Blood gases are widely used in emergency and resuscitation services and are the key examination for exploring acid-base balance disorders (using pH, PaCO2 and HCO3 ) and gas exchange disorders (using PaO2 and PaCO2). This examination can be taken from both venous and arterial sample and its analysis depends on the type of blood sample. Currently, several studies have already shown the existence of a good correlation of pH and bicarbonates level between a venous and arterial sample. Thus, when this examination is prescribed for the purpose of highlighting and analyzing an acid-base disorder, venous blood gas is theoretically as efficient as arterial blood gas.

Due to the lack of evidence of benefit for the patient or the health care team of a venous blood gas rather than an arterial blood gas in the absence of suspicion of hypoxemia, arterial blood gas is currently the standard of care for the analysis of acid-base disorders. Indeed, among the university hospitals affiliated to the Paris Diderot University, the emergency departments carry out in their vast majority (4 of 5 E.D.) arterial blood gases. Demonstration of the superiority of veinous sample over arterial sample regarding pain could substantially modify current practices.

The investigator's main hypothesis is that, in the absence of suspicion of hypoxemia (normal oxygen saturation measured by plethysmography), the realization of a venous blood gas for the evaluation of the acid-base balance in the context of emergencies is less painful for patients, simpler for the health care team and provides sufficient biochemical information for the doctor in comparison with an arterial blood gas.

Inclusion Criteria:

• necessity of blood gas analysis
• age > 18 yo
• SpO2>95% without supplemental oxygen
• no altered level of consciousness: Glasgow Coma Scale=15

Exclusion Criteria:

• Patient under guardianship or curatorship
• confusional state or patient unable to understand the protocol
• no social security