Effect of a cervical collar on optic nerve sheath diameter in trauma patients

Abstract

BACKGROUND:

As advocated in advanced trauma life support and prehospital trauma life support protocols, cervical immobilization is applied until cervical spine injury is excluded. This study aimed to show the difference in optic nerve sheath diameter (ONSD) between patients with and without a cervical collar using computed tomography (CT).

METHODS:

This was a single-center, retrospective study examining trauma patients who presented to the emergency department between January 1, 2021, and December 31, 2021. The ONSD on brain CT of the trauma patients was measured and analyzed to determine whether there was a difference between the ONSD with and without the cervical collar.

RESULTS:

The study population consisted of 169 patients. On CT imaging of patients with (n=66) and without (n=103) cervical collars, the mean ONSD in the axial plane were 5.43 ± 0.50 mm and 5.04 ± 0.46 mm respectively for the right eye and 5.50 ± 0.52 mm and 5.11 ± 0.46 mm respectively for the left eye. The results revealed an association between the presence of a cervical collar and the mean ONSD, which was statistically significant (P<0.001) for both the right and left eyes.

CONCLUSION:

A cervical collar may be associated with increased ONSD. The effect of this increase in the ONSD on clinical outcomes needs to be investigated, and the actual need for cervical collar in the emergency department should be evaluated on a case-by-case basis.

INTRODUCTION

For many years, trauma patients were routinely immobilized due to the possibility of cervical injury, and rigid cervical collars and spine boards were used during transport in prehospital trauma care. As advocated in advanced trauma life support and prehospital trauma life support protocols, cervical immobilization is applied until cervical spine injury is excluded.[1,2] Its purpose is to prevent secondary spinal cord injuries.[3]

Previously studies have shown that rigid cervical collars may cause increased intracranial pressure (ICP) in trauma patients.[4-7] This condition must be prevented in trauma patients because it may cause secondary brain injury.

In various studies, the optic nerve sheath diameter (ONSD) has been shown to be a useful marker for indirectly measuring the ICP.[8-10] ONSD can be measured with computed tomography (CT), magnetic resonance imaging (MRI), or ultrasound (US).[11,12]

In the literature, there are many studies in which ONSD measurements of trauma patients with cervical collars were obtained using the US. However, the number of studies using CT is limited. This study aimed to show the difference in the ONSD between patients with and without a cervical collar using CT.

METHODS

Study design and population

This was a retrospective, single-center study of trauma patients admitted to the emergency department between January 1, 2021, and December 31, 2021. Approval was obtained from the local ethics committee (Decision No: 2021/215) before the data were scanned.

All trauma patients admitted to the emergency department who did not meet the exclusion criteria were enrolled in the study. Patients without cranial CT, younger than 18 years, with cardiac arrest, with cranial pathology on imaging, with a history of cranial mass, with history of orbital injury, with repeated cranial CT imaging (since there may be two different ONSDs with the same demographic characteristics, trauma mechanisms, and trauma scores despite two CTs taken at different times), and with cranial CT imaging with artifacts for measurement were excluded from the study.

The demographic characteristics, trauma mechanisms, Glasgow Coma Scores (GCS), Revised Trauma Scores (RTS), Injury Severity Scores (ISS), and cranial CT images of the patients included in this study were retrieved from the hospital’s electronic medical record system.

Measurements

The images and measurements were evaluated in Akgun PACS Viewer 4.0. All CT scans were obtained with a 16-slice CT scanner (Toshiba Alexion™, Toshiba Medical Systems Corporation, Japan) with a slice thickness of 3–5 mm. Measurements were made in the abdominal view window (W400 L40) by an emergency medicine specialist using a caliper in the axial plane through both eyes, 3 mm behind the optic disc, at 500-fold magnification. The presence of a cervical collar was determined in the bone view window (W2500 L480). The evaluator was blinded to the patients’ information extracted and to whether or not a cervical collar was worn as he or she used an abdominal window for measurements. The ONSD measurements in the axial plane are shown in Figure 1.

Figure 1.

The optic nerve sheath diameter (ONSD) measurements on the computed tomography (CT).

The emergency medicine specialist who performed the measurements performed ONSD measurements on randomly selected cranial CT scans before the study. These measurements were evaluated by a radiologist experienced in cranial CT, and the study was planned after the accuracy of the measurements was confirmed.

Endpoints

The endpoint of this study was the difference in the ONSD between patients with and without a cervical collar using CT.

Statistical analysis

All the statistical analyses were conducted using Jamovi v.1.6 Statistics Package programs (Jamovi Project Computer Software, Version 1.6, Australia). In our study, type I errors were accepted as 5% for all comparisons. Continuous variables with a normal distribution were expressed as the mean and standard deviation, and non-normally distributed data were expressed as the median and interquartile range (IQR). Categorical data are presented as the frequency (n) and percentage (%). The Shapiro-Wilk test was used to check whether the data were normally distributed. For comparisons of continuous variables, normally distributed data were compared with the t-test, and non-normal distributed data were compared with the Mann-Whitney U test. The Chi-square test was used to compare categorical variables between the groups. A P-value <0.05 indicates a statistically significant difference.

RESULTS

Throughout the study period, a total of 412 patients (without cranial CT [n=341], younger than 18 years [n=38], with cardiac arrest [n=3], with cranial pathology on imaging [n=5], with a history of cranial mass [n=1], with history of orbital injury [n=4], with repeated cranial CT imaging [n=1], and with cranial CT imaging with artifacts for measurement [n=19]) were excluded. Ultimately, the study population consisted of 169 patients. The study flowchart is shown in Figure 2.

Figure 2.

Study flowchart.

Of the 169 patients included in the study, 112 (66.3%) were male, and 57 (33.7%) were female. The median age of the patients was 40 years, and the IQR was 25–55 years. A total of 66 patients (46 men, 20 female) wore cervical collar, while 103 patients (66 men, 37 female) did not wear it. The most common trauma mechanism was vehicle traffic accidents in 72 cases (42.6%) and fall from height in 49 cases (29.0%), followed by motorcycle accident in 34 cases (20.1%) and object falling on in 14 cases (8.3%). The mean GCS score was 15, the mean RTS was 11.9, and the mean ISS was 0.6. The patients’ demographic data and trauma scores are summarized in Table 1. There was no significant difference in the genernal information between the patients with and without cervical collars.

Table 1.

Demographic data, trauma scores, and trauma mechanisms of the patients

On CT images of patients with and without cervical collars, the mean ONSD in the axial plane was 5.43 ± 0.50 mm and 5.04 ± 0.46 mm respectively for the right eye and 5.50 ± 0.52 mm and 5.11 ± 0.46 mm respectively for the left eye. There was a statistically significant difference in the mean ONSD between patients with and without the cervical collar (P=0.001, Table 2).

Table 2.

The comparison of ONSD measurements according to cervical collar wearing or not, mm

As shown in Table 3, there was no statistically significant difference between the mean ONSD of patients with cervical collars regarding gender (P=0.997, P=0.992). In contrast, there was a statistically significant difference in the mean ONSD between patients without cervical collars stratified by gender (P=0.001, P=0.002, Table 3).

Table 3.

The comparison of ONSD values subgrouped by gender, mm

DISCUSSION

Head trauma is a significant cause of morbidity and mortality in trauma patients. An increase in ICP can result in decreased cerebral perfusion. Rigid cervical collars may cause increased ICP in trauma patients, even in patients without head trauma.[4-7] The ONSD is used as a noninvasive index for measuring ICP, which can be measured with CT, MRI, and US.[11-14]

Vaiman et al[15] evaluated the ONSDs of 300 healthy patients using CT, the results varied from 5.17 ± 1.34 mm to 3.55 ± 0.82 mm at different locations (3 mm–8 mm behind the optic disc) within the intraorbital space. Since our study included trauma patients by design, the measurements of healthy human ONSD are not included. However, since we included patients who were closest to normal (high GCS and low ISS), we minimized the conditions affecting ONSD measurements. The mean ONSD in the axial plane for the right and left optic nerves was 5.04 ± 0.46 mm and 5.11 ± 0.46 mm respectively on CT images without cervical collar patients. These findings suggest that patients without cervical collars and without orbital or cranial pathology have similar mean ONSD measurements to those made in healthy patients on CT.

Yard et al[10] evaluated whether the cervical collar change the ONSDs, and it was observed that the cervical collar increased the ONSD. Colak et al[16] evaluated the relationship between the ONSD and cervical collar use in trauma patients. They found that cervical collars increased the ICP and ONSD in trauma patients and non-trauma patients. In our study, CT images were used to measure ONSD in the axial plane 3 mm behind the optic disc. A significant difference of the mean ONSD measurements was observed between the groups with and without a cervical collar. This result is similar to that of ONSD measurements at US studies.[11,12] Since there are limited studies on ONSD measurements on CT in trauma patients, we believe that our study contributes to the literature.

Goeres et al[17] evaluated the ONSD was by US in healthy volunteers. The mean ONSD was 3.68 mm (95% confidence interval 2.85–4.40 mm). Upon regression analysis, mean ONSD did not vary with age, weight, or height but did vary with sex. Our study evaluated the association of gender and the mean ONSD with and without a cervical collar. As a result, no association was found between gender and mean ONSD in patients with cervical collars. In contrast, an association was found between gender and mean ONSD measurements in patients without cervical collars. Our findings suggest that the ONSD may be associated with gender independently of the cervical collar.

Ladny et al[18] investigated the effect of different types of cervical collars on the ONSD. ONSD was measured before and after the cervical collar was attached. The cervical collar was found to increase the ONSD. It is important to consider if cervical collars are indeed necessary for trauma patients. In our study, a single type of cervical collar was worn, and it was observed that these attached cervical collar increased the ONSD.

Limitations

This study has several limitations. Primarily, the study was small in scope, limited in population (high GCS and low ISS), single-center, and retrospective. In addition, ONSD measurements were not made by a radiologist but by an emergency medicine specialist. This is not an obvious limitation because the literature has shown a strong correlation between ONSD taken by emergency medicine specialists and those taken by radiologists.[19] Another limitation is that the ONSD measurements were only in the axial plane. Nevertheless, a study has shown that ONSD measurements are better correlated with the US in the axial plane on CT images.[20] Finally, we do not know the duration of wearing a cervical collar or the clinical reflection of the increase in ONSD. Therefore, multicenter prospective studies with large sample size, evaluating all CT findings of increased ICP are needed.

CONCLUSION

A cervical collar may be associated with an increased ONSD. The effect of this increase in the ONSD on clinical outcomes needs to be investigated, and the actual need for a cervical collar in the emergency department should be evaluated on a case-by-case basis.