This prospective observational study aims to evaluate the association between anesthetic depth, measured by the Bispectral Index (BIS), and first-pass endotracheal intubation success in adult patients undergoing rapid sequence intubation (RSI) in the emergency department.

Endotracheal intubation is one of the most critical procedures performed in emergency medicine. Multiple intubation attempts are associated with an increased risk of adverse events, including hypoxemia, aspiration, cardiovascular complications, and death. Although several factors influence first-pass intubation success, the contribution of anesthetic depth at the time of intubation has not been adequately investigated in the emergency department.

Patients for whom the treating emergency physician decides to perform RSI will undergo noninvasive BIS monitoring using a disposable forehead sensor. The physician performing the intubation will remain blinded to the BIS value throughout the procedure and will perform intubation according to routine clinical practice. A separate investigator, who is not involved in patient management, will record the BIS value at the time of intubation.

The BIS measurements will not be disclosed to the treating team and will not influence clinical decision-making, medication dosing, or patient management. The study is purely observational and does not evaluate the performance or effectiveness of the BIS device itself.

The primary objective is to determine whether patients who achieve first-pass intubation success differ in anesthetic depth from those requiring multiple intubation attempts.

Endotracheal intubation is a life-saving intervention frequently performed in the emergency department for patients with airway compromise, respiratory failure, or critical illness. Despite its importance, emergency airway management is associated with a substantial risk of adverse events. Previous studies have consistently demonstrated that multiple intubation attempts significantly increase the likelihood of hypoxemia, aspiration, hypotension, cardiac arrest, airway trauma, and mortality. Therefore, achieving first-pass success has become one of the principal quality indicators in emergency airway management.

Several patient-, operator-, and procedure-related factors influence first-pass success, including anatomical difficulty, operator experience, type of laryngoscope, choice of sedative and neuromuscular blocking agents, and optimization of preoxygenation. Another potentially important but understudied factor is the depth of anesthesia at the moment of laryngoscopy and intubation.

Adequate anesthetic depth before laryngoscopy suppresses airway reflexes, minimizes patient movement, and improves intubating conditions. Previous studies comparing succinylcholine and rocuronium have suggested differences in intubation conditions; however, subsequent investigations demonstrated that these differences were largely attributable to dosing strategies rather than the neuromuscular blocking agent itself. Current evidence indicates that when appropriate doses are administered, both agents provide comparable intubating conditions. Nevertheless, regardless of the neuromuscular blocking agent used, insufficient hypnotic depth may adversely affect intubation conditions.

The Bispectral Index (BIS) is a processed electroencephalographic parameter ranging from 0 to 100 that provides an objective assessment of the patient's level of consciousness. BIS monitoring has been extensively validated in the operating room and has demonstrated a strong correlation with anesthetic depth. Randomized clinical trials have shown that BIS-guided anesthesia reduces the incidence of intraoperative awareness and may facilitate individualized anesthetic administration. However, BIS monitoring is not routinely incorporated into emergency airway management, and limited evidence exists regarding its relationship with first-pass intubation success in emergency department patients.

This study is designed as a prospective observational study. Adult patients undergoing rapid sequence intubation after a clinical decision by the treating emergency physician will be consecutively enrolled. A disposable BIS sensor will be placed on the patient's forehead immediately before induction, and BIS monitoring will be performed continuously. The emergency physician performing the intubation will remain blinded to the BIS values throughout the procedure. A separate investigator, independent of clinical management, will record the BIS value at the time of laryngoscopy and intubation.

Importantly, BIS measurements will not be communicated to the treating physician and will not influence the timing of intubation, medication selection, medication dosing, or any other aspect of patient care. Therefore, this investigation is not intended to evaluate or validate the BIS device as a medical device intervention. Rather, BIS is used solely as a noninvasive measurement tool to objectively quantify anesthetic depth. The monitor consists of a disposable adhesive forehead sensor and poses minimal risk to participants.

The primary analysis will compare BIS values between patients with successful first-pass intubation and those requiring more than one intubation attempt. The study seeks to determine whether inadequate anesthetic depth is associated with failure of first-pass intubation. The findings may improve understanding of the role of anesthetic depth during emergency airway management and may contribute to strategies aimed at increasing first-pass success while reducing intubation-related complications.

Inclusion Criteria:

• Adults aged 18 years or older
• Patients undergoing rapid sequence intubation (RSI) in the emergency department
• No traumatic injury to the frontal region that would interfere with placement of the Bispectral Index (BIS) sensor

Exclusion Criteria:

• Age younger than 18 years
• Pregnant patients
• Patients with cardiac arrest or hemodynamic instability at the time of enrollment
• Patients intubated without the rapid sequence intubation (RSI) protocol
• Refusal to participate in the study (by the patient or, where applicable, a legally authorized representative)

Adult patients ındergoing RSı in the ED

De-identified individual participant data collected during the study may be shared with qualified researchers upon reasonable request and after approval by the study investigators. Shared data may include demographic characteristics, clinical variables, intubation-related parameters, Bispectral Index values, and outcome data related to first-pass endotracheal intubation success. All shared data will be anonymized to protect participant confidentiality.

De-identified individual participant data and supporting documents will be available after publication of the primary results. The data will be available for a period of 5 years following publication.

De-identified individual participant data may be shared with qualified researchers upon reasonable request and approval by the study investigators. Researchers will be provided access to data necessary for the approved research purpose, including demographic characteristics, clinical variables, Bispectral Index measurements, intubation-related variables, and primary outcome data. Access will be provided after ensuring appropriate data protection and confidentiality measures.