The objective of this clinical trial is to investigate if local anesthesia using topical analgesic drug (10% lidocaine spray) or cryo-analgesic (Ice pack) can reduce pain levels during and after arterial blood sampling procedure. The research questions of this study includes:

• Can local anesthesia using topical analgesic drug (10% lidocaine spray) or cryo-analgesic (Ice pack) reduce pain levels during arterial blood sampling?
• Is the first-attempt success rate of arterial blood sampling higher when using local anesthesia (lidocaine spray or ice pack) compared to standard practice without anesthesia?

This single center randomized controlled trial was conducted at the Emergency Department of Queen Savang Vadhana Memorial Hospital, Thailand.

Total of 126 Participants will be sequentially assigned to one of three study groups (A, B, or C) to receive different local anesthesia methods prior to arterial blood sampling procedure.

• Group A (Cold Application): A standard cold pack chilled to -4°C will be applied to the arterial puncture site for 2 minutes. Following cleaning, the physician will immediately perform the arterial blood sampling.
• Group B (Topical Anesthetic): 10% lidocaine spray will be applied to the puncture site, covering a circular area with a 2-3 cm radius. After allowing 2 minutes for anesthetic effect, the site will be cleaned and the physician will perform the arterial blood sampling.
• Group C (Control): This group will receive standard antiseptic preparation with chlorhexidine in alcohol applied in a circular area with a 2-3 cm around the puncture site. After 2 minutes, the site will be cleaned and the physician will perform the arterial blood sampling.

Participants will complete a questionnaire assessing pain levels both during and after the arterial blood sampling procedure. Arterial blood sampling procedure was conducted by trained research assistants or attending experienced physicians.

All collected data will be entered into a secure, encrypted form, ensuring patient confidentiality and preventing access to individual patient identifiers.

Inclusion Criteria:

• Patients aged 18 years or older, who present to the emergency department of Queen Savang Vadhana Memorial Hospital that requires arterial blood sampling procedure for diagnostic purposes

Exclusion Criteria:

• Altered level of consciousness (Glasgow Coma Scale < 15)
• Cognitive impairment or communication barriers precluding accurate pain assessment (e.g., severe dementia, aphasia, intoxication, delirium)
• Contraindications to radial artery cannulation (e.g., severe peripheral vascular disease, history of arteriovenous fistula at the puncture site, active infection at the puncture site)
• Pregnancy
• Need for emergency management which any delay could worsen patient care (e.g., cardiac arrest, respiratory failure requiring immediate intubation)
• Known allergy or hypersensitivity to lidocaine or amide-type local anesthetics
• Severe pain from other sources that could distracting pain assessment related to the arterial blood sampling procedure (e.g., significant trauma, bone fractures, severe burns)
• Failure to obtain successful arterial access after two attempts by an experienced operator.