Although the process whereby noxious stimuli sensitize the nociceptive pathways has been elucidated in considerable detail (1), translating this knowledge into perioperative interventions that reduce pain and improve functional outcomes that may be related to pain has been more difficult than originally anticipated (2–4). Preemptive analgesia is one such strategy, but it is associated with uncertainty with respect to its definition, efficacy, and ultimate role in treating acute perioperative pain (3,5–7). We present a case in which unilateral epidural blockade enabled a patient to serve as her own control and which illustrates the capacity for surgery to produce long-term alterations in pain perception that can be modulated by preemptive epidural analgesia.
A healthy 45-yr-old woman presented for abdominal hysterectomy and cystocele repair. An epidural catheter was placed at the L3-4 interspace. After a 3-mL test dose, 15 mL of 2% lidocaine with 1:200,000 epinephrine was administered and followed by an additional 10 mL. When it became apparent that a unilateral left-sided block to T8 was present, general anesthesia was induced. During the 5-h surgical procedure, performed through a horizontal 15-cm incision, the patient received additional doses of lidocaine for a total of 55 mL. In the postanesthesia care unit (PACU), a left-sided unilateral sensory block to T8 was still appreciated, but the patient was complaining of right-sided abdominal pain of 7 on a 0–10 scale. The epidural catheter was replaced at the L2-3 interspace. Shortly after 12 mL of 0.2% ropivacaine was administered epidurally, the level of rest pain decreased to 0/10, and this was accompanied by a bilateral T8 sensory level to pinprick. Thereafter, an infusion of ropivacaine 0.1% with fentanyl 2 μg/mL at 6 mL/h with 4-mL boluses and a lockout of 20 min provided patient-controlled epidural analgesia. A total of 388 mL of the infusate was administered by the time the epidural catheter was removed on the second postoperative day (POD). Additional analgesics included an IV dose of ketorolac 30 mg on the operative day and oxycodone 5 mg with acetaminophen 325 mg twice on POD 2 after the epidural catheter was removed and once on POD 3. After discharge from the hospital on POD 3, analgesic therapy consisted of ibuprofen 400 mg twice daily for 4 days and oxycodone 5 mg with acetaminophen 325 mg, which was taken on four occasions. The last use of opiates occurred on POD 6. Thereafter, ibuprofen 400 mg was taken one or two times per week. After discharge from the PACU, the patient reported greater discomfort on the right side of the abdomen. Subjective pain levels at rest and with movement were assessed on each POD. Wound hyperalgesia was also determined on each side of the horizontal incision with an algometer (8,9). These data are shown in Figure 1. On POD 21, the first signs of what would become a small localized abscess on the left side of the incision were observed, and this ended further data collection.
This case demonstrates that even imperfect attenuation of input from intraoperative noxious stimuli can favorably alter pain perception for a period of weeks and illustrates some of the details of this process. Many factors may have influenced the patient's pain perception. Foremost is the possibility that, though not appreciated by the subject's surgeons, some aspect of the surgery may have produced an asymmetric level of tissue trauma. This may have altered pain perception on either side, either enhancing pain intensity on the side that did not experience intraoperative blockade or providing a relatively greater level of noxious input on the side that did. The unilateral blockade produced by the administration of local anesthetic through the epidural catheter may have represented a sufficiently inadequate positioning of the epidural catheter such that the blockade on the “blocked” side may have been less than is usually achieved with epidural anesthesia. However, none of this precluded a smaller, although far less than surgical, level of anesthesia on the opposite “unblocked” side. Furthermore, minimal or absent attenuation of noxious input on the “unblocked” side may have contributed to sensitization of spinal cord neurons on the contralateral side (10,11). The extent that two days of postoperative epidural analgesia contributed to the observed differences in pain perception is also unknown. Postoperative epidural analgesia may have limited further central sensitization on the side that was not effectively blocked during surgery. However, postoperative analgesia capable of limiting sensitization may also have been necessary on the side that was “blocked” during surgery, so that noxious postoperative stimulation does not overwhelm any intraoperative success at preventing sensitization (12). Although a small abscess did form at one side of the incision, no data were collected after the first signs of its appearance. Moreover, it formed on the “blocked” side and would have served only to exaggerate the level of pain on that side. Thus, with the exception of unappreciated asymmetries in the level of surgical trauma, which could differentially affect either side, the remaining considerations each contribute in a manner that would have led to greater symmetry in the pain experienced on each side. Consequently, the differences reported here could be considered a lower limit to what might be observed when comparing patients undergoing the same surgery with a bilateral epidural block with those without any intraoperative epidural blockade.
This report is consistent with the observation of short- and long-term benefits after a period of intraoperative epidural blockade for lower abdominal surgery (13–15). In one study (15), reductions in pain were noted three weeks, but not six months, after surgery. In another study (14), an increase in activity without differences in reported pain levels was observed approximately three weeks after surgery. This improvement in activity levels may have represented an increased capacity for exercise that is reported to accompany epidural analgesia (16). However, the current report demonstrates that long-term alterations in pain associated with movement are possible with perioperative epidural analgesia, and it is conceivable that these could influence activity levels. It is possible that activity levels influenced the overall pattern of pain with movement reported in Figure 1B. The reported pain levels remained relatively constant throughout the observation period, whereas the force necessary to elicit a painful sensation increased throughout, as shown in Figure 1C. One interpretation of this is that patients will titrate their activities to the point at which movements associated with these activities produce a tolerable level of discomfort. Over time, patients are able to increase their activity levels without increasing the level of pain they are willing to tolerate, so the pain they report with movement remains relatively constant. This is consistent with the increase over time in the amount of force necessary to elicit a painful sensation, shown in Figure 1C. Such an interpretation is supported by observations of different levels of activity but similar pain scores in patients receiving different intraoperative analgesic regimens (14).
The authors gratefully acknowledge comments from Christopher Wu, MD, and Srinivasa N. Raja, MD (Department of Anesthesiology and Critical Care Medicine, Johns Hopkins Medical Institutions, Baltimore, MD).
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