Effects of acute controlled changes in end-tidal carbon dioxide on the diameter of the optic nerve sheath: a transorbital ultrasonographic study in healthy volunteers

Impact of Permissive Hypercapnia on Postoperative Early Plasma Neurofilament Light Chain in Elderly Patients Undergoing Laparoscopic Surgery: A Prospective, Randomized Controlled Trial

Background

The effects of intraoperative permissive hypercapnia (PaCO2 of 45-55 mmHg) on the central nervous system remain unclear. Neurofilament light chain (NfL, a protein found in the axons and nerve fibers of neurons) has been associated with central nervous system disorders. This study investigated the effect of intraoperative permissive hypercapnia on plasma NfL concentration 1 day postoperatively, and in turn on the central nervous system, during laparoscopic surgery.

Methods

This investigation was a prospective, single-blind randomized controlled trial. Eighty-four individuals aged above 60 years were randomly allocated to either the normocapnia group with an PaCO2 of 35-45 mmHg (n=42) or the hypercapnia group with a PaCO2 of 45-55 mmHg (n=42). The primary outcome was the 1-day postoperative plasma NfL concentration. Secondary outcomes included the area under the curve (AUC) values for PaCO2 and regional cerebral oxygen saturation (rSO2). The Mann-Whitney U-test was mainly used to analyze the outcomes.

Results

The final analysis included 38 and 40 patients in the normocapnia and hypercapnia groups, respectively. There was no statistically significant difference observed between the groups regarding the preoperative and 1-day postoperative plasma NfL concentration (14.0 [11.1, 19.9] vs 16.3 [9.06, 19.9] pg/mL, P>0.05; 23.4 [16.8, 32.3] vs 21.5 [15.6, 29.9] pg/mL, P>0.05, respectively). However, in both groups, the postoperative plasma concentration of NfL showed a significant increase when compared with the preoperative levels (both P < 0.001). The AUCs of PaCO2 and rSO2 from the beginning to the end of the pneumoperitoneum were significantly higher in the hypercapnia group compared with the normocapnia group (both P<0.05).

Conclusion

Our results indicate that intraoperative permissive hypercapnia targeting a PaCO2 of 45-55 mmHg does not significantly influence postoperative early plasma NfL elevation levels in elderly patients undergoing laparoscopic surgery. During general anesthesia, intraoperative permissive hypercapnia might not significantly impact the central nervous system.

Evaluation of the effect of fluid management on intracranial pressure in patients undergoing laparoscopic gynaecological surgery based on the ratio of the optic nerve sheath diameter to the eyeball transverse diameter as measured by ultrasound: a randomised controlled trial

BACKGROUND

During gynecological laparoscopic surgery, pneumoperitoneum and the Trendelenburg position (TP) can lead to increased intracranial pressure (ICP). However, it remains unclear whether perioperative fluid therapy impacts ICP. The purpose of this research was to evaluate the impact of restrictive fluid (RF) therapy versus conventional fluid (CF) therapy on ICP in gynecological laparoscopic surgery patients by measuring the ratio of the optic nerve sheath diameter (ONSD) to the eyeball transverse diameter (ETD) using ultrasound.

METHODS

Sixty-four patients who were scheduled for laparoscopic gynecological surgery were randomly assigned to the CF group or the RF group. The main outcomes were differences in the ONSD/ETD ratios between the groups at predetermined time points. The secondary outcomes were intraoperative circulatory parameters (including mean arterial pressure, heart rate, and urine volume changes) and postoperative recovery indicators (including extubation time, length of post-anaesthesia care unit stay, postoperative complications, and length of hospital stay).

RESULTS

There were no statistically significant differences in the ONSD/ETD ratio and the ONSD over time between the two groups (all p > 0.05). From T2 to T4, the ONSD/ETD ratio and the ONSD in both groups were higher than T1 (all p < 0.001). From T1 to T2, the ONSD/ETD ratio in both groups increased by 14.3%. However, the extubation time in the RF group was shorter than in the CF group [median difference (95% CI) -11(-21 to -2) min, p = 0.027]. There were no differences in the other secondary outcomes.

CONCLUSION

In patients undergoing laparoscopic gynecological surgery, RF did not significantly lower the ONSD/ETD ratio but did shorten the tracheal extubation time, when compared to CF.

TRIAL REGISTRATION

ChiCTR2300079284. Registered on December 29, 2023.

Sonographic evaluation of intracranial hemodynamics and pressure after out-of-hospital cardiac arrest: An exploratory sub-study of the TAME trial

Objective

Targeted mild hypercapnia is a potential neuroprotective therapy after cardiac arrest. In this exploratory observational study, we aimed to explore the effects of targeted mild hypercapnia on cerebral microvascular resistance assessed by middle cerebral artery pulsatility index (MCA PI) and intracranial pressure estimated by optic nerve sheath diameter (ONSD) in resuscitated out-of-hospital cardiac arrest (OHCA) patients.

Design setting participants and interventions

Comatose adults resuscitated from OHCA were randomly allocated to targeted mild hypercapnia (PaCO2 50-55 mmHg) or targeted normocapnia (PaCO2 35-45 mmHg) for 24 h in the TAME trial.

Main outcome measures

Using transcranial Doppler and transorbital ultrasound, we obtained MCA PI and ONSD at 4, 24, and 48 h after randomization. Ultrasound parameters were compared between groups using a linear mixed effects model.

Results

Twelve consecutive patients were included, with seven patients in the mild hypercapnia group. MCA PI decreased from 4 to 24 h (p = 0.019) and was lower over the first 24 h in patients allocated to targeted mild hypercapnia compared with targeted normocapnia (p = 0.047). ONSD did not differ between groups or over time.

Conclusion

Cerebral microvascular resistance assessed by MCA PI decreased over 24 h and was lower in OHCA patients treated with targeted mild hypercapnia compared with targeted normocapnia. Targeted mild hypercapnia did not exert substantial effect on intracranial pressure as estimated by ONSD.

Progress on the Effects of Permissive Hypercapnia on the CNS During the Intraoperative Period: A Narrative Review

Previous experimental findings and clinical evidence have shown the important role of carbon dioxide (CO2) in regulating cerebral vascular tension. CO2 can affect the CNS through various mechanisms. With factors such as patient physiology or surgical interventions potentially causing increased arterial partial pressure of carbon dioxide (PaCO2) levels during mechanical ventilation in general anesthesia, it is important to explore the potential risks or benefits of intraoperative permissive hypercapnia on brain function. In November 2023, we conducted a thorough review of PubMed to establish the article outline. Articles that were non-English or repetitive were eliminated. We collected information on the year, topic, key findings, and opinions of each article. This review not only comprehensively summarizes the factors that contribute to the elevation of intraoperative PaCO2, but also explores the impact of fluctuations in PaCO2 levels on the CNS and the underlying mechanisms involved. At the same time, this article provides our understanding of the potential clinical significance of actively regulating PaCO2 levels. In addition, we propose that the aspects of permissive hypercapnia can be further studied to provide a reliable basis for clinical decision-making. The effects of permissive hypercapnia on the CNS remain a topic of debate. Further prospective randomized controlled studies are needed to determine if permissive hypercapnia can be safely promoted during mechanical ventilation in general anesthesia.

High myopia at high altitudes

Background: Optic nerve sheath diameter (ONSD) increases significantly at high altitudes, and is associated with the presence and severity of acute mountain sickness (AMS). Exposure to hypobaria, hypoxia, and coldness when hiking also impacts intraocular pressure (IOP). To date, little is known about ocular physiological responses in trekkers with myopia at high altitudes. This study aimed to determine changes in the ONSD and IOP between participants with and without high myopia (HM) during hiking and to test whether these changes could predict symptoms of AMS. Methods: Nine participants with HM and 18 without HM participated in a 3-day trek of Xue Mountain. The ONSD, IOP, and questionnaires were examined before and during the trek of Xue Mountain. Results: The ONSD values increased significantly in both HM (p = 0.005) and non-HM trekkers (p = 0.018) at an altitude of 1,700 m. In the HM group, IOP levels were greater than those in the non-HM group (p = 0.034) on the first day of trekking (altitude: 3,150 m). No statistically significant difference was observed between the two groups for the values of ONSD. Fractional changes in ONSD at an altitude of 1,700 m were related to the development of AMS (r pb = 0.448, p = 0.019) and the presence of headache symptoms (r pb = 0.542, p = 0.004). The area under the ROC curve for the diagnostic performance of ONSD fractional changes at an altitude of 1,700 m was 0.859 for predicting the development of AMS and 0.803 for predicting the presence of headache symptoms. Conclusion: Analysis of changes in ONSD at moderate altitude could predict AMS symptoms before an ascent to high altitude. Myopia may impact physiological accommodation at high altitudes, and HM trekkers potentially demonstrate suboptimal regulation of aqueous humor in such environments.

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.

Relation between partial arterial carbon dioxide pressure and pH value and optic nerve sheath diameter: a prospective self-controlled non-randomized trial study

OBJECTIVE

This study aims to determine if there is a correlation between differences in optic nerve sheath diameter (ONSD) and changes in PaCO2 and pH values that were measured in the arterial blood gas (ABG) before and after treatment in COPD patients with acute hypercarbic respiratory failure (AHRF).

MATERIALS AND METHODS

This study serves as a prospective self-controlled non-randomized trial study conducted in the emergency clinic of a tertiary hospital. Forty-four patients with COPD, who were found to have acidosis and hypercarbia in ABG and had an indication for non-invasive mechanic ventilation (NIMV), were analyzed prospectively. Demographic information, vital findings, initial ABG values, the ONSD measurement (before the NIMV treatment), consciousness state, and the ABG results obtained in the second hour of the monitoring and the ONSD measurement (after the NIMV treatment) were recorded.

RESULTS

In this study, 13 (29.5%) of the patients were female and 31 (70.5%) were male. The age distribution was evaluated as 68.3 ± 9.2 years; the minimum age was 54 and the maximum was 91. A high level of positively significant correlation was found between the mean ONSD and PaCO2 (p < 0.0001). There is a high fit (0.72) between the mean ONSD and PaCO2. A moderate level of negatively significant correlation was found between the mean ONSD and the pH (p < 0.0001). However, there is an insignificant low fit (0.32) between the mean ONSD and the pH.

CONCLUSION

The ONSD changed significantly and in a highly correlated manner to acute changes in PaCO2 levels.

Intravenous lidocaine attenuates distention of the optical nerve sheath, a correlate of intracranial pressure, during endotracheal intubation

BACKGROUND

By preventing hypoxia and hypercapnia, advanced airway management can save lives among patients with traumatic brain injury. During endotracheal intubation (ETI), tracheal stimulation causes an increase in intracranial pressure (ICP), which may impair brain perfusion. It has been suggested that intravenous lidocaine might attenuate this ICP response. We hypothesized that adding lidocaine to the standard induction medication for general anesthesia might reduce the ICP response to ETI. Here, we measured the optical nerve sheath diameter (ONSD) as a correlate of ICP and evaluated the effect of intravenous lidocaine on ONSD during and after ETI in patients undergoing anesthesia.

METHODS

This double-blinded, randomized placebo-controlled trial included 60 patients with American Society of Anesthesiologists I or II physical status that were scheduled for elective surgery under general anesthesia. In addition to the standard anesthesia medication, 30 subjects received 1.5 mg/kg 1% lidocaine (0.15 mL/kg, ONSD lidocaine) and 30 received 0.15 mL/kg 0.9% NaCl (ONSD placebo). ONSDs were measured with ultrasound on the left eye, before (T0), during (T1), and 4 times after ETI (T2-5 at 5-min intervals).

RESULTS

Compared to placebo, lidocaine did not significantly affect the baseline ONSD after anesthesia induction measured at T0. During ETI, the ONSD lidocaine was significantly smaller (β=-0.24 mm P=0.022) than the ONSD placebo. At T4 and T5, the ONSD placebo increased steadily, up to 20 min after ETI, but the ONSD lidocaine tended to return to baseline levels.

CONCLUSIONS

We found that the ONSD was distended during and after ETI in anesthetized patients, and intravenous lidocaine attenuated this effect.

Extracorporeal Circulation and Optic Nerve Ultrasound: A Pilot Study

Background and Objectives: Cardiopulmonary bypass (CPB) is an extracorporeal circuit that provides surgical access to an immobile and bloodless area, allowing for technical and procedural advances in cardiothoracic surgery. CBP can alter the integrity of the blood–brain barrier and cause changes in intracranial pressure (ICP) postoperatively. Optical nerve sheath diameter (ONSD) measurement is among the alternative non-invasive methods for ICP monitoring. In this study, we aimed to evaluate the optic nerve sheath diameter measurements under the guidance of ultrasonography for ICP changes during the extracorporeal circulation process. Materials and Methods: The study population included 21 patients over 18 years of age who required extracorporeal circulation. Demographic data of the patients, such as age, gender, comorbidity, American Society of Anesthesiologists (ASA) classification and reason for operation (coronary artery disease or mitral or aortic valve disease) were recorded. The ONSD was measured and evaluated before the extracorporeal circulation (first time) and at the 30th minute (second time), 60th minute (third time) and 90th minute (fourth time) of the extracorporeal circulation. Non-invasive ICP (ICP ONSD) values were calculated based on the ONSD values found. Results: The mean ONSD values measured before the extracorporeal circulation of the patients were found to be 4.13 mm (3.8–4.6) for the right eye and 4.36 mm (4.1–4.7) for the left eye. Calculated nICPONSD values of 11.0 mm Hg (1.0–21.0) for the right eye and 10.89 mm Hg (1.0–21.0) for the left eye were found. It was observed that there was a significant increase in the ONSD and nlCPONSD values recorded during the extracorporeal circulation of all patients compared to the baseline values (p < 0.005). Conclusions: During extracorporeal circulation, ultrasound-guided ONSD measurement is an easy, inexpensive and low-complication method that can be performed at the bedside during the operation to monitor ICP changes.

Non-Invasive Intracranial Pressure Monitoring and Its Applicability in Spaceflight

INTRODUCTION: Neuro-ophthalmic findings collectively defined as Spaceflight-Associated Neuro-ocular Syndrome (SANS) are one of the leading health priorities in astronauts engaging in long duration spaceflight or prolonged microgravity exposure. Though multifactorial in etiology, similarities to terrestrial idiopathic intracranial hypertension (IIH) suggest these changes may result from an increase or impairing in intracranial pressure (ICP). Finding a portable, accessible, and reliable method of monitoring ICP is, therefore, crucial in long duration spaceflight. A review of recent literature was conducted on the biomedical literature search engine PubMed using the search term “non-invasive intracranial pressure”. Studies investigating accuracy of noninvasive and portable methods were assessed. The search retrieved different methods that were subsequently grouped by approach and technique. The majority of publications included the use of ultrasound-based methods with variable accuracies. One of which, noninvasive ICP estimation by optical nerve sheath diameter measurement (nICP_ONSD), presented the highest statistical correlation and prediction values to invasive ICP, with area under the curve (AUC) ranging from 0.75 to 0.964. One study even considers a combination of ONSD with transcranial Doppler (TCD) for an even higher performance. Other methods, such as near-infrared spectroscopy (NIRS), show positive and promising results [good statistical correlation with invasive techniques when measuring cerebral perfusion pressure (CPP): r = 0.83]. However, for its accessibility, portability, and accuracy, ONSD seems to present itself as the up to date, most reliable, noninvasive ICP surrogate and a valuable spaceflight asset.Félix H, Santos Oliveira E. Non-invasive intracranial pressure monitoring and its applicability in spaceflight. Aerosp Med Hum Perform. 2022; 93(6):517–531.

Effect of end-tidal carbon dioxide level on the optic nerve sheath diameter measured by transorbital ultrasonography in anesthetized pediatric patients: A randomized trial

BACKGROUND

Intraoperative hypercapnia and hypocapnia are common during pediatric anesthesia, and the cerebral blood flow and intracranial pressure may be affected by the partial pressure of arterial carbon dioxide. Transorbital ultrasound measurement of the optic nerve sheath diameter is a simple and non-invasive method for intracranial pressure assessment. The objective of this study was to evaluate the effect of end-tidal carbon dioxide (E_T CO₂ ) on optic nerve sheath diameter in a healthy anesthetized pediatric population.

METHODS

Pediatric patients scheduled for elective surgery under general anesthesia and mechanical ventilation in the supine position were enrolled and divided into four subgroups; age <2 years, 2-6 years, 6-12 years, and 12-18 years. Mechanical ventilation was adjusted to achieve target E_T CO₂ levels in a randomized sequence (40-35-45-40 mmHg or 40-45-35-40 mmHg). Three minutes after reaching each target E_T CO₂ level, transorbital ultrasound images of optic nerve sheath diameter were obtained and analyzed. The primary outcome was the optic nerve sheath diameter at each E_T CO₂ level.

RESULTS

Sixty-four pediatric patients were enrolled and analyzed. At E_T CO₂  = 40 mmHg, the optic nerve sheath diameter was 5.6 ± 0.6 mm, 6.4 ± 0.5 mm, 6.8 ± 0.6 mm, and 7.1 ± 0.5 mm in children aged <2 years, 2-6 years, 6-12 years, and 12-18 years, respectively. The overall percent decreases in the optic nerve sheath diameter was -5.6 ± -4.3% (95% CI; -6.7 to -4.5%) at E_T CO₂  = 35 mmHg while the overall percent increases of optic nerve sheath diameter (ONSD) was 4.9 ± 5.1% (95% CI; 3.6 to 6.1%) at E_T CO₂  = 45 mmHg compared with those at E_T CO₂  = 40 mmHg. Spearman rank correlation analysis indicated that there were weak to moderate correlation between E_T CO₂ and the optic nerve sheath diameter (correlation coefficient [p-value] = .355 [.004], .318 [.014], .373 [<.001], and .420 [<.001] in children aged <2 years, 2-6 years, 6-12 years, and 12-18 years, respectively).

CONCLUSIONS

The optic nerve sheath diameter measured by transorbital ultrasound showed rapid reactivity from E_T CO₂ 35 to 45 mmHg in healthy pediatric patients under inhalation general anesthesia.

Optic Nerve Ultrasound Evaluation in Animals and Normal Subjects

In recent years, ultrasonographic measurement of the optic nerve sheath diameter (ONSD) has been widely used to identify the presence of increased intracranial pressure (ICP). Intracranial hypertension is a life-threatening condition that can be caused by various neurological and non-neurological disorders, and it is associated to poor clinical results. Ultrasonography could be used to qualitatively and efficiently detect ICP increases, but to reach this purpose, clear cut-off values are mandatory. The aim of this review is to provide a wide overview of the most important scientific publications on optic nerve ultrasound normal values assessment published in the last 30 years. A total of 42 articles selected from PubMed medical database was included in this review. Our analysis showed that ocular ultrasonography is considered to be a valuable diagnostic tool, especially when intracranial hypertension is suspected, but unfortunately this research provided conflicting results that could be due to the different ultrasound protocols. This is mainly caused by the use of B scan alone, which presents several limitations. The use of B-scan coupled with the standardized A-scan approach could give more accurate, and reliable ultrasound evaluation, assuring higher data objectivity.

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.

Comparison of the Effects of Normocapnia and Mild Hypercapnia on the Optic Nerve Sheath Diameter and Regional Cerebral Oxygen Saturation in Patients Undergoing Gynecological Laparoscopy with Total Intravenous Anesthesia

Cerebral hemodynamics may be altered by hypercapnia during a lung-protective ventilation (LPV), CO₂ pneumoperitoneum, and Trendelenburg position during general anesthesia. The purpose of this study was to compare the effects of normocapnia and mild hypercapnia on the optic nerve sheath diameter (ONSD), regional cerebral oxygen saturation (rSO₂), and intraoperative respiratory mechanics in patients undergoing gynecological laparoscopy under total intravenous anesthesia (TIVA). Sixty patients (aged between 19 and 65 years) scheduled for laparoscopic gynecological surgery in the Trendelenburg position. Patients under propofol/remifentanil total intravenous anesthesia were randomly assigned to either the normocapnia group (target PaCO₂ = 35 mmHg, n = 30) or the hypercapnia group (target PaCO₂ = 50 mmHg, n = 30). The ONSD, rSO₂, and respiratory and hemodynamic parameters were measured at 5 min after anesthetic induction (Tind) in the supine position, and at 10 min and 40 min after pneumoperitoneum (Tpp10 and Tpp40, respectively) in the Trendelenburg position. There was no significant intergroup difference in change over time in the ONSD (p = 0.318). The ONSD increased significantly at Tpp40 when compared to Tind in both normocapnia and hypercapnia groups (p = 0.02 and 0.002, respectively). There was a significant intergroup difference in changes over time in the rSO2 (p < 0.001). The rSO₂ decreased significantly in the normocapnia group (p = 0.01), whereas it increased significantly in the hypercapnia group at Tpp40 compared with Tind (p = 0.002). Alveolar dead space was significantly higher in the normocapnia group than in the hypercapnia group at Tpp40 (p = 0.001). In conclusion, mild hypercapnia during the LPV might not aggravate the increase in the ONSD during CO₂ pneumoperitoneum in the Trendelenburg position and could improve rSO₂ compared to normocapnia in patients undergoing gynecological laparoscopy with TIVA.

Optic nerve sheath diameter assessment by neurosonology: A review of methodologic discrepancies

BACKGROUND AND PURPOSE

Reported cutoff values of the optic nerve sheath diameter (ONSD) for the diagnosis of elevated intracranial pressure (ICP) are inconsistent. This hampers ONSD as a possible noninvasive bedside monitoring tool for ICP. Because the influence of methodological differences on variations in cutoff values is unknown, we performed a narrative review to identify discrepancies in ONSD assessment methodologies and to investigate their effect on reported ONSD values.

METHODS

We used a structured and quantitative approach in which each ONSD methodology found in the reviewed articles was categorized based on the characteristic appearance of the ultrasound images and ultrasound marker placement. Subsequently, we investigated the influence of the different methodologies on ONSD values by organizing the ONSDs with respect to these categories.

RESULTS

In a total of 63 eligible articles, we could determine the applied ONSD assessment methodology. Reported ultrasound images either showed the optic nerve and its sheath as a dark region with hyperechoic striped band at its edges or as a single dark region surrounded by lighter retrobulbar fat. Four different ultrasound marker positions were used to delineate the optic nerve sheath, which resulted in different ONSD values and more importantly, different sensitivities to changes in ICP.

CONCLUSIONS

Based on our observations, we recommend to place ultrasound markers at the outer edges of the hyperechoic striped bands or at the transitions from the single dark region to the hyperechoic retrobulbar fat because these locations yielded the highest sensitivity of ONSD measurements for increased ICP.

Comparison of different end-tidal carbon dioxide levels in preventing postoperative nausea and vomiting in gynaecological patients undergoing laparoscopic surgery

The aim of this study was to compare different end-tidal carbon dioxide (EtCO₂) levels to prevent postoperative nausea and vomiting (PONV) caused by increased intracranial pressure due to pneumoperitoneum and Trendelenburg position in gynaecological laparoscopic surgery. A total of 60 female patients aged 25-50 years who would undergo laparoscopic gynaecological surgery under general anaesthesia were randomised into two groups: group A (EtCO₂: 26 - 35 mmHg, n = 30) and group B (EtCO₂: 36 - 45 mmHg, n = 30). In both groups, ONSD and EtCO₂ of the patients were measured at baseline after anaesthesia induction (T_b), at 5 min after pneumoperitoneum (T_PP5), and at 10 min intervals after Trendelenburg position (T_PP10, T_PP20, T_PP30). At 5 (T_D5) and 10 min (T_D10) after deflation, ONSD measurements were repeated. The incidence and severity of PONV of the patients, and antiemetic drugs used in both groups were assessed in the postoperative period. In the intraoperative follow-up periods, T_PP5 and subsequent EtCO₂ values, as well as T_PP10 and subsequent ONSD values, were significantly higher in group B and the incidence of nausea, the PONV scores and the incidence of rescue antiemetic use significantly lower in group A than in group B (p<.001 for all). This result indicates that low EtCO₂ levels have beneficial effects on ICP and PONV in laparoscopic gynaecological operations.Impact statementWhat is already known on this subject? Laparoscopic gynaecologic surgery has been a more preferred technique. The incidence of postoperative nausea and vomiting (PONV) after laparoscopic gynaecologic surgery is remarkably high. In the prevention of PONV after gynaecologic laparoscopic surgery, single and multiple drug therapies and methods have been used.What the results of this study add? Postoperative nausea and vomiting caused by intracranial pressure (ICP) increase due to carbon dioxide pneumoperitoneum and Trendelenburg position in gynaecologic laparoscopic surgeries were decreased in the early postoperative period by low end-tidal carbon dioxide levels in the intraoperative period. It was shown that low end-tidal carbon dioxide levels have beneficial effects on ICP and PONV in laparoscopic gynaecologic operations.What the implications are of these findings for clinical practice and/or further research? This result indicates that low end-tidal carbon dioxide levels have beneficial effects on ICP and PONV in laparoscopic gynaecologic operations.

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.

Ultrasonographic optic nerve sheath diameter monitoring of elevated intracranial pressure: two case reports

Ultrasonography assessments of optic nerve sheath diameter (ONSD) is a non-invasive method that may help identify elevated intracranial pressure (ICP). However, this technique was used to evaluate the elevated ICP caused by traumatic brain injury. The objective of this study was to examine clinical cases of the changes in ICP with venous sinus stenosis and venous sinus thrombosis found the advantage of this technique in the application. And we dynamically monitor ONSD and ICP as a lens for understanding the dynamic assessment for ICP. The first case of venous sinus stenosis with elevated ICP identified in real-time by changes in ONSD, which are correlated with ICP before and after stenting. Another case of venous sinus thrombosis with elevated ICP. And after treatment, the patient underwent an ultrasound ONSD examination and lumbar puncture (LP) at the 1st, the 2nd and 3rd month of follow-up. The previously enlarged ONSDs retracted and LP opening pressure gradually returned to normal. These cases indicate that ONSD examination may help dynamically assess ICP changes and evaluate the efficacy of ICP treatment. These results provide utile, evidence based, preliminary clinical recommendations and indicate that ONSD examination might be a useful method of evaluating ICP, especially if repeated evaluations are needed.

Ultrasonography Assessments of Optic Nerve Sheath Diameter as a Noninvasive and Dynamic Method of Detecting Changes in Intracranial Pressure

Importance

The crtierion standard method for monitoring intracranial pressure (ICP) can result in complications and pain. Hence, noninvasive, repeatable methods would be valuable.

Objective

To examine how ultrasonographic optic nerve sheath diameter (ONSD) correlated with noninvasive and dynamically monitored ICP changes.

Design, Setting, and Participants

The ONSD was measured before the lumbar puncture (LP) in 60 patients on admission. Patients with elevated ICP were divided into group 1 (200 < LP ≤ 300 mm H2O) and group 2 (LP > 300 mm H2O). Patients underwent follow-up ONSD and LP measurements within 1 month. We analyzed the correlations between the ONSD and ICP on admission and between the changes in ONSD and ICP, which were the respective changes in ONSD and ICP from admission to follow-up.

Main Outcomes and Measures

The ultrasonographic ONSD and ICP were measured on admission and follow-up. The correlations between the ONSD and ICP on admission and between the changes in ONSD and ICP were analyzed using Pearson correlation analyses.

Results

For 60 patients (Han nationality; mean [SD] age, 36.2 [12.04] years; 29 [48%] female) on admission, the ONSD and ICP values were strongly correlated, with an r of 0.798 (95% CI, 0.709-0.867; P < .001). Twenty-five patients with elevated ICP who completed the follow-up were included. The mean (SD) ONSD and ICP on admission were 4.50 (0.54) mm and 302.40 (54.26) mm H2O, respectively. The ONSD and ICP values obtained on admission were strongly correlated , with an r of 0.724 (95% CI, 0.470-0.876; P < .001). The mean (SD, range) changes in ICP and ONSD were 126.64 (52.51 mm H2O, 20-210 mm H2O) (95% CI, 106.24-146.07) and 1.00 (0.512 mm, 0.418-2.37 mm) (95% CI, 0.83-1.20), respectively. The change in ONSD was strongly correlated with the change in ICP, with an r of 0.702 (95% CI, 0.425-0.870; P < .001). The follow-up evaluations revealed that the elevated ICP and dilated ONSD had returned to normal, and no evidence of difference was found in the mean ONSDs between group 1 (3.49 mm; 95% CI, 3.34-3.62 mm) and group 2 (3.51 mm; 95% CI, 3.44-3.59 mm) (P = .778) at follow-up.

Conclusions and Relevance

The dilated ONSDs decreased along with the elevated ICP reduction. Ultrasonographic ONSD measurements may be a useful, noninvasive tool for dynamically evaluating ICP.

Validity and reliability of pocket-sized ultrasound devices in measurement of optic nerve sheath diameter in ICU patients

The measurement of the optic nerve sheath diameter (ONSD) by ultrasonography (USG) is particularly important for intracranial pressure (ICP) monitoring when invasive measurements are not possible or are contraindicated. Standard USG (SUDs) devices can be bulky and may break down the workflow. The validity and reliability of pocket-sized USG devices (PSUDs) compared to SUDs for ONSD measurement has not been investigated, yet. We compared the reliability and validity of PSUDs with SUDs for ONSD measurement. 35 patients were included in the study. ONSD measurements with PSUDs and SUDs were performed by two clinicians as three different measurements in both sagittal and transverse axis of the eye. There was agreement between mean transverse ONSD (mtONSD), mean sagittal ONSD (msONSD), and mean ONSD(mONSD) values measured with each device according to Bland-Altman test (p = 0.166, p = 0.135, p = 0.066, respectively) with no proportional bias (p = 0.544, p = 0.868, p = 0.929, respectively). Intraclass correlation coefficients (ICC) were found to be greater than 0.7 for mtONSD, msONSD, and mONSD values measured by SUD (ICC = 0.790, ICC = 0.817, and ICC = 0.844, respectively). Similarly, for mtONSD, msONSD, and mONSD values measured by PSUD, ICC were found greater than 0.7 (ICC = 0.763, ICC = 0.814, and ICC = 0.843, respectively). There was no statistically significant difference between mtONSD and msONSD (p = 0.441 for SUD and p = 0.893 for PSUD). There was a good correlation between mtONSD and msONSD (r = 0.767 for SUD and r = 0.816 for PSUD). The total variance between three different measurements in the transverse and sagittal axis was ± 0.6 mm. PSUDs can be used with similar validity and reliability as SUDs for ONSD measurement.

A study to evaluate effect of PEEP and end-tidal carbon dioxide on optic nerve sheath diameter

Background and Aims:

PEEP is commonly used to improve postoperative respiratory outcomes in surgical and ICU patients. It is thought to increase ICP by impending CSF outflow and cerebral venous drainage. Hyperventilation is used to decrease ICP in patients having intracranial hypertension. We investigated the effect of various levels of PEEP and EtCO₂ on ONSD as an indirect predictor of ICP in patients undergoing surgery under GA.

Methods:

After induction, different levels of PEEP and EtCO₂ were applied to 50 patients. Sonographic ONSD was measured 5 minutes after stabilization of each new setting. Haemodynamic parameters like pulse, SpO₂, BP were also recorded. Quantitative variables were expressed as Mean ± SD and compared across between follow-ups using paired t-test. Qualitative variables were expressed in number and percentage.

Results:

Baseline ONSD was 0.44 ± 0.06 cm. It increased significantly to 0.45 ± 0.07 cm, 0.47 ± 0.07 cm and 0.49 ± 0.07 cm after applying PEEP of 8, 12 and 15 cm H₂O PEEP, respectively. It significantly decreased to 0.42 ± 0.06 cm, 0.41 ± 0.06 cm and 0.40 ± 0.06 cm after hyperventilation, EtCO₂ range 35–37, 32–34 and 29–31 mm Hg. Results were statistically significant but clinically not significant.

Conclusion:

We conclude that there are acute and dynamic alterations in ONSD in response to hyperventilation and presence of PEEP in anaesthetised patients. Ocular sonography may be used as a reliable indicator of acute variations in ICP.

The effects of spinal immobilization at 20° on intracranial pressure

OBJECTIVE

In this study, it was aimed to evaluate whether spinal immobilization at 20°, instead of the traditional 0°, affects intracranial pressure (ICP) via the ultrasonographic (USG) measurement of optic nerve sheath diameter (ONSD).

METHODS

140 healthy, adult, non-smoking volunteers who had no acute or chronic diseases were included this study. Volunteers were randomly divided into two groups; performed spinal immobilization at 0° (Group 1) and at 20° (Group 2). After spinal immobilization (at 0 or 20°), measurements of ONSD were performed at 0, 30, and 60 min in an immobilized position.

RESULTS

When evaluating the change in ONSD over time (at 30 and 60 min) as compared to basal measurements at 0 min, it was found that the ONSD values of both sides (the right and left eyes) were significantly increased in Group 1 and Group 2. For Groups 1 and 2, these differences existed both between 0 and 30 min and between 30 and 60 min. In addition, in this study, the amounts of increase in the ONSD measurements from 0 to 30 min and from 30 to 60 min (ΔONSD0-30 min and ΔONSD30-60 min) in both groups were compared. The results showed that there was no significant difference between Group 1 and Group 2 in terms of ΔONSD measurements.

CONCLUSIONS

Spinal immobilization at 0° as a part of routine trauma management increased ONSD and thus ICP. Secondly, we found that similar to immobilization at 0°, spinal immobilization at 20° increased ONSD.

Effect of Mannitol on Ultrasonographically Measured Optic Nerve Sheath Diameter as a Surrogate for Intracranial Pressure During Robot-Assisted Laparoscopic Prostatectomy with Pneumoperitoneum and the Trendelenburg Position

INTRODUCTION

CO2 pneumoperitoneum and the steep Trendelenburg position during robot-assisted laparoscopic prostatectomy (RALP) can increase intracranial pressure (ICP). Mannitol is widely used to treat increased ICP. However, no studies to date have specifically evaluated the effect of mannitol on ICP in patients undergoing RALP. Ultrasonographic measurement of the optic nerve sheath diameter (ONSD) is considered a reliable technique to noninvasively evaluate the ICP. Therefore, this study compared ONSDs as a surrogate for ICP before and after mannitol administration in prostate cancer patients undergoing RALP.

METHODS

Mannitol (0.5 g/kg) was administered after pneumoperitoneum establishment and shifting to the Trendelenburg position. ONSDs were measured at six predetermined time points: 10 minutes after anesthesia induction (T0); 5 minutes after pneumoperitoneum and the Trendelenburg position before mannitol administration (T1); 30 minutes (T2), 60 minutes (T3), and 90 minutes (T4) after completion of mannitol administration during pneumoperitoneum and the Trendelenburg position; and at skin closure in the supine position (T5). Moreover, intraoperative hemodynamic and respiratory variables were evaluated simultaneously.

RESULTS

Thirty-six patients were analyzed. ONSDs were significantly lower at T2, T3, and T4 than at T1 (all p < 0.001), with the greatest decrease observed at T4 compared with T1 (4.46 ± 0.2 mm vs 4.81 ± 0.3 mm, p < 0.001). Regional cerebral oxygen saturation, cardiac output, corrected flow time, peak velocity, body temperature, arterial CO2 partial pressure, peak airway pressure, plateau airway pressure, dynamic compliance, and static compliance were not significantly different during pneumoperitoneum and the Trendelenburg position; however, mean arterial blood pressure and heart rate were significantly different.

CONCLUSIONS

Mannitol decreases the ONSD in patients undergoing RALP with CO2 pneumoperitoneum and the steep Trendelenburg position. This result provides useful information on the beneficial effects of mannitol administration on prostate cancer patients who may develop increased ICP during RALP.

Ultrasonographic measurement of the optic nerve sheath diameter and its association with eyeball transverse diameter in 585 healthy volunteers

The optic nerve sheath diameter (ONSD) is considered as an indirect marker for intracranial pressure (ICP). However, the optimal cut-off value for an abnormal ONSD indicating elevated ICP and its associated factors have been unclear. Thus, we investigated normative values for the ONSD using ultrasonography and investigate the potential factors affecting it. We prospectively recruited healthy volunteers between September 2016 and March 2017. A total of 585 individuals were included, in which the mean ONSD was 4.11 mm [95% confidence interval (CI), 4.09–4.14 mm]. Although ONSD was correlated with sex (p = 0.015), height (p = 0.003), and eyeball transverse diameter (ETD) (p < 0.001) in simple linear regression analyses, multiple linear regression analysis revealed that only ETD was independently associated with ONSD (p < 0.001). Accordingly, we further established a normative value for the ONSD/ETD ratio and its associated factors. The mean ONSD/ETD ratio was 0.18 (95% CI, 0.18–0.18), but the ONSD/ETD ratio was not correlated with sex, height, weight, body mass index, and head circumference. Our findings suggest that the ONSD had a strong correlation with ETD, and ONSD/ETD ratio might provide more reliable data than ONSD itself as a marker of ICP.