Since there have been no published dose-response studies investigating the effective analgesic dose of ropivacaine for use in a TAP block for post-Cesarean delivery analgesia, the investigators propose a study primarily examining the effect on 24 hour post-Cesarean delivery opioid consumption of using either a placebo, 0.25% ropivacaine, 0.5% ropivacaine, or 0.75% ropivacaine for TAP blocks.
Cesarean delivery is the most commonly performed surgical procedure in the United States today, with over 1.2 million cases performed in 2005. One of the most important aspects of cesarean delivery is the provision of safe, effective postoperative analgesia for the mother, while simultaneously ensuring minimal side effects for both the mother and neonate. Studies have suggested that a multimodal approach to post-cesarean pain utilizing both intravenous, oral, and neuraxial opioids and non-steroidal anti-inflammatory drugs is highly effective in providing effective analgesia. A significant component of post-cesarean pain is incisional pain from the Pfannenstiel incision on the anterior abdominal wall. The sensory supply to the skin, muscles, and parietal peritoneum of the anterior abdominal wall is derived from the anterior rami of T7-L1. After exiting the spinal column, these nerves proceed through the lateral abdominal wall within the transversus abdominal fascial plane, terminating in the anterior abdominal wall. Recent studies have suggested that blocking these afferent sensory nerves with local anesthetics, as part of a multimodal postoperative pain regimen, provides superior pain relief in terms of decreased pain scores and morphine consumption for up to 48 hours postoperatively. The technique utilized for these studies employed a surface anatomical approach to the transversus abdominal fascial plane via the lumbar triangle of Petit, a technique validated in both cadaveric and radiologic studies. However, as ultrasonography has emerged as the "gold standard" for initiating many nerve blocks, reports have described the successful use of ultrasound imaging for initiation of transversus abdominis plane (TAP) blocks for both abdominal surgeries and cesarean deliveries. In the published studies investigating the use of the TAP block for post-operative analgesia, either ropivacaine or bupivacaine was utilized in concentrations of 0.75% and 0.375%, respectively. Studies comparing ropivacaine with bupivacaine for use in interscalene, femoral, or sciatic nerve blocks have found no difference in terms of potency, time to onset or duration of postoperative analgesia between the two local anesthetics. Although no similar studies have been done with TAP blocks, one can assume that utilization of ropivacaine for this nerve block would yield similar results in terms postoperative analgesia. Moreover, the cardiotoxicity of ropivacaine has been shown to be significantly less than bupivacaine, making it a safer alternative for use in nerve blocks when used in high doses. Risk factors for respiratory depression after the administration of neuraxial opioids in the non-obstetric population include morbid obesity and obstructive sleep apnea. For the obstetric population, a study of 856 patients revealed that all 8 patients who experienced respiratory depression after intrathecal morphine for cesarean delivery were markedly obese. Furthermore, the onset of respiratory depression after intrathecal morphine can occur up to 12 hours after administration, a time period when the patient is not being as closely monitored as she is during the 1:1 nursing care in the recovery room. Therefore, it is the investigators policy on the Labor and Delivery unit to not administer intrathecal morphine to any parturient with a history of obstructive sleep apnea or a BMI \> 40 kg/m2. These patients often require intravenous opioid patient-controlled analgesia postoperatively, which has been shown to provide inferior pain relief and greater opioid consumption than neuraxial opioids. The current clinical standard is to administer the TAP block to those patients who have not received morphine in their neuraxial anesthetic. The TAP block offers a novel addition to the management of post-cesarean pain for this patient population.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
TREATMENT
Masking
DOUBLE
Enrollment
120
The abdominal muscle layers will be located by placing the ultrasound transducer perpendicular to the coronal anatomic plane at the T-10 dermatome level in the patient's midaxillary line. Under ultrasound guidance, a 70mm or 90mm, 21 gauge blunted Stimuplex needle will be advanced from the skin until the tip reaches the fascial layer between the internal oblique and transversus abdominis. 15ml of the study drug will be injected incrementally. The needle will then be removed and the process repeated in the same manner on the patient's opposite side.
The abdominal muscle layers will be located by placing the ultrasound transducer perpendicular to the coronal anatomic plane at the T-10 dermatome level in the patient's midaxillary line. Under ultrasound guidance, a 70mm or 90mm, 21 gauge blunted Stimuplex needle will be advanced from the skin until the tip reaches the fascial layer between the internal oblique and transversus abdominis. 15ml of the study drug will be injected incrementally. The needle will then be removed and the process repeated in the same manner on the patient's opposite side.
Northwestern University
Chicago, Illinois, United States
Morphine Equivalents 0-24 Hours (Mgs)
Total dose of morphine equivalents (IV equivalent of morphine) taken by the participant 0-24 hours after completion of the TAP block.
Time frame: 24 hours
Morphine Equivalents 24-72 Hours (Mgs)
Total dose of morphine equivalents (IV equivalent of morphine) taken by the participant 24-72 hours after completion of the TAP block.
Time frame: 24-72 hours
Morphine Equivalents Total (Mgs)
Total dose of morphine equivalents (IV equivalent of morphine) taken by the participant 0-72 hours after completion of the TAP block.
Time frame: 72 hours
Time to First PCA Request
The elapsed time in minutes of the first PCA (patient controlled analgesia) request in time (minutes) from the end of the TAP block.
Time frame: Elapsed time in minutes
Pain Scores at Rest
Pain scores at rest ( 0 low 10 high) using an 11 point VRS (verbal pain scale) at the following hour time points, at the first request for patient controlled analgesia (PCA) then at 2,6,24,and 74 hours after the first request for PCA (patient controlled analgesia).
Time frame: Request for first patient controlled analgesia then at 2,6,24,72 hours after initial PCA request
Pain Scores With Movement
Pain scores with movement ( 0 low 10 high) using an 11 point VRS (verbal pain scale) at the first request for patient controlled analgesia (PCA) then at 2,6,24,and 74 hours after the first request for PCA (patient controlled analgesia).
Time frame: First PCA request then at 2,6,24,72 hours after first PCA request.
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The abdominal muscle layers will be located by placing the ultrasound transducer perpendicular to the coronal anatomic plane at the T-10 dermatome level in the patient's midaxillary line. Under ultrasound guidance, a 70mm or 90mm, 21 gauge blunted Stimuplex needle will be advanced from the skin until the tip reaches the fascial layer between the internal oblique and transversus abdominis. 15ml of the study drug will be injected incrementally. The needle will then be removed and the process repeated in the same manner on the patient's opposite side.
The abdominal muscle layers will be located by placing the ultrasound transducer perpendicular to the coronal anatomic plane at the T-10 dermatome level in the patient's midaxillary line. Under ultrasound guidance, a 70mm or 90mm, 21 gauge blunted Stimuplex needle will be advanced from the skin until the tip reaches the fascial layer between the internal oblique and transversus abdominis. 15ml of the study drug will be injected incrementally. The needle will then be removed and the process repeated in the same manner on the patient's opposite side.
Pain Burden at Rest
Pain burden at rest calculated as area under the pain score \* time (hr) curve 0-72 hours.
Time frame: 72 hours
Pain Burden With Movement
Pain burden with movement calculated as area under the pain score \* time (hr) curve 0-72 hours.
Time frame: 72 hours