US Patent 7618370 Venous-arterial detector and pressure indicator

A venous-arterial detector is disclosed. The detector includes a first chamber in fluid communication with a needle, and an indicator chamber in selective fluid communication with the first chamber through a valve. The indicator chamber is pre-pressurized to a defined pressure that preferably exceeds typical venous pressure, and the valve retains that pressure within the indicator chamber. When the needle is inserted into a vessel, if the pressure in the vessel is greater than the defined pressure in the indicator chamber, blood will flow into the indicator chamber, indicating that the vessel is most likely to be an artery.