Background: In the emergency department (ED), medical procedures, such as arterial blood gas (ABG) testing, can cause pain and high stress levels. However, ABG testing is a routine procedure assessing the severity of the patient's condition. To reduce the pain of ABG, several methods have been investigated without significant difference in pain perception. Communication, a key element of care, has shown a significant effect on pain perception. A positive communication strategy, including positive, kind, or reassuring words, can reduce pain perception, while negative words can raise this perception, causing discomfort, known as the “nocebo effect.” Although some studies have compared the impact of verbal attitudes, particularly in anesthesia and mainly with staff already trained in hypnosis, to the best of our knowledge, none have investigated the effect of communication in the emergency setting, where patients may be more suggestible to the words used. Objective: In this study, we will investigate the effect of positive therapeutic communication on pain, anxiety, discomfort, and global satisfaction in patients requiring ABG compared to nocebo and neutral communication. Methods: A single-center, double-blind randomized controlled trial (RCT) with 3 parallel arms will be conducted with 249 patients requiring ABG during their ED visit. Patients will be randomly assigned to 1 of 3 groups before receiving ABG: positive communication group, negative communication (nocebo) group, or neutral communication (neutral) group. The communication and the words used by the physicians during hygiene preparation, artery location, and puncture will be imposed in each group. The study will be proposed to each patient corresponding to the inclusion criteria. The physicians will not be trained in hypnosis or in positive therapeutic communication. The procedure will be recorded with audio recorders to test its quality. Intention-to-treat analysis will be performed. The primary endpoint is the onset of pain. The secondary outcomes are patient comfort, patient anxiety, and global satisfaction of the patient with the communication strategy used. Results: On average, 2000 ABG procedures are performed each year in the EDs of hospitals. In this study, 249 patients are expected to be included. With a projected positive response rate of 80%, we intend to include 25 (10%) patients per month. The inclusion period began in April 2023 and will run until July 2024. We hope to publish the results of the study during the fall of 2024. Conclusions: To the best of our knowledge, this study is the first RCT assessing the use of positive communication on pain and anxiety in patients undergoing the ABG procedure in the ED. A reduction in pain, discomfort, and anxiety is expected when using positive communication. If the results are positive, this could be useful to the medical community and encourage clinicians to monitor their communication during care. Trial Registration: ClinicalTrials.gov NCT05434169 https://clinicaltrials.gov/ct2/show/NCT05434169 International Registered Report Identifier (IRRID): PRR1-10.2196/42043