This will be a prospective, observational, single-center study to evaluate the accuracy of sensory testing by blunt 16-gauge plastic cannula during the 15 minutes after spinal injection for predicting spinal failure. While previous studies assessed the minimal sensory level required for painless cesarean delivery at skin incision or delivery, no studies have assessed the accuracy of sensory testing at an earlier time point.

Primary Objective:

1. Evaluate the accuracy of sensory testing with blunt plastic 16-gauge cannula during the 15 minutes after spinal injection for predicting spinal failure. Cephalad sensory dermatomal levels will be assessed at 1 (t1), 3 (t3), 5 (t5), 7 (t7), 9 (t9), 11 (t11), 13 (t13), and 15 (t15) minutes after intrathecal 1.6 ml 0.75% bupivacaine in 8.25% dextrose combined with 15 mcg fentanyl and 150 mcg morphine (study solution). Spinal failure, which is defined as inability to achieve a T4 level to pinprick by the 15-minute timepoint or intraoperative pain (VAS > 0) requiring treatment

Secondary Objectives:

1. Conversion to another anesthetic technique (general anesthesia or activation of the epidural catheter)
2. Inadequate anesthesia (analgesic supplementation with ketamine, > 20 mg propofol, > 2 mg midazolam, > 10 mg parental morphine equivalents, or intraperitoneal chloroprocaine).
3. Patient satisfaction upon arrival to the postanesthesia care unit, rated on a 1-5 Likert scale

A sample size calculation

Population: 250 pregnant females undergoing non-emergency cesarean section delivery in the Labor & Delivery Operating Rooms at Oregon Health & Science University.

Number of Sites: Single center trial

Study Duration: Institutional Review Board approval has been obtained. Study initiation, enrollment, and data collection is expected to take 24 months. Data analysis, manuscript writing, editing, submission and revision to a peer-reviewed journal is expected to take an additional 6 months.

In summary, the study should be completed in under 3 years.

Subject Participation Duration: Total time of subject participation including time for recruitment, enrollment, data collection during the preanesthesia consult, and post-consult data collection will be less than 3 hours.

Estimated Time to Complete Enrollment: Estimated time from enrollment into study of the first subject to enrollment into study of the last subject is 24 months.

Inclusion Criteria:

• Patients undergoing cesarean delivery under spinal or combined spinal epidural anesthesia
• BMI between 20 and 40 kg/m2
• Height between 5 feet 2 inches and 5 feet 10 inches.
• English and non-English speaking patients, if interpretive services are available

Exclusion Criteria:

• Patient refusal
• Contraindications to neuraxial anesthesia (coagulopathy, CNS pathology, infection at site of needle puncture)
• Allergy to any study medications
• Use of epidural anesthesia
• Emergency (red) cesarean delivery
• Conditions that impact dermatomal sensory testing including spinal cord injury with sensory deficits and abdominoplasty
• Prison inmates
• Decisionally impaired individuals
• Pregnancies involving multiple fetuses

Participants must be biologically female, this study evaluates spinal anesthesia given to pregnant individuals undergoing cesarean section delivery

Pregnant females receiving spinal or combined spinal epidural anesthesia for cesarean delivery

Due to patient data protection regulations within the study site there is not a plan to make individual participant data available to other researchers. Reasonable requests emailed to the PI will considered on a case-by-case basis.