The Time Required to Remain Sitting After Spinal Anesthesia for 50% of Patients to Not Experience Hypotension
Description:
Up down sequential analysis is a method developed by Dixon to determine the point where 50%
of people will have a positive response and 50% will have a negative response to an
intervention. It is a very powerful technique that has been used to determine the median
effective dose (referred to as ED50) of many medications. Using this method, patient number 1
is given a certain amount of the intervention being studied. If patient 1 has the desired
response, patient 2 in the series is given less of the intervention, and if patient 1 does
not have the desired response, patient 2 is given more of the intervention. This is repeated
through a series of patients until the dose where there is a 50% response rate is determined.
In this study, we wish to use up down sequential analysis to determine the time period a
patient should remain seated after intrathecal injection of hyperbaric medication that result
in a 50% rate of hypotension, what we will call the ET50 (Estimated Time for 50% of patients
to have hypotension). We would like to explore this relationship with 2 clinically used doses
of hyperbaric bupivicaine.
Patients scheduled for cesarean delivery arrive in the birthing centre 1-2 The patients will
be given the same anesthetic care routinely used in the birthing centre, except that we will
control the time that the patient remains seated after injection of intrathecal hyperbaric
bupivacaine. The baseline blood pressure and heart rate will be recorded. After intravenous
access is obtained, an infusion of normal saline will be commenced at a rate of 100 cc per
hour. The patient will be brought to the operating room, and the standard monitors will be
placed. The intravenous fluid will be administered at a rate of 500 ml per hour for one hour.
The patient will be placed in a sitting position. The landmarks of the spinal canal will be
identified with an ultrasound, then using sterile technique, an epidural catheter will be
placed in the L2-L3 spinal interspace, and then a 27 gauge whitacre needle will be used to
access the intrathecal space at the L4-L5 spinal interspace. After identification of the
intrathecal space, hyperbaric bupivacaine will be injected over 30 seconds. The patient will
then be left in the sitting position for the predetermined time. The patient will then be
placed supine, with a 15 degree wedge under the right hip. The noninvasive blood pressure
will be set to measure the blood pressure every minute. Hypotension will be defined as a drop
in blood pressure to more than 20% of the patient’s preoperative blood pressure. The
medications used for treatment of hypotension will be left to the discretion of the treating
anesthesiologist. The height of the anesthetic blockade will be measured bilaterally with ice
at 1, 5, 10, 15, and 20 minutes after the patient has been placed supine. If the block has
not reached T6 by 20 minutes after the patient has assumed the supine position, or if the
patient experiences any pain during the cesarean delivery, 5 ml of 2% lidocaine will be
administered through the epidural catheter. If this does not suitably manage the pain, the
treating anesthesiologist will be allowed to manage the pain as they see fit.
Determination of the time in the sitting position:
The study patient will be considered a success if the duration of time in the sitting
position results in no pre-delivery hypotension. The study patient will be considered a
failure if the time spent in the sitting position results in pre-delivery hypotension. A
patient will be considered an indeterminate result if the ice test fails to show a block
reaching T6 by 15 minutes. A patient following a success will be left in the sitting position
for 15 seconds less than the preceding patient, and the patient following a failure will be
left in the sitting position for 15 seconds more than the preceding patient. A patient
following an indeterminate result will remain in the sitting position for the same time as
the preceding patient. The first patient in the series will be left in the sitting position
for 3 minutes after the injection of the intrathecal medication.
Dosage determination and blinding:
To see if ET50 is dependent on the dosage of medication given, we will determine the ET50 for
2 doses of hyperbaric bupivicaine. Both of the doses we will study are used routinely in
clinical practice. Using a computerized randomization schedule, we will randomly assign
patients to receive either 2 ml or 1.5 ml of 0.75% hyperbaric bupivacaine, for a total of 15
mg or 12.5 mg of bupivacaine respectively.
Recorded data:
We will record the demographic data of the patient, including height, weight, age, gravidity,
parity, weeks gestation, and reason for the cesarean delivery. We will record the medical
history of the patient, and medications that the patient takes. We will record the admission
heart rate, blood pressure and saturation. We will record the time that the intrathecal
medication is injected, and the time that that the patient remains seated after the spinal
anesthesia has been commenced. We will record the level of anesthetic blockade at
1,5,10,15,and 20 minutes after the patient has been placed supine. We will record the blood
pressure, and heart rate every minute after the patient has been placed supine until the baby
has been delivered. We will record any medications used to treat blood pressure before the
baby has been born, and any medications used to treat breakthrough pain. We will record the
birth time, the baby gender, weight, apgar, and umbilical cord pH.
Condition:
Hypotension
Treatment:
2 ml bupivacaine
Start Date:
March 2012
Sponsor:
McGill University Health Centre/Research Institute of the McGill University Health Centre
For More Information:
https://clinicaltrials.gov/show/NCT01561274