Epidural analgesia (pain relief) is an effective treatment for post-surgical acute pain. The factors that determine the effectiveness of pain relief with epidural analgesia have been studied almost exclusively in the lumbar (low back) spaces for obstetrics (childbirth). These factors include the design of the epidural catheter, the type and dose of medications, and the volume of solution used. One of the important issues specific to the catheter design is whether the tip has a one end-hole, or multiple side holes. The number of holes has been suggested to affect the spread of epidural anesthetic over time, especially with low volume solutions. This has been demonstrated in older, stiffer epidural catheter designs, but has not been shown to be true with the newer, flexible epidural catheters.
The thoracic (upper back) epidural analgesia is widely employed for a many types of surgical pain. While the mechanism of pain relief is similar to that in the lumbar space, there may be differences between the two sites. Firstly, thoracic catheters tend to use low volume, high concentration medication solutions, which likely do not spread as effectively. Secondly, the thoracic catheters often need to be used for prolonged periods of time. Whereas the typical obstetric epidural is used for less than 12 hours, the post-surgical catheter is typically required for one to three days (or more). Finally, the thoracic space is narrow, with a thinner thecal sac, which might promote a difference in the spread of epidural solution.
Thoracic epidural analgesia is routinely used to control post-operative pain for a wide variety of surgical procedures. Based on the improved effectiveness of the one end-hole flexible epidural catheter in obstetrics, this design is commonly used in thoracic epidural analgesia. It has been observed that thoracic epidurals are somewhat less effective after a period of time when compared to the effectiveness of labor epidurals. This may be in part due to the inappropriate assumption that the thoracic epidural space of a post-surgical patient is the same as the lumbar space of a parturient.
The investigators seek to determine whether there is a difference in the analgesia provided by a thoracic multi-port epidural catheter when compared to a thoracic uniport epidural catheter as measured by pain scores, medication given for breakthrough pain, and need to add intravenous opioids. As mentioned previously, these catheters have been studied extensively in laboring patients but there is a striking paucity of literature regarding how anesthetic solutions spread in the thoracic epidural spaces of non-pregnant post-surgical patients and how this may be affected by catheter type. If the hypothesis is supported by results, it may change the practice within the study institution, and possibly, on a much larger scale. This study may also provide a foundation for further research into the physiology of the thoracic epidural space, how it differs from the lumbar epidural space, and how a medication solution spreads within this unique space.
