***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 During the last years huge amounts of literature have been review ed systematic ally . Recently , guidelines have been proposed . For the first time a large prospect i ve study has been performed on the effect of combining antiemetics . In this review we try to propose a rational approach to  postoperative nausea and vomiting .  The scoring of patients at risk , rational anaesthetic agents , prophylactic administration of antiemetics to patients at risk and effective postoperative antiemetic treatment are suggested 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 The incidence of postoperative nausea and vomiting and requirements for anti-emetic medication were assessed in 80 female patients undergoing day-case anaesthesia during assisted conception therapy . Anaesthesia was induced with alfentanil 50 μg · kg−1 and propofol 1 mg · kg−1 ; atracurium 0.5 mg · kg−1 was given to facilitate tracheal intubation . The patients were allocated to receive either total intravenous maintenance of anaesthesia with an infusion of propofol and increments of alfentanil ( Group P ) or inhalational maintenance of anaesthesia with nitrous oxide and enflurane ( Group E ) . Postoperative nausea , retching , vomiting , requirements for anti-emetic therapy , and unplanned admission for overnight stay in hospital were recorded . Overall incidence of nausea was 64 % in group E and 39 % in Croup P ( P < 0.05 ) . Incidence of vomiting was 67 % in Group E and 34 % in Group P ( P < 0.05 ) . Metoclopramide was requested by 62 % of patients in Group E , and 32 % of those in Group P ( P < 0.05 ) ; 21 % of the patients in Group E were admitted to hospital overnight , while only 5 % of the patients in Group P required unscheduled admission to hospital ( P < 0.05 ) . We conclude that total intravenous anaesthesia with propofol and alfentanil is superior to inhalational maintenance with nitrous oxide and enflurane in that it is associated with less nausea and vomiting , less requirement for anti-emetic medication , and a lower probability of unplanned admission to hospital after day-care gynaecological surgery . RésuméL’incidence de nausées et vomissements en période postopératoire et le besoin de médication antiémétique a été évalué chez 80 patientes devant subir une anesthésie ( cas d’un jour ) pendant une séance de conception assistée . L’induction de l’anesthésie s’est faite à l’aide d’alfentanil 50 μg · kg−1 et de propofol 1 mg · kg−1 ; l’intubation endotrachéale a été facilitée à l’aide d’atracurium 0,5 mg · kg−1 . L’anesthésie était maintenue soit à l’aide d’une technique intraveineuse totale , en utilisant une infusion de propofol et des bolus d’alfentanil ( groupe P ) , soit à l’aide d’une technique d’inhalation en utilisant le protoxyde d’azote et l’enflurane ( groupe E ) . Pendant la période postopératoire , les nausées , les efforts de vomissement , les vomissements , le besoin de thérapie antiémétique , et les admissions hospitalières imprévues pour une nuit étaient notés . L’incidence globale de nausées était de 64 % dans le groupe E et 39 % dans le groupe P ( P < 0,05 ) . L’incidence de vomissements était de 67 % dans le groupe E et de 34 % dans le groupe P ( P < 0,05 ) . Soixante-deux pourcent des patientes du groupe E ont dem and é du métoclopramide , comparativement à 32 % du groupe P ( P < 0,05 ) ; 21 % des patientes du grope E ont été admises à l’hôpital pour une nuit , t and is que seulement 5 % des patientes du groupe P l’ont été ( P < 0,05 ) . Nous concluons que l’anesthésie à l’aide d’une technique intraveineuse totale , avec propofol et alfentanil , est supérieure à une anesthésie par inhalation à l’aide de protoxyde d’azote et d’enflurane car elle est associée à une incidence moins élevée de nausées et vomissements , un besoin moindre de médication antiémétique , et une probabilité plus faible d’admissions hospitalières imprévues après une chirurgie gynécologique d’un jour An intravenous anesthetic drug , propofol was considered to pose antiemetic action . A r and omized controlled trial was conducted to evaluate whether propofol could effectively reduce  post-operative nausea and vomiting ( PONV )  compared to thiopental-nitrous oxide ( N2O ) .  One-hundred and eight patients undergoing outpatient gynecologic laparoscopy were assigned to receive 3 techniques of anesthesia ; thiopental-N2O ( T/N ) , propofol-N2O ( P/N ) and total intravenous anesthesia ( TIVA ) using propofol ( P/P ) . The results showed that in the early period ( 0 - 5 hours ) , post-operative nausea in T/N , P/N and P/P groups was 72 per cent , 44 per cent and 31 per cent , respectively ( P = 0.002 ) , and post-operative vomiting was 58 per cent , 36 per cent and 11 per cent respectively ( P = 0.00014 ) . Patients in the P/N and P/P groups experienced nausea less frequently than the T/N group [ relative risk ( RR ) = 0.62 , ( 95 % CI 0.41 - 0.93 ) and RR = 0.42 ( 0.25 - 0.72 ) respectively ] . Patients in the P/N and P/P groups experienced vomiting less frequently than the T/N group [ RR = 0.62 ( 0.37 - 1.04 ) and RR = 0.19 ( 0.07 - 0.5 ) respectively ] . Two patients in the T/N group were admitted because of severe nausea and vomiting . In conclusion , TIVA using propofol and propofol-N2O anesthesia can significantly reduce the incidence of PONV in the early period . Concerning the economic crisis of the country as well as the quality of care , propofol-N2O would be the most appropriate anesthetic of choice Background It is commonly stated that risk factors for postoperative nausea are the same as for vomiting . The authors design ed a prospect i ve study to identify and differentiate the risk factors for postoperative nausea and vomiting in various surgical population s in a clinical audit setting . Methods The study included 671 consecutive surgical in patients , aged 15 yr or more , undergoing various procedures . The study focused on postoperative  nausea visual analog scale scores every 4 h and vomiting episodes within 72 h. Both vomiting and retching were considered as emetic events . Patient- , anesthesia- , and surgery-related variables that were considered to have a possible effect on the proportion of patients experiencing postoperative nausea and /or vomiting were examined . The bivariate Dale model for binary correlated outcomes was used to identify selectively the potential risk factors of postoperative nausea and vomiting . Results Among the 671 patients in the study , 126 ( 19 % ) reported one or more episodes of nausea , and 66 patients ( 10 % ) suffered one or more emetic episodes during the studied period . There was a highly significant association between the two outcomes . Some risk factors were predictive of both nausea and vomiting ( female gender , nonsmoking status , and general anesthesia ) . History of migraine and type of surgery were mainly responsible for nausea but not for vomiting . The predictive effect of risk factors was controlled for postoperative pain and analgesic drugs . Conclusion This study shows that differences exist in risk factors of postoperative nausea and vomiting . These could be explained by differences in the physiopathology of the two symptoms BACKGROUND Refractory postoperative nausea and vomiting ( PONV ) requiring repeated treatment with antiemetic drugs is a miserable experience for the patient that may substantially increase the cost of care . As risk stratification may aid in prophylaxis and treatment , we explored risk factors for severe PONV in patients enrolled in a large international , r and omized controlled trial ( the ENIGMA trial ) . METHODS Two thous and and fifty patients , aged > or = 18 yr and undergoing surgery anticipated to exceed 2 h in duration , were recruited . Patients were r and omized to nitrous oxide ( N(2)O)-based or N(2)O-free anaesthesia . Choice of other anaesthetic , analgesic , and antiemetic drugs was left to the discretion of the anaesthetist . Anaesthetic depth was adjusted according to clinical judgement and , if available , bispectral index ( BIS ) monitoring . Severe PONV was defined as : ( i ) two or more episodes of expulsion of gastric contents at least 6 h apart ; ( ii ) received at least three doses of antiemetic medication for treatment of PONV , within 24 h of surgery ; or both . We used logistic regression , and classification and regression tree analysis , to define risk factors for severe PONV . RESULTS Three hundred and thirty-three ( 16.6 % ) patients experienced severe PONV . Age < 55 yr , female sex , abdominal surgery , N(2)O administration , absence of BIS monitoring , and longer duration of anaesthesia were predictors of severe PONV [ area under receiver operating characteristic curve=0.70 ( 95 % confidence interval : 0.67 - 0.73 ) ] . CONCLUSIONS Severe 
    Output:
    
We conclude that avoiding nitrous oxide does reduce the risk of  postoperative nausea and vomiting  , especially in women , but the overall impact is modest