***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: Are meta-analyses the brave new world , or are the critics of such combined analyses right to say that the biases inherent in clinical trials make them uncombinable ? Negative trials are often unreported , and hence can be missed by meta-analysts . And how much heterogeneity between trials is acceptable ? A recent major criticism is that large r and omised trials do not always agree with a prior meta- analysis . Neither individual trials nor meta-analyses , reporting as they do on population effects , tell how to treat the individual patient . Here we take a more rounded approach to meta-analyses , arguing that their strengths outweigh their weaknesses , although the latter must not be brushed aside Despite improvements in anesthetic techniques postoperative vomiting still remains a problem , particularly in ambulant out patients , and when an opioid is given before or during anesthesia . Anti-emetic are of limited value and often cause drowsiness or other side effects . We report a study in which a simple acupuncture procedure was used in patients undergoing fraction D & C under st and ard intravenous anesthesia . Sixty-four patients were included and allocated r and omly into one of the two groups : control group receiving st and ard fentanyl-valium-thiopentone anesthesia alone , and the other group receiving injection of 3 mL normal saline into the P6 acupuncture point after the anesthesia . Ten out of the 32 control patients experienced nausea or vomiting compared with only 2 out of 32 patients receiving acupoint injection . The reduction in nausea was significant . These findings can not be well explained , but it is recommended that the use of acupuncture as an anti-emetic should be explored further We studied the effect of P6 acupressure on 46 women undergoing laparotomy for major gynaecological surgery who received patient-controlled analgesia . Half the patients received acupressure at the P6 site , the remainder received acupressure at a “ sham ” site . There was a reduction in the requests for anti-emetic therapy in the group receiving P6 acupressure but there was no difference in the incidence of nausea and vomiting . There was no difference in total morphine consumption between the two groups The efficacy of intra‐operative acupuncture at the PC6 point in the prevention of postoperative nausea or vomiting was studied . A double‐blind r and omised controlled study of acupuncture versus placebo was performed in 81 patients scheduled for day case gynaecological laparoscopic surgery . Failure of treatment was defined as the occurrence of nausea or vomiting prior to or within 24 h of discharge . The use of acupuncture  reduced the incidence of postoperative nausea or vomiting in hospital from 65 % to 35 % compared with placebo and after discharge from 69 % to 31 % compared with placebo Postoperative vomiting causes patients distress and delays discharge after outpatient surgery . Although P6 electroacupuncture is recognized as having an antiemetic effect , its inconvenient instrumentation may limit its clinical applicability . The purpose of this study was to explore a simple and effective alternative method for control of postoperative vomiting in outpatient surgery . We prospect ively compared the effect of P6 acupoint injection with 0.2 ml 50 % glucose in water ( G/W ) and intravenous injection of 20 μg/kg droperidol for prevention of vomiting in 120 consecutive out patients undergoing gynecological laparoscopy with general anesthesia .  Patients were r and omly allocated to receive P6 acupoint injection , i.v . droperidol , or nothing as control group . Both P6 acupoint injection and i.v . droperidol 20 μg/kg were found to have a significant antiemetic effect when compared with the control group . We conclude that P6 acupoint injection with 50 % G/W is a simple and effective method for reducing the incidence of postoperative emesis in outpatient surgery We have studied the effect of P6 acupuncture on postoperative vomiting in 45 children undergoing tonsillectomy .  After induction of anaesthesia and before the start of surgery , 50 % of the patients received P6 acupuncture ( in the middle of the ventral surface of the wrist ) for 5 min . There was no difference in the incidence of vomiting between the acupuncture ( 39 % ) and non-acupuncture ( 36 % ) groups . We conclude that , when administered after induction of anaesthesia , P6 acupuncture is ineffective in reducing vomiting after tonsillectomy in children Nausea and vomiting occur frequently during cesarean section under spinal anesthesia .  Metoclopramide reduces intraoperative nausea and vomiting , but not without potential side effects . Acupressure , a noninvasive variation of acupuncture that involves constant pressure on the wrist , has been suggested as an alternative method to prevent nausea and vomiting . The aim of this study was to compare acupressure and intravenous ( IV ) metoclopramide for the prevention of nausea and vomiting during  elective cesarean section  under spinal anesthesia . Seventy-five patients were studied in a r and omized , prospect i ve , double-blind comparative trial . Group I patients received acupressure b and s + 2 mL IV saline , Group II patients received placebo wrist b and s + 10 mg IV metoclopramide , and Group III patients received placebo wrist b and s + 2 mL IV saline . Patients who received either acupressure or metoclopramide prior to initiation of spinal anesthesia for cesarean section had much less nausea than patients in the placebo group . Acupressure is an effective , nonpharmacologic method to reduce intraoperative nausea during elective cesarean section in the awake patient . ( Anesth Analg 1997;84:342 - 5 UNLABELLED Nausea is the most common postoperative complication of anesthesia . Appropriately applied acupressure offers a safe and cost-effective nursing approach to the prevention of this problem . This study tested the effect of acupressure on the incidence of postoperative nausea in same-day surgery patients . METHODS Ninety outpatient surgery patients were r and omly assigned to one of three groups . The treatment group ( n = 30 ) received bilateral elastic b and s design ed to exert pressure on the appropriate location on the distal aspect of the wrist during the perioperative period . The placebo group ( n = 30 ) had elastic b and s incapable of acupressure placed on their wrists . The control group ( n = 30 ) received routine nursing and medical interventions for nausea and vomiting . Antiemetics were prescribed by the anesthesiologist and administered to patients in all three groups if nausea persisted and /or emesis occurred . The incidences of nausea or vomiting were tabulated separately for operating room , PACU phase I , and PACU phase II , and compared using Fisher 's Exact Test . RESULTS The incidence of nausea and vomiting did not differ overall in the OR or PACU phase I. However , in PACU phase II the incidence was 10 % in the treatment group , 20 % in the placebo group , and 50 % in the control group ( overall , P = .0001 ) . Treatment wrist b and s reduced the incidence of nausea and vomiting as compared with the control group ( P = .0001 ) , as did the placebo wrist b and s ( P = .0033 ) . The numerical trend suggests that the incidence is reduced by half . The incidence of nausea can be significantly reduced by the use of placebo and suggests that further reduction can be obtained by using acupressure The possible postoperative antiemetic effect of transcutaneous electrical nerve stimulation ( TENS ) on the P6 point ( on the Pericardium Channel of H and -Jueyin ) was evaluated in 103 women undergoing hysterectomy .  TENS on the P6 point was applied 30 - 45 min before induction of anesthesia in 51 patients and continued for 6 h postoperatively . The control group , 52 patients , was treated exactly in the same way but with the electrical stimulator turned off . Incidence of vomiting was assessed blindly 2 h , 4 h , 6 h , and 8 h postoperatively . The incidence of vomiting postoperatively was significantly less in the TENS-treated group when compared with the control group ( between 0 h and 2 h : 23 % vs 43 % , P < 0.05 ; between 2 h and 4 h : 27 % vs 50 % , P < 0.025 ; and between 4 h and 6 h : 31 % vs 67 % , P < 0.001 , respectively ) . Six hours postoperatively TENS was discontinued , and 8 h postoperatively the two groups did not differ significantly for incidence of vomiting ( between 6 h and 8 h : 51 % vs 65 % ) . The authors conclude that TENS reduces the incidence of vomiting after hysterectomy The antiemetic action of stimulation of the P6 ( Neiguan ) acupuncture ( ACP ) point has been studied in women , premedicated with nalbuphine 10 mg , undergoing minor gynaecological operations under methohexitone-nitrous oxide-oxygen anaesthesia . Invasive ACP -- manual or electrical at 10 Hz -- applied for 5 min at the time of administration of the premedication markedly reduced the incidence of vomiting and nausea in the first 6 h after operation , compared with untreated controls . This did not occur with stimulation of a " dummy " ACP point outside the recognized ACP meridians . Non-invasive methods ( stimulation via a conducting stud or by pressure ) were equally as effective as invasive ACP  during the early postoperative period . However , both these non-invasive approaches were less effective than invasive ACP in the 1 - 6 h postoperative period , although each was as effective as two st and ard antiemetics ( cyclizine  50 mg , metoclopramide 10 mg ) . In view of the total absence of any side effects in more than 500 ACP procedures , the clinical applications of this finding are worthy of further study BACKGROUND A problem acupuncture research has to face is the concept of a control group . If , in control groups , non-acupoint needling is done , physiological acupuncture effects are implied . Therefore the effects shown in this group are often close to those shown in the acupuncture group . In other trials , control groups have received obviously different treatments , such as transcutaneous electrical nervous stimulation or TENS-laser treatment ; it is not clear if the effects of acupuncture are due only to the psychological effects of the treatment . METHODS We developed a placebo acupuncture needle , with which it should be possible to simulate an acupuncture procedure without penetrating the skin . In a cross-over experiment with 60 volunteers we tested whether needling with the placebo needle feels any different from real acupuncture . FINDINGS Of 60 volunteers , 54 felt a penetration with acupuncture  ( mean visual analogue scale [ VAS ] 13.4 ; SD 10.58 ) and 47 felt it with placebo ( VAS 8.86 ; SD 10.55 ) , 34 felt a dull pain sensation ( DEQI ) with acupuncture and 13 with placebo . None of the volunteers suspected that the needle may not have penetrated the skin . INTERPRETATION The placebo needle is sufficiently credible to be used in investigations of the effects of acupuncture Two consecutive studies were undertaken to evaluate the effectiveness of acupuncture as an antiemetic used in addition to premedication with opioids in patients undergoing minor gynaecological operations . In the first study 25 of the 50 patients underwent acupuncture immediately after premedication with 100 mg meptazinol , the rest receiving the drug alone , and in the second 75 patients were allocated r and omly to one of three groups : a group receiving 10 mg nalbuphine and acupuncture , a group receiving premedication and dummy acupuncture , and a group receiving premedication alone . Manual needling for five minutes at the P6 acupuncture point ( Neiguan ) result ed in a significant reduction in perioperative nausea and vomiting in the 50 patients who underwent acupuncture compared with the 75 patients who received no acupuncture . These findings can not be explained , but it is recommended that the use of acupuncture as an antiemetic should be explored further One hundred unpremedicated female patients of ASA grade 1 or 2 who underwent laparoscopy as out patients were allocated r and omly to one of four groups . All patients received general anaesthesia withfentanyl , thiopentone , halothane , nitrous oxide and oxygen ; suxamethonium was given to facilitate tracheal intubation . In the recovery room , group I ( control ) received no treatment ; group 2 received electro‐acupuncture at the P6 point ( Neiguan ) on the right side for 15 minutes , group 3 received transcutaneous electrical nerve stimulation at the P6 point on the right side for 15 minutes and group 4 received prochlorperazine 5 mg intravenously . Any act of vomiting , including dry retching , during the first 3 postoperative hours was regarded as postoperative emesis . The incidence of postoperative emesis was 11/25 ( 44 % ) in group 1 , 3/25 ( 12 % , p > 0.05 ) in group 2 , 9/25 ( 36 % ) in group 3 , and 3/25 ( 12 % , p < 0.05 ) in group 4 . Our results suggest that 
    Output:
    
In children , no benefit was found .
Some results in adults were significant .
Using nonpharmacologic techniques , 20%-25 % of adults will not have early PONV compared with placebo .
It may be an alternative to receiving no treatment or first-line antiemetics .
IMPLICATION S This systematic review showed that nonpharmacologic techniques were equivalent to commonly used antiemetic drugs in preventing vomiting after surgery .
Nonpharmacologic techniques were more effective than placebo in preventing nausea and vomiting within 6 h of surgery in adults , but there was no benefit in children