anesthesia with lidocaine infiltration at the intended puncture site, insert the overthe-needle catheter over the radial artery 0.5 to cm proximal to the distal wrist crease and slowly advance toward the arterial pulse After puncturing the artery and obtaining blood flow, advance the needle to mm farther, and then hold the needle steady and slowly advance the catheter into the vessel FIGURE 130.3 Radial artery puncture or cannulation If blood flow never occurs or stops spontaneously, the needle tip may have penetrated the posterior wall of the vessel, as shown in Figure 130.3 Remove the needle, holding the catheter steady, and begin pulling back the catheter mm at a time until a sudden flash of arterial blood is identified ( Fig 130.3 ) Then, advance the catheter forward into the artery If no blood returns, make another attempt starting over again with new equipment as previously described If blood flow is satisfactory in the position shown in Figure 130.3 , attach the connecting tubing to the catheter with a T-connector, stopcock, and syringe, and recheck arterial flow The catheter should be securely taped or sewn to the forearm to prevent dislodgment Use of a transparent sterile dressing is recommended to enhance visibility and security Alternatively, the Seldinger technique can be used by passing a thin guide wire through a 22-gauge introducer needle that is used to gain access to the lumen of the radial artery and then removing the needle (leaving the wire in place) and