Three-Dimensional Ultrasound (3D US) in Parturients

Traditionally, the manual palpation of lower back is used to identify the skin insertion point for the epidural needle placement in obstetric patients. Recently, two-dimensional ultrasound (2D US) scanning before the epidural needle insertion proved to improve an accurate determination of inter-vertebral levels and spine midline. 2D US is also useful in determining the depth to the epidural space and needle insertion angle. A three-dimensional ultrasound (3D US) technique is a new advancement in the ultrasound technology. 3D US allows for a real-time, visual guidance of the epidural needle insertion. This study will assess weather 3D US, compared to palpation, can accurately identify the skin needle insertion site for the epidural needle placement.

• Lumbar 3D ultrasound scanning and palpation (Ultrasonix ) (Device), also known as Ultrasonix US machine (model Sonix Touch): Paramedian ultrasound scanning of L2-3 and L3-4 lumbar interspaces to visualize ligamentum flavum. Palpation of the same intervertebral spaces to identify spine midline and needle insertion point.

Primary outcomes

• Distance between two needle insertion points [20 minutes of testing prior to delivery]: To measure the distance between the needle puncture site identified by the 3D US transducer to the needle puncture site identified by palpation, measured on a transparency film.

Secondary outcomes

• Distance between needle insertion point and spine midline [20 minutes of testing prior to delivery]: To measure the perpendicular distance between the needle puncture site identified by the 3D US transducer to the midline identified by manual palpation (to the P-line), measured on a transparency film.
• assess quality of 3D US images [one year]: To obtain US images of the epidural anatomy with various settings of the image-processing system to determine the optimal 3D US parameters that give the clearest images. An experienced sonographer will analyze the US images in the UBC laboratory using a qualitative measure of clarity (scale of 1 to 5) of the depiction of the ligamentum flavum and laminae. This quality measure will be correlated to the image acquisition parameters to determine the optimal set of parameters.

Sex: Female, ages: 19 Years to any

Inclusion Criteria:

* ASA I or II
* Greater than or equal to 19 years old
* Term pregnancy (greater than or equal to 38 weeks gestation age)
* Ability to read English in order to understand the consent form

Exclusion Criteria:

* BMI greater than or equal to 40
* Scoliosis
* Previous difficult regional anesthesia/analgesia
* Previous lower back surgery
* Active labour
* Allergy to epidural tape, surgical paper tape, or felt pen

• Allaudin Kamani, MD, Principal investigator, University of British Columbia and BC Women's Hospital