***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: Background : Different anesthetic agents have different effects on cerebrovascular physiology . However , the importance of these differences In neuroanesthetic practice are unclear . In an effort to determine whether important clinical differences are present , the authors compared three anesthetic techniques in 121 adults undergoing elective surgical removal of a supratentorial , intracranial mass lesion . Methods : Patients were assigned r and omly to one of three groups . In group 1 ( n=40 ) , anesthesia was induced with propofol and maintained with fentanyl ( ≊10 µg/kg load , 2 - 3 µg · kg-1 · h-1 infusion ) and propofol ( 50 - 300 µg · kg-1 · mln-1 ) . In group 2 ( n=40 ) , anesthesia was induced with thiopental and maintained with isoflurane and nitrous oxide . Up to 2 µg/kg fentanyl was given after replacement of the bone flap . In group 3 ( n=41 ) , anesthesia was induced with thiopental and maintained with fentanyl ( ≊10 µg/kg load , 2 - 3 µg · kg-1 · h1 infusion ) , nitrous oxide , and low-dose Isoflurane , if required . Blood pressure , heart rate , expired gas concentrations , and ventilatory parameters were recorded automatically in all patients . Epidural intracranial pressure ( ICP ) was measured via the first burr hole , brain swelling was rated at the time of dural opening , and emergence was monitored closely . Preoperative computed tomography or magnetic resonance imaging scans were evaluated , and pre- and postoperative neurologic exams were performed by a neurosurgeon unaware of group assignments . Total hospital stay ( days ) and total hospital cost ( exclusive of physician charges ) also were review ed . Results : During induction , higher heart rates were seen in isoflurane/nitrous oxide patients , whereas mean arterial pressure was ≊10 mmHg less during the maintenance phase ( compared with both other groups ) . Otherwise , there were few intergroup hemodynamic differences . While there were no clinical ly important intergroup differences in mean ICP (±SD)—group 1 , ICP=12 ± 7 mmHg ; group 2,15 ± 12 mmHg ; group 3 , ICP=11 ± 8 mmHg — more isoflurane/nitrous oxide patients ( nine , group 2 ) had an ICP £ 24 mmHg than in the other groups ( two each ) . Emergence was , overall , more rapid with fentanyl/nitrous oxide . For example , the median time until the patient could be awakened by quiet verbal comm and , e.g. , “ Open your eyes , ” was 5 min , versus 10 min in the other groups . There were no relationships between ICP and any measurement of emergence ( e.g. , time to response to comm and s ) . Seven of 41 ( 17 % ) fentanyl/nitrous oxide patients vomited In the early postoperative period , compared with only 1 of 40 ( 2.5 % ) of those given propofol/fentanyl and 2 of 40 ( 5 % ) receiving isoflurane/nitrous oxide ( P=0.03 ) . There were no differences in the incidence of new postoperative deficits , total hospital stay , or cost . Conclusions : Although there are modest differences among the three tested anesthetics , short-term outcome was not affected . These results indicate that , despite their respective cerebrovascular effects , all of the anesthetic regimens used were acceptable in these patients undergoing elective surgery BACKGROUND Postoperative delirium and cognitive decline are common in elderly surgical patients after non-cardiac surgery . Despite this prevalence and clinical importance , no specific aetiological factor has been identified for postoperative delirium and cognitive decline . In experimental setting in a rat model , nitrous oxide ( N(2)O ) produces neurotoxic effect at high concentrations and in an age-dependent manner . Whether this neurotoxic response may be observed clinical ly has not been previously determined . We hypothesized that in the elderly patients undergoing non-cardiac surgery , exposure to N(2)O result ed in an increased incidence of postoperative delirium than would be expected for patients not receiving N(2)O. METHODS Patients who were > or=65 yr of age , undergoing non-cardiac surgery and requiring general anaesthesia were r and omized to receive an inhalational agent and either N(2)O with oxygen or oxygen alone . A structured interview was conducted before operation and for the first two postoperative days to determine the presence of delirium using the Confusion Assessment Method . RESULTS A total of 228 patients were studied with a mean ( range ) age of 73.9 ( 65 - 95 ) yr . After operation , 43.8 % of patients developed delirium . By multivariate logistic regression , age [ odds ratio ( OR ) 1.07 ; 95 % confidence interval ( CI ) 1.02 - 1.26 ] , dependence on performing one or more independent activities of daily living ( OR 1.54 ; 95 % CI 1.01 - 2.35 ) , use of patient-controlled analgesia for postoperative pain control ( OR 3.75 ; 95 % CI 1.27 - 11.01 ) and postoperative use of benzodiazepine ( OR 2.29 ; 95 % CI 1.21 - 4.36 ) were independently associated with an increased risk for postoperative delirium . In contrast , the use of N(2)O had no association with postoperative delirium . CONCLUSIONS Exposure to N(2)O result ed in an equal incidence of postoperative delirium when compared with no exposure to An investigation was undertaken to assess the use of a total intravenous anaesthetic technique offentanyl and methohexilonc for outpatient vaginal termination of pregnancy . When compared with a technique offentanyl , methohexitone , nitrous oxide and trichloroethylene the total intravenous method caused snifter recovery , minimal side‐effects and no cardiovascular depression . However , both anaesthetic techniques produced significant postoperative reduction of memory for new facts when compared with a control group receiving no general anaesthesia . There is a need to continue the search for anaesthetic methods appropriate for day cases Background : Nitrous oxide rapidly inflates gas‐filled spaces such as the intestines ; but whether the result ing bowel distension is clinical ly important remains unclear . We therefore tested the hypothesis that nitrous oxide produces clinical ly important bowel distension Sixty unpremedicated patients undergoing short urological and gynaecological procedures were r and omly allocated to three groups to receive either methohexitone , alfentanil , nitrous oxide and oxygen , methohexitone , isoflurane and oxygen or methohexitone , isojurane , nitrous oxide and oxygen . The group receiving methohexitone , isoflurane and oxygen was ab and oned after 11 patients had been studied , due to poor conditions during induction of anaesthesia . Therefore , data from only 51 patients are presented . Early recovery was assessed by time to opening eyes , giving correct name and date of birth ; later , recovery was assessed by using the postbox test and deletion of‘p 's . During anaesthesia and surgery , there was a high incidence of coughing and laryngospasm in the isoflurane groups . The patients in the alfentanil group opened their eyes and gave their names and date s of birth significantly faster post‐operatively ( p < 0.01 ) than those in the isofurane groups . However , there were no significant differences between the three groups regarding the later tests of recovery . The late recovery after isofurane was equal to that obtained using an intravenous technique with alfentanil , although the peroperative complication rate was higher Background : Nitrous oxide ( N2O ) is frequently used to supplement more potent anesthetic agents . One side-effect of N2O is its ability to exp and an air-containing space . We investigated if N2O adversely affected operating conditions by distending normal bowel during laparoscopic bariatric procedures . Methods : 50 morbidly obese patients were divided into 2 study groups . Group 1 patients were ventilated with a halogenated anesthetic/oxygen/air mixture , while Group 2 received a halogenated anesthetic/oxygen/N2O mixture . At 30 , 60 , and 90 min intervals during the operation , the surgeon was asked if N2O was being used . Results : The surgeons responded correctly only 42 % ( 30 min ) , 50 % ( 60 min ) , and 48 % ( 90 min ) of the time . In Group 2 ( N2O ) patients , they incorrectly answered that N2O was not being used 88 % ( 30 min ) , 68 % ( 60 min ) , and 68 % ( 90 min ) ; and in Group 1 ( air ) patients , they incorrectly answered that  N2O was being used 28 % ( 30 min ) , 32 % ( 60 min ) , and 36 % ( 90 min ) of the time . Conclusion : We found that using N2O did not cause noticeable bowel distention during laparoscopic bariatric procedures of relatively short duration Summary Chronic postsurgical pain  was common after major surgery in the Evaluation of Nitrous Oxide in the Gas Mixture for Anaesthesia ( ENIGMA ) trial . Nitrous oxide administration was associated with a decrease in the risk of chronic wound pain after surgery . ABSTRACT Nitrous oxide is an antagonist at the N‐methyl‐D‐aspartate receptor and may prevent the development of chronic postsurgical pain . We conducted a follow‐up study in the Evaluation of Nitrous Oxide in the Gas Mixture for Anaesthesia ( ENIGMA ) trial patients to evaluate the preventive analgesic efficacy of nitrous oxide after major surgery . The ENIGMA trial was a r and omized controlled trial of nitrous oxide‐based or nitrous oxide‐free general anesthesia in patients presenting for noncardiac surgery lasting more than 2 hours . Using a structured telephone interview , we contacted all ENIGMA trial patients recruited in Hong Kong ( n = 640 ) . We recorded the severity of postsurgical pain of at least 3 months ’ duration that was not due to disease recurrence or a pre‐existing pain syndrome , using the modified Brief Pain Inventory . The impact of postsurgical pain on quality of life was also measured . Pain intensity , opioid and other analgesic requirements during the first week of surgery , were retrieved from the trial case report form and medical records . A total of 46 ( 10.9 % ) patients reported pain that persisted from the index surgery , and 39 ( 9.2 % ) patients had severe pain . In addition , patients with chronic pain rated poorly in all attributes of the quality ‐of‐life measures compared with those who were pain free . In a multivariate analysis , nitrous oxide decreased the risk of chronic postsurgical pain . In addition , severe pain in the first postoperative week , wound complication , and abdominal incision increased the risk of chronic pain . In conclusion , chronic postsurgical pain was common after major surgery in the ENIGMA trial . Intraoperative nitrous oxide administration was associated with a reduced risk of chronic postsurgical pain Forty‐two patients undergoing major colonic surgery were assigned at r and om to receive isoflurane‐fentanyl anaesthesia with nitrous oxide in oxygen , propofol‐fentanyl anaesthesia with air in oxygen or propofol‐fentanyl anaesthesia with nitrous oxide in oxygen . The groups were comparable in demographic data . Atelectases were identified , and the area measured by computerised tomography of the chest 203±69 min after extubation . and oxygenation was determined by arterial blood gas sample s taken during operation at 30 , 60 , 90 and 120 min after extubation and on postoperative days 1 , 2 and 3 . Atelectases were seen in all three groups with no differences in the mean area between groups . After operation , the effect of 4 l.min−1 of oxygen by nasal catheter on Pao2 was similar in all groups . A significant decrease in PaO2 was found during the first 3 days after surgery , and was also the same in all groups . There was no correlation between area of atelectasis and postoperative PaO2 . We conclude there is no difference in the incidence of postoperative atelectasis or oxygenation when using propofol , with or without nitrous oxide or isoflurane Eighty‐seven patients undergoing routine laparcscopy were divided r and omly into two groups to study the effect of nitrous oxide anaesthesia on the incidence of postoperative vomiting . Patients in group A received nitrous oxide as part of their anaesthetic , while in group B nitrous oxide was omitted . Significantly fewer patients in group B vomited when compared with group A ( 17 percent and 49 percent respectively ; p < 0.005 ) . We suggest that an anaesthetic technique which avoids nitrous oxide may be especially indicated in patients undergoing laparoscopy Background : Endothelial function is impaired with hyperhomocysteinemia . Plasma homocysteine is increased by nitrous oxide anesthesia . The current study was design ed to determine whether endothelial function is impaired after surgery and whether this is made worse by exposure to nitrous oxide . Methods : The authors studied 59 patients with cardiovascular disease undergoing noncardiac surgery . Patients were r and omly allocated to 
    Output:
    
The sensitivity analyses suggested that the results of the meta-analyses were all robust except for the outcomes of pneumonia , and severe nausea and vomiting .
Given the evidence from this Cochrane review , the avoidance of nitrous oxide may be reasonable in participants with pre-existing poor pulmonary function or at high risk of postoperative nausea and vomiting .