Pain
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Randomized Controlled Trial Clinical Trial
Lack of analgesic efficacy of oral delta-9-tetrahydrocannabinol in postoperative pain.
We have evaluated the efficacy of delta-9-tetrahydrocannabinol (delta-9-THC), the main psychoactive constituent of cannabis, in postoperative pain. In a randomized double-blind, placebo-controlled, single-dose trial, we investigated 40 women undergoing elective abdominal hysterectomy. Randomization took place when postoperative patient-controlled analgesia was discontinued on the second postoperative day. ⋯ Increased awareness of surroundings was reported more frequently in patients receiving delta-9-THC (40 vs 5%, P=0.04). There were no other significant differences with respect to adverse events. This study demonstrates no evidence of an analgesic effect of orally administered delta-9-THC 5 mg in postoperative pain in humans.
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Randomized Controlled Trial Comparative Study Clinical Trial
Naloxone provokes similar pain facilitation as observed after short-term infusion of remifentanil in humans.
In contrast to an expected preventive analgesic effect, clinical observations suggest that intraoperatively applied opioids can induce postoperative hyperalgesia. We tested the development of post-infusion hyperalgesia in a newly developed experimental model of electrically induced pain and secondary mechanical hyperalgesia. In a double-blind, placebo controlled, cross-over study, 13 subjects received either saline placebo, remifentanil (0.05 or 0.1 microg/kg/min) or naloxone (0.01 mg/kg). ⋯ Naloxone infusion similarly resulted in increased pain (anti-analgesia) (p<0.001) and mechanical hyperalgesia (p<0.01). Increased pain ratings following withdrawal of remifentanil significantly correlated to anti-analgesia evoked by the mu-opioid antagonist naloxone (p<0.01) and was of similar magnitude, suggesting inhibition of endogenous opioids as an underlying mechanism. In contrast, hyperalgesia after remifentanil was more pronounced than hyperalgesia after naloxone administration and did not correlate to the observed anti-analgesic effects, suggesting the involvement of additional receptors systems other than the endorphin system.
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Randomized Controlled Trial Clinical Trial
Short-term infusion of the mu-opioid agonist remifentanil in humans causes hyperalgesia during withdrawal.
Numerous animal studies suggest that acute and chronic exposure to opioids can be associated with the development of hyperalgesia, i.e. an increased sensitivity to noxious stimuli. Hyperalgesia has been documented during withdrawal and on occasion while animals were still exposed to opioids. A pivotal role in the genesis of opioid-associated hyperalgesia has been attributed to a pain facilitating system involving the N-methyl-D-aspartate (NMDA)-receptor. ⋯ Co-administration of the NMDA-receptor antagonist S-ketamine abolished observed enlargement of the hyperalgesic skin area. This study provides direct evidence in humans that short-term administration of an opioid can enhance hyperalgesia as observed during withdrawal and points to a potential role of the NMDA-receptor system in mediating such a hyperalgesic response. This study also points to a differential susceptibility of different pain modalities for the expression of hyperalgesia associated with opioid administration.
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Comparative Study
Gender and laterality differences in thermosensation throughout the perceptible range.
Several studies suggest that females exhibit greater sensitivity to experimentally induced thermal pain than males. These investigations have focused mainly on the sensory-discriminative rather than the affective aspect of pain. Moreover, potential gender differences for the affective components of innocuous thermal sensations have yet to be examined. ⋯ Ratings of unpleasantness also tended to be higher for the left vs. right hand, but this difference fell just short of statistical significance (P=0.06). These findings indicate that sex differences in thermosensory perception are not general, but occur only for the painful and affective components. Of particular note is the sex difference for affective but not intensive ratings of innocuous temperatures, revealing sex differences in thermal perception outside the nociceptive system.
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This paper reports upon: (1) the value of acceptance of pain in predicting well-being in patients suffering from chronic pain and (2) the construct validity of acceptance by comparing two questionnaires designed to measure acceptance (the Chronic Pain Acceptance Questionnaire, CPAQ, unpublished doctoral dissertation, University of Nevada, Reno, NV, 1992 and the Illness Cognitions Questionnaire, ICQ, J Consult Clin Psychol 69 (2001) 1026). The results of two independent cross-sectional studies are reported. Study 1 included 120 patients seeking help in tertiary care settings. ⋯ Acceptance in both instruments was strongly related to a cognitive control over pain. Study 2 further revealed that the correlation between the CPAQ and the ICQ is moderate, indicating that both instruments measured different aspects of acceptance. It is concluded that acceptance of chronic pain is best conceived of as the shift away from pain to non-pain aspects of life, and the shift away from a search for a cure with an acknowledgement that pain may not change.