Arterial puncture for blood gas analysis is a diagnostic procedure used to assess arterial blood gases and monitor a patient's oxygenation status. It is widely regarded by nursing staff as one of the most painful routine procedures. Despite this, the use of local anesthesia prior to arterial puncture remains uncommon in clinical practice.

Several types of anesthetic agents and administration techniques have been evaluated, with mixed results regarding their effectiveness in reducing patient-reported pain. Studies comparing subcutaneous lidocaine injection or ethyl chloride spray to no analgesic intervention have shown that ethyl chloride does not significantly reduce pain. Moreover, the discomfort caused by lidocaine injection appears to be comparable to that of the arterial puncture itself, suggesting limited overall benefit from this approach.

Other investigations have similarly reported a lack of significant pain reduction with ethyl chloride spray, although some contradictory findings exist. Ultrasound-guided arterial puncture has been shown to improve success rates and shorten procedure duration; however, it does not appear to influence pain perception.

The impact of needle size on pain intensity has also been explored, with conflicting results. Some studies found no significant difference in pain when using different gauge needles, while others reported reduced pain with the use of finer needles, such as insulin needles, compared to standard arterial puncture needles.

Topical anesthetic creams combining lidocaine and prilocaine have been assessed in randomized, double-blind trials. These studies found no significant difference between anesthetic and placebo groups in terms of pain intensity or the proportion of painful procedures.

More recently, cryotherapy has been investigated as a non-pharmacological method to reduce pain prior to arterial puncture. Several randomized controlled trials using varying cryotherapy protocols have generally reported a significant reduction in pain compared to control groups, with longer application times appearing to enhance effectiveness.

However, these findings must be interpreted with caution due to methodological limitations. In some studies, sample size calculations were not justified, randomization procedures were poorly described, and reported pain levels were unusually high compared to those typically observed in European populations, raising concerns about external validity. In certain cases, although pain reduction was statistically significant, it did not reach the minimal clinically important difference, limiting its clinical relevance.

Conversely, other trials reported very low pain scores following cryotherapy, suggesting a substantial clinical benefit. The short application time required for cryotherapy also makes it far more practical than topical anesthetic creams, which require prolonged application. This practicality supports its use in both emergency and outpatient settings.

Some authors have noted that blinding is challenging when using cryotherapy and have suggested incorporating placebo interventions in future studies to improve methodological rigor.

Overall, systematic analyses indicate that cryotherapy appears to be a safe and potentially effective method for reducing pain during arterial puncture. Nevertheless, the existing evidence is limited by a high risk of bias, underscoring the need for further high-quality randomized controlled trials.

Conclusion: Given the promising but methodologically constrained evidence, there is a strong justification for conducting a rigorously designed, placebo-controlled randomized trial to accurately assess the effectiveness of cryotherapy in reducing pain associated with radial arterial puncture.

Inclusion Criteria:

• Patient with a respiratory condition requiring arterial blood gas sampling via radial puncture
• Patients able to assess their pain using a numerical rating scale
• Patients reporting a pain score of 0 on the numerical scale at the wrist prior to sampling
• Patients with no contraindications or allergies to local anesthetics such as lidocaine/prilocaine
• Patients aged 18 years or older
• Patients affiliated with or benefiting from a social security scheme
• Patients able to give consent and who have signed an informed consent form

Exclusion Criteria:

• Patients reporting a pain score >0 on the numerical rating scale before sampling
• Emergency context requiring immediate arterial blood gas results
• Patients for whom radial arterial puncture is not feasible
• Known hypersensitivity to local amide-type anesthetics or any component of the lidocaine/prilocaine cream
• Pregnant or breastfeeding women
• Refusal to participate
• Patients under legal guardianship or conservatorship

This is an open-label study whose primary objective is to compare cryotherapy with placebo cream for pain. However, both the investigator and the patient will be blinded to whether the applied cream is neutral (placebo) or active (lidocaine), making the comparison between lidocaine and placebo double-blind.