Does Ultrasound Help With Placement of Labor Analgesia in Pregnant Patients?

Epidurals provide superior labor analgesia and anesthesia. Unfortunately, failure of epidural anesthesia and analgesia is a frequent clinical problem. In a heterogeneous cohort of 2,140 surgical patients, a failure rate of 27% for lumbar epidural was described. However, the definition of a failed epidural is broad. Different definitions include insufficient analgesia to catheter dislodgement to conversion to general anesthesia. Epidural analgesia failures may result from technical difficulties, insufficiencies or overdosing of local anesthetics, epidural septum or midline adhesions, and placement of the epidural catheter through an intervertebral foramen or into the anterior epidural space. In an imaging study of failed epidurals, incorrect catheter placement accounted for half of the failures, while the remaining patients experienced suboptimal analgesia through a correctly positioned catheter.

The incidence of overall failure was lower in patients receiving combined spinal-epidural (CSE) catheters versus epidural analgesia. In one study, the CSE technique provided decreased failure rates for labor analgesia and comparable or decreased failure rates for surgical anesthesia, when compared with reported failure rates for epidural anesthesia. It is believed that positive CSF flow in the spinal needle confirms correct epidural needle placement in the epidural space and also confirms the epidural needle to be in the midline position. Placement of the epidural needle in the midline position will minimize the incorrect placement of the catheter to one side, providing a symmetrical analgesia versus unilateral analgesia.

However, the practice of CSE and epidural catheter placement relies on the palpation of anatomical landmarks that are not always easy to feel. Therefore, the epidural needle maybe placed "off midline" despite positive loss of resistance (LOR) that causes negative CSF flow in the spinal needle and an incorrectly placed catheter. As a result, the incorrect catheter placement will result in a "failed" or suboptimal epidural analgesia.

Ultrasound has recently been utilized to facilitate lumbar epidurals and spinals. The US imaging of the lumbar spine in different scanning planes facilitates the identification of the landmarks necessary for appropriate epidural space location in pregnant patients. There are two acoustic windows that are effective for lumbar spine sonographic assessment: one seen on the transverse approach, and the other seen on the longitudinal paramedian approach. The ultrasound single-screen method using the transverse approach of the lumbar spine provides reliable information regarding the landmarks required for labor epidurals. The correct interspace and midline position are identified for correct placement of the CSE analgesia.

Inclusion criteria

• Nulliparious
• Term (>37 weeks gestation)
• Vertex presentation
• Singleton gestation
• Ability to provide informed consent
• Request for analgesia for labor pain
• Maternal age 18 years or greater

Exclusion criteria

• Multiparous
• Preterm (< 37 weeks gestation)
• Presentation other than vertex (breech, transverse)
• Active drug/alcohol dependence
• Previous spinal surgeries
• Known spinal deformities