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Optic nerve sheath diameter and lumbar puncture opening pressure in nontrauma patients suspected of elevated intracranial pressure
American Journal of Emergency Medicine 32 (2014) 1513–1515
Contents lists available at ScienceDirect
American Journal of Emergency Medicine journal homepage: www.elsevier.com/locate/ajem
Brief Report
Optic nerve sheath diameter and lumbar puncture opening pressure in nontrauma patients suspected of elevated intracranial pressure☆,☆☆,★,★★ Terrell S. Caffery, MD, J. Nelson Perret, MD, Mandi W. Musso, PhD ⁎, Glenn N. Jones, PhD Emergency Medicine Residency Program, LSU Health–Baton Rouge, 5246 Brittany Drive, Baton Rouge, LA 70808
a r t i c l e
i n f o
Article history: Received 6 August 2014 Received in revised form 8 September 2014 Accepted 11 September 2014
a b s t r a c t Objective: The purpose of this study was to determine if patients with nontraumatic causes of elevated intracranial pressure (ICP) could be identified by ultrasound measurement of optic nerve sheath diameter (ONSD). It was hypothesized that an ONSD greater than or equal to 5 mm would identify patients with elevated ICP. Method: This was a prospective observational trial comparing ONSD with ICP measured by opening pressure manometry on lumbar puncture (LP). The cohort consisted of a convenience sample of adult patients presenting to the emergency department, requiring LP. The ONSD measurement was performed before computed tomography and LP. The physician performing the LP was blinded to the result of the ONSD measurement. An opening pressure on manometry of greater than or equal to 20 cm H2O and an ONSD greater than or equal to 5 mm were considered elevated. Results: Fifty-one patients were included in our study, 24 (47%) with ICP greater than or equal to 20 cm H2O and 27 (53%) with ICP less than 20 cm H2O. The sensitivity of ONSD greater than or equal to 5 for identifying elevated ICP was 75% (95% confidence interval, 53%-90%) with specificity of 44% (25%-65%). The area under the receiver operator characteristic curve was 0.69 (0.54-0.84), suggesting a relationship between ONSD and ICP. Conclusion: An ONSD greater than or equal to 5 mm was associated with elevated ICP in nontraumatic causes of elevated ICP. Although a relationship exists, a sensitivity of 75% does not make ONSD measurement an adequate screening examination for elevated ICP in this patient population. © 2014 Elsevier Inc. All rights reserved.
1. Introduction Diagnosing elevated intracranial pressure (ICP) has historically required invasive procedures such as placing a catheter into the ventricles via ventriculostomy or placing a needle into the subarachnoid space of the spine via lumbar puncture (LP). In the last decade, sonographic measurement of the optic nerve sheath diameter (ONSD), a noninvasive procedure, has been investigated as a marker for elevated ICP in patients with traumatic brain injuries [1-5]. Some studies report encouraging findings for using ONSD as a marker of ICP. Dubourg et al [6] found that ultrasonography of ONSD yielded a pooled sensitivity of 0.90 and ☆ ☆☆ ★ ★★
Meetings: This work has not been previously presented at any meetings. Sources of support: This project was not funded. Conflict of interest: The authors have no conflicts of interest to disclose. Author contributions: All authors actively contributed to conception and design of the study. TSC and JNP supervised the conduct of the trial. GNJ provided statistical advice on study design and analyzed the data. TSC, MWM, and GNJ drafted the manuscript; and all authors contributed substantially to its revision. TSC takes responsibility for the article as a whole. ⁎ Corresponding author. Emergency Medicine Residency Program, 5246 Brittany Drive, Baton Rouge, LA 70808. Tel.: +225 757 4148. E-mail addresses: [email protected] (T.S. Caffery), [email protected] (J.N. Perret), [email protected], [email protected] (M.W. Musso), [email protected] (G.N. Jones). http://dx.doi.org/10.1016/j.ajem.2014.09.014 0735-6757/© 2014 Elsevier Inc. All rights reserved.
a pooled specificity of 0.85 in patients with traumatic brain injury and intracranial hemorrhage. Other studies have been more discouraging. For example, Strumwasser et al [4] compared ONSD measurements with invasive monitoring (Camino Bolt or ventriculostomy; Integra, Plainsboro, NJ) in a sample of patients with traumatic brain injury. They reported an overall sensitivity of 0.38 and specificity of 0.36. Fewer studies have examined the relationship between ONSD and ICP in patients with nontraumatic causes of elevated ICP. Good sensitivity has been reported for ONSD measurement of idiopathic intracranial hypertension (IIH) [7]. Amini et al [8] examined ICP in a sample of patients with nontraumatic causes of elevated ICP and noted 100% sensitivity and specificity when a cutoff of 5.5 mm diameter of the optic nerve was used. The objective of our study was to determine whether patients with nontraumatic causes of elevated ICP (measured by manometry on LP) could be identified using ONSD assessments. 2. Method 2.1. Participants Participants were recruited from a state-run, urban emergency department (ED) that cares for approximately 43 000 patients per year. This was a cross-sectional, convenience sample of patients, presenting
1514
T.S. Caffery et al. / American Journal of Emergency Medicine 32 (2014) 1513–1515
to the ED between July 2010 and May 2011, who required LP. Patients were excluded if they were younger than the age of 18 years, nonEnglish speaking, incarcerated, or had contraindications for LP [9]. Patients signed informed consent if they were willing to participate in the study. This study was approved by the hospital's institutional review board and was performed in compliance with the ethical standards of the 1964 Declaration of Helsinki. 2.2. Measures 2.2.1. Transorbital sonography Optic nerve sheath diameter was measured using Sonosite M-turbo system (FUJIFILM SonoSite, Inc., Bothell, WA) and a L25 (13-6 MHz) highfrequency linear transducer. During the procedure, patients were placed in a supine position. A thick layer of gel was applied to the eyelid, and the optic nerve was imaged in the axial plane. The optic nerve sheath measurements were obtained 3 mm posterior to the papilla of the optic nerve. Optic nerve sheath diameter measurements were obtained before LP. 2.2.2. Lumbar puncture Before LP, written informed consent was obtained from all patients. The procedure was performed with the patient lying in the lateral decubitus position. Patients' hips and knees were flexed during the procedure. Opening pressure was measured by manometry by the physician performing the LP. 2.3. Procedure Patients willing to participate in the current study underwent ONSD measurements, performed by one, emergency medicine physician with 2 years of experience as an academic ultrasound director. The physician was not involved in measurement of ICP via LP and remained blinded to both indication for and results of LP for the duration of the patient encounter. Some patients underwent computed tomographic (CT) scans of the head after ONSD ultrasounds were performed to rule out contraindications for LP. The use of CT and fundoscopy was left to the discretion of the attending physician. Immunocompromised patients received CT scans in compliance with the Infectious Diseases Society of America guidelines. If not contraindicated, patients underwent LP, performed by an emergency medicine physician who was blinded to the results of the ultrasound. 2.4. Data analysis The cutoff scores for ONSD (≥ 5 mm) and LP (≥ 20 cm H2O) were chosen a priori. Sensitivity and specificity were calculated using standard formulae. Exact (Clopper-Pearson) binomial 95% confidence intervals (95% CI) were computed. The results are presented for the average of the 2 measurements (ONSD), consistent with previous literature [1,5,7,8]. A receiver operating characteristic (ROC) curve was constructed to obtain area under the curve (AUC) and its 95% CI using an opening pressure of greater than or equal to 20 cm H2O as indicative of elevated ICP. Means and SDs were computed to describe continuous variables. Pearson r was used to examine the relations among continuous variables. Significance was set to P b .05. Analyses were conducted using IBM SPSS Statistics v22 (Chicago, IL).
Table 1 Sample descriptive statistics Mean (SD) Age ONSD Left eye Right eye Average Opening pressure (centimeters of water) Sex Female Male Indication R/O infection R/O subarachnoid hemorrhage R/O IIH R/O multiple sclerosis Ataxia Papilledema
n (%)
39.9 (11.9) 5.3 (0.8) 5.4 (0.8) 5.35 (0.8) 21.0 (8.9) 28 (54.9%) 23 (45.1) 30 (58.8%) 11 (21.6%) 5 (9.8%) 3 (5.9%) 1 (2.0%) 1 (2.0%)
Note: R/O = Rule Out.
and 27 (53%) had opening pressures less than 20 cm H2O. The correlation between the mean ONSD and the opening pressure was r = 0.53. Table 2 presents the classic 4-fold table using greater than or equal to 5 mm as the cutoff and opening LP pressures of greater than or equal to 20 cm H20 as indicative of elevated ICP. The sensitivity of this ONSD cutoff for identifying elevated opening pressures was 0.75 (0.53-0.90) with specificity of 0.44 (0.25-0.65). The AUC was significant (AUC = 0.69; 0.54-0.84). The Figure presents the sensitivity and specificity plotted against ONSD (with 95% CI). To achieve a sensitivity above 0.90, the curve suggests moving the ONSD average cut point to greater than or equal to 4.7 mm (sensitivity 0.92; 0.73-0.99). This would come at a tremendous cost to specificity, reducing it to 0.15 (0.04-0.34). The point that maximized overall accuracy was 5.5, which yielded a sensitivity of 0.58 (0.37-0.78) and a specificity of 0.74 (0.54-0.89). 4. Discussion There is a paucity of research investigating whether elevated ICP manifests similarly in the ONSDs of patients with traumatic and nontraumatic conditions. Although a number of studies indicate that ONSD may be a useful, noninvasive screening tool in neurocritically ill trauma patients, fewer studies have investigated its utility in nontrauma patients. The purpose of the current study was to examine whether ONSD measurements could identify patients with nontraumatic causes of elevated ICP, measured by manometry on LP. It was hypothesized that an ONSD cutoff score of greater than or equal to 5 mm would effectively discriminate patients with elevated ICP from those without evidence of elevated ICP. We found that ONSD measurements did not yield acceptable sensitivity for such a high-stakes diagnosis as elevated ICP, suggesting that ultrasound measurement of ONSD is not an appropriate screen in this population. One critique of this body of literature is that studies propose various cut points for ONSD measurements. For example, ROC curves examining ONSD and elevated ICP in neurocritical patients with invasive ICP monitoring have produced optimal cutoffs ranging from 4.8 mm [3] to 5.9 mm [2]. For patients with nontraumatic causes of ICP, Amini et al [8] reported that a cutoff score of 5.5 mm yielded 100% sensitivity and specificity. Bauerle and Nedelmann [7] found that a cutoff score of
3. Results Fifty-six patients met inclusion criteria, with complete data available for 51. One patient had an intracranial mass with midline shift, contraindicating LP. Lumbar puncture was unsuccessful for 4 patients. Descriptive statistics for the remaining 51 patients are presented in Table 1. Most patients were female, with indications for LP that included rule out: infection, subarachnoid hemorrhage, or IIH. Twenty-four patients (47%) had opening pressures greater than or equal to 20 cm H2O
Table 2 Diagnostic accuracy of average ONSD predicting elevated ICP (based on manometry on LP) Opening pressure ONSD average
≥20 cm H2O
b20 cm H2O
≥5 mm (+) b5 mm (−)
18 (35.3%) 6 (11.8%) Sensitivity = 0.75
15 (29.4%) 12 (23.5%) Specificity = 0.44
T.S. Caffery et al. / American Journal of Emergency Medicine 32 (2014) 1513–1515 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 3.00
3.50
4.00
4.50
5.00
5.50
6.00
6.50
7.00
7.50
8.00
8.50
9.00
1515
this is a population in which invasive monitoring of ICP is not feasible, and manometry on LP for measuring ICP has been used in previous studies in similar populations [7,8]. In addition, this study used a convenience sample of patients presenting to the ED who were at risk for elevated ICP and for whom LP was indicated. The use of a convenience sample could introduce bias. Although this is one of the largest samples of nontraumatic ICP patients in the literature, the sample size was relatively small, leading to large confidence intervals. The generalizability of the results may also be threatened in that one physician with specialized training in ultrasonography performed the ONSD measurements. However, previous research has demonstrated high interrater reliability with minimal training [10]. In addition, using only one physician may be considered a strength of the current study, as there is likely to be less variability in ratings. Another potential issue is that individuals with elevated ICP and those without were not matched for demographic variables such as age or sex. However, no relationship has been reported between age, sex, or body mass index and ONSD measurements [7].
Optic Nerve Sheath Diameter 95%CI
Sensitivity
95%CI
95%CI
Specificity
95%CI
Figure. Sensitivity and specificity (with 95% CIs) for detecting elevated ICP (indicated by opening pressure, N20 cm H2O) plotted against average ONSD.
5.8 mm produced 90% sensitivity and 84% specificity in patients with IIH. It is important to note that ONSD measurements do not appear to be reliable to the 0.1 mm. SDs in a recent reliability study range from .26 to .51 mm for intraobserver and interobserver reliability, respectively [10]. This caveat may explain why a wide range of cutoff scores have been offered and is certainly a current limitation of sonographic assessment of ONSD. Despite the variety of recommended cutoffs, several studies used an ONSD measurement of 5 mm as an a priori cutoff score for elevated ICP, [1,5] and anecdotally, this is a well-accepted cutoff score in clinical practice among emergency physicians. However, ONSD measurements in healthy adults may be as high as 6.4 mm [10]. In the current study, greater than or equal to 5 mm did not produce acceptable sensitivity. Furthermore, ROC curve analysis failed to indicate alternative cutoff scores that yield an acceptable balance of sensitivity and specificity. A measurement of 4.5 mm produced greater than or equal to 0.90 sensitivity, but specificity was only 0.15. One explanation for the differences between our findings and the findings of Bauerle and Nedelmann [7] and Amini et al [8] may be methodological. For example, Bauerle and Nedelmann [7] assumed normal ICP in their control group, but they did not measure ICP. Although these differences would not affect sensitivity, they would affect reported specificity and positive predictive power. In addition, the patient populations varied significantly. Bauerle and Nedelmann [7] included individuals with infections such as viral meningitis and Lyme borreliosis in their control group, whereas we considered these individuals at risk for elevated ICP. Amini et al [8] did not report specific diagnoses for their patients, making comparison impossible. Many individuals in our sample had IIH, likely because the hospital has one of the only neuroophthalmologists in the region who referred patients to the ED for LP for suspicion of IIH. Limitations of the current study include the lack of invasive monitoring procedures, which are considered the gold standard. However,
5. Conclusion The current study raises serious questions about using ONSD measurements to detect elevated ICP in patients with nontraumatic causes of ICP. A cutoff score of greater than or equal to 5 mm resulted in misidentification of approximately 25% of patients with elevated ICP in this study. Furthermore, we were unable to find any cutoff score that yielded high sensitivity and acceptable specificity. Few studies have examined the utility of ONSD measurements in patients with nontraumatic causes of elevated ICP. Previously identified scores were not replicated here. Therefore, further research is needed to assess the clinical utility of ONSD measurement in patients for whom invasive ICP monitoring is not feasible. References [1] Blaivas M, Theodoro D, Sierzenski PR. Elevated intracranial pressure detected by bedside emergency ultrasonography of the optic nerve sheath. Acad Emerg Med 2003;10:376–81. [2] Geeraerts T, Launey Y, Martin L, Pottecher J, Vigue B, Duranteau J, et al. Ultrasonography of the optic nerve sheath may be useful for detecting raised intracranial pressure after severe brain injury. Intensive Care Med 2007;33:1704–11. [3] Rajajee V, Vanaman M, Fletcher JJ, Jacobs TL. Optic nerve ultrasound for the detection of raised intracranial pressure. Neurocrit Care 2011;15:506–15. [4] Strumwasser A, Kwan RO, Yeung L, Miraflor E, Ereso A, Castro-Moure F, et al. Sonographic optic nerve sheath diameter as an estimate of intracranial pressure in adult trauma. J Surg Res 2011;170:265–71. [5] Tayal VS, Neulander M, Norton HJ, Foster T, Saunders T, Blaivas M. Emergency department sonographic measurement of optic nerve sheath diameter to detect findings of increased intracranial pressure in adult head injury patients. Ann Emerg Med 2007;49:508–14. [6] Dubourg J, Javouhey E, Geeraerts T, Messerer M, Kassai B. Ultrasonography of optic nerve sheath diameter for detection of raised intracranial pressure: a systematic review and meta-analysis. Intensive Care Med 2011;37:1059–68. [7] Bauerle J, Nedelmann M. Sonographic assessment of the optic nerve sheath in idiopathic intracranial hypertension. J Neurol 2011;258:2014–9. [8] Amini A, Kariman H, Arhami Dolatabadi A, Hatamabadi HR, Derakhshanfar H, Mansouri B, et al. Use of the sonographic diameter of optic nerve sheath to estimate intracranial pressure. Am J Emerg Med 2013;31:236–9. [9] Edlow JA, Panagos PD, Godwin SA, Thomas TL, Decker WW, American College of Emergency Physicians. Clinical policy: critical issues in the evaluation and management of adult patients presenting to the emergency department with acute headache. Ann Emerg Med 2008;52:407–36. [10] Bauerle J, Schuchardt F, Schroeder L, Egger K, Weigel M, Harloff A. Reproducibility and accuracy of optic nerve sheath diameter assessment using ultrasound compared to magnetic resonance imaging. BMC Neurol 2013;13.
Contents lists available at ScienceDirect
American Journal of Emergency Medicine journal homepage: www.elsevier.com/locate/ajem
Brief Report
Optic nerve sheath diameter and lumbar puncture opening pressure in nontrauma patients suspected of elevated intracranial pressure☆,☆☆,★,★★ Terrell S. Caffery, MD, J. Nelson Perret, MD, Mandi W. Musso, PhD ⁎, Glenn N. Jones, PhD Emergency Medicine Residency Program, LSU Health–Baton Rouge, 5246 Brittany Drive, Baton Rouge, LA 70808
a r t i c l e
i n f o
Article history: Received 6 August 2014 Received in revised form 8 September 2014 Accepted 11 September 2014
a b s t r a c t Objective: The purpose of this study was to determine if patients with nontraumatic causes of elevated intracranial pressure (ICP) could be identified by ultrasound measurement of optic nerve sheath diameter (ONSD). It was hypothesized that an ONSD greater than or equal to 5 mm would identify patients with elevated ICP. Method: This was a prospective observational trial comparing ONSD with ICP measured by opening pressure manometry on lumbar puncture (LP). The cohort consisted of a convenience sample of adult patients presenting to the emergency department, requiring LP. The ONSD measurement was performed before computed tomography and LP. The physician performing the LP was blinded to the result of the ONSD measurement. An opening pressure on manometry of greater than or equal to 20 cm H2O and an ONSD greater than or equal to 5 mm were considered elevated. Results: Fifty-one patients were included in our study, 24 (47%) with ICP greater than or equal to 20 cm H2O and 27 (53%) with ICP less than 20 cm H2O. The sensitivity of ONSD greater than or equal to 5 for identifying elevated ICP was 75% (95% confidence interval, 53%-90%) with specificity of 44% (25%-65%). The area under the receiver operator characteristic curve was 0.69 (0.54-0.84), suggesting a relationship between ONSD and ICP. Conclusion: An ONSD greater than or equal to 5 mm was associated with elevated ICP in nontraumatic causes of elevated ICP. Although a relationship exists, a sensitivity of 75% does not make ONSD measurement an adequate screening examination for elevated ICP in this patient population. © 2014 Elsevier Inc. All rights reserved.
1. Introduction Diagnosing elevated intracranial pressure (ICP) has historically required invasive procedures such as placing a catheter into the ventricles via ventriculostomy or placing a needle into the subarachnoid space of the spine via lumbar puncture (LP). In the last decade, sonographic measurement of the optic nerve sheath diameter (ONSD), a noninvasive procedure, has been investigated as a marker for elevated ICP in patients with traumatic brain injuries [1-5]. Some studies report encouraging findings for using ONSD as a marker of ICP. Dubourg et al [6] found that ultrasonography of ONSD yielded a pooled sensitivity of 0.90 and ☆ ☆☆ ★ ★★
Meetings: This work has not been previously presented at any meetings. Sources of support: This project was not funded. Conflict of interest: The authors have no conflicts of interest to disclose. Author contributions: All authors actively contributed to conception and design of the study. TSC and JNP supervised the conduct of the trial. GNJ provided statistical advice on study design and analyzed the data. TSC, MWM, and GNJ drafted the manuscript; and all authors contributed substantially to its revision. TSC takes responsibility for the article as a whole. ⁎ Corresponding author. Emergency Medicine Residency Program, 5246 Brittany Drive, Baton Rouge, LA 70808. Tel.: +225 757 4148. E-mail addresses: [email protected] (T.S. Caffery), [email protected] (J.N. Perret), [email protected], [email protected] (M.W. Musso), [email protected] (G.N. Jones). http://dx.doi.org/10.1016/j.ajem.2014.09.014 0735-6757/© 2014 Elsevier Inc. All rights reserved.
a pooled specificity of 0.85 in patients with traumatic brain injury and intracranial hemorrhage. Other studies have been more discouraging. For example, Strumwasser et al [4] compared ONSD measurements with invasive monitoring (Camino Bolt or ventriculostomy; Integra, Plainsboro, NJ) in a sample of patients with traumatic brain injury. They reported an overall sensitivity of 0.38 and specificity of 0.36. Fewer studies have examined the relationship between ONSD and ICP in patients with nontraumatic causes of elevated ICP. Good sensitivity has been reported for ONSD measurement of idiopathic intracranial hypertension (IIH) [7]. Amini et al [8] examined ICP in a sample of patients with nontraumatic causes of elevated ICP and noted 100% sensitivity and specificity when a cutoff of 5.5 mm diameter of the optic nerve was used. The objective of our study was to determine whether patients with nontraumatic causes of elevated ICP (measured by manometry on LP) could be identified using ONSD assessments. 2. Method 2.1. Participants Participants were recruited from a state-run, urban emergency department (ED) that cares for approximately 43 000 patients per year. This was a cross-sectional, convenience sample of patients, presenting
1514
T.S. Caffery et al. / American Journal of Emergency Medicine 32 (2014) 1513–1515
to the ED between July 2010 and May 2011, who required LP. Patients were excluded if they were younger than the age of 18 years, nonEnglish speaking, incarcerated, or had contraindications for LP [9]. Patients signed informed consent if they were willing to participate in the study. This study was approved by the hospital's institutional review board and was performed in compliance with the ethical standards of the 1964 Declaration of Helsinki. 2.2. Measures 2.2.1. Transorbital sonography Optic nerve sheath diameter was measured using Sonosite M-turbo system (FUJIFILM SonoSite, Inc., Bothell, WA) and a L25 (13-6 MHz) highfrequency linear transducer. During the procedure, patients were placed in a supine position. A thick layer of gel was applied to the eyelid, and the optic nerve was imaged in the axial plane. The optic nerve sheath measurements were obtained 3 mm posterior to the papilla of the optic nerve. Optic nerve sheath diameter measurements were obtained before LP. 2.2.2. Lumbar puncture Before LP, written informed consent was obtained from all patients. The procedure was performed with the patient lying in the lateral decubitus position. Patients' hips and knees were flexed during the procedure. Opening pressure was measured by manometry by the physician performing the LP. 2.3. Procedure Patients willing to participate in the current study underwent ONSD measurements, performed by one, emergency medicine physician with 2 years of experience as an academic ultrasound director. The physician was not involved in measurement of ICP via LP and remained blinded to both indication for and results of LP for the duration of the patient encounter. Some patients underwent computed tomographic (CT) scans of the head after ONSD ultrasounds were performed to rule out contraindications for LP. The use of CT and fundoscopy was left to the discretion of the attending physician. Immunocompromised patients received CT scans in compliance with the Infectious Diseases Society of America guidelines. If not contraindicated, patients underwent LP, performed by an emergency medicine physician who was blinded to the results of the ultrasound. 2.4. Data analysis The cutoff scores for ONSD (≥ 5 mm) and LP (≥ 20 cm H2O) were chosen a priori. Sensitivity and specificity were calculated using standard formulae. Exact (Clopper-Pearson) binomial 95% confidence intervals (95% CI) were computed. The results are presented for the average of the 2 measurements (ONSD), consistent with previous literature [1,5,7,8]. A receiver operating characteristic (ROC) curve was constructed to obtain area under the curve (AUC) and its 95% CI using an opening pressure of greater than or equal to 20 cm H2O as indicative of elevated ICP. Means and SDs were computed to describe continuous variables. Pearson r was used to examine the relations among continuous variables. Significance was set to P b .05. Analyses were conducted using IBM SPSS Statistics v22 (Chicago, IL).
Table 1 Sample descriptive statistics Mean (SD) Age ONSD Left eye Right eye Average Opening pressure (centimeters of water) Sex Female Male Indication R/O infection R/O subarachnoid hemorrhage R/O IIH R/O multiple sclerosis Ataxia Papilledema
n (%)
39.9 (11.9) 5.3 (0.8) 5.4 (0.8) 5.35 (0.8) 21.0 (8.9) 28 (54.9%) 23 (45.1) 30 (58.8%) 11 (21.6%) 5 (9.8%) 3 (5.9%) 1 (2.0%) 1 (2.0%)
Note: R/O = Rule Out.
and 27 (53%) had opening pressures less than 20 cm H2O. The correlation between the mean ONSD and the opening pressure was r = 0.53. Table 2 presents the classic 4-fold table using greater than or equal to 5 mm as the cutoff and opening LP pressures of greater than or equal to 20 cm H20 as indicative of elevated ICP. The sensitivity of this ONSD cutoff for identifying elevated opening pressures was 0.75 (0.53-0.90) with specificity of 0.44 (0.25-0.65). The AUC was significant (AUC = 0.69; 0.54-0.84). The Figure presents the sensitivity and specificity plotted against ONSD (with 95% CI). To achieve a sensitivity above 0.90, the curve suggests moving the ONSD average cut point to greater than or equal to 4.7 mm (sensitivity 0.92; 0.73-0.99). This would come at a tremendous cost to specificity, reducing it to 0.15 (0.04-0.34). The point that maximized overall accuracy was 5.5, which yielded a sensitivity of 0.58 (0.37-0.78) and a specificity of 0.74 (0.54-0.89). 4. Discussion There is a paucity of research investigating whether elevated ICP manifests similarly in the ONSDs of patients with traumatic and nontraumatic conditions. Although a number of studies indicate that ONSD may be a useful, noninvasive screening tool in neurocritically ill trauma patients, fewer studies have investigated its utility in nontrauma patients. The purpose of the current study was to examine whether ONSD measurements could identify patients with nontraumatic causes of elevated ICP, measured by manometry on LP. It was hypothesized that an ONSD cutoff score of greater than or equal to 5 mm would effectively discriminate patients with elevated ICP from those without evidence of elevated ICP. We found that ONSD measurements did not yield acceptable sensitivity for such a high-stakes diagnosis as elevated ICP, suggesting that ultrasound measurement of ONSD is not an appropriate screen in this population. One critique of this body of literature is that studies propose various cut points for ONSD measurements. For example, ROC curves examining ONSD and elevated ICP in neurocritical patients with invasive ICP monitoring have produced optimal cutoffs ranging from 4.8 mm [3] to 5.9 mm [2]. For patients with nontraumatic causes of ICP, Amini et al [8] reported that a cutoff score of 5.5 mm yielded 100% sensitivity and specificity. Bauerle and Nedelmann [7] found that a cutoff score of
3. Results Fifty-six patients met inclusion criteria, with complete data available for 51. One patient had an intracranial mass with midline shift, contraindicating LP. Lumbar puncture was unsuccessful for 4 patients. Descriptive statistics for the remaining 51 patients are presented in Table 1. Most patients were female, with indications for LP that included rule out: infection, subarachnoid hemorrhage, or IIH. Twenty-four patients (47%) had opening pressures greater than or equal to 20 cm H2O
Table 2 Diagnostic accuracy of average ONSD predicting elevated ICP (based on manometry on LP) Opening pressure ONSD average
≥20 cm H2O
b20 cm H2O
≥5 mm (+) b5 mm (−)
18 (35.3%) 6 (11.8%) Sensitivity = 0.75
15 (29.4%) 12 (23.5%) Specificity = 0.44
T.S. Caffery et al. / American Journal of Emergency Medicine 32 (2014) 1513–1515 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 3.00
3.50
4.00
4.50
5.00
5.50
6.00
6.50
7.00
7.50
8.00
8.50
9.00
1515
this is a population in which invasive monitoring of ICP is not feasible, and manometry on LP for measuring ICP has been used in previous studies in similar populations [7,8]. In addition, this study used a convenience sample of patients presenting to the ED who were at risk for elevated ICP and for whom LP was indicated. The use of a convenience sample could introduce bias. Although this is one of the largest samples of nontraumatic ICP patients in the literature, the sample size was relatively small, leading to large confidence intervals. The generalizability of the results may also be threatened in that one physician with specialized training in ultrasonography performed the ONSD measurements. However, previous research has demonstrated high interrater reliability with minimal training [10]. In addition, using only one physician may be considered a strength of the current study, as there is likely to be less variability in ratings. Another potential issue is that individuals with elevated ICP and those without were not matched for demographic variables such as age or sex. However, no relationship has been reported between age, sex, or body mass index and ONSD measurements [7].
Optic Nerve Sheath Diameter 95%CI
Sensitivity
95%CI
95%CI
Specificity
95%CI
Figure. Sensitivity and specificity (with 95% CIs) for detecting elevated ICP (indicated by opening pressure, N20 cm H2O) plotted against average ONSD.
5.8 mm produced 90% sensitivity and 84% specificity in patients with IIH. It is important to note that ONSD measurements do not appear to be reliable to the 0.1 mm. SDs in a recent reliability study range from .26 to .51 mm for intraobserver and interobserver reliability, respectively [10]. This caveat may explain why a wide range of cutoff scores have been offered and is certainly a current limitation of sonographic assessment of ONSD. Despite the variety of recommended cutoffs, several studies used an ONSD measurement of 5 mm as an a priori cutoff score for elevated ICP, [1,5] and anecdotally, this is a well-accepted cutoff score in clinical practice among emergency physicians. However, ONSD measurements in healthy adults may be as high as 6.4 mm [10]. In the current study, greater than or equal to 5 mm did not produce acceptable sensitivity. Furthermore, ROC curve analysis failed to indicate alternative cutoff scores that yield an acceptable balance of sensitivity and specificity. A measurement of 4.5 mm produced greater than or equal to 0.90 sensitivity, but specificity was only 0.15. One explanation for the differences between our findings and the findings of Bauerle and Nedelmann [7] and Amini et al [8] may be methodological. For example, Bauerle and Nedelmann [7] assumed normal ICP in their control group, but they did not measure ICP. Although these differences would not affect sensitivity, they would affect reported specificity and positive predictive power. In addition, the patient populations varied significantly. Bauerle and Nedelmann [7] included individuals with infections such as viral meningitis and Lyme borreliosis in their control group, whereas we considered these individuals at risk for elevated ICP. Amini et al [8] did not report specific diagnoses for their patients, making comparison impossible. Many individuals in our sample had IIH, likely because the hospital has one of the only neuroophthalmologists in the region who referred patients to the ED for LP for suspicion of IIH. Limitations of the current study include the lack of invasive monitoring procedures, which are considered the gold standard. However,
5. Conclusion The current study raises serious questions about using ONSD measurements to detect elevated ICP in patients with nontraumatic causes of ICP. A cutoff score of greater than or equal to 5 mm resulted in misidentification of approximately 25% of patients with elevated ICP in this study. Furthermore, we were unable to find any cutoff score that yielded high sensitivity and acceptable specificity. Few studies have examined the utility of ONSD measurements in patients with nontraumatic causes of elevated ICP. Previously identified scores were not replicated here. Therefore, further research is needed to assess the clinical utility of ONSD measurement in patients for whom invasive ICP monitoring is not feasible. References [1] Blaivas M, Theodoro D, Sierzenski PR. Elevated intracranial pressure detected by bedside emergency ultrasonography of the optic nerve sheath. Acad Emerg Med 2003;10:376–81. [2] Geeraerts T, Launey Y, Martin L, Pottecher J, Vigue B, Duranteau J, et al. Ultrasonography of the optic nerve sheath may be useful for detecting raised intracranial pressure after severe brain injury. Intensive Care Med 2007;33:1704–11. [3] Rajajee V, Vanaman M, Fletcher JJ, Jacobs TL. Optic nerve ultrasound for the detection of raised intracranial pressure. Neurocrit Care 2011;15:506–15. [4] Strumwasser A, Kwan RO, Yeung L, Miraflor E, Ereso A, Castro-Moure F, et al. Sonographic optic nerve sheath diameter as an estimate of intracranial pressure in adult trauma. J Surg Res 2011;170:265–71. [5] Tayal VS, Neulander M, Norton HJ, Foster T, Saunders T, Blaivas M. Emergency department sonographic measurement of optic nerve sheath diameter to detect findings of increased intracranial pressure in adult head injury patients. Ann Emerg Med 2007;49:508–14. [6] Dubourg J, Javouhey E, Geeraerts T, Messerer M, Kassai B. Ultrasonography of optic nerve sheath diameter for detection of raised intracranial pressure: a systematic review and meta-analysis. Intensive Care Med 2011;37:1059–68. [7] Bauerle J, Nedelmann M. Sonographic assessment of the optic nerve sheath in idiopathic intracranial hypertension. J Neurol 2011;258:2014–9. [8] Amini A, Kariman H, Arhami Dolatabadi A, Hatamabadi HR, Derakhshanfar H, Mansouri B, et al. Use of the sonographic diameter of optic nerve sheath to estimate intracranial pressure. Am J Emerg Med 2013;31:236–9. [9] Edlow JA, Panagos PD, Godwin SA, Thomas TL, Decker WW, American College of Emergency Physicians. Clinical policy: critical issues in the evaluation and management of adult patients presenting to the emergency department with acute headache. Ann Emerg Med 2008;52:407–36. [10] Bauerle J, Schuchardt F, Schroeder L, Egger K, Weigel M, Harloff A. Reproducibility and accuracy of optic nerve sheath diameter assessment using ultrasound compared to magnetic resonance imaging. BMC Neurol 2013;13.