Patients scheduled for mastectomy and suitable for paravertebral block will be randomized to one of 2 groups.

Group 1 will have the nerve block performed using a standard non-echogenic needle and catheter under ultrasound guidance. Group 2 will have the block performed using the control needle and an echogenic catheter, all under ultrasound (US) guidance.

The clinician will be blinded to the catheter type and will assess the quality of catheter visualisation of the US image during the procedure, along with adequacy of spread of local anesthetic. The primary outcome will be needle visibility, and secondary outcomes will be block success rate and block quality. An assessment of the patient's pain levels after the procedure will also be conducted.

Inclusion Criteria:

• Patients scheduled to undergo breast surgery requiring use of a peripheral nerve block catheter for establishing a paravertebral block
• Patients classified as ASA (American Society of Anesthesiologists) physical status I, II or III
• Patients at least 18 years old
• Patient is willing and able to provide informed consent for study participation
• Patient has a good understanding of written and verbal English

Exclusion Criteria:

• Patient with contraindications to regional anesthesia technique (e.g. allergy to local anesthetic or other medications used in study)
• Patient with known coagulopathy
• Patient whose target nerve cannot be seen with linear ultrasound probe in a pre-procedure scan. All patients who need a curvilinear probe to visualize the target nerve will be excluded from the study.
• Patients having mastectomy and immediate reconstruction