Radial artery puncture is a medical procedure performed to obtain a sample of arterial blood for gas analysis.^[1] A needle is inserted into the radial artery and spontaneously fills with blood. The syringe is either prepacked with a small amount of heparin to prevent coagulation, or must be heparinised, by drawing up a small amount of heparin and squirting it out again.^{[citation needed]}. The available evidence suggests that the use of local anaesthesia, prior to arterial puncture, does not reduce the perceived pain of the procedure.^[2]