***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Background The minimum local analgesic concentration ( MLAC ) has been defined as the median effective local analgesic concentration ( EC50 ) in a 20-ml volume for epidural analgesia in the first stage of labor . The aim of this study was to determine the relative local anesthetic sparing efficacies of intravenous and epidural fentanyl by comparison of their effects on the MLAC of bupivacaine . Methods In this double-blind , r and omized , prospect i ve study , 84 parturients at ≤ 7-cm cervical dilation who requested epidural analgesia were allocated to one of two groups . After lumbar epidural catheter placement , 20 ml bupivacaine ( n = 44 ) or bupivacaine with 3 & mgr;g/ml ( 60 & mgr;g ) fentanyl ( n = 40 ) was administered . The plain bupivacaine group then received 60 & mgr;g intravenous fentanyl . The bupivacaine – fentanyl group received intravenous saline . The concentration of bupivacaine was determined by the response of the previous patient in that group to a higher or lower concentration using up – down sequential allocation . Analgesic efficacy was assessed using 100-mm visual analog pain scores , with ≤ 10 mm within 30 min defined as effective . Results The MLAC  of bupivacaine – intravenous fentanyl was 0.064 % wt/vol ( 95 % confidence interval , 0.049–0.080 ) , and the MLAC of bupivacaine – epidural fentanyl was 0.034 % wt/vol ( 95 % confidence interval , 0.017–0.050 ) . Epidural fentanyl significantly increased the analgesic potency of bupivacaine  by a factor of 1.88 ( 95 % confidence interval , 1.09–3.67 ) compared with intravenous fentanyl . The epidural fentanyl group demonstrated significantly higher dermatomal spread ( P = 0.0064 ) and increased pruritus ( P = 0.01 ) . Conclusions Epidural fentanyl significantly reduced the MLAC of bupivacaine when compared with intravenous fentanyl for the parturients in this study . The significantly enhanced local anesthetic sparing , dermatomal level , and pruritus with epidural fentanyl suggest a primarily spinal site of action BACKGROUND The pharmacokinetics of remifentanil suggests that it may be suitable for analgesia during labour . METHODS In an open pilot study , 36 women requesting meperidine for analgesia were recruited early in labour and r and omized to receive either meperidine i.m . or remifentanil given as patient-controlled analgesia ( PCA ) .  Pain severity , sedation and anxiety were assessed with visual analogue scales and overall effective analgesia was assessed by the woman and midwife . RESULTS The pain scores were lower in the remifentanil group : median pain score at 60 min was 72 mm for meperidine and 48 mm for remifentanil ( P=0.004 ) and median maximum pain score during the first 2 h was 82.5 mm for the meperidine group and 66.5 mm for the remifentanil group ( P=0.009 ) . Both the midwives ' and the women 's assessment s of overall effective analgesia were higher in the remifentanil group [ Likert scale ( 5 = excellent to 1 = poor ) : chi2=12.10 , P=0.002 for mothers ' assessment ; chi2=12.80 , P=0.002 for midwives ' assessment ] . CONCLUSION In this pilot study , remifentanil by PCA gave better pain relief to mothers in labour than intramuscular meperidine . However , remifentanil is a potent respiratory depressant and adequate continuous monitoring is necessary OBJECTIVE This study was undertaken to evaluate whether the administration of meperidine decreases the length of labor in patients with a diagnosis of dystocia during the first stage of labor . STUDY DESIGN Women with term singleton pregnancies who received a diagnosis of dystocia and required an active management of labor were r and omly assigned to receive either 100 mg of meperidine or placebo . The primary outcome measure was length of labor . RESULTS Four hundred seven pregnant women were included . There were no significant statistical differences between meperidine and placebo groups in length of labor and operative delivery rates such as forceps and cesarean section by intention-to-treat analysis . Low Apgar scores , umbilical artery acidosis , and admission to neonatal care units were increased in the meperidine group . CONCLUSION Because of the absence of any benefits in patients with dystocia in labor and the presence of harmful effects on neonatal outcomes , meperidine should not be used during labor for this specific indication The aim of this quasi‐experimental study was to examine the effects of maternal pethidine during labour on the developing breast feeding behaviour in infants in the first 2 h after birth compared with infants not exposed to pethidine . Forty‐four healthy infants were observed immediately after birth . They were placed skin‐to‐skin on their mothers ' chests . The development of mouth and sucking movements as well as rooting behaviour and state of sleep/wakefulness were noted . The observer was blind as to the pain relief the mother had received during labour . Of the 44 mothers 18 had received pethidine .  The main findings were that infants exposed to pethidine had delayed and depressed sucking and rooting behaviour . In addition , a smaller proportion of infants exposed to pethidine started to suckle the breast . Rooting movements which are expected to be vigorous at 30 min after birth were affected both by administration of pethidine and a longer second stage of labour . It is suggested that the differences found in sucking behaviour may be a central effect of pethidine . Depression of rooting movements in the pethidine group may be caused by exhaustion due to a longer second stage of labour and administration of pethidine . It is recommended that pethidine‐exposed mother‐infant couples stay together after birth long enough to enable the infant to make the choice to attach or not to attach to the nipple without the forceful helping h and of the health staff A sequential study of  intravenous analgesic treatment during labour has shown that pentazocine 40 mg provides pain relief comparable to pethidine 100 mg alone or combined with levallorphan 1.25 mg ( Pethilorfan ) , but is significantly more effective than pethidine 50 mg . Pethilorfan gave less sustained analgesia and a high incidence of dysphoria . Emetic sequelae were much more frequent with either dose of pethidine than with pentazocine . Placebo treatment was easily identified by mother and observer . Its inclusion and early sequential exclusion may have had a significant effect on observer estimations of pain relief . The effect of the treatments on labour or on the condition of the infant at birth were not studied Preliminary observations have shown that fentanyl citrate , a potent narcotic , is helpful during labor without undue side effects . This r and omized prospect i ve investigation compared the patient-controlled administration of fentanyl with that of administration by nurses on request .  Eighty healthy women beginning active labor ( cervical dilation 4 cm ) at term were assigned to receive fentanyl intravenously by either patient-controlled administration ( n=37 ) or nurse administration on dem and ( n=43 ) .  Pain intensity measurements during early and late labor revealed the degree of analgesia to be the same in both groups . The delay in setting up the infusion system and the short time between requesting analgesia and vaginal delivery were limitations with self-administration . Maternal oversedation and vomiting did not occur . Neonatal naloxone therapy was used infrequently , umbilical serum levels of fentanyl were the same in both groups , and postnatal neuroadaptive testing revealed comparable results in both groups . Despite the usefulness of fentanyl during labor , administration by the patient had no advantages over administration by the nurses in significantly reducing drug use , improving pain relief , or avoiding drowsiness A single dose block r and omised double-blind study comparing intramuscular ketorolac , 50 mg of pethidine and 100 mg pethidine was carried out in multiparous women .  Pain intensity and sedation effect were recorded at inclusion to the study , half hourly for the first 2 h , then hourly until 6 h after delivery . Maternal and neonatal side effects were noted including the Apgar scores and the baby 's requirements for resuscitation . All three treatments are relatively ineffective in relieving labour pain . There was no difference in the analgesic efficacy between the two doses of pethidine but both doses of pethidine were statistically more effective compared with ketorolac . There was no difference in the retrospective assessment of the three groups or when comparison was made with the previous labour . A similar number of patients required further analgesia in each group . In all three groups , no adverse effect occurred in the mother or fetus . Maternal sedation and fetal depression were statistically less in the ketorolac group . Although ketorolac had inferior analgesic effect , its use was not associated with clinical ly significant sequelae and it showed a superior safety profile compared with either dose of pethidine . The study was not powerful enough to detect a difference between 50 mg and 100 mg of pethidine Preliminary reports about patient-controlled analgesia during labor have been promising . The purpose of this investigation was to compare our experience with meperidine given intravenously by the patient versus by a nurse . Sixtyfour healthy women beginning active labor ( cervical dilation 3 cm ) at term were r and omly assigned to either self administer a 10-mg dose as often as every 20 minutes or have a nurse administer 25 - 50 mg every 3 hours as requested . The total meperidine dose and consumption rates were greater when administered by the patient than by a nurse . Maternal side effects occurred with similar frequency in both groups , and pain relief was judged to be equivalent . Maternal and umbilical serum concentrations of meperidine at delivery increased in the patient-controlled group if active labor lasted longer than 2 hours . Neonatal naloxone therapy was used more often when meperidine was administered by the patient than by a nurse ( five of 31,16 % , versus three of 33 , 10 % , respectively ) . Self-administration of intravenous meperidine by the laboring patient was not found to be advantageous over nursing administration , and may pose an increased threat to the BACKGROUND Although epidural anaesthesia has become a st and ard method for labour analgesia all over the world , it is far from being ideal because of side effects and contraindications . Many alternative techniques have therefore been proposed , including the continuous infusion of remifentanil . Encouraged by positive reports , we compared the efficacy of patient-controlled remifentanil infusion ( PCA ) with patient-controlled continuous epidural analgesia ( PCEA ) . METHODS Fifty-two ASA I and II parturients were arbitrarily allocated , without r and omisation , to two groups to receive PCEA with 0.125 % bupivacaine and 0.2 microg kg(-1 ) fentanyl ( basic infusion 1 mL h(-1 ) , bolus 4 mL , lock-out time 15 min ) or remifentanil PCA ( 0.2 microg kg(-1 ) bolus doses , without basic infusion , lock-out time 2 min ) . The intensity of pain was assessed using the VAS scale every 15 min in the PCEA group and every 10 min in the PCA group . RESULTS During the first two hours of labour , the VAS score was significantly lower in the PCEA group . Later there was no difference between the groups . The clinical status of the newborns was similar . CONCLUSION The results are difficult to interpret since there was no r and omisation and parturients participated in decisions about allocation to one of the study groups . Analgesia provided by remifentanil was assessed as highly acceptable by the patients and the drug can be regarded as a safe alternative to epidural analgesia during labour Background : We compared the efficacy and side‐effects of remifentanil with those of nitrous oxide during the first stage of labour OBJECTIVE To evaluate the association between the use of pethidine during the first stage of labor and the presence , type and timing of  acidosis in the newborn at birth . STUDY DESIGN Secondary data analysis of a r and omized controlled trial , which included term singleton pregnancies diagnosed with dystocia and requiring active management of labor . Women were r and omized to receive either 100 mg of pethidine or placebo . Statistical analyses were performed using chi(2 ) or Fisher 's exact tests for proportions and multiple linear regression for continuous outcomes . RESULTS Three hundred and eighty-three pregnant women with a valid arterial blood cord sample were included in the final analysis .  Lower pH and bicarbonate levels , as well as higher pCO(2 ) levels were found in the pethidide group . A higher incidence of acidosis was found in the pethidine group ( pH<7.12 OR : 8.59 95 % C.I. 3.29 , 22.46 ) . The highest frequency of acidosis was encountered when pethidine-delivery interval was 5 h. CONCLUSION Pethidine use during the first stage of labor was associated with an increased risk of acidosis at birth Two series of patients , r and omly selected , 29 of whom had pethidine and 29 of whom had a placebo  , were compared in order to study the influence of intra-muscular pethidine on uterine 
    Output:
    
Overall the evidence was of poor quality regarding the analgesic effect of opioids , satisfaction with analgesia , adverse effects and harm to women and babies .
There were few statistically significant results .
Overall , findings indicated that parenteral opioids provided some pain relief and moderate satisfaction with analgesia in labour , although up to two-thirds of women who received opioids reported moderate or severe pain and /or poor or moderate pain relief one or two hours after administration .
Opioid drugs were associated with maternal nausea , vomiting and drowsiness , although different opioid drugs were associated with different adverse effects .
There was no clear evidence of adverse effects of opioids on the newborn .
We did not have sufficient evidence to assess which opioid drug provided the best pain relief with the least adverse effects .
AUTHORS ' CONCLUSIONS Parenteral opioids provide some relief from pain in labour but are associated with adverse effects .
Maternal satisfaction with opioid analgesia was largely unreported but appeared moderate at best .