intraoperative hemodynamic monitoring used can effectively guide the use of fluid resuscitation with the goal of reducing length of stay- . non- or minimally - invasive methods of determining cardiac output ( co ) may allow guided fluid therapy in a goal - directed fashion and mitigate the risks inherent in insertion of a central line and/or pulmonary arterial catheter . in this case report , we present a comparison of hemodynamic measurements made during a routine surgical case , as measured by three non- and minimally- invasive hemodynamic methods as part of the product evaluation : the vigileo / flotrac system ( edwards lifesciences corporation , irvine , california ) , the cardio - q odm ( deltex medical limited , chichester , west sussex ) , and the nexfin ( bmeye b.v . ,
the purpose of this case report is to examine the measurements obtained from all three devices , with the goal of further understanding their ability to measure co , as well as their ability to trend hemodynamic changes and guide fluid resuscitation therapy .
a : vigileo / flotrac system ( edwards lifesciences corporation , irvine , california ) ; b : the nexfin ( bmeye b.v . ,
amsterdam , the netherlands ) ; c : the cardio - q odm ( deltex medical limited , chichester , west sussex ) ,
a 72 year old , 72  kg man presented with right upper quadrant pain .
he was brought to the operating room for an elective laparoscopic converted to open cholecystectomy with liver resection and portal vein lymphadenectomy .
the patient was placed in the supine position with arms abducted at near ninety degrees from the body .
after an uneventful intravenous induction with 100  mcg of fentanyl , 60  mg of lidocaine , 140  mg of propofol , and 100 mg of rocuronium , a right radial arterial line was placed and connected to a flotrac / vigileo monitor .
the nexfin finger cuff was then placed on the middle phalanx of the right middle finger .
all three monitors were placed , calibrated , and programmed per their respective manufacturer recommendations .
averaging times for the three monitors were programmed as follows : flotrac / vigileo , 20  seconds ; nexfin , 5 beats ; cardio - q odm , 10 beats .
the monitors were run for 30  minutes prior to incision ; during the case , the cardiac index ( ci ) , flotrac / vigileo and nexfinstroke volume variation ( svv ) , left arm non - invasive blood pressure , arterial line blood pressure , and nexfin non - invasive blood pressure were recorded in the anesthesia record in fifteen minute intervals .
additionally , the cardio - q odm transducer was refocused every fifteen minutes or more frequently to maintain an optimized signal .
when allowable , fluid resuscitation was guided by svv increasing beyond 10% , as measured by the flotrac / vigileo monitor . during periods of rapid blood loss , fluid resuscitation was guided by svv in conjunction with visual estimation of blood loss .
total blood loss was 2,200  ml ; total urine output over the case duration was 790  ml ; fluid resuscitation was provided with crystalloid ( 2,800  ml ) , hydroxyethyl starch colloid ( 2,000  ml ) , and packed red blood cells ( 900  ml ) .
this case provides a real world comparison between the nexfin monitor , a completely non - invasive co monitor , with other methods of minimally invasive co measurement , the flotrac / vigileo monitor and cardio - q odm as part of the internal product evaluation . unlike the flotrac / vigileo and cardioq odm , which require an arterial line and an esophageal placed ultrasound transducer respectively , the nexfin monitor is non - invasive by utilizing external pressure to negate any plethysmographic changes in the measured finger , thereby reconstructing the arterial waveform externally .
calculation of the stroke volume ( sv ) and co is based on pulse contour algorithms , . utilizing a proprietary transfer function based on a clinical database that accounts for age , gender , height , and weight
, this finger arterial pressure waveform is used to reconstruct a brachial arterial waveform which is then used as a substitute for aortic pressure . whereas the flotrac / vigileo monitor has found widespread intraoperative use due to its robustness in patients without cardiac rhythm and valvular abnormalities , the use of the cardio - q odm has been more limited due to its susceptibility to electrocautery noise ( fig .  2 ) .
in our experience , the frequency with which electrocautery is used by surgeons is often high enough to prevent measurement , and often negates the usefulness of this monitor as periods of extensive electrocautery use often coincide with significant hemodynamic changes for which these monitors are used .
intraoperative fluid resuscitation in this case was guided by svv when possible ( maintaining svv below 10% ) , and in conjunction with visual estimation during periods of brisk blood loss .
here , we focus our discussion on comparing the performance of the nexfin device , with the vigileo / flotrac and cardio - q odm systems , in regards to measurements of mean arterial pressure , cardiac output , and stroke volume variation .
co : cardiac output ; sv : stroke volume ; ftc : flow time corrected ; pv : peak velocity ; ma : mean acceleration ; hr : heart rate.b : an example of electrocautery interference ( arrow ) with the cardio - q odm signal . throughout the surgery ,
the nexfin estimated a consistently higher mean arterial pressure ( map ) than either the flotrac / vigileo monitor or cardio - q odm .
however , nexfin map trended consistently with both the arterial line and blood pressure cuff , and response time to changes in map were not measurably different between devices , suggesting the likelihood of a measurement bias due to device positioning , or calibration error .
correlations between the nexfin and peripheral arterial blood pressure measurements have been demonstrated in adult and pediatric cardiac surgeries ; however , this correlation may not translate to the adult abdominal case .
although blood pressure correlation has been demonstrated between the nexfin and manual and automatic non - invasive cuff measurements in non - operative environments , bias may be introduced secondary to surgical factors such as positioning .
additionally , the nature of the noninvasive and minimally invasive systems can create questionable results during extreme vasoconstriction , conditions seen with reynaud 's disease or shock as cited by the manufacturer .
the degree to which measurements are sensitive to less severe vaso - constrictive conditions that may be seen in the operating room such as distal hypothermia is unknown .
it has been shown that measured co can differ substantially depending on the method of determining co , with variations as large as 41.3% , 42.1% , and 39% for arterial pulse contour analysis , esophageal doppler , and nexfin respectively , versus thermodilution , .
these figures exceed the 30% criteria suggested by critchley and critchley . for the purposes of intraoperative management , however , the ability to identify trends in co may in itself be of use in guiding fluid resuscitation . in this regard
, the nexfin monitor was able to display ci changes in the same direction as the flotrac / vigileo and cardio - q at several points ( fig . 
3 ) , displaying a drop after induction , and increases after each dose of vaso - constrictive medication ( markers a , e , and g ) ; marker j shows a drop in output with all three measurement techniques , due to rapid surgical blood loss .
although a recent study demonstrated that earlier flotrac system did not accurately track changes in co following the administration of phenylephrine , a predominantly 1-adrenergic receptor agonist , newer version has been developed to track the change well .
surgical events are marked by vertical bars as follows : a , phenylepherine administered ; b , oral - gastric tube placed , ephedrine administered ; c , surgical incision ; d , abdominal insufflation , patient positioned in reverse trendelenburg ; e , phenylepherine administered ; f , conversion from laparoscopic to open case , phenylepherine administered , loss of cardio - q monitor signal due to electrocautery interference ; g , phenylepherine administered ; h , end of extensive electrocautery use , cardio - q monitor reinitialized ; i , significant portal vein bleeding noted by surgeon ; j , vaso - active medication given ; k , patient returned to level , supine position ; l , abdominal wall closure . stroke volume variation has been shown to be efficacious in predicting fluid responsiveness , and in this regard may serve as an intraoperative tool to guide fluid resuscitation .
3 compares svv as determined by the flotrac / vigileo and nexfin monitors , demonstrating increase with surgical blood loss , and decrease with fluid resuscitation , and demonstrates correlation between svv and nexfin - determined ci . during this case , increasing trends in svv were associated with decreasing trends in ci , and vice versa .
prior work has questioned the efficacy of minimally invasive cardiac output monitoring versus clinical observation ; but the data was from 2006 - 2007 icu patients who are very different from patients in the operating room .
furthermore , the technology has improved significantly since then . in this case , and intraoperatively in general , we believe that the value of svv can be used safely and effectively to determine fluid responsiveness and guide fluid therapy
. however , when svv / ppv is between 9 - 13% ( gray zone ) , there are about 25% of the cases for whom svv / ppv may not accurately predict the volume responsiveness under general anesthesia . for those instances ,
the averaging times were different in all the three devices that may show the delayed response .
additionally , the value of intraoperative svv must also be interpreted within the surgical context .
this particular case involved surgical manipulation in close proximity to the inferior vena cava , very likely with alternating compression and decompression .
the subsequent effect on cardiac preload can theoretically bias measurements of svv , and any fluctuation must also account for this or any other surgically induced bias . in conclusion , during operative situations where objective determination of co is critical to clinical decision - making , non- or minimally - invasive methods of co may provide measurements that correlate within approximately 40% of thermodilution measurements via a pulmonary arterial catheter .
however , in surgical situations where objective measurement is unnecessary , where the risks of pulmonary artery placement outweigh the utility of thermodilution measurements , or where ci or svv trends alone provide utility in guiding goal - directed fluid management , the nexfin monitor may provide useful hemodynamic information regarding fluid responsiveness for clinical decision making in a completely non - invasive fashion and it is comparable to that obtained by vigileo / flotrac and cardio - q odm monitors .
throughout the surgery , the nexfin estimated a consistently higher mean arterial pressure ( map ) than either the flotrac / vigileo monitor or cardio - q odm .
however , nexfin map trended consistently with both the arterial line and blood pressure cuff , and response time to changes in map were not measurably different between devices , suggesting the likelihood of a measurement bias due to device positioning , or calibration error .
correlations between the nexfin and peripheral arterial blood pressure measurements have been demonstrated in adult and pediatric cardiac surgeries ; however , this correlation may not translate to the adult abdominal case .
although blood pressure correlation has been demonstrated between the nexfin and manual and automatic non - invasive cuff measurements in non - operative environments , bias may be introduced secondary to surgical factors such as positioning .
additionally , the nature of the noninvasive and minimally invasive systems can create questionable results during extreme vasoconstriction , conditions seen with reynaud 's disease or shock as cited by the manufacturer .
the degree to which measurements are sensitive to less severe vaso - constrictive conditions that may be seen in the operating room such as distal hypothermia is unknown .
it has been shown that measured co can differ substantially depending on the method of determining co , with variations as large as 41.3% , 42.1% , and 39% for arterial pulse contour analysis , esophageal doppler , and nexfin respectively , versus thermodilution , .
these figures exceed the 30% criteria suggested by critchley and critchley . for the purposes of intraoperative management , however , the ability to identify trends in co may in itself be of use in guiding fluid resuscitation . in this regard
, the nexfin monitor was able to display ci changes in the same direction as the flotrac / vigileo and cardio - q at several points ( fig . 
3 ) , displaying a drop after induction , and increases after each dose of vaso - constrictive medication ( markers a , e , and g ) ; marker j shows a drop in output with all three measurement techniques , due to rapid surgical blood loss .
although a recent study demonstrated that earlier flotrac system did not accurately track changes in co following the administration of phenylephrine , a predominantly 1-adrenergic receptor agonist , newer version has been developed to track the change well .
surgical events are marked by vertical bars as follows : a , phenylepherine administered ; b , oral - gastric tube placed , ephedrine administered ; c , surgical incision ; d , abdominal insufflation , patient positioned in reverse trendelenburg ; e , phenylepherine administered ; f , conversion from laparoscopic to open case , phenylepherine administered , loss of cardio - q monitor signal due to electrocautery interference ; g , phenylepherine administered ; h , end of extensive electrocautery use , cardio - q monitor reinitialized ; i , significant portal vein bleeding noted by surgeon ; j , vaso - active medication given ; k , patient returned to level , supine position ; l , abdominal wall closure .
stroke volume variation has been shown to be efficacious in predicting fluid responsiveness , and in this regard may serve as an intraoperative tool to guide fluid resuscitation .
3 compares svv as determined by the flotrac / vigileo and nexfin monitors , demonstrating increase with surgical blood loss , and decrease with fluid resuscitation , and demonstrates correlation between svv and nexfin - determined ci . during this case , increasing trends in svv were associated with decreasing trends in ci , and vice versa .
prior work has questioned the efficacy of minimally invasive cardiac output monitoring versus clinical observation ; but the data was from 2006 - 2007 icu patients who are very different from patients in the operating room .
furthermore , the technology has improved significantly since then . in this case , and intraoperatively in general , we believe that the value of svv can be used safely and effectively to determine fluid responsiveness and guide fluid therapy
. however , when svv / ppv is between 9 - 13% ( gray zone ) , there are about 25% of the cases for whom svv / ppv may not accurately predict the volume responsiveness under general anesthesia . for those instances ,
the averaging times were different in all the three devices that may show the delayed response .
additionally , the value of intraoperative svv must also be interpreted within the surgical context .
this particular case involved surgical manipulation in close proximity to the inferior vena cava , very likely with alternating compression and decompression .
the subsequent effect on cardiac preload can theoretically bias measurements of svv , and any fluctuation must also account for this or any other surgically induced bias . in conclusion , during operative situations where objective determination of co is critical to clinical decision - making , non- or minimally - invasive methods of co may provide measurements that correlate within approximately 40% of thermodilution measurements via a pulmonary arterial catheter . however , in surgical situations where objective measurement is unnecessary , where the risks of pulmonary artery placement outweigh the utility of thermodilution measurements , or where ci or svv trends alone provide utility in guiding goal - directed fluid management , the nexfin monitor may provide useful hemodynamic information regarding fluid responsiveness for clinical decision making in a completely non - invasive fashion and it is comparable to that obtained by vigileo / flotrac and cardio - q odm monitors .
 abstractas part of the enhanced recovery after surgery ( eras ) protocol , the goal - directed fluid management with hemodynamic monitoring can effectively guide perioperative fluid use and significantly improve the outcomes in high - risk patients undergoing major surgeries . 
 several minimally invasive and non - invasive monitoring devices are commercially available for clinical use . as part of an internal evaluation 
 , we reported the results from three different hemodynamic monitoring devices used in a patient undergoing a major abdominal surgery . 
INTRODUCTION
CASE REPORT
DISCUSSION
Mean arterial pressure
Cardiac output
Stroke volume variation