The goal of this clinical trial was to evaluate methods to prevent pain on intravenous administration of propofol during induction of anesthesia. Propofol frequently causes a burning or painful sensation when injected into a peripheral vein.

This randomized study compared three approaches in adult patients scheduled for elective surgery: propofol alone (control), propofol with 40 mg lidocaine mixed directly, and a brief intravenous lidocaine under venous occlusion (Bier block) using 40 mg for 2 minutes before propofol.

The primary outcome was the incidence of pain on propofol injection measured with a 4-point verbal rating scale (0 = no pain to 3 = severe pain). Secondary outcomes included pain intensity, peri-induction hemodynamic parameters, and local injection-site adverse effects.

Study Design and Setting This study was designed as a prospective, single-center, randomized, double-blind, parallel-group clinical trial conducted at the Maternity and Neonatology Center of Monastir (Tunisia). The trial was carried out between March 2025 and July 2025 in accordance with institutional standards for general anesthesia.

Study Procedures Upon arrival in the operating room, standard monitoring was applied, including non-invasive blood pressure, electrocardiography, and pulse oximetry. A peripheral intravenous catheter was inserted in a vein of the upper limb used for propofol administration. No analgesic or sedative premedication was administered prior to induction.

Patients were allocated to one of three study groups according to a predefined randomization sequence. All study drugs were administered through the same intravenous access under standardized conditions.

In the control group, propofol was administered intravenously without lidocaine pretreatment. In the lidocaine-propofol mixture group, lidocaine was added directly to the propofol syringe immediately before injection. In the Bier block group, lidocaine was administered intravenously under venous occlusion using a tourniquet applied proximally for a short, predefined duration, followed by release of the tourniquet and intravenous administration of propofol.

Randomization and Blinding Randomization was performed using a block randomization method. Study syringes were prepared by an anesthesiologist not involved in patient management or outcome assessment. Patients, anesthesia providers, investigators, and outcome assessors remained blinded to group allocation throughout the study.

Data Collection and Monitoring Pain during propofol injection was assessed immediately at the time of administration by an independent observer using a standardized verbal rating scale. Hemodynamic parameters were recorded at predefined time points during induction of anesthesia. Patients were monitored for local adverse effects at the injection site following propofol administration.

Ethical Considerations The study was conducted in accordance with the principles of the Declaration of Helsinki. Ethical approval was obtained prior to study initiation, and written informed consent was obtained from all participants before enrollment.

Inclusion Criteria:

• Adult patients aged 18 years or older
• American Society of Anesthesiologists (ASA) physical status I to III
• Scheduled for elective surgery under general anesthesia requiring intravenous induction with propofol

Exclusion Criteria:

• Patient refusal
• Known hypersensitivity to local anesthetics or propofol
• Pre-existing vascular disease
• Infection at the intended injection site
• Chronic use of analgesics or anxiolytics
• Inability to understand the pain assessment scale
• History of drug abuse

Individual participant data (de-identified) that underlie the results reported in this article will be made available upon reasonable request to the principal investigator (Dr Asma Ladib, asmaladib@yahoo.com) after publication, for researchers who provide a methodologically sound proposal. Data will be available in an anonymized format for academic and non-commercial use.

6 months after publication, for 5 years

Researchers with sound proposals may request anonymized data from Dr Asma Ladib for academic, non-commercial use

Both the participant and the investigator assessing pain were blinded to group allocation. The propofol syringes were prepared by an anesthesiologist not involved in data collection.