***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 
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    Input: The second stage of labour is associated with relative fetal hypoxia and progressive metabolic acidosis . Maternal analgesia can increase the danger , especially for the high-risk fetus . In 152 patients the effect on the fetus of  pethidine alone , pethidine + trichloroethylene , or pethidine + Entonox was assessed by fetal scalp blood sampling . Fetal pH , Pco2 , and Po2 were measured and base excess was calculated . Capillary sample s were also taken 45 to 60 minutes after birth in 88 of the babies to estimate the rate of neonatal recovery .  Entonox proved safer than trichloroethylene , and babies treated with it maintained their Po2 before birth , had better Apgar scores at birth , and one hour later were significantly less acidotic and much better oxygenated OBJECTIVE To study the pain relief effectiveness of the combined spinal-epidural analgesia ( CSEA ) and the inhalation of nitrous oxide , and the influences on the mothers and infants . METHODS The 300 cases of pregnant women were r and omly divided into 3 groups : CSEA group , nitrous oxide group and control group . The nitrous oxide group was that pregnant women inhaled nitrous oxide premixed with oxygen ( 50%:50 % ) , the pregnant women of the CSEA group were injected fentanyl and bupivacaine in the subarachnoid and epidural space , analgesic was not used in the control group . The degree of labor pain , duration of the labor , way of delivery , bleeding volume , rate of anoxia of newborn , blood gas analysis to maternal radius artery and fetal umbilical blood among 3 groups were observed . RESULTS The effect for analgesia labor of the CSEA group was much better than that of the nitrous oxide group ( P < 0.01 ) . In the first stage of labor and total stage of labor , the CSEA group was shorter than the others ( P < 0.05 ) , but there was no difference between the nitrous oxide group and the control group ( P > 0.05 ) . In the second stage of labor , the 3 groups were alike to each other . The bleeding volume of caesarean section ( 373 + /- 77 ) ml in the nitrous oxide group was much more than the other 2 groups , there was no difference between the CSEA group ( 259 + /- 78 ) ml and the control group ( 239 + /- 89 ) ml . The rate of obstetric forceps of CSEA group was higher than the control group ( P < 0.01 ) , and the rate of caesarean section of the nitrous oxide group was much higher than the CSEA group . The blood gas analysis to maternal radius artery and fetal umbilical blood and the rate of anoxia of newborn of 3 groups revealed no significant difference . CONCLUSIONS The effectiveness of the combined spinal-epidural analgesia CSEA for analgesia labor is confirmed and has rarely side-effect , and it can be the first choice , and the inhalation of nitrous oxide can safely provide effective labor analgesia , too The use of subanaesthetic concentration of inhalational anaesthetic for vaginal delivery offers many advantages to the mother and newborn‐ Desflurane , with the characteristics of rapid onset and minimal metabolism , may provide better analgesia and safety for labour pain control Methoxyflurane ( 0·35 % ) in air and nitrous oxide/oxygen ( 50%/50 % ) self-administered intermittently in the usual way have been compared as analgesics for labour . There were 25 patients in each group . Objective assessment by an anaesthetist showed that methoxyflurane is the more effective analgesic , and this was supported by the opinion of the multiparae . Nausea and vomiting were significantly less with methoxyflurane . Fifty per cent . nitrous oxide in oxygen given intermittently does not appear to be the best analgesic concentration . Nevertheless , since a considerable variation in sensitivity exists , it would probably be unwise to consider the introduction of higher concentrations for use by unsupervised midwives . This trial confirms the predictions made by us using a method for screening inhalational analgesics , in which methoxyflurane and nitrous oxide were given continuously In a r and omised controlled trial epidural analgesia with bupivacaine 0·5 % ( mean dose 112·8 mg ) was compared with pethidine ( mean dose 200 mg ) and inhalational analgesia in primipara ( 28 and 30 mothers ) and multipara ( 17 and 18 mothers ) . Mothers who had an uneventful pregnancy and labour and agreed to have either treatment were studied during labour and followed‐up at interviews for 5 months after delivery . Epidural block was rated significantly superior in respect of pain relief and comfort , there were no differences between the groups in reports of perineal discomfort . Twice as many primipara  required forceps delivery after epidural block . Very few mothers , in each group , reported something missing in their experience of childbirth . Two thirds of each group would use the same method again . Epidural block can therefore be recommended to uncommitted mothers as a satisfying and effective method of pain relief for labour Since Minnitt ’ introduced an apparatus for the self-administration of nitrous oxide in air during labour , many attempts have been made to improve its effectiveness . One investigatorZ suggested the substitution of air by oxygen , so that a higher concentration of nitrous oxide could be used . It was found3 that 70 % nitrous oxide with 30 % oxygen was the optimum analgesic mixture but this led to a small and unacceptable incidence of mothers who became unconscious4 and therefore 50 % nitrous oxide with 50 % oxygen is recommended for use by midwives . The arterial concentration of nitrous oxide , which is relatively insoluble , rapidly equilibrates with the inspired concentration but when used intermittently for short periods there is always a vital delay between starting self-administration and reaching an effective arterial concentration . On stopping self-administration between uterine contractions nitrous oxide is almost completely eliminated , so that the start of each inhalation is a re-induction . Timing is therefore crucial to successful pain relief with nitrous oxide analge ~ ia.~ When breathed continuously , the inspired concentration being adjusted by an anaesthetist , the optimum mean concentration of nitrous oxide for pain relief in labour was 41.2%.6 However , when 50 % nitrous oxide with 50 % oxygen is self-administered intermittently during labour , in the usual way , the mean peak arterial concentration is equivalent to 26.4 % nitrous oxide concentration . ’ In an attempt to reduce the vital need for accurate timing a low concentration of nitrous oxide has been administered continuously by the nasal route , and in volunteers,8 and mothers in labour.g This raised the end-tidal concentration at the beginning of each period of selfadministration . This study extends those investigations . During labour , the reduction in time to reach specified end-expired nitrous oxide concentrations has been measured during each period of inhalation and the effectiveness of a nasal supplement to intermittent inhalation of Entonox  has been assessed Background Intermittent self-administered nitrous oxide has long had widespread use as an analgesic in labor , but its efficacy has not been adequately established . Questions about its effect on maternal oxygenation between labor contractions also have been raised . Methods Twenty-six women were recrulted to participate in a r and omized , double-blind , cross-over , placebo-controlled study to assess the effect of intermittent nitrous oxide inhalation on labor pain and maternal hemoglobin oxygen saturation ( SpO2 ) during the first stage of labor . Visual analog scale pain scores for each of five consecutive labor contractions were measured after administration of either nitrous oxide or compressed air . Results Mean visual analog scale pain scores for five contractions were 5.1 , 5.2 , 5.7 , 5.2 , and 5.6 ( nitrous oxide ) and 4.9 , 5.2 , 6.1 , 5.6 , and 5.7 ( compressed air ) . There were no statistically significant differences in pain when nitrous oxide as compared with compressed air was administered . Pain scores did not differ significantly over time as a function of inhaled substance ( F = 0.41 , P = 0.53 ) . The mean lowest SpO2 observed between these contractions after self-administration of nitrous oxide and air were 97 , 97 , 97 , 97 , and 97 % ( nitrous oxide ) and 97 , 96 , 96 , 96 , and 96 % ( compressed air ) . SpO2 was significantly higher after nitrous oxide administration ( F = 8.8 , P = 0.007 ) . Conclusions While intermittent self-administered 50 % nitrous oxide in oxygen does not appear to predispose parturient women to hemoglobin oxygen desaturation , its analgesic effect has yet to be clearly demonstrated This study aims to investigate the effectiveness of nitrous oxide on  pain of labor contractions and on maternal SaO2 . The patients were r and omized to receive either a pre-prepared mixture of 50 % nitrous oxide and oxygen or 50 % oxygen by a coin . Study drugs started as early as the onset of pain with each contraction . The patient herself administered gases via a facemask connected to the uni-directional valve which enables the patients to breathe fresh gas in each inspiration . The gas administration was continued to the end of contraction pain at which the patient breathed the room air . Variables such as SaO2 , blood pressure , pain and side effects were recorded . 534 ASA I and II parturients , aged from 16 to 35 years , scheduled for elective labor from September 2004 to 2006 were evaluated . Four patients were lost from the study . The mean age of patients was 25.5+/-4.3 years . During the first three measurements , the SaO2 was significantly higher in control group . In addition , the mean arterial pressure was comparable between groups except two first measurements in which the control group was higher . All the Visual Analogue Scale ( VAS ) values were significantly lower in nitrous oxide group . There were no significant differences in 1st and 5th min apgar scores between groups . All of the side effects were significantly higher among patients in nitrous oxide . In conclusion , our data indicate that using nitrous oxide 50 % provides significant pain relief . Nonetheless , it is associated with few side effects , nitrous oxide can be quickly implemented during advanced painful labor A comparison of the analgesic efficacy of Entonox ( 50 % nitrous oxide in oxygen ) and Entonox with 0.2 % isofturane was made in 18 consenting mothers during the first stage of labour . The inhalational gases were self‐administered during contractions over a 3 h study period using a st and ard Entonox dem and valve and breathing system . Isoflurane 0.2 % was added from an Ohmeda Isotec drawover vaporizer and the inspired concentration ofisoflurane was analysed continuously using a Date x Ultima analyser . Linear analogue scores for pain were significantly lower ( p < 0.001 ) during the Entonox‐isoflurane administration compared with Entonox  alone . Drowsiness was not a clinical problem and there was a high acceptance rate for Entonox‐isoflurane inhalational analgesia during labour BACKGROUND We determined the optimal inspired sevoflurane concentration for use during labour as 0.8 % in our previous study . This study compared sevoflurane at a concentration of 0.8 % and Entonox((R ) ) ( nitrous oxide 50 % : oxygen 50 % ) for analgesia during labour in 32 healthy parturients . METHODS Each mother underwent two open-label , three-part sequences in r and om order , Entonox-sevoflurane-Entonox or sevoflurane-Entonox-sevoflurane . In each part the agent was self-administered during 10 contractions . A 100 mm visual analogue scores for pain relief and sedation was completed immediately after each contraction . RESULTS Two patients withdrew during administration of sevoflurane ( because of its odour ) and five during Entonox ( requesting epidural analgesia ) . Of the remaining women , data were available for analysis from 29 participants :  median ( IQR [ range ] ) pain relief scores were significantly higher for sevoflurane 67 ( 55 - 74 [ 33 - 100 ] ) mm than for Entonox 51 ( 40 - 69.5 [ 13 - 100 ] ) mm ( P<0.037 ) . Nausea and vomiting were more common in the Entonox group [ relative risk 2.7 ( 95 % CI 1.3 - 5.7 ) ; P=0.004 ] . No other adverse effects were observed in the mothers or babies . There was significantly more sedation with sevoflurane than with Entonox { 74 ( 66.5 - 81 [ 32.5 - 100 ] ) and 51 ( 41 - 69.5 [ 13 - 100 ] ) mm , respectively ; P<0.001}. Twenty-nine patients preferred sevoflurane to Entonox and found its sedative effects helpful . CONCLUSIONS We conclude that self-administered sevoflurane at subanaesthetic concentration ( 0.8 % ) can provide useful pain relief during the first stage of labour , and to a greater extent than Entonox . Although greater sedative effects were experienced with sevoflurane , it was preferred to Enton 
    Output:
    
The highest score for pain relief is the most positive in contrast to ' pain intensity ' in which the higher score is more negative .
AUTHORS ' CONCLUSIONS Inhaled analgesia appears to be effective in reducing pain intensity and in giving pain relief in labour .
However , substantial heterogeneity was detected for pain intensity .
Furthermore , nitrous oxide appears to result in more side effects compared with flurane derivatives .
Flurane derivatives result in more drowsiness when compared with nitrous oxide .
When inhaled analgesia is compared with no treatment or placebo , nitrous oxide appears to result in even more side effects such as nausea , vomiting , dizziness and drowsiness .
There is no evidence for differences for any of the outcomes comparing one strength verus a different strength of inhaled analgesia , comparing different delivery systems or comparing inhaled analgesia with TENS