Ultrasound Measurements of Basilica Vein Diameter at Room Air Breathing and at Positive Pressure on Healthy Volunteers

Peripherally Inserted Central Catheters (PICC) and midline placement requires the catheter size to be one third of the venous diameter, or less. However, measurements during CPAP (Continous Positive Airway Pressure) might overestimate the diameter of veins in patients requiring a PICC line. The investigators will enroll 28 healthy subjects to measure their basilica vein diameter at atmospheric pressure and at 10 cmH2O of Positive End-Expiratory Pressure (PEEP). PEEP will be applied through a CPAP helmet with the straps placed under the arms or tied to the bed. The investigators will test the hypothesis that positive airway pressure significantly increases vein diameter. Under this hypothesis, the indication of avoiding catheters larger than one third of the vein diameter should be revised, as venous enlargement during PEEP may lead to the placement of inappropriately large catheters.