Can Optic Nerve Sheath Diameter Measurement Predict Negative Neurological Outcome ?

Introduction:

Current medical literature reveals that the life expectancy after cardiopulmonary resuscitation (CPR) for out of hospital cardiac arrest (OHCA) is 6.7-9.6%.1,2 The hypoxic process, also referred to as post-resuscitation encephalopathy (PRE), is a major factor affecting the neurological outcome following return of spontaneous circulation (ROSC).3 Many studies, aiming the early prediction of the neurological outcome via vital signs, scoring systems, various biochemical markers and imaging techniques exist in literature.1-8 Optic nerve is a part of central nervous system and its posterior part is covered with dura mater. Studies have found that, elevations in intracranial pressure (ICP) resulted in elevated subarachnoid fluid pressure, leading to increased optic nerve sheath diameter (ONSD).9 Bedside USG measurements of ONSD are reported to be utilizable for evaluation of ICP.9,10

Aim of the study:

The primary aim of this study is to evaluate the relationship of bedside USG measurements of ONSD following the ROSC after CPR for OHCA patients, with early (3rd day) neurological evaluation and 30 days survival rate, proposing that increased ONSD may be related to negative neurological outcomes. Considering a relationship is found, the secondary goals of the study are established as, identifying a cut-off value for ONSD related to negative neurological outcome and the optimal time to measure ONSD.

Material and Methods:

This study is designed as a multicenter, prospective, cohort clinical study. The Utstein Templates for Resuscitation Registries are used for OHCA records.11 The associate researchers are demanded to have an experience of at least 5 years in USG use and be certified by the Emergency Medicine Association of Turkey (EMAT) for participating and/or being a faculty in the Emergency USG courses on ONSD evaluation, by the EMAT USG study group (EMATUS), which organizes planned USG courses for Emergency Physicians. A one-day education to standardize the researchers of the study, with theoretical and implementation sections are planned to be held by the authors of the study, regarding the methodology of the study and standardization of the USG techniques for ONSD measurements. In the implementation section, the researchers will perform ONSD measurements with ocular USG on healthy volunteers and the reliability among performers will be measured with Interclass Correlation test.

This study will be performed in the adult emergency departments of the participating hospitals, after the ethics committee approval. The OHCA patients presenting to the adult emergency departments of the participating hospitals will render the study population. The non-traumatic, non-intracranial event related OHCA patients in whom the ROSC is achieved will render the sampling group. The sampling size with a power of 95% is calculated to be 203 patients. The patients whose available next of kin has given consent will be admitted to the study.

All patients will receive standardized advanced cardiac life support (ACLS) measures in line with the most recent American Heart Association (AHA) guidelines by emergency department teams, uncommitted to the study. Following the ROSC, a time period of 20 minutes is determined in order to appropriate tissue perfusion to be stated, with a systolic blood pressure ≥90 mmHg or mean arterial pressure ≥65 mmHg and peripheral capillary saturation ≥94%.14 ONSD measurements will be performed in patients who had uninterrupted ROSC for 20 minutes with bedside USG and the time between the achievement of ROSC and the measurement will be recorded. The routine care plan of the patients will not be manipulated. In case the clinician decides that a cranial computed tomography (CT) is indicated according to routine practices and current guidelines, a copy of the CT images will be taken to investigate the presence of an intracranial mass leading to increased ICP.

The neurologic evaluation of the patients in the study group will be performed in three steps. Primary neurological evaluation will be performed following the achievement of appropriate tissue perfusion after ROSC, prior to any sedative or paralyzing drug application. This step is about identifying and recording the alertness, presence of activity, and the level of motor response, brain stem reflexes and myoclonic status epilepticus. The second neurological evaluation will take place after the 72nd hour following the ROSC. The alertness, presence of spontaneous motor activity, and the level of motor response, brain stem reflexes and myoclonic status epilepticus will also be identified and recorded in the second step, as well. The third evaluation will be the evaluation of neurological final outcome at 30th day or hospital discharge, utilizing the Modified Rankin Scale (MRS).

Statistical Package for the Social Sciences 22.0 for Windows will be used for statistical analysis. Descriptive statistical values will be presented as quantity and percentiles for categorical variables and as mean and standard deviation for numerical variables. Comparisons of numerical variables between two independent groups will be performed by Student-t Test if normal distribution is obtained and by Mann-Whitney U test if it is not obtained. The differences between the mean values of categorical variables of two independent groups will be tested with Chi-Square analysis. The relationships between the numerical variables will be reviewed with Pearson Correlation analysis under parametric test conditions, and Spearman Correlation Analysis under non-parametric test conditions. The appropriateness of four separately measures ONSD values will be evaluated with concordance correlation coefficient measurement. The cut-off value will be determined with Receiver Operating Characteristics Curve Analysis. The statistical alpha significance level will be accepted as p<0.05.