A Randomized Study Evaluating the Role of Ultra-sound Guidance When Drawing Radial Arterial Blood Samples

Inclusion Criteria: * The patient must have given his/her informed and signed consent * The patient must be insured or beneficiary of a health insurance plan * The patient's health status necessitates an arterial blood sample AND his/her radial arteries are deemed unpalpable OR two previous attempts at radial arterial puncture by a nurse resulted in failure Exclusion Criteria: * The patient is participating in another study * The patient is in an exclusion period determined by a previous study * The patient is under judicial protection, or any kind of guardianship * The patient refuses to sign the consent * It is impossible to correctly inform the patient * The patient is pregnant, parturient, or breastfeeding * Arterial puncture is required on femoral, humeral or axillary arteries * The patient is in cardiac arrest * The patient has known circulatory problems, ischemia, local infection * The patient has a severe bleeding or hemostasis disorder (hemophilia, hypoprothrombinemia, platelets \<50,000) * The patient is an upper limb amputee, or his/her arm is in a cast * The patient has known allergies to methyl or propylbenzoate, propylene glycol or chlorexhidine gluconate