ED50 and ED95 of Isobaric Bupivacaine for Post-Partum Bilateral Tubal Ligation
ED50 and ED95 of Isobaric Bupivacaine for Post-Partum Bilateral Tubal Ligation
Spinal anesthesia is one of the preferred anesthetic techniques for post-partum bilateral
 tubal ligation (PBTL). Bupivacaine is the most commonly used local anesthetic for neuraxial
 anesthesia for post-partum tubal ligation. Typically, hyperbaric bupivacaine would be
 injected into the spinal (intrathecal) space via a spinal needle; however, ongoing medication
 shortages have resulted in limited availability on a local and national level. One proposed
 alternative is isobaric bupivacaine; however, studies investigating its use for post-partum
 bilateral tubal ligation are limited.

 The purpose of this prospective study is to determine the minimal effective dose (ED50 and
 ED95) of isobaric bupivacaine for adequate anesthesia during post-partum tubal ligation after
 vaginal delivery.
This prospective study proposes to enroll 40 post-partum women who are undergoing elective
 post-partum bilateral tubal ligation. The patient will be positioned sitting, and combined
 spinal anesthesia will be performed at L2-3 or L3-4 level. The presence of an epidural
 catheter enables the provider to supplement the spinal anesthetic if required. The starting
 dose of isobaric bupivacaine will be 10 mg based on prior similar studies1,4 and our
 institution's current practice. The dose of intrathecal isobaric bupivacaine was decided by
 using the up-down sequential method.

 The motor block will be graded by a modified Bromage score: Score 1 = complete block, unable
 to move feet or knees; 2 = almost complete block, able to move feet only; 3 = partial block,
 just able to move knees; 4 = detectable weakness of hip flexion while supine, full flexion of
 knees; 5 = no detectable weakness of hip flexion while supine; and 6 = able to perform
 partial knee bend. The score of 1 or 2 within 10-15 minutes of injection will be evaluated as
 successful motor block.

 The success of the sensory spinal block will be noted when bilateral T6 sensory level to
 pinprick is attained after 10 mins from the intrathecal drug administration, this is in
 accordance with previous studies1.

 If spinal anesthesia is inadequate, the epidural catheter will be dosed up for
 supplementation. All observations, including block characteristics and the associated outcome
 (i.e., adequate or inadequate block), will be evaluated by a dedicated anesthesia provider.

 Intraoperative adverse effects, such as hypotension, bradycardia, nausea, or vomiting,
 pruritus, or shivering were noted. Hypotension is defined as a decrease of more than 20% in
 basal systolic blood pressure within 30 minutes of intrathecal injection. The management of
 blood pressure including dose of pressor: phenylephrine and ephedrine will be at the
 discretion of the attending anesthesiologist. The use of pressor and anti-emetics will also
 be recorded.

 The study will be take place in standard clinical context. The study does not deviate from
 our current practice, which includes the use of combined spinal anesthesia where the epidural
 catheter is available if supplemental local anesthetic is required.
Inclusion Criteria:

 -  Age 18 and older

 -  Patients undergoing elective post-partum bilateral tubal ligation after vaginal
 delivery

 -  Patients receiving spinal epidural anesthesia with combination of bupivacaine and
 fentanyl

 Exclusion Criteria:

 -  American Society of Anesthesiologists physical status score >3,

 -  Contraindications to neuraxial analgesia

 -  Patients in whom a combined spinal epidural cannot be performed

 -  Body mass index >40 kg/m2

 -  Allergy or hypersensitivity to local anesthetics and fentanyl

 -  Severe liver, kidney or respiratory disease.

 -  Inability to understand the study protocol

 -  Refusal to provide written consent