This observational study aims to evaluate the clinical applicability of the Equivalent Minimum Alveolar Concentration (eMAC) parameter during general anesthesia. eMAC is a recently developed index that combines the effects of both inhalational and intravenous anesthetics, providing a unified measure of anesthetic depth. While the traditional Minimum Alveolar Concentration (MAC) is widely used for inhalational agents, it does not reflect intravenous anesthetics or combined techniques such as Combined Intravenous and Inhalational Anesthesia (CIVIA).

In this study, adult patients undergoing elective surgery under general anesthesia will be observed. Standard clinical practice will not be altered. Demographic and clinical parameters, including eMAC, MAC, Bispectral Index (BIS), and hemodynamic variables, will be recorded at defined perioperative time points. No experimental drugs or additional procedures will be administered.

The primary aim is to investigate the correlation between eMAC and MAC values obtained during anesthesia. Secondary objectives include assessing the relationship between eMAC and BIS values, comparing eMAC, MAC, and BIS across different anesthetic techniques, and evaluating hemodynamic stability in relation to anesthetic depth.

The results of this study may contribute to a better understanding of eMAC and its potential role in clinical anesthesia practice.

This is a prospective, observational study designed to evaluate the Equivalent Minimum Alveolar Concentration (eMAC) parameter during general anesthesia. eMAC is a composite index that incorporates the anesthetic effects of both inhalational agents and intravenous anesthetics, such as propofol and remifentanil, allowing assessment of anesthetic depth under combined techniques (CIVIA). While the traditional Minimum Alveolar Concentration (MAC) is well established for inhalational agents, its applicability is limited in cases where intravenous agents are administered. eMAC has been proposed as a more comprehensive measure, but clinical validation is lacking.

Adult patients (ages 18-65, ASA I-III) scheduled for elective surgical procedures under general anesthesia will be enrolled. No experimental interventions will be performed; anesthetic management will follow routine clinical practice. Participants will be observed in two groups, based on the anesthetic technique selected by the attending anesthesiologist.

Data collection will include demographic and baseline clinical variables, as well as anesthetic depth parameters (eMAC, MAC, Bispectral Index [BIS]) and hemodynamic variables (heart rate, mean arterial pressure, SpO₂). Measurements will be recorded at predefined time points: prior to induction (T0), 5 minutes after induction (T1), at the beginning of surgery (T2), at the midpoint of surgery (T3), and at the end of surgery (T4).

The primary outcome measure is the correlation between eMAC and MAC values obtained during anesthesia. Secondary outcome measures include the correlation between eMAC and BIS values, comparisons of eMAC, MAC, and BIS among different anesthetic techniques, and evaluation of hemodynamic stability in relation to anesthetic depth.

Statistical analysis will be performed using appropriate parametric or non-parametric tests, depending on the distribution of variables. Correlation analyses will be conducted using Pearson or Spearman methods, and the impact of demographic factors on eMAC will be explored using multivariate regression. A p-value <0.05 will be considered statistically significant.

The anticipated enrollment is 60 patients. The study is planned to start in September 2025 and is expected to be completed by November 2025. Findings may provide novel insights into the clinical validity of eMAC as a tool for assessing anesthetic depth, and its relationship with established parameters such as MAC and BIS.

Inclusion Criteria:

• Adults aged 18-65 years
• Scheduled for elective surgery under general anesthesia
• American Society of Anesthesiologists (ASA) Physical Status I-III
• Feasibility of Bispectral Index (BIS) monitoring
• Provision of written informed consent

Exclusion Criteria:

• History of neurological disease (e.g., epilepsy, dementia, severe brain injury)
• Known allergy to anesthetic agents
• Severe cardiovascular or respiratory failure

Adult patients scheduled for elective surgical procedures under general anesthesia at Sakarya University Training and Research Hospital, Department of Anesthesiology and Reanimation, will be considered for enrollment. Patients represent a typical surgical population with ASA physical status I-III.

Individual participant data (IPD) will not be shared because this is a single-center observational study with a limited sample size, and data contain potentially identifiable clinical information. Only aggregated results will be reported in publications.