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this phenomenon is more evident in obese than in normal - weight patients [ 3 , 4 ] .
increase in body mass index ( bmi ) is directly related to the impairment of arterial oxygenation , which is mainly attributable to development of ventilation - perfusion ( v / q ) mismatches and intrapulmonary shunt ( i.e. , atelectasis ) ; in fact this is more common during laparoscopy [ 5 , 6 ] . for these reasons in
morbidly obese patients , various strategies have been proposed to improve gas exchange during general anesthesia [ 7 , 8 ] .
xenon is a n - methyl - d - aspartate ( nmda ) receptor blocking agent which has become an alternative to the currently used inhaled anaesthetics [ 9 , 10 ] .
the element xenon is a noble gas , has no harmful environmental effects , is associated with cardiovascular stability [ 911 ] , and owns organoprotective properties , being able to interact with a variety of molecular targets .
several experimental studies have demonstrated a reduction in cerebral and myocardial infarction size after xenon inhalation and the up - regulation of several genes involved in cellular surviving pathways in several tissues [ 1215 ] .
xenon has the lowest blood - gas coefficient ( 0.115 ) of all known anaesthetics making induction and recovery from anesthesia very fast .
furthermore ,  xenon in oxygen  is a high - density mixture that increases airway pressure and resistance by a rising the reynold 's number , but this reproducible effect does not assume certain clinic implications .
on the contrary , as elegantly described by wood et al . , breathing gas mixtures with increased density may cause a reduction of alveolar - arterial oxygen difference ( aado2 ) and improves respiratory performances and distribution of ventilation , minimizing v / q variances . despite arterial oxygen partial pressure ( pao2 ) , hemoglobin oxygen saturation ( sao2 ) and aado2 are clinical indices commonly used for assessing lung function , as described by zetterstrm et al . ; the ratio of pao2 to the inspired oxygen fraction ( pao2/fio2 ratio ) seems the most accurate and independent off all extrapulmonary variables [ 20 , 21 ] .   in this paper , we present for the first time intra and postoperative data on respiratory function , hemodynamic status , and recovery times from morbidly obese patients ( bmi>35 ) receiving xenon - remifentanil ( xr ) or sevoflurane - remifentanil ( sr ) anaesthesia .
in particular , we tested the hypothesis that xenon anesthesia is able to improve pao2/fio2 ratio .
furthermore , we tested the hypothesis that xenon , even in morbidly obese patients , maintains its pharmacologic properties characterized by cardiovascular stability and rapid recovery times .
the protocol was approved by the local ethics committee , and all patients gave their informed consent before participation .
a total of 20 adult morbidly obese patients scheduled for roux - en - y laparoscopic gastric bypass were randomly recruited .
exclusion criteria were asa iv , age < 18 or > 60  yr , mallampati iv .
monitoring included ecg , pulse oximetry , invasive arterial pressure , temperature , end - tidal carbon dioxide , oxygen and xenon concentrations .
arterial blood gas analysis was performed in the preoperative assessment , at 15  min after the induction of anaesthesia , and every 60  min during surgery .
the a - line arx index ( aai ) was also monitored ( aep monitor , alaris medical systerns , inc , san diego , ca ) to provide information about depth of anaesthesia .
monitoring was performed to ensure aai values < 30 , and data were recorded every 5  min .
after preoxygenation with o2 100% for 5  min , anaesthesia was induced in all patients with propofol 2  mg / kg i.v . dosed on real body weight ( rbw ) and remifentanil 0.5  mcg / kg / min dosed on ideal body weight ( ibw ) according to lorenz 's formula ( ideal weight = [ height in cm-100 ]  [ height in cm-150]/2 ) by i.v .
all patients received remifentanil continuous infusion after intubation starting with 0.25  mcg / kg / min ibw and cisatracurium 0.02  mg / kg ibw every 40  min titrated to clinical needs .
no cisatracurium was given after the end of 2nd anastomosis ( 30 minutes before end of surgery ) .
in both groups , a closed - circuit anaesthesia machine ( felix dual , taema , france ) was used for gas delivery .
xe ( lenoxe , airliquide ) administration started after accurate patient 's denitrogenation ( fio2 > 97% , feo2 > 92 ) ; midazolam 0.05  mg / kg ibw was given in order to keep aai < 30 for the time , 7 to 10 minutes , occurring to reach 40% fexe in closed circuit .
hypnosis was maintained with sevoflurane 1  mac in a mixture of oxygen - air . in both groups ,
ventilation was pressure - controlled ( pcv ) , with fio2 35% , peep 5 , vt 810  ml / kg ibw in order to maintain an end - expiratory carbon dioxide partial pressure ( etco2 ) at 4.86.0  kpa .
aai < 30 was kept until the bandaging of the surgical fields were completed then anaesthesia was discontinued .
the eyes opening time started with the closure of gas delivery and ended with eyes opening on command .
when an adequate spontaneous ventilation , with an etco2 at 5.36.6  kpa , was maintained , the trachea was extubated and the patient was transferred into the post anesthesia care unit ( pacu ) .
a patient - controlled analgesia ( pca ) device was then connected to a venous line delivering morphine on command .
we decided to consider as clinically relevant a difference of 60 on pao2-fio2 ratio among the groups , measured at 120 minutes after induction . assuming a mean pao2-fio2 ratio ( standard deviation ) of 370 ( 55 ) in xenon group and 310 ( 35 ) in the other group
, we estimated a sample size of 10 patients per group enough to detect a difference of 60 , at 5% level of significance with 80% power .
we verified the existence of no significant differences in patient 's demographic characteristics ( age , sex , bmi ) , preoperative clinic characteristics , and duration of anaesthesia using the mann - whitney test for continuous variables and the fisher 's exact test for categorial variables .
differences in intraoperative and postoperative data including heart rate , systolic and diastolic pressure , oxygen saturation , plateau pressure , eyes opening and extubation time , and aldrete score in the pacu were compared by the mann - whitney test and were considered as secondary aims .
the existence of a significant difference on morphine consumption after 72 hours between the two groups was compared , and the occurrence of adverse events ( hypertension , hypotension , bradycardia , ponv , postoperative headache , awareness ) was finally evaluated .
statistical analysis was performed using stata , version 9.2 , on a mac os x operating system .
no significant difference was recorded in anesthesia duration among the two groups , 150 ( 120190 )  min in sr group and 152.5 ( 120220 )  min in xr group ; p = .849 .
intraoperative data are shown in table 2 : there was no difference among the two groups in pao2-fio2 ratio at 15  min after the induction of anesthesia , but in xr group , pao2-fio2 ratio was significantly higher after 60 and 120  min .
heart rate was significantly lower in xr group , while systolic pressure was significantly lower in sr group .
no significant differences were recorded in diastolic pressure and oxygen saturation among the two groups ; plateau pressure was significantly higher and overall remifentanil consumption significantly lower in xr group .
postoperative data are shown in table 3 : the eyes opening time and the extubation time were significantly shorter in xr group ; morphine consumption after 72 hours was significantly lower in xr group . no difference among groups was noticed in aldrete score on admission to the pacu .
adverse events occurrence is exposed in table 4 : hypertension , bradycardia , postoperative headache occurred rarely but more frequently in xr group ; ponv was more common in xr group and only nausea was noticed ; no patient experienced vomiting in the two groups .
in this study , we verify that xenon anesthesia is associated with better arterial oxygenation and cardiovascular stability in morbidly obese patients .
as argued by wood et al   the effect on aado2 of a high - density gas mixture may be due to a more uniform distribution of ventilation during anesthesia ; however , xenon , which pharmacologically is a nmda receptor antagonist , is not considered a biologically inert gas [ 1215 , 22 , 23 ] and the improvement of   pao2/fio2 ratio may be related not only to  high - density effect  of the inhaled mixture but also to its organoprotective and preconditioning effects [ 1215 ] .
recovery times recorded after xenon anesthesia were faster according to the blood - gas coefficient of the molecule ; no considerable difference was noticed with respect to normal - weight patients trials , taking into account the sample size of our study .
xenon anesthesia was characterized by a significative higher arterial systolic pressure and by a minimal variation from   preoperative baseline ( tables 1 and 2 ) .
heart rate was lower ; more evident were bradycardia , hypertension , and incidence of postoperative nausea ; airway pressure was significantly and constantly increased .
all these data are aligned to normal - weight patients trials findings and experimental literature about xenon anesthesia [ 9 , 17 , 18 , 24 ] .  
xenon exerts a potent analgesic action due to nmda receptor inhibition   which may explain the lower overall remifentanil consumption during surgery ; however , wash in and wash out of xenon are very fast [ 9 , 13 ] , and nmda receptor blocking ability may not explain an effect on pain pathways up to 72 hours . nowadays the evidence is that xenon is able to modulate long - term pathways [ 12 , 14 , 22 ] which are considered the end effectors producing the long - term organoprotective effects of the gas .
it is possible that a long - term modulation of pain could be inserted in such scenario but further studies are required .
background . 
 xenon - in - oxygen is a high density gas mixture and may improve pao2/fio2 ratio in morbidly obese patients uniforming distribution of ventilation during anesthesia 
 . methods . 
 we compared xenon versus sevoflurane anesthesia in twenty adult morbidly obese patients ( bmi > 35 ) candidate for roux - en - y laparoscopic gastric bypass and assessed pao2/fio2 ratio at baseline , at 15  min from induction of anaesthesia and every 60  min during surgery . 
 differences in intraoperative and postoperative data including heart rate , systolic and diastolic pressure , oxygen saturation , plateau pressure , eyes opening and extubation time , aldrete score on arrival to the pacu were compared by the mann - whitney test and were considered as secondary aims . 
 moreover the occurrence of side effects and postoperative analgesic demand were assessed . 
 results . in xenon group 
 pao2-fio2 ratio was significantly higher after 60  min and 120  min from induction of anesthesia ; heart rate and overall remifentanil consumption were lower ; the eyes opening time and the extubation time were shorter ; morphine consumption at 72  hours was lower ; postoperative nausea was more common . conclusions . 
 xenon anesthesia improved pao2/fio2 ratio and maintained its distinctive rapid recovery times and cardiovascular stability . 
 a reduction of opioid consumption during and after surgery and an increased incidence of ponv were also observed in xenon group .