ICU patients are at high risk of ionic or metabolic disturbances during the course of their critical illness. Some of these disturbances might be life-threatening and require rapid response from physicians. Point-of-Care determination of electrolytes, glucose, hemoglobin and hematocrit ensures early detection (within 1 minute) of abnormal values and allows rapid and appropriate therapy. This technology has largely improved the quality of care in ICU. However, the accuracy of the measurement of those parameters had to be close enough to the reference method, usually perfomed in the central lab but time consuming. Recently, a novel generation of blood gas analyser has been released. Among them, the RapidPoint 500 is mounted with a 28-day cartridge which provides automatic calibrations and quality controls several times a day. Such a technology dramatically decreases the need for labs technical interventions. To date, there is no data reporting the accuracy of this device. Therefore, the investigators' aim is to compare the accuracy of the RapidPoint 500 with a reference measurement performed at the central laboratory (Beckman&Coulter AU5800 for electrolytes and Beckman&Coulter DXH for hemoglobin).

Inclusion Criteria:

• Current stay in ICU
• Presence of an indwelling arterial catheter (radial or femoral)
• Prescription by physicians of a blood gas analysis and a laboratory analysis for the next morning

Exclusion Criteria:

• None

All patients staying in our ICU and equipped with an indwelling arterial catheter for whom clinicians prescribe together an arterial blood gas analysis and a biological laboratory analysis.

The study will take place over a 1 month period. A total of 300 pairs of samples is targeted.