantly correlated with NCCU mortality (p = 0.02).

CONCLUSIONS

ONSD measured at NCCU admission can give important information about patients at risk of developing intracranial hypertension and impaired autoregulation. ONSD examination could be useful to screen patients at admission to determine who would benefit from further invasive ICP monitoring.