Transversus Abdominis Plane (TAP) Block for Cesarean Section

The purpose of this study is to determine whether a transversus abdominis plane (TAP) block with Clonidine added to the injectate (Clo-TAP) performed approximately 2hrs after the cesarean section (CS) will decrease the amount of postoperative hyperalgesia and ultimately reduce post-CS chronic pain.

Acute severe pain after cesarean section (CS) occurs more often than is thought and 10-15% of the women having a cesarean section develop chronic pain (Kehlet et al. 2006). With over 1.3 million cesarean deliveries per year in the US, this is bound to create a significant health problem. One way to address this health burden is to refine techniques that may help control the pain women experience after CS and ultimately reduce the potential to develop chronic pain. The purpose of this randomized, double-blinded study is to evaluate the ability of an established anesthetic technique called the transversus abdominis plane (TAP) block to reduce the amount of hyperalgesia women develop around their incision after CS. Measuring the amount of punctuate mechanical hyperalgesia is used as a tool to assess postoperative central sensitization (Lavand'homme et al. 2005), which contributes to postoperative acute pain. Since postoperative acute pain has been shown to be predictive of developing postoperative chronic pain (Eisenach et al. 2008; Yarnitsky et al. 2008), an effective TAP block could help diminish the incidence of chronic pain after CS. In addition, blood samples will be collected for future genetic analysis and we will test preoperatively for mechanical temporal summation (mTS) to evaluate CNS (central nervous system) sensitization and nociceptive system hyperexcitability and see if this correlates with the amount of hyperalgesia women develop around their incision after surgery. The primary aim of this study is to evaluate the benefits of two different solutions injected by TAP block technique on postoperative peri-incisional hyperalgesia.