***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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    ***EXAMPLES*** 
    Input: Background Recently , a new device has been developed to measure cardiac output noninvasively using partial carbon dioxide ( CO2 ) rebreathing . Because this technique uses CO2 rebreathing , the authors suspected that ventilatory setting s , such as tidal volume and ventilatory mode , would affect its accuracy : they conducted this study to investigate which parameters affect the accuracy of the measurement . Methods The authors enrolled 25 pharmacologically paralyzed adult post – cardiac surgery patients . They applied six ventilatory setting s in r and om order : ( 1 ) volume-controlled ventilation with inspired tidal volume ( VT ) of 12 ml/kg ; ( 2 ) volume-controlled ventilation with VT of 6 ml/kg ; ( 3 ) pressure-controlled ventilation with VT of 12 ml/kg ; ( 4 ) pressure-controlled ventilation with VT of 6 ml/kg ; ( 5 ) inspired oxygen fraction of 1.0 ; and ( 6 ) high positive end-expiratory pressure . Then , they changed the maximum or minimum length of rebreathing loop with VT set at 12 ml/kg . After establishing steady-state conditions ( 15 min ) , they measured cardiac output using CO2 rebreathing and thermodilution via a pulmonary artery catheter . Finally , they repeated the measurements during pressure support ventilation , when the patients had restored spontaneous breathing . The correlation between two methods was evaluated with linear regression and Bl and -Altman analysis . Results When VT was set at 12 ml/kg , cardiac output with the CO2 rebreathing technique correlated moderately with that measured by thermodilution ( y = 1.02x , R = 0.63 ; bias , 0.28 l/min ; limits of agreement , −1.78 to + 2.34 l/min ) , regardless of ventilatory mode , oxygen concentration , or positive end-expiratory pressure . However , at a lower VT of 6 ml/kg , the CO2 rebreathing technique underestimated cardiac out-put compared with thermodilution ( y = 0.70x ; R = 0.70 ; bias , −1.66 l/min ; limits of agreement , −3.90 to + 0.58 l/min ) . When the loop was fully retracted , the CO2 rebreathing technique overestimated cardiac output . Conclusions Although cardiac output was underreported at small VT values , cardiac output measured by the CO2 rebreathing technique correlates fairly with that measured by the thermodilution method OBJECTIVE Noninvasive partial CO2 rebreathing ( NICO ; Novametrix Medical Systems , Inc , Wallingford , CT ) is a relatively new alternative to thermodilution ( TDCO ) for measurement of cardiac output . This study compares the 2 methods during thoracic surgery and one-lung ventilation . DESIGN A prospect i ve , observational study . SETTING A tertiary hospital . PARTICIPANTS Twelve adult patients undergoing elective thoracotomy and one-lung ventilation in the lateral decubitus position . INTERVENTIONS Paired measurements of cardiac output were performed during ( 1 ) 2-lung ventilation in the supine position ( postinduction of anesthesia ) , ( 2 ) 10 minutes after initiation of one-lung ventilation in the lateral decubitus position with the nondependent chest open , and ( 3 ) after 30 minutes on one-lung ventilation . An average of 3 consecutive ( 10 mL 20 degrees C saline ) TDCO measurements made during end-expiration was compared with corresponding NICO measurements . MEASUREMENTS AND MAIN RESULTS The NICO showed a tendency to underestimate cardiac output compared with TDCO at all measurement times . Overall , bias was -0.29 L/min and limits of agreement -1.69 to 1.43 L/min . CONCLUSIONS There was a moderate agreement between cardiac output measurements obtained with the NICO and TDCO . The present data suggest that the NICO technique may be useful during thoracic surgery Introduction New technology using partial carbon dioxide rebreathing has been developed to measure cardiac output . Because rebreathing increases respiratory effort , we investigated whether a newly developed system with 35 s rebreathing causes a lesser increase in respiratory effort under partial ventilatory support than does the conventional system with 50 s rebreathing . We also investigated whether the shorter rebreathing period affects the accuracy of cardiac output measurement . Method Once a total of 13 consecutive post-cardiac-surgery patients had recovered spontaneous breathing under pressure support ventilation , we applied a partial carbon dioxide rebreathing technique with rebreathing of 35 s and 50 s in a r and om order . We measured minute ventilation , and arterial and mixed venous carbon dioxide tension at the end of the normal breathing period and at the end of the rebreathing periods . We then measured cardiac output using the partial carbon dioxide rebreathing technique with the two rebreathing periods and using thermodilution . Results With both rebreathing systems , minute ventilation increased during rebreathing , as did arterial and mixed venous carbon dioxide tensions . The increases in minute ventilation and arterial carbon dioxide tension were less with 35 s rebreathing than with 50 s rebreathing . The cardiac output measures with both systems correlated acceptably with values obtained with thermodilution . Conclusion When patients breathe spontaneously the partial carbon dioxide rebreathing technique increases minute ventilation and arterial carbon dioxide tension , but the effect is less with a shorter rebreathing period . The 35 s rebreathing period yielded cardiac output measurements similar in accuracy to those with 50 s rebreathing Objectives : Radial artery applanation tonometry allows completely noninvasive continuous cardiac output estimation . The aim of the present study was to compare cardiac output measurements obtained with applanation tonometry ( AT-CO ) using the T-Line system ( Tensys Medical , San Diego , CA ) with cardiac output measured by intermittent pulmonary artery thermodilution using a pulmonary artery catheter ( PAC-CO ) with regard to accuracy , precision of agreement , and trending ability . Design : A prospect i ve method comparison study . Setting : The study was conducted in a cardiosurgical ICU of a German university hospital . Patients : We performed cardiac output measurements in 50 patients after cardiothoracic surgery . Interventions : None . Measurements and Main Results : Three independent sets of three consecutive thermodilution measurements ( i.e. , PAC-CO ) each were performed per patient , and AT-CO was measured simultaneously . The average of the three thermodilution cardiac output measurements was compared with the average of the corresponding three AT-CO values result ing in 150 paired cardiac output measurements . In 13 patients , cardiac output – modifying maneuvers performed for clinical reasons additionally allowed to evaluate trending ability . For statistical analysis , we used Bl and -Altman analysis , the percentage error , four-quadrant plot , and concordance analysis . Mean PAC-CO was 4.7 ± 1.2 L/min and mean AT-CO was 4.9 ± 1.1 L/min . The mean of differences was –0.2 L/min with 95 % limits of agreement of –1.8 to + 1.4 L/min . The percentage error was 34 % . The concordance rate was 95 % . Conclusions : Continuous cardiac output measurement using the noninvasive applanation tonometry technology is basically feasible in ICU patients after cardiothoracic surgery .  The applanation tonometry technology provides cardiac output values with reasonable accuracy and precision of agreement compared with intermittent pulmonary artery thermodilution measurements in a clinical study setting and is able to reliably track cardiac output changes induced by cardiac output – modifying maneuvers Background In the partial CO2 rebreathing method , monitored changes in CO2 elimination and end-tidal CO2 in response to a brief rebreathing period are used to estimate cardiac output . However , dynamic changes in CO2 production during ischemia and reperfusion may affect the accuracy of these estimates . This study was design ed to compare measurements of cardiac output as produced by the partial CO2 rebreathing ( NICO ) , bolus ( BCO ) , and continuous thermodilution ( CCO ) methods of monitoring cardiac output . Methods Cardiac output was continuously monitored using both NICO and CCO in 28 patients undergoing aortic reconstruction .  BCO measurements were taken at the following intervals when hemodynamic stability was achieved : ( 1 ) after anesthetic induction ; ( 2 ) during aortic cross-clamp ; ( 3 ) at reperfusion of the iliac artery ; and , ( 4 ) during peritoneal closure . Results The bias and precision ( 1 SD ) derived from all the measurements between NICO and BCO was −0.58 ± 0.9 l/min , whereas for CCO and BCO it was 0.38 ± 1.17 l/min . The bias between NICO and BCO was small after anesthetic induction and during cross-clamp , but increased following reperfusion . The bias between CCO and BCO was relatively small until reperfusion but increased significantly at peritoneal closure . Conclusions Results indicate that in aortic reconstruction surgery the performance of NICO monitoring is comparable with that of CCO ; however , the direction of bias in these continuous measurement devices is the opposite OBJECTIVE Thoracic bioimpedance has been proposed for cardiac output ( CO ) determination and monitoring without calibration or thermodilution ( ICG Monitor 862146 , Philips Medical System , Philips , Suresnes , France ) . The accuracy and clinical applicability of this technology has not been fully evaluated in the cardiac surgery setting . We design ed this prospect i ve study to compare the accuracy of the ICG Monitor ( CO(ICG ) ) versus pulmonary artery catheter st and ard bolus thermodilution ( CO(PAC ) ) in patients after cardiac surgery or having benefited from cardiac surgery . STUDY DESIGN Prospect i ve , monocentric . MATERIAL AND METHODS We studied 13 patients in the postoperative period .  CO(ICG ) and CO(PAC ) were determined at the arrival in the intensive care unit and every four hours . Bl and -Altman and Critchley and Critchley 's analysis were used to assess the agreement between CO(ICG ) and CO(PAC ) . RESULTS CO(PAC ) ranged from 2.6 to 11.0 l/min and CO(ICG ) ranged from 1.8 to 11.7 l/min . There was a significant relationship between CO(PAC ) and CO(ICG ) ( r=0.61 ; p<0.001 ) . Agreement between CO(PAC ) and CO(ICG ) was -0.5+/-1.3 l/min ( Bl and -Altman analysis ) . Percentage error between the two methods was 49 % ( Critchley and Critchley 's analysis ) . CONCLUSION We found clinical ly unacceptable agreement between CO(ICG ) and CO(PAC ) in this setting . Despite its non invasiveness , this device can not be recommended for CO monitoring in the postoperative period following cardiac surgery Introduction Several studies have demonstrated that perioperative hemodynamic optimization has the ability to improve postoperative outcome in high-risk surgical patients . All of these studies aim ed at optimizing cardiac output and /or oxygen delivery in the perioperative period . We conducted a survey with the American Society of Anesthesiologists ( ASA ) and the European Society of Anaesthesiology ( ESA ) to assess current hemodynamic management practice s in patients undergoing high-risk surgery in Europe and in the United States . Methods A survey including 33 specific questions was emailed to 2,500 r and omly selected active members of the ASA and to active ESA members . Results Overall , 368 question naires were completed , 57.1 % from ASA and 42.9 % from ESA members . Cardiac output is monitored by only 34 % of ASA and ESA respondents ( P = 0.49 ) while central venous pressure is monitored by 73 % of ASA respondents and 84 % of ESA respondents ( P < 0.01 ) . Specifically , the  pulmonary artery catheter  is being used much more frequently in the US than in Europe in the setup of high-risk surgery ( 85.1 % vs. 55.3 % respectively , P < 0.001 ) . Clinical experience , blood pressure , central venous pressure , and urine output are the most widely indicators of volume expansion . Finally , 86.5 % of ASA respondents and 98.1 % of ESA respondents believe that their current hemodynamic management could be improved . Conclusions In conclusion , these results point to a considerable gap between the accumulating evidence about the benefits of perioperative hemodynamic optimization and the available technologies that may facilitate its clinical implementation , and clinical practice s in both Europe and the United States Background Although evaluation of cardiac output by the partial carbon dioxide rebreathing technique is as accurate as thermodilution techniques under controlled mechanical ventilation , it is less accurate at low tidal volume . It is not clear whether reduced accuracy is due to low tidal volume or low minute ventilation . The effect of spontaneous breathing on the accuracy of partial carbon dioxide rebreathing measurement has not been fully investigated . The objectives of the current study were to investigate whether tidal volume or minute ventilation is the dominant factor for the accuracy , and the accuracy of the technique when spontaneous breathing effort is present . Methods The authors enrolled 25 post – cardiac surgery patients in two serial protocol s. First , the authors applied three setting s of controlled mechanical ventilation in r and om order : large tidal volume ( 12 ml/kg ) , the same minute ventilation with a small tidal volume ( 6 ml/kg ) , and 50 % decreased minute ventilation with a small tidal volume ( 6 ml/kg ) . Second , when the patient recovered spontaneous breathing , the authors applied three conditions of partial ventilatory support in r and om order : synchronized intermittent m and atory ventilation – pressure support ventilation , pressure support ventilation with an appropri 
    Output:
    
With a wide percentage error , completely non-invasive CO devices are not interchangeable with bolus thermodilution .