Sonography for determining the optic nerve sheath diameter with increasing intracranial pressure in a porcine model

Optic nerve sheath diameter and spaceflight: defining shortcomings and future directions

Neuro-ocular changes during long-duration space flight are known as spaceflight-associated neuro-ocular syndrome (SANS). The ability to detect, monitor, and prevent SANS is a priority of current space medicine research efforts. Optic nerve sheath diameter (ONSD) measurement has been used both terrestrially and in microgravity as a proxy for measurements of elevated intracranial pressure. ONSD shows promise as a potential method of identifying and quantitating neuro-ocular changes during space flight. This review examines 13 studies measuring ONSD and its relationship to microgravity exposure or ground-based analogs, including head-down tilt, dry immersion, or animal models. The goal of this correspondence is to describe heterogeneity in the use of ONSD in the current SANS literature and make recommendations to reduce heterogeneity in future studies through standardization of imaging modalities, measurement techniques, and other aspects of study design.

Assessing ultrasonographic optic nerve sheath diameter in animal model with anesthesia regimens

Purpose:

To determine the normal optical nerve sheath (ONS) diameter ultrasonography (ONSUS) and evaluate the possible effects of drugs on ONS diameter during anesthetic induction in healthy pigs.

Methods:

Healthy piglets were divided into three groups: a control group, that received xylazine and ketamine (X/K); other that received xylazine, ketamine and propofol (X/K/P); and a third group that received xylazine, ketamine, and thiopental (X/K/T). The sheath diameter was assessed by ultrasonography calculating the average of three measurements of each eye from the left and right sides.

Results:

118 animals were anesthetized (49 X/K 33 X/K/P and 39 X/K/T). Mean ONS sizes on both sides in each group were 0.394 ± 0.048 (X/K), 0.407 ± 0.029 (X/K/P) and 0.378 ± 0.042 cm (X/K/T) (medians of 0.400, 0.405 and 0.389, respectively). The ONS diameter varied from 0.287–0.512 cm (mean of 0.302 ± 0.039 cm). For group X/K, the mean diameter was 0.394 ± 0.048 cm. Significant differences in ONS sizes between the groups P and T (X/K/P > X/K/T, p = 0.003) were found. No statistically significant differences were detected when other groups were compared (X/K = X/K/P, p = 0.302; X/K = X/K/T, p = 0.294).

Conclusions:

Sedation with thiopental lead to significative ONS diameter reduction in comparison with propofol. ONSUS may be useful to evaluate responses to thiopental administration.

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.

Ultrasound of the Optic Nerve Does Not Appear to Be a Consistently Reliable or Generalizable Method to Monitor Changes in Intracranial Pressure

OBJECTIVE

Invasive intracranial pressure (ICP) monitoring is the gold standard, but is not always readily accessible or practical. Ultrasound of the optic nerve sheath diameter (ONSD) has been proposed for detecting both elevation and change in the ICP. Our study is a prospective observational trial that seeks to determine if ultrasound can be reliably used to identify changes in ICP with naturally occurring variations in patient care.

METHODS

A convenience sample of patients with invasive ICP monitoring were enrolled. Patients were identified prior to interventions that were suspected to cause a change in ICP. Measurement of ICP and ONSD was obtained prior to the intervention, with repeated measurements of both variables obtained immediately following the intervention.

RESULTS

36 total patients were enrolled. There was a positive correlation between the ICP and the right ONSD (r = 0.255, P = 0.0003) and the ICP and the left ONSD (r = 0.274, P < 0.0001). There was no statistically significant relationship between the change in either the ICP and the right ONSD (r -0.2 P = 0.282) or left ONSD (r 0.05 P = 0.805). The location of the lesion in the brain appears to significantly affect discordance between the ONSD and the ICP.

CONCLUSIONS

Ultrasound of the ONSD has shown promise as both a marker of elevated ICP and as a method to identify changes in pressure. Although the size of the ONSD and the measurement of ICP were correlated in our study, the ability to follow changes in ICP was not statistically significant. This indicates that use of ultrasound to track changes in ICP cannot be generalized and may be limited to specific circumstances. The location of the intracranial pathology appears to be a significant factor in discordance between the ICP and ONS diameter.

Correlation of optic nerve and optic nerve sheath diameter with intracranial pressure in pigs

Objective

Several studies have shown an association between intracranial pressure and the diameter of the optic nerve sheath measured by transbulbar ultrasonography. To understand the pathophysiology of this phenomenon, we aimed to measure the changes of the optic nerve, optic nerve sheath and perineural space separately with increasing intracranial pressure in a porcine model.

Methods

An external ventricular drain was placed into the third ventricle through a right paramedian burrhole in eight anesthesized pigs. The diameters of the optic nerve and the optic nerve sheath were measured while the intracranial pressure (ICP) was increased in steps of 10mmHg from baseline up to 60 mmHg.

Results

The median diameters of the optic nerve (ON) increased from 0.36 cm (baseline– 95% confidence interval (CI) 0.33 cm to 0.45 cm) to 0.68 cm (95% CI 0.57 cm to 0.82 cm) at ICP of 60 mmHg (p<0.0001) and optic nerve sheath (ONS) from 0.88 cm (95% CI 0.79 cm to 0.98 cm) to 1.24 cm (95% CI 1.02 cm to 1.38 cm) (p< 0.002) while the median diameter of the perineural space (PNS) (baseline diameter 95% CI 0.40 cm to 0.59 cm to diameters at ICP 60 95% CI 0.38 cm to 0.62 cm) did not change significantly (p = 0.399). Multiple comparisons allowed differentiation between baseline and values ≥40 mmHg for ON (p = 0.017) and between baseline and values ≥ 50mmHg for ONS (p = 0.006). A linear correlation between ON (R² = 0.513, p<0.0001) and ONS (R² = 0.364, p<0.0001) with ICP was found. The median coefficient of variation for intra- and inter-investigator variability was 8% respectively 2.3%.

Conclusion

Unexpectedly, the increase in ONS diameter with increasing ICP is exclusively related to the increase of the diameter of the ON. Further studies should explore the reasons for this behaviour.

Point-of-care resuscitation research: From extreme to mainstream: Trauma Association of Canada Fraser Gurd Lecture 2019

The Gurd Family surgical legacy was deeply intertwined with National service in both World Wars. My own personal research mission has attempted to emulate such service, by enhancing the tools and techniques available to facilitate point-of-care diagnosis and resuscitation in extreme and adverse environments. Our efforts involving point-of-care diagnosis/resuscitation and the telementored guidance of those remotely responding to catastrophic injury have included collaborations with National Aeronautics and Space Administration (NASA) the Canadian Space Agency, the Canadian Forces, its democratic allies, and non-governmental surgical organizations. Research has been conducted in resuscitative suites and operating theaters, research laboratories, parabolic flight aircraft, on humanitarian surgical missions, and from ski-hills and firehalls. The initial phases of these efforts involved inaugural studies in resuscitative sonography including defining the Extended Focused Assessment with Sonography for Trauma (EFAST) examination. Although the original work was commissioned for Space Medicine, generalization to mainstream practice further justifies space medicine research. Iterative steps in advancing telementored resuscitation have subsequently involved the maturation of space-mandated telementored ultrasound support (TMUS), exploration of TMUS in terrestrial clinical practice, and the creation of increasingly mobile (hand-held) TMUS solutions. Subsequently it was recognized that teleultrasound is simply one informatic dimension of remote telemedicine, and current efforts are focused in a Program known as TeleMentored Ultrasound Supported Medical Interactions (TMUSMI) of remote responders required to intervene with catastrophic trauma. While this research program has yielded many techniques and findings that have benefited mainstream terrestrial practice, these investigations are currently ongoing, and we hope to demonstrate that TMUSMI may benefit all Canadians especially those in remote areas, as well as potentially every global inhabitant without immediate access to care. Further, we propose that to fully utilize these techniques, a new specialty, that of the remote medical mentor will be required, a new specialty that will require the creation and scientific validation of its principles and techniques.

Increased Intracranial Pressure Damages Optic Nerve Structural Support

Optic nerve sheath diameter (ONSD) is used clinically as a noninvasive measure for elevated intracranial pressure (ICP). This study had two purposes: to investigate the immediate effects optic nerve sheath (ONS) dilation post-ICP increase on trabecular fibers connecting the optic nerve to the ONS and to document any changes in these fibers 30 days post-increased ICP. In a swine model, ICP was increased by inflating a Foley catheter balloon in the epidural space. Three control pigs received the catheter insertion without inflation (no increase in ICP) and four experimental pigs received the catheter with inflation (increased ICP). The control and two randomly selected pigs with increased ICP were euthanized immediately after the procedure. The two other pigs were euthanized 30 days post-catheter inflation. For all pigs, the ONS was removed and imaged using a scanning electron microscope, calculating percent porosity values. Porosity values for the experimental groups (Immediately measured [IM] μ = 0.5749; Delayed measured [DM] μ = 0.5714) were larger than the control group (μ = 0.4336) and statistically significant (IM vs. Control, p = 0.0018; DM vs. Control, p = 0.0092). There was no significant difference (p = 0.9485) in porosity of the DM group when compared with the IM group. This study demonstrated that the trabecular fibers immediately post-increased ICP (ONS dilation) were more porous than the control and remained statistically different (more porous) after 30 days. These results suggest a structural change that occurs in the ONS with elevations in ICP.

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.

Cerebral Venous Thrombosis: An Uncommon Cause of Papilledema on Bedside Ocular Ultrasound

BACKGROUND

Cerebral venous thrombosis (CVT) is a rare, difficult-to-diagnose form of venous thromboembolic disease and is considered a type of stroke. Its presentation is highly variable and may be easily confused for more common and less debilitating or life-threatening diagnoses such as migraine, seizure, or idiopathic intracranial hypertension.

CASE REPORT

A 25-year-old woman presented with a complaint of bifrontal throbbing headache and blurry vision. A bedside ultrasound of the orbit suggested increased intracranial pressure. A subsequent computed tomography venogram demonstrated a left transverse sinus thrombosis. The patient was started on enoxaparin and admitted for bridging to warfarin and evaluation for hypercoagulable state. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: CVT is a rare form of stroke that carries a high rate of mortality and morbidity and masquerades as more common and benign diagnoses. Emergency department bedside ultrasound of the orbit may make the diagnosis of CVT more attainable by identifying patients with increased intracranial pressure.

Increase in intracranial pressure by application of a rigid cervical collar: a pilot study in healthy volunteers

OBJECTIVES

Rigid cervical collars are known to increase intracranial pressure (ICP) in severe traumatic brain injury (TBI). Cerebral blood flow might decrease according to the Kellie Monroe doctrine. For this reason, the use of the collar in patients with severe TBI has been abandoned from several trauma protocols in the Netherlands. There is no evidence on the effect of a rigid collar on ICP in patients with mild or moderate TBI or indeed patients with no TBI. As a first step we tested the effect in healthy volunteers with normal ICPs and intact autoregulation of the brain.

METHODS

In this prospective blinded cross-over study, we evaluated the effect of application of a rigid cervical collar in 45 healthy volunteers by measuring their optical nerve sheath diameter (ONSD) by transocular sonography. Sonographic measurement of the ONSD behind the eye is an indirect noninvasive method to estimate ICP and pressure changes.

RESULTS

We included 22 male and 23 female volunteers. In total 360 ONSD measurements were performed in these 45 volunteers. Application of a collar resulted in a significant increase in ONSD in both the left (β=0.06, 95% confidence interval: 0.05-0.07, P<0.001) and the right eye (β=0.01, 95% confidence interval: 0.00-0.02, P=0.027) CONCLUSION: Application of a rigid cervical collar significantly increases the ONSD in healthy volunteers with intact cerebral autoregulation. This suggests that ICP may increase after application of a collar. In healthy volunteers, this seems to be of minor importance. On the basis of our findings the effect of a collar on ONSD and ICP in patients with mild and moderate TBI needs to be determined.

A comparison of non-invasive versus invasive measures of intracranial pressure in hypoxic ischaemic brain injury after cardiac arrest

AIM

Increased intracranial pressure (ICP) in hypoxic ischaemic brain injury (HIBI) can cause secondary ischaemic brain injury and culminate in brain death. Invasive ICP monitoring is limited by associated risks in HIBI patients. We sought to evaluate the agreement between invasive ICP measurements and non-invasive estimators of ICP (nICP) in HIBI patients.

METHODS

Eligible consecutive adult (age>18) cardiac arrest patients with HIBI were included as part of a single centre prospective interventional study. Invasive ICP monitoring and nICP measurements were undertaken using: a) transcranial Doppler ultrasonography (TCD), b) optic nerve sheet diameter ultrasound (ONSD) and c) jugular venous bulb pressure (JVP). Multiple measurements applied in linear mixed-effects models were considered to obtain the correlation coefficient between ICP and nICP as well as their predictive abilities to detect intracranial hypertension (ICP≥20mm Hg).

RESULTS

Eleven patients were included (median age of 47 [range 20-71], 8 males and 3 females). There was a linear relationship between ICP and nICP with ONSD (R=0.53 [p<0.0001]), JVP (R=0.38 [p<0.001]) and TCD (R=0.30 [p<0.01]). The ability to predict intracranial hypertension was highest for ONSD and TCD (area under the receiver operating curve (AUC)=0.96 [95% CI: 0.90-1.00] and AUC=0.91 [95% CI: 0.83-1.00], respectively). JVP presented the weakest prediction ability (AUC=0.75 [95% CI: 0.56-0.94]).

CONCLUSIONS

ONSD and TCD methods demonstrated agreement with invasively-monitored ICP, suggesting their potential roles in the detection of intracranial hypertension in HIBI after cardiac arrest.

Sonography of the optic nerve sheath diameter before and after microsurgical closure of a dural CSF fistula in patients with spontaneous intracranial hypotension - a consecutive cohort study

OBJECTIVE

Spontaneous intracranial hypotension is caused by spinal cerebrospinal fluid leakage. Patients with orthostatic headaches and cerebrospinal fluid leakage show a decrease in optic nerve sheath diameter upon movement from supine to upright position. We hypothesized that the decrease in optic nerve sheath diameter upon gravitational challenge would cease after closure of the leak.

METHODS

We included 29 patients with spontaneous intracranial hypotension and refractory symptoms admitted from 2013 to 2016. The systematic workup included: Optic nerve sheath diameter sonography, spinal MRI and dynamic myelography with subsequent CT. Microsurgical sealing of the cerebrospinal fluid leak was the aim in all cases.

RESULTS

Of 29 patients with a proven cerebrospinal fluid leak, one declined surgery. A single patient was lost to follow-up. In 27 cases, the cerebrospinal fluid leak was successfully sealed by microsurgery. The width of the optic nerve sheath diameter in supine position increased from 5.08 ± 0.66 mm before to 5.36 ± 0.53 mm after surgery ( p = 0.03). Comparing the response of the optic nerve sheath diameter to gravitational challenge, there was a significant change from before (-0.36 ± 0.32 mm) to after surgery (0.00 ± 0.19 mm, p < 0.01). In parallel, spontaneous intracranial hypotension-related symptoms resolved in 26, decreased in one and persisted in a single patient despite recovery of gait.

CONCLUSIONS

The sonographic assessment of the optic nerve sheath diameter with gravitational challenge can distinguish open from closed spinal cerebrospinal fluid fistulas in spontaneous intracranial hypotension patients. A response to the gravitational challenge, that is, no more collapse of the optic nerve sheath while standing up, can be seen after successful treatment and correlates with the resolution of clinical symptoms. Sonography of the optic nerve sheath diameter may be utilized for non-invasive follow-up in spontaneous intracranial hypotension.

A randomised trial to compare the increase in intracranial pressure as correlated with the optic nerve sheath diameter during propofol versus sevoflurane-maintained anesthesia in robot-assisted laparoscopic pelvic surgery

Robot-assisted surgery can cause raised intracranial pressures (ICP) due to steep trendelenburg position and pneumoperitoneum. The choice of anesthetic agents can influence the ICP, which can be measured indirectly by correlating it with the sonographically measured optic nerve sheath diameter (ONSD). In this study, our primary aim was to compare the change from baseline of the ONSD during propofol versus sevoflurane-maintained anesthesia in patients undergoing robotic pelvic surgery. In this prospective, interventional, double-blinded study, we randomised 50 patients into two groups P and S. Subjects in group P received intravenous propofol infusion while those in group S received inhalation sevoflurane for maintenance of anesthesia. The ONSD at fixed intervals was noted as the mean of four values measured using ultrasound in both eyes by two independent anesthesiologists who were blinded to the group allocation. The patient demographics and baseline parameters were similar. The mean maximum rise in ONSD from baseline was 0.01 ± 0.01 cm in group P while it was 0.03 ± 0.01 cm in group S (p = 0.001). Percentage change from baseline in group P was 3.41 ± 1.81% and 8.00 ± 2.95% in group S (p = 0.001). We found a positive correlation between the duration of surgery and the maximum rise in ONSD in group S (p = 0.003), but not in group P. Propofol-based total intravenous anesthesia is more effective than inhalation sevoflurane in attenuating the increase in ICP as correlated with the ONSD during robotic pelvic surgery.Clinical trial registration: Yes; Principal investigator: Nambiath Sujata; Trial number: REF/2016/11/012713 (registered); Trial registry: CTRI- http://ctri.nic.in .

Effect of History of Mild Traumatic Brain Injury on Optic Nerve Sheath Diameter Changes after Valsalva Maneuver

Optic nerve sheath diameter (ONSD) measured by transocular ultrasound is a marker of real-time intracranial pressure (ICP). The objective of this study was to evaluate the association between optic nerve sheath (ONS) dilation after a Valsalva maneuver and a prior history of mild to moderate traumatic brain injury (mTBI) in a heterogeneous sample of participants. Participants were excluded if they had had a recent brain injury, were symptomatic from a prior brain injury, had a history consistent with severe TBI and/or had undergone intracranial surgery. Ninety-five participants with and without a history of mTBI were included in the study. Transocular ultrasound of the ONS was performed before and after a Valsalva maneuver. Differences in the ONSD before and after a Valsalva maneuver were analyzed and correlated to the participants' history of mTBI. Baseline ONSD measurements between groups were not statistically significant. Following Valsalva, participants with a history of mTBI had a statistically significant increase in the ONSD compared with participants with no history of mTBI. This significant difference persisted after controlling for age, race, and sex. This study demonstrated an association between a prior history of mTBI and dilation of the ONS after Valsalva maneuver in a sample of asymptomatic participants, which was not seen in participants without a history of mTBI.

Noninvasive Brain Physiology Monitoring for Extreme Environments: A Critical Review

Our ability to monitor the brain physiology is advancing; however, most of the technology is bulky, expensive, and designed for traditional clinical settings. With long-duration space exploration, there is a need for developing medical technologies that are reliable, low energy, portable, and semiautonomous. Our aim was to review the state of the art for noninvasive technologies capable of monitoring brain physiology in diverse settings. A literature review of PubMed and the Texas Medical Center library sites was performed using prespecified search criteria to identify portable technologies for monitoring physiological aspects of the brain physiology. Most brain-monitoring technologies require a moderate to high degree of operator skill. Some are low energy, but many require a constant external power supply. Most of the technologies lack the accuracy seen in gold standard measures, due to the need for calibration, but may be useful for screening or monitoring relative changes in a parameter. Most of the technologies use ultrasound or electromagnetic radiation as energy sources. There is an important need for further development of portable technologies that can be operated in a variety of extreme environments to monitor brain health.

Management of spontaneous intracranial hypotension - Transorbital ultrasound as discriminator

OBJECTIVE

Spontaneous intracranial hypotension (SIH) is most commonly caused by cerebrospinal fluid (CSF) leakage. Therefore, we hypothesised that patients with orthostatic headache (OH) would show decreased optic nerve sheath diameter (ONSD) during changes from supine to upright position.

METHODS

Transorbital B-mode ultrasound was performed employing a high-frequency transducer for ONSD measurements in the supine and upright positions. Absolute values and changes of ONSD from supine to upright were assessed. Ultrasound was performed in 39 SIH patients, 18 with OH and 21 without OH, and in 39 age-matched control subjects. The control group comprised 20 patients admitted for back surgery without headache or any orthostatic symptoms, and 19 healthy controls.

RESULTS

In supine position, mean ONSD (±SD) was similar in patients with (5.38±0.91 mm) or without OH (5.48±0.89 mm; p=0.921). However, in upright position, mean ONSD was different between patients with (4.84±0.99 mm) and without OH (5.53±0.99 mm; p=0.044). Furthermore, the change in ONSD from supine to upright position was significantly greater in SIH patients with OH (-0.53±0.34 mm) than in SIH patients without OH (0.05±0.41 mm; p≤0.001) or in control subjects (0.01±0.38 mm; p≤0.001; area under the curve: 0.874 in receiver operating characteristics analysis).

CONCLUSIONS

Symptomatic patients with SIH showed a significant decrease of ONSD, as assessed by ultrasound, when changing from the supine to the upright position. Ultrasound assessment of the ONSD in two positions may be a novel, non-invasive tool for the diagnosis and follow-up of SIH and for elucidating the pathophysiology of SIH.

Relationship between intracranial pressure as measured by an epidural intracranial pressure monitoring system and optic nerve sheath diameter in healthy dogs

OBJECTIVE

To evaluate the association between ultrasonographically measured optic nerve sheath diameter (ONSD) and acute increases in intracranial pressure (ICP) as measured by an epidural intracranial pressure monitoring system (EICPMS) in healthy dogs.

ANIMALS

6 young healthy dogs.

PROCEDURES

An EICPMS connected to a pressure monitor was used to generate a continuous pressure waveform in each anesthetized dog. A 22-gauge IV catheter was inserted into the brain parenchyma through the contralateral parietal bone, and 0.5 to 2.0 mL of anticoagulated autologous blood was injected at predetermined intervals. At baseline (immediately after EICPMS placement) and following each injection, the ICP as indicated by EICPMS was recorded, and 3 ultrasonographic images of the optic nerve sheath of each eye were obtained. The ONSD was measured at maximum diameter and at 5 mm caudal to the optic disk.

RESULTS

In linear models, the maximum ONSD was positively associated with increasing ICP. Specifically, the rate of maximum ONSD increase was greater for pressures ≤ 20 mm Hg above baseline (0.0534 mm/1 mm Hg ICP increase) than for pressures > 40 mm Hg above baseline (0.0087 mm/1 mm Hg ICP increase). The relationship of ICP to maximum ONSD was slightly nonlinear and best explained by comparison of fractional polynomial regression models.

CONCLUSIONS AND CLINICAL RELEVANCE

ICP was positively and nonlinearly associated with increasing maximum ONSD, especially when ICP was ≤ 20 mm Hg above baseline, supporting the conclusion that ultrasonographic measurement of maximum ONSD may provide a noninvasive monitoring tool for evaluation of ICP in dogs. Further research is needed to assess the utility of these measurements in clinical patients.

The International Multi-disciplinary Consensus Conference on Multimodality Monitoring: future directions and emerging technologies

Neuromonitoring has evolved rapidly in recent years and there now are many new monitors that have revealed a great deal about the ongoing pathophysiology of brain injury and coma. Further evolution will include the consolidation of multi-modality monitoring (MMM), the development of next-generation informatics tools to identify complex physiologic events and decision support tools to permit targeted individualized care. In this review, we examine future directions and emerging technologies in neuromonitoring including: (1) device development, (2) what is the current limitation(s) of MMM in its present format(s), (3) what would improve the ability of MMM to enhance neurocritical care, and (4) how do we develop evidence for use of MMM?

Neuromuscular ultrasound of cranial nerves

Ultrasound of cranial nerves is a novel subdomain of neuromuscular ultrasound (NMUS) which may provide additional value in the assessment of cranial nerves in different neuromuscular disorders. Whilst NMUS of peripheral nerves has been studied, NMUS of cranial nerves is considered in its initial stage of research, thus, there is a need to summarize the research results achieved to date. Detailed scanning protocols, which assist in mastery of the techniques, are briefly mentioned in the few reference textbooks available in the field. This review article focuses on ultrasound scanning techniques of the 4 accessible cranial nerves: optic, facial, vagus and spinal accessory nerves. The relevant literatures and potential future applications are discussed.

Optimal optic nerve sheath diameter threshold for the identification of elevated opening pressure on lumbar puncture in a Chinese population

Ultrasonography of the optic nerve sheath diameter (ONSD) is a non-invasive and rapid method that might be helpful in the identification of increased intracranial pressure (ICP). The use of an ONSD greater than 5 mm on ultrasound as an indicator of increased ICP in a Caucasian population has been studied. However, the cut-off point of this predictor in Chinese patients has not been established. Thus, we conducted this study to identify the ONSD criterion for the detection of elevated opening pressure on lumbar puncture (LP) in a Chinese population and to investigate the influencing factors. This study was a blind cross-sectional study. Patients who presented with suspected increased ICP were included. The opening pressure on LP of each participant was confirmed. We analyzed the clinical differences between the groups of patients with abnormal and normal opening pressures on LP. A receiver operating characteristic curve was constructed to determine the ONSD cut-off point for the identification of abnormal opening pressure on LP. In total, 279 patients were recruited, and 101 patients presented with elevated opening pressure on LP. ONSD was a significant independent predictor of elevated opening pressure on LP (p<0.001). However, no statistical significance was observed regarding the factors that might have affected this relationship including gender, age, body mass index, waistline, head circumference, hypertension and pathological subtype. The ONSD cut-off point for the identification of elevated opening pressure on LP was 4.1 mm; this cut-off yielded a sensitivity of 95% and a specificity of 92%. ONSD is a strong and accurate predictor of elevated opening pressure on LP. The cut-off point of this predictor in a Chinese population was remarkably lower than that found in a Caucasian population. Thus, ethnic differences should be noted when using the ONSD as an indicator of increased ICP.

Increased intracranial pressure in mini-pigs exposed to simulated solar particle event radiation

Changes in intracranial pressure (ICP) during space flight have stimulated an area of research in space medicine. It is widely speculated that elevations in ICP contribute to structural and functional ocular changes, including deterioration in vision, which is also observed during space flight. The aim of this study was to investigate changes in OP occurring as a result of ionizing radiation exposure (at doses and dose-rates relevant to solar particle event radiation). We used a large animal model, the Yucatan mini-pig, and were able to obtain measurements over a 90 day period. This is the first investigation to show long term recordings of ICP in a large animal model without an invasive craniotomy procedure. Further, this is the first investigation reporting increased ICP after radiation exposure.