Participants will be brought to the main operating rooms. The patient will not be required to do anything different than if they were not enrolled in the study. The anesthesiologist will be asked to confirm that the patient still requires an arterial line. The patient will be randomized either to palpation or ultrasound group. Patients would be placed in supine position on the operating room table and all regular monitors (electrocardiogram, pulse oximeter, non-invasive blood pressure) applied. After preoxygenation, the patient would be induced and the airway secured. For those requiring an arterial catheter before induction of general anesthesia, subcutaneous lidocaine will be used to anesthetize the planned puncture site.

The arms would be abducted and the decision on which side to place the arterial line will be determined by the operator after palpation or scanning the wrists with ultrasound. An ultrasound image of the radial artery to be cannulated will be obtained. A wrist roll would then be placed under the wrist and the hand secured with tape. The wrist would then be prepped with chlorhexidine and sterile towels placed around the prepped site. Timing would begin once the ultrasound or the operator fingers touch the prepped wrist. For those randomized to ultrasound, a Sonosite linear ultrasound probe would then be used to locate the radial artery. After satisfactory position is obtained, a 20 ga angiocath 45mm long would be used to puncture the artery and then would be advanced until the tip appears on the ultrasound view. When this happens the ultrasound is advanced about 2mm proximal along the artery. The needle is advanced until the tip is again visualized. This is repeated until the needle tip is in the lumen of the radial artery. At this point the needle is sequentially advanced in the lumen of the artery in small steps under ultrasound vision and then the cannula is advanced over the needle. The needle core is then retracted and the transducer is connected to the cannula. If the first attempt is unsuccessful, then more attempts may be made until 5 minutes elapse. Success is defined as arterial cannulation as shown by an arterial waveform that is obtained within 5 minutes of touching the prepped skin with an ultrasound probe or the operator fingers. After that the operator may use the arterial cannulation method of choice or decide to change to the other wrist.

For the palpation method, the radial artery would be palpated and then a 20 ga angiocath used to puncture the artery. After a return of blood in the catheter an attempt will be made to advance the catheter over the needle core. If this is not successful, the operator can make multiple attempts until 5 minutes elapse. After this time, the operator can use any desired method to cannulate the artery and may also decide to use the other wrist.

Investigators will record the successful first pass cannulation, and time to cannulate the vessel. Other measures will be number of attempts, number of catheters, radial artery depth, radial artery diameter, blood pressure, heart rate, and failure rate. Other data that will be recorded will include patient age, gender, weight, height , body mass index, and history of peripheral vascular disease, and diabetes.

Patients will not require any followup for the study.