***TASK*** the task is to summarize an input biomedical literature in six sentences 
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    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
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    Input: Background Although acute tolerance to opioids , especially to remifentanil , has been demonstrated consistently in animal studies , the results of clinical trials in humans are controversial . The aim of this study was to determine whether intraoperative infusions of remifentanil used as an adjuvant in general anesthesia result in acute tolerance , an event manifested by increased postoperative pain and a higher opioid requirement than usual . Methods Sixty patients who underwent surgery under general anesthesia for spinal fusion were r and omly assigned to receive sevoflurane-nitrous oxide-oxygen ( group SO , n = 20 ) , sevoflurane-remifentanil-nitrous oxide-oxygen ( group SR , n = 20 ) , or propofol-remifentanil-oxygen ( group PR , n = 20 ) in a double-blinded manner . All patients within 1 hour after induction received PCA ( fentanyl 0.4 µg/kg/ml and ondansetron 16 mg ) administered intravenously at a basal infusion rate of 1 ml/h , after being intravenously injected with a loading dose of fentanyl ( 1 µg/kg ) . Data for fentanyl requirement , verbal Numerical Rating Scale ( NRS ) pain score at rest , and presence of nausea or vomiting were collected at 1 , 24 , and 48 hours after surgery . Results We did not find any significant difference in postoperative PCA fentanyl requirements , NRS or side effects among the groups . Conclusions Remifentanil as an adjuvant to sevoflurane or propofol in general anesthesia for adults having surgery for spinal fusion does not appear to cause acute opioid tolerance or hyperalgesia in patients . However , further studies are needed to eluci date whether sevoflurane and propofol exert a clinical ly significant effect on opioid-induced tolerance or hyperalgesia and whether this effect is related to the age of the patient , the dose and duration of remifentanil given and the intensity of pain experienced postoperatively Background Adenosine has been shown to have a wide spectrum of unique pain-relieving effects in various clinical situations . The aim of this study was to investigate the effects of intraoperative adenosine infusion on acute opioid tolerance and opioid induced hyperalgesia induced by remifentanil in adult patients undergoing tonsillectomy . Methods For this study , ninety patients were r and omly allocated into groups that receive either adenosine ( adenosine group ) or saline ( remifentnail group ) intravenously under remifentanil based anesthesia and saline ( sevoflurane group ) under sevoflurane anesthesia . The patients in adenosine group received adenosine at dose of 80 µg/kg/min , and those in remifentnail group and sevoflurane group received an equal volume of saline 10 minutes after the induction of anesthesia until the end of surgery . Intraoperative evaluation included time weighted mean remifentanil dose , and postoperative evaluations included degree of pain severity at 1 , 6 , 12 , and 24 hours , time to first postoperative requirement , and analgesic dose required during 24 hours after operation . Results Time weighted mean remifentanil dose during intraoperative period in adenosine group was significantly lower than that of remifentnail group ( P = 0.00 ) . The first postoperative analgesic were required earlier in remifentanil group than sevoflurane group or adenosine group ( P = 0.00 ) . Pethidine requirement during 24 hours in sevoflurane group and adenosine group was significantly lower than that of remifentnail group ( P = 0.00 ) . The visual analog scale scores for pain in sevoflurane group and adenosine group were significantly lower than those of remifentnail group for 12 hours after operation ( P = 0.00 ) . Incidence of hypotension ( P = 0.024 ) and number of ephedrine administered ( P = 0.011 ) in adenosine group were significantly higher than those of sevoflurane group . Conclusions The above results suggest that intraoperative adenosine infusion prevent acute opioid tolerance and opioid induced hyperalgesia induced by remifentanil Purpose In a r and omized , double-blind clinical trial , we compared the postoperative analgesic effect and dose consumption of fentanyl after intraoperative high dose and low dose fentanyl administration . Methods Sixty ASA class I to II female patients undergoing total abdominal hysterectomy ( TAH ) , were r and omly allocated to receive either 1 μg · kg−1 ( low dose group , n = 30 ) or 15 μg · kg−1 ( high dose group , n = 30 ) fentanyl during induction of anesthesia . Anesthesia depth was maintained with inhalation of halothane in the low dose group , or combined with 100 μg · hr−1 fentanyliv in the high dose group . Postoperative pain was treated with an intravenous  patient-controlled analgesia system and was assessed with a visual analog pain score at rest . Results Patients in the high dose group had higher pain intensity at four and eight hours postoperatively , more fentanyl consumption and a greater incidence of emesis in the postoperative period of 16 hr than those in the low dose group ( P < 0.05 ) . Heart rate , blood pressure , and respiratory rate were similar between the two groups . Conclusion : Our results suggest that acute fentanyl tolerance develops after administration of high dose fentanyl during surgery and , consequently , results in a higher postoperative pain intensity and greater fentanyl consumption . RésuméObjectifComparer , dans un essai clinique r and omisé , à double insu , l’effet analgésique postopératoire et la consommation de fentanyl après l’administration peropératoire de forte et faible dose de fentanyl . MéthodeSoixante patientes de classes I et II ASA devant subir une hystérectomie abdominale totale ( HAT ) ont été réparties au hasard et ont reçu , soit 1 μg · kg−1 ( groupe de faible dose , n = 30 ) , soit 15 μg · kg−1 ( groupe de forte dose , n = 30 ) de fentanyl pendant l’induction de l’anesthésie . La profondeur de l’anesthésie a été maintenue avec l’inhalation d’halothane dans le groupe à faible dose , ou en combinaison avec 100 μg · hr−1 de fentanyliv , dans le groupe à forte dose . La douleur postopératoire a été soulagée avec une analgésie intraveineuse contrôlée par la patiente et évaluée , au repos , à l’aide d’une échelle visuelle analogue . RésultatsLes patientes qui ont reçu la forte dose ont connu des douleurs plus intenses quatre et huit heures après l’opération , ont pris davantage de fentanyl et ont eu une plus gr and e incidence de vomissements dans les 16 h qui ont suivi l’opération , que celles qui ont reçu une faible dose ( P < 0,05 ) . La fréquence cardiaque , la tension artérielle et le rythme respiratoire n’ont pas présenté de différence intergroupe . Conclusion Les résultats suggèrent qu’une tolérance soudaine au fentanyl se développe après l’administration peropératoire d’une forte dose et qu’elle entraîne , par conséquent , des douleurs postopératoires plus intenses et une plus gr and e consommation de fentanyl OBJECTIVE One of the strategies to attenuate opioid-induced hyperalgesia ( OIH ) may be to decrease intraoperative doses of opioids by using target-controlled infusion ( TCI ) . DESIGN Double-blind and r and omized study . SETTING A single university hospital . PARTICIPANTS Forty American Society of Anesthesiologists II to III patients scheduled for elective cardiac surgery . INTERVENTIONS patients were r and omized to 1 of the 2 groups : 1 group received an infusion of intraoperative remifentanil using TCI ( target : 7 ng/mL ) , and the 2nd one was given an intraoperative continuous infusion ( CI ) ( 0.3 μg/kg/min ) . The anesthestic protocol and postoperative pain management were the same in both groups . The extent of mechanical dynamic hyperalgesia on the middle line perpendicular to the wound was considered the primary endpoint . The secondary endpoints were other results of dynamic and punctuate hyperalgesia until postoperative day 7 , visual analog scale ( VAS ) and verbal rating scale ( VRS ) scores , and total morphine consumption until postoperative day 2 . MEASUREMENTS AND MAIN RESULTS Morphometric and demographic characteristics and duration of surgery were comparable in both groups . Intraoperative remifentanil consumption was greater in CI than in TCI group ( 5,329 [ 1,833 ] v 3,662 [ 1,160 ] μg , p = 0.003 ) . During the first 44 hours , there were no differences in morphine consumption , VAS , and VRS . The extent of hyperalgesia was significantly lower on postoperative days 1 , 2 , and 4 in the TCI group than in the CI group on the 3 evaluated lines ( p < 0.05 ) . Punctuate hyperalgesia evaluating 3 different points was lower in the TCI than in the CI group from postoperative day 1 until postoperative day 7 ( p < 0.05 ) . CONCLUSIONS The intraoperative decrease of opioid consumption when comparing the CI versus TCI mode of administration of remifentanil led to less OIH after cardiac surgery BACKGROUND : IV morphine titration ( IMT ) is widely used in the postanesthesia care unit to achieve pain relief . Numerous factors contribute to variability in postoperative pain or morphine consumption . We analyzed prospect ively the pre- and intraoperative predictive factors of severe postoperative pain defined as a dose of IMT > 0.15 mg/kg or a failure of IMT . METHODS : We assessed the role of preoperative information about pain , medical treatments , and intraoperative events and their role on postoperative pain . After IMT , patients were divided into two groups : severe pain ( SP ) and nonsevere pain . Data are expressed as mean ± sd . RESULTS : Three hundred forty-two patients were included in the study : 200 ( 58 % ) in the nonsevere pain group and 142 ( 42 % ) in the SP group . Using a univariate analysis , there was no significant difference between groups related to medical or surgical history except for more frequent preoperative treatments in the SP group ( P < 0.05 ) . Duration of the surgical procedure and anesthesia were longer in the SP group ( P < 0.001 ) . The dose of sufentanil and visual analog scale scores before and at the end of IMT were higher in the SP group ( P < 0.001 ) . Using a multivariate analysis , a high dose of  intraoperative opioid ( sufentanil dose > 0.6 μg/kg ) ( Odds ratio = 2.68 , P < 0.001 ) , a general anesthetic procedure ( Odd ratio = 3.96 , P = 0.03 ) , and the use of preoperative analgesic drugs ( Odds ratio = 1.91 , P < 0.01 ) were independent factors associated with severe postoperative pain . CONCLUSION : A higher intraoperative dose of sufentanil , general anesthesia , and preoperative treatment with analgesics were significantly associated with severe postoperative pain Background Pregabalin is an antiepileptic drug that is effective for treating postoperative pain , neuropathic pain , anxiety , and hemodynamic instability . The aim of this study was to investigate the effect of a single preoperative dose of pregabalin in patients with opioid-induced hyperalgesia ( OIH ) . Methods Ninety ASA I-II patients undergoing laparoendoscopic single-site urologic surgery were r and omly assigned to one of the following three groups that received either pregabalin or placebo 1 h before anesthesia and an intraoperative remifentanil infusion . Group plL received placebo and 0.05 µg/kg/min remifentanil , group plH received placebo and 0.3 µg/kg/min remifentanil , and group prH received 300 mg pregabalin plus 0.3 µg/kg/min remifentanil . The primary endpoint was pain intensity upon movement 1 , 6 , 12 , and 24 h after surgery . Secondary endpoints were the area of hyperalgesia and mechanical hyperalgesia threshold 24 h after surgery , time to first postoperative analgesic requirement , and cumulative postoperative volume of morphine administered via a patient-controlled analgesia ( PCA ) pump over 24 h. Results The time to first postoperative analgesic requirement in group plH was significantly shorter than that in group plL. The injected PCA volume was significantly greater in group plH than that in the other two groups . Postoperative pain intensity in group plH was significantly greater than that in the other two groups at 6 , 12 , and 24 h after surgery . The mechanical hyperalgesia threshold and the area of hyperalgesia around the surgical incision 24 h after surgery in group plH differed significantly from those in the other 
    Output:
    
These results were mainly associated with the use of remifentanil .
DISCUSSION This review suggests that high intra-operative doses of remifentanil are associated with small but significant increases in acute pain after surgery