Anesth Analg 1999;88:146-148
© 1999 International Anesthesia Research Society
REGIONAL ANESTHESIA AND PAIN MANAGEMENT
The Intensity of Preoperative Pain Is Directly Correlated with the Amount of Morphine Needed for Postoperative Analgesia
Robert Slappendel, MD*,
Eric W. G. Weber, MD*,
Marian L. T. Bugter, MD*, and
Ris Dirksen, PhD, MD
*Department of Anesthesiology, Sint Maartenskliniek; and
Department of Anesthesiology, University Hospital Nijmegen, Nijmegen, The Netherlands
Address correspondence and reprint requests to Robert Slappendel, MD, Department of Anesthesiology, Sint Maartenskliniek, P.O. Box 9011, 6500 GM Nijmegen, The Netherlands.
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Abstract
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The aim of this study was to examine whether severity of preoperative pain intensity is related to postoperative pain and morphine consumption. Sixty consecutive patients scheduled for total hip surgery during intrathecal anesthesia were studied. Preoperative visual analog scale (VAS) scores and analgesic intake was assessed 1 day before surgery. Three groups of patients were identified: those with mild pain (n = 12, VAS score 04), moderate pain (n = 18, VAS score 47), and severe pain (n = 28, VAS score 710). Postoperative pain scores were recorded in the first 24 h, as was the amount of morphine delivered by the patient-controlled analgesia pump. There were no differences among the groups in VAS scores at any time. Severe preoperative pain levels correlated with significantly greater postoperative morphine intake. The mean morphine intake during the first 24 h postoperatively was 19.2 mg in the mild pain group, 21.2 mg in the moderate pain group, and 29.5 mg in the severe pain group (P < 0.05 compared with both other groups). We conclude that patients with severe preoperative pain self-medicate to achieve postoperative pain scores equivalent to those of patients with mild and moderate pain and require a greater postoperative morphine intake for adequate analgesia than patients with mild or moderate preoperative pain.
Implications: In this study, we showed that severity of preoperative pain intensity relates to postoperative pain levels and morphine consumption. Patients scheduled for total hip surgery with severe preoperative pain require more postoperative morphine in the first 24 h.
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Introduction
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Severe postoperative pain can influence patient outcome after surgery (1,2). Undertreatment of pain may impede short-term recovery and may even have a detrimental long-term effect on health (3,4). Appropriate postoperative pain management contributes to earlier mobilization, shortened hospital stays, and reduced costs (5). Preclinical studies in experimental animals suggest that preemptive analgesia may improve the quality of postoperative pain management (6). Although the beneficial effects of preemptive analgesia are less evident clinically (7), severe pain syndromes, such as phantom limb pain, may be reduced or even prevented by preemptive epidural blockade (8). Thus, we proposed that preoperative pain can increase postoperative pain.
The aim of this study was to examine whether the severity of preoperative pain is related to postoperative pain levels and morphine intake in patients undergoing first hip replacement.
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Methods
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The ethical committee of our hospital approved the study. Sixty consecutive patients suffering from osteoarthritis of the hip scheduled for first total hip surgery were included. Preoperative visual analog scale (VAS) scores and analgesics were assessed 1 day before surgery. Three groups of patients were recognized: patients with mild pain (VAS score 04), moderate pain (VAS score 47), or severe pain (VAS score 710).
All patients began taking a nonsteroid antiinflammatory drug, nabumetone 2000 mg, on the day of surgery and continued this dose for at least 3 days postoperatively. All patients were premedicated with midazolam 5, 7.5, or 10 mg (i.e., ±0.1 mg/kg) orally 1 h before spinal anesthesia. All patients received intrathecal anesthesia with bupivacaine 20 mg and 0.1 mg morphine dissolved in 4 mL. At the patient's request, further sedation was given using midazolam 1 mg every 5 min until the desired level of sedation was achieved. In the postoperative period, pain was treated with oral nabumetone 2000 mg once a day, starting on the day of surgery. A patient-controlled analgesia (PCA) pump was connected immediately after surgery and set at the baseline infusion rate of 0.5 mg/h morphine, with bolus dose 1 mg of morphine set at a minimum interval of 5 min.
Noninvasive blood pressure, electrocardiogram, transcutaneous oxygen saturation, and respiratory frequency were continuously monitored during anesthesia and in the intensive care unit during the first 24 h after surgery. All postoperative side effectspain (VAS scores), postoperative nausea and vomiting, itching, urinary retention (>400 mL), hypotension (decrease of mean arterial blood pressure to <80% of its preoperative value)were registered during 3-h observation periods, as was the amount of morphine administered through the PCA pump.
Statistical analysis was performed by using analysis of variance, followed by Newman-Keuls post hoc analysis when appropriate. P value <0.05 was considered significant. Data are expressed as mean ± SD.
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Results
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Two patients were excluded from the study because their postoperative records were not complete. The group with mild preoperative pain consisted of 12 patients, the group with moderate pain included 18 patients, and the group with severe pain consisted of 28 patients.
Age, weight, height, and preoperative intake of nonsteroid antiinflammatory drugs were not different among the three groups (Table 1). None of the patients used narcotics preoperatively. The incidence of postoperative side effects, nausea and vomiting, urinary retention, and itching were not different among groups. Respiratory depression did not occur in any patient.
Excellent pain relief was achieved in all groups in the postoperative period (Fig. 1). There were no differences among groups in VAS scores during any of the 3-h observation periods. Likewise, the total VAS scores were not different. The morphine intake during the first 24 h was different among the three groups (analysis of variance: F[2.55]) = 4.54, P = 0.015), and post hoc analysis showed the greatest intake by patients in the severe pain group (Fig. 2).

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Figure 1. Pain visual analog scale (VAS) scores in relation to time after surgery. 0 = no pain and 10 = most severe pain. There were no statistical differences among groups.
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Figure 2. The mean amount of morphine administered via the patient-controlled analgesia (PCA) pump in the first 24 h postoperatively. VAS = visual analog scale. 0 = no pain and 10 = most severe pain. The severe pain group is significantly different from the mild and moderate pain groups.
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Discussion
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In this study, we showed that patients with severe preoperative pain require an approximately 50% greater morphine intake by PCA pump to attain the same level of postoperative analgesia in the first 24 h after total hip surgery than patients with mild or moderate preoperative pain. In addition, patients want to lower their pain scores to the same range regardless of the original score.
Pain is an extremely complex process that involves the interaction of an array of neurotransmitters and neuromodulators at all levels of the neuraxis (911). A long duration of severe pain may change the processing of pain; for instance, by involving pain memory and/or neuroplastic changes (10,12). Identification of various receptors and processes that are involved in the transmission of pain at the spinal level has led to the use of new drugs and techniques in pain management (9). These include the use of preemptive analgesia and techniques such as intrathecal drug administration and epidural spinal cord stimulation (9,13,14). For example, the preoperative administration of sodium naproxen or IV morphine significantly reduces the analgesic requirements in the postoperative period (13). Preemptive epidural morphine was found to be superior to epidural morphine given postoperatively for pain relief after lumbar laminectomy (15). Pre- or postincision administration of either intrathecal morphine or bupivacaine reduced hyperalgesia on the day of surgery (6). In our study, all of these measures were included to minimize postoperative pain and postoperative morphine requirements: i.e., administration of nabumetone preoperatively and presurgical intrathecal administration of bupivacaine and morphine. The relationship between preoperative pain level and postoperative morphine intake indicates that preoperative assessment of pain in an individual patient allows anticipation of the patient's needs; this can lead to better postoperative pain relief.
Our data contrast with those of a recent study on major joint surgery, in which no such relationship was found (16). However, in that study, five types of orthopedic surgery were included (total hip arthoplasty, total knee arthroplasty, total hip revision, total knee revision, and total knee bilateral), and as well as various preoperative diagnoses (osteoarthritis, rheumatoid arthritis, degenerative joint disease, avascular necrosis, juvenile rheumatoid arthritis, and "other"). Differences in types of surgeries and underlying diagnosis could affect the degree of postoperative pain. Further, the authors' analysis in that study consisted only of a questionnaire dealing with patient satisfaction that was completed on the day of discharge.
Severe chronic pain syndromes require specific attention by the anesthesiologist and other medical attendants. Preemptive analgesia in patients with severe chronic pain was effective in avoiding the postoperative pain problem of phantom limb (8). Our study shows that pain perseveres in the more common pain syndromes, such as osteoarthritis of the hip. To improve the quality of postoperative pain control, one may consider starting analgesic treatment in the preoperative period. We wonder whether such improvement can be achieved by simple measures, e.g.,: by performing total hip surgery in an earlier phase when pain is not yet severe; by extended pretreatment with nonsteroidal antiinflammatory drugs; or by the administration of a larger preoperative dose of intrathecal morphine. Specific attention to this aspect of the total hip procedure may improve the outcome.
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References
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Accepted for publication October 2, 1998.
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