Intraoperative neurophysiological monitoring, especially motor evoked potentials, plays a crucial role in spine surgeries by providing real-time assessment of the functional integrity of motor pathways and helping to prevent neurological injury. MEPs are generated by transcranial electrical stimulation and recorded from peripheral muscles, but their reliability can be significantly affected by the depth of anesthesia. The bispectral index, derived from EEG analysis, is widely used to monitor anesthetic depth, with values ranging from 0 to 100. Anesthetic agents suppress cortical excitability and hence influence MEP responses. Studies have shown that lower BIS values, indicating deeper anesthesia, are associated with reduced MEP amplitudes and delayed latencies, while lighter anesthesia enhances MEP signal quality. Older adults present unique challenges in anesthetic management due to age-related alterations in pharmacodynamics and pharmacokinetics. Evidence suggests that elderly patients tend to have lower BIS values under similar anesthetic conditions compared to younger individuals, reflecting increased sensitivity to anesthetic agents. This heightened sensitivity could suppress cortical excitability further, potentially impairing MEP monitoring. Therefore, investigating the relationship between BIS guided anesthetic depth and MEP responses in older adults undergoing spine surgery is essential. Understanding this interaction may help optimize neurophysiological monitoring and improve surgical outcomes in the geriatric population.

Significance of the Study: 

This study will provide valuable data on how different depths of sedation affect MEPs in older adults. The findings will help refine anesthesia protocols and monitoring strategies, leading to: Improved accuracy of intraoperative neurological assessment Reduced risk of false-positive or false negative MEP findings Enhanced patient safety during surgical procedures The results may contribute to the development of age specific guidelines for MEP monitoring. 

Objectives 

Primary Objective To evaluate the effect of varying depths of sedation, measured using the Bispectral Index, in allowable range ,on the amplitude and latency of MEPs in older adult patients 

Secondary Objectives To assess the relationship between age-related physiological factors and MEP changes under different sedation depths. Decremental time reliability in TCI pump To determine the optimal BIS range for reliable MEP monitoring in older adults. 

Hypothesis Does BIS have any Effect on Motor Evoked Potentials in Older Adults in spine surgeries. 

Null hypothesis  There is no any Effect of BIS on Motor Evoked Potentials in Older Adults in spine surgeries.

Materials and Methods

Study Design Prospective Observational study 

Study Population Older Patients who were undergoing spine surgery will be recruited. 

Inclusion Criteria

1.Patients aged 65 years or older 

2.Patients undergoing elective spinal surgery or other surgeries where MEP monitoring is indicated 

3.American Society of Anesthesiologists physical status classification I to III 

Exclusion Criteria

1.Pre-existing neurological deficits affecting motor function 

2.Contraindications to MEP monitoring.

3.Severe cardiac conditions e.g., severe coronary artery disease, heart failure.

Anesthesia Protocol: Patients will receive total intravenous anesthesia with propofol and fentanyl to allow for controlled adjustment of sedation depth. Sedation depth will be titrated to target BIS levels of 40 to 45 deep sedation, 45-50 (moderate sedation), and 50-60 value. , a step-wise approach could be used, depending on the final study design and ethical considerations. Neuromuscular blocking agents will be avoided after intubation to prevent interference with MEP recording. MEP Monitoring: Transcranial electrical stimulation will be used to elicit MEPs. MEPs will be recorded from appropriate muscle groups using standard techniques. MEP amplitude and latency will be measured at baseline and at each target BIS level. Stimulation parameters will be optimized and kept constant throughout the monitoring period.

Sample Size Formula: 95 subjects.

Statistical analysis Collected data will be coded and entered into a Microsoft excel sheet. Qualitative data will be described as frequency and percentages and analysed by using chi square test. P value less than 0.05 considered stastically significant. Repeated measures ANOVA or mixed-effects models will be used to compare MEP parameters across different BIS levels. Correlation and regression analyses will be performed to assess the relationship between age, comorbidities, medication use, and MEP changes. 

Data Collection Patient demographics like age, sex, medical history, medications, ASA physical status, BIS values at specified time points, MEP amplitude and latency measurements and Surgical details will be collected. 

Expected Outcomes and Dissemination Expected Outcomes The study will provide evidence on how sedation depth affects MEPs in older adults. The results will help identify the optimal sedation depth for reliable MEP monitoring in this population. The findings will contribute to improved patient safety and neurological outcomes during surgery. 

Dissemination Plan Publication of results in peer-reviewed scientific journals Presentation of findings at national and international conferences Development of clinical guidelines or recommendations for MEP monitoring in older adults.