Effective perioperative pain management is a significant challenge for healthcare practitioners, and the responsibility for inadequate pain control is often spread over many providers. The anesthesia care team, the “specialists” in perioperative medicine, can facilitate better postoperative pain management by developing and utilizing evidence-based pain management practices. Your perioperative partners will certainly notice how effective management of post operative pain relieves patient suffering, leads to earlier mobilization, shortened hospital and PACU stays, reduced hospital costs, and increased patient satisfaction. Pain management regimens often cannot be standardized. They are customized to the needs of the individual patient, taking into account medical, physical and psychological conditions as well as age, anxiety level, surgical procedure and response to agents given.
It is important to understand the pathways involved in the perception of pain. The surgical experience directly causes a noxious signal that stimulates peripheral nociceptors. Repeated stimulation leads to “central sensitization”, which is further enhanced by many tissue factors and inflammatory mediators released in the course of tissue injury. Sensitization in central pain pathways results in an enhanced responsiveness of pain transmission neurons. The prevention of “central sensitization” is the theoretical basis for the use of preemptive analgesia. In this process, by giving an analgesic before the onset of noxious stimuli, the nociceptive stimuli are not transmitted to the dorsal horn neurons and central alterations are thereby prevented, resulting in less pain and a shorter duration of symptoms.
Multimodal preemptive analgesia attacks multiple targets along the pain pathway. By modifying peripheral and central processing of noxious stimuli, hyperalgesia and allodynia are reduced. As a direct result, post-operative opioid use and opioid side effects are minimized.
Local anesthetics are critical when employing a multimodal approach. They can be injected at the site of incision to block stimulation at the origin of the peripheral nociception, at the peripheral nerve level, or at the central level via a spinal or epidural technique. Commonly used peripheral nerve blocks include the brachial plexus (interscalene, supraclavicular, infraclavicular, or axillary approach) to manage upper extremity pain, and femoral, sciatic or popliteal block for lower extremity pain. These neural structures are most commonly localized using ultrasound guidance, with or without nerve stimulation. A “single shot” of anesthetic agent can be injected or a peripheral catheter placed to initiate continuous infusions. For post-operative chest wall and abdominal pain, a paravertebral block can be similarly be utilized. This approach delivers local anesthetic to the vicinity of the spinal nerves after they exit from the neural foramens. Usually, multiple spinal levels need to be blocked individually to provide effective pain relief.
Systemic agents commonly used to provide effective preemptive analgesia include opiates, NMDA receptor antagonists, NSAIDS including the more selective COX-2 inhibitors, and acetaminophen. Synergism between medications decreases the required dosing and combining drugs can help to avoid the unwanted effects often seen with the higher doses needed in single agent therapy.
Opiates work by decreasing the transmission of nociceptive information at the brain and spinal cord levels thereby raising the pain threshold. The release of several neurotransmitters is inhibited by narcotic analgesics; these transmitters include acetylcholine, norepinephrine, dopamine, and substance P, a pain transmitter. Opiates can be administered systemically or neuraxially via the epidural or intrathecal route. NMDA receptors play a key role in central sensitization process described above. As such, NMDA receptor antagonists such as Ketamine produce a pre-emptive analgesic effect by modulating this sensitization response. This drug also has been shown to have intrinsic analgesic properties. It can be particularly useful as an adjunct when used in patients taking chronic opioids whose pain is poorly controlled despite high dose opioid therapy. NSAIDs given pre-emptively will reduce tissue inflammation and post-op pain. Selective COX-2 inhibitors provide the anti-inflammatory and analgesic benefits while minimizing GI adverse reactions common with non-selective NSAIDS. They are effective in reducing the amount of narcotic analgesics requested by patients and as a result, reduce opioid side effects. The intravenous form of acetaminophen is another potent agent with dramatic analgesic effects. It has been shown to be more effective than NSAIDS alone when used in combination therapies. IV administration has a more rapid and predictable onset of effect (5-10 minutes) and time to peak concentration (15 minutes) compared with rectal or oral administration (onset 10-60 minutes or more). Parenteral administration also bypasses initial hepatic metabolism and the “first pass effect”.
Other agents employed in the multimodal approach to post-operative pain control include tramadol, which acts as a central opioid agonist. This agent binds to mu opioid receptors and weakly inhibits norepinephrine and serotonin reuptake producing analgesia. Gabapentin acts by blocking calcium channels modulating excitatory neurotransmitter release. The use of transcutaneous electrical nerve (TENS) stimulation at paravertebral dermatomes corresponding to the surgical incision has also been reported to improve postoperative pain management. As this technique causes few adverse effects, its use as an adjunct to conventional pharmaceutical therapy should also be considered as part of multimodal analgesia in the future, particularly for patients in whom conventional analgesic techniques fail and/or are accompanied by severe medication related adverse events.
To effectively treat postoperative pain it is necessary to fully understand the intrinsic pain pathways. Using a multimodal approach that modulates and/or inhibits the transmission of pain signals at various points in the continuum allows multiple agents and therapies to have a synergistic effect, which will provide superior post op pain management for your patients. Always remember that these regimens should be carefully tailored to the needs of each individual patient.