Ultrasound-guided regional anesthesia is increasingly being used in the modern surgical environment to provide specific intraoperative anesthesia and postoperative analgesia. Infiltration of local anesthesics around peripheral nerves firs blocks sympathetic, then sensory, then motor nerve function. Sympathectomy-induced vasodilation following brachial plexus block results in increased skin temperature and arterial flow within minutes.

Although it has not been shown to reliably increase diameter or cross-sectional area of distal arteries, brachial plexus block does change the pattern and quantity of blood flow to the hand. Given that the magnitude of change of flow cannot be attributed to vessel radius, the investigators suspect that the more laminar fluid dynamics are due to vascular tone.

The investigators study aims to quantify alterations in physiology and peripheral vasodilator response. The investigators anticipate that axially block will significantly improve regional blood flow.

Inclusion Criteria:

• ASA physical status I, II, III
• BMI less than or equal to 39
• Presenting for elective upper limb surgery
• Does not meet any exclusion criteria

Exclusion Criteria:

• Age over 80
• ASA physical status IV or V
• BMI greater or equal to 40
• Language barrier precluding ability to give informed consent
• History of coagulopathy
• INR < 1.4
• Platelet count < 100
• Allergy to local anesthetics
• Known peripheral vascular disease of the upper limbs
• Amputation of one or both upper limbs, not including digits
• Peripheral neurological disease
• Does not consent to participate in study

Individuals coming for elective upper extremity surgery who would already be having a brachial plexus block for their anesthesia.