ED90 for Hyperbaric Bupivacaine in Super Obese Parturients

ED90 for Hyperbaric Bupivacaine in Spinal Anesthesia for Cesarean Delivery in Super Obese Parturients

The aim of this study is to determine the ED90 of hyperbaric intrathecal bupivacaine for the super obese population undergoing cesarean section under a combined spinal epidural technique.

The starting dose of hyperbaric bupivacaine for the first patient in this study will be 9mg; the dose for the subsequent subject will be based on the response of the preceding subject as per the Narayana Rule, a modification of the biased-coin design (BCD) up-down sequential method (UDM).

Blinded study drugs will be prepared by an anesthesia provider not involved in the study. The anesthesia provider providing care to the patient will be blinded to the dosage of the hyperbaric bupivacaine. In order to preserve the blinding of the provider, the total volume of study drug will be maintained at a constant of 2.05mL. The difference in total volume based on the variation of hyperbaric bupivacaine dosing will be replaced with preservative free normal saline.

The starting dose of hyperbaric bupivacaine for the first patient in this study will be 9mg; the dose for the subsequent subject will be based on the response of the preceding subject as per the Narayana Rule, a modification of the biased-coin design (BCD) up-down sequential method (UDM).

Determination of the dose will rely on the outcomes of the preceding 7 patients receiving the same dose, as the number of previous patients to consider is a function of the target dose. Among all patients who received a certain dose, a proportion of successful outcomes will be determined (P(d)); if P(d) <0.90, and at least one of the previous 7 patients who received the same dose had an unsatisfactory outcome, the next patient will receive a pre-determined increment of 0.75 mg of bupivacaine. Alternatively, if P(d) 0.90 and the previous 7 patients who received the same dose had successful outcomes, the next patient will receive a pre-determined decrement of 0.75mg of bupivacaine. Otherwise, the dose will remain the same.

Inclusion Criteria: American Society of Anesthesiology (ASA) class 2 and 3 English speaking Gestational age > 36 weeks Scheduled for cesarean delivery under combined spinal epidural anesthesia 18 years or older BMI > 50 kg/m2 Exclusion Criteria: History of past or current intravenous drug or chronic opioid abuse Allergy or contraindication to any study medications Intrapartum cesarean delivery under epidural anesthesia Cesarean delivery under general anesthesia