Ethyl chloride vapocoolant sprays provide transient skin anesthesia within seconds of application. The current investigation aim is to compare the effect of ethyl chloride based vapocoolant spray to placebo in reducing pain associated with arterial puncture for gasometry determinations.

The investigators will conduce a double-blind randomized placebo-controlled trial at Emergency Department.

We will enroll patients who come to Emergency Department who need an arterial gasometry determination. Patients will be randomized to intervention-group (ethyl chloride vapocoolant sprays will be usad before arterial puncture) or to placebo-group (alcohol spray as placebo will be used before arterial puncture.) and after the puncture they will rate their pain using a 10 points visual analogue scale.

Single-blind, randomized placebo-controlled trial in an emergency department of Hospital de Basurto in Bilbao, Spain. Patients for whom arterial blood gas analysis had been ordered will be included. They will be randomly assigned to receive application of the experimental ethyl chloride spray or a placebo aerosol spray of a solution of alcohol in water. The assigned spray will be applied just before arterial puncture. The main outcome variable is pain intensity reported on an 11-point numeric rating scale.

Inclusion Criteria:

• age: 18-85 years old.
• arterial gasometry determination needed
• III, IV or V level classification on Manchester triage.

Exclusion criteria:

• refusal to participate,
• inability to provide informed consent (non-Spanish speaking, dementia or altered mental state),
• skin disease associated with cold intolerance (Raynaud's phenomenon),
• known allergy to spray contents,
• Glasgow Coma Scale <15,
• pregnancy,
• under effects of alcohol or drugs,
• Allen test +.