Effect of Body Mass Index on the Dose of Intrathecal Hyperbaric Bupivacaine for Elective Cesarean Section
Condition: Pain; Obesity
MeSH terms: Obesity
Study type: Interventional

Summary: 
      Combined spinal - epidural (CSE) anesthesia is a well established technique used for elective
      Cesarean section. As its name suggests, it combines two anesthesia techniques - spinal and
      epidural. Adjusting the dose of freezing medication for body size is not as simple as giving
      a larger dose to a larger person. This study asks a simple, yet important question: does your
      body mass index (BMI) influence the amount of freezing medication needed for adequate CSE
      anesthesia for Cesarean section? BMI is a number calculated from your height and weight. In
      patients with a higher BMI, freezing medication appears to spread farther (to a higher level)
      in the spinal fluid. When freezing is too high, it can cause unwanted side effects.
      Therefore, in order to provide optimal spinal anesthesia to patients with a higher BMI, it
      may be advisable to administer less freezing medication. In this study, we want to find the
      ideal dose of freezing medication for patients with a higher body mass index, and compare it
      to the dose found to be ideal for patients with normal body mass index.
    

Detailed description: 
      Spinal anesthesia is the most common anesthetic technique used for Cesarean section. It
      offers many advantages over epidural and general anesthesia. However, one of the limitations
      of spinal anesthesia in Obstetrics is the use of a single shot technique as the continuous
      technique is associated with unacceptable incidence of PDPH. It is difficult to predict the
      exact level of sensory block because many factors affect the spread of local anesthetic
      injected into the CSF. Theoretically, obese patients may have greater intra-abdominal
      pressure, leading to compression of the inferior vena cava and engorgement of the epidural
      venous plexus, which in turn increases the pressure inside the epidural space. This augmented
      pressure is transmitted to the dural sac and diverge the CSF from the lumbosacral region,
      leading to a decrease in CSF volume. It has been demonstrated that the volume of CSF in
      lumbosacral region is an important factor affecting intrathecal spread of anesthetics.

      Our hypothesis is that obese women require less intrathecal hyperbaric bupivacaine than do
      normal weight women to achieve satisfactory surgical anesthesia for elective Cesarean
      section.Two groups of patients will be studied separately. Patients with BMI greater than or
      equal to 30 will be included in the obese group, also denominated study group. Patients with
      BMI less than 25 will be included in the normal weight group, also denominated control group.
      BMI will be calculated based on the patient's pre-pregnancy weight. For each group, the
      up-down sequential allocation method based on the Narayana rule will be used to find the
      minimum effective dose of intrathecal hyperbaric bupivacaine 0.75% associated with opioids
      necessary for satisfactory outcome in 95% of the pregnant women undergoing cesarean section,
      i.e. ED95.

      There are two possible outcomes in our study: a satisfactory outcome is defined if the
      sensory block reaches at least at T6 and the patient does not complain of any pain or
      discomfort that requires intraoperative supplemental drugs; an unsatisfactory outcome is
      defined if the sensory block reaches a level lower than T6 or the patient complains of pain
      or discomfort that requires intraoperative supplemental drugs. The decision whether or not
      the supplementation is required will be made exclusively by the patient, and not by the
      physician in charge.
    

Intervention name(s): bupivacaine 0.75% with fentanyl and morphine
Intervention type(s): Drug
Intervention description(s): the following administered once, by spinal injection; 9-12 mg 0.75% hyperbaric bupivacaine 10 mcg fentanyl 100 mcg morphine
Intervention MeSH terms: Fentanyl; Morphine; Bupivacaine
Allocation: Non-Randomized
Intervention model: Parallel Assignment
Masking: Single (Participant)
Primary purpose: Treatment
Keywords: Body mass index; Combined Spinal-Epidural Anesthesia; Cesarean section; Obesity