If you've ever given patients opioids for post-operative pain and found that the drugs failed to achieve the needed relief, here's some enlightening—but troubling—news. A recent comprehensive summary of basic and clinical research shows that, under certain conditions, including some post-operative conditions, opioids actually worsen pain. Researchers believe this to be a physiologic phenomenon distinct from that experienced during opioid withdrawal or maintenance. It's a vexing problem, because we don't yet know which patients will be helped by opioids and which patients will not. This, along with the fact that we have lost access to COX-2 inhibitors due to their cardiovascular risks, has left us with an analgesic gap.
Of course, challenges create opportunity, and one tremendous opportunity lies in peripheral nerve blocks, or PNBs. While uncertainty may surround opioids, the efficacy and safety of peripheral nerve blocks is proven. These blocks carry few risks, do not interact with systemic analgesics, and render excellent pain control.
The new formula for pain control should use peripheral nerve blocks as the analgesic foundation. By adding small or even micro-doses of other analgesics on top of nerve blocks, we can create multimodal regimens that may combat even severe post-op pain more effectively than opioids, with few or no side effects.
Clinical studies show that when we add very small doses of intravenous ketamine as an adjuvant for surgical procedures using interscalene and continuous femoral nerve blocks, for example, we achieve additional analgesia that lasts beyond the duration of action of either drug. And although more research needs to be done, mounting clinical data also show that small doses of oral anticonvulsant drugs like gabapentin may reduce both spontaneous and motion-evoked post-op pain, alleviate anxiety, accelerate functional recovery, and reduce chronic post-surgical pain.
Thanks to peripheral nerve blocks, we are already reducing patient stays while improving comfort levels. Our total shoulder patients, for example, typically stay just one night and leave our facility with continuous infusions in place. As we move further into the era of ambulatory surgery, we can build upon this success to create new multimodal regimens that hold great potential to provide pain control superior to any that our patients have ever experienced.
Model at left adapted from Celerier E, et al. Progressive enhancement of delayed hyperalgesia induced by repeated heroin administration: A sensitization process. J Neurosci. 2001 Jun 1;21(11):4074-80.
Dr. Greengrass has lectured nationally and internationally on regional anesthesia. He is Associate Professor of Anesthesiology at the Mayo Medical School.